The preparation of the bulky secondary amide N-(2,6-diisopropylphenyl)-2,2-dimethylpropanamide and the determination of its crystal structure at 173(2) K are reported. The structure displays disorder of the( t)Bu methyl groups due to thermal motion and an infinite N-H center dot center dot center dot center dot O=C hydrogen-bonded chain described by a C-1(1)(4) graph set. Reaction of this amide with ZnCl2 or ZnBr2 in tetrahydrofuran (THF) results in clihalo-(tetrahydrofurano)-(N-(2,6-diisopropylphenyl)-2,2-dimethylpropan amido)-zinc(II) complexes (Cl, Br) for which the crystal structures have also been determined. These complexes, as well as a chloroform solvate of the dichloro-complex, contain N-H center dot center dot center dot center dot X-Zn hydrogen-bonded chains described by C;(6) graph sets. Evaporative crystallization results in the loss of both chloroform and THF to afford crystals determined to be bis(mu(2)-chloroydichloro-bis(N-(2,6-diisopropylphenyl)-2,2-dimethylprop anamido)-dizinc(II) by single crystal X-ray diffraction. This dimeric complex shows a complex network of N-H center dot center dot center dot center dot Cl-Zn hydrogen bonds describable by C-1(1)(6), C(1)(()(1)8), and C-2(2)(16) chains, small R-4(4)(28) molecular ``squares'', and larger R-6(6)(44) rings.

An extended pi-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the pi-accepting properties of the capping NHCs.

An improved synthetic pathway to the nanobelt-like 1,1,9,9-tetramethyl[9](2,11)teropyrenophane(I) has been developed, and enables the synthesis of gram quantities of material.  Key innovations are the development of a sequential chlorination/Friedel-Crafts alkylation reaction, a sequential iodination/Wurtz coupling reaction, and a room-temp. teropyrene-forming reaction.  The teropyrenophane was found to form a very stable radical cation and undergo a completely regioselective fourfold bromination reaction.  Safety: care required for exothermic Grignard.

Reaction of the bicyclic sulfur-nitrogen heterocycles RC6H4CN5S3 (R=4-CH3O, 4-CH3, 4-H, 4-Cl, 4-CF3, 3-CF3) with PR'3 (R'=C6H5 or 4-CH3OC6H4) produces 3-phosphoraniminato-7-aryl-1,3,5-trithia-2,4,6,8-tetrazocines RC6H4CN4S3NPR'3.  In all cases, only the endo-isomers were isolated and characterized by 1H, 31P, and 19F NMR as well as UV spectroscopy and X-ray crystallog.  RB3LYP/6-311+G(d,p)// RB3LYP/6-31G(d,p) computations were undertaken to help explain the atom-exact syntheses via intermediates previously detected spectroscopically.  Three reasonable intermediates have been computed as stationary points with energies consistent with the obsd. reaction path.  Cyclic and square-wave voltammetry studies of RC6H4CN4S3NPR'3, using a glassy carbon working electrode in CH2Cl2 with 0.4 M [nBu4N][PF6], reveal two IRR redn. processes at RT in all cases at approx. -1.9 and -2.2 V, resp., and one IRR oxidn. process at approx. +1.0 V (vs. Fc+/0). [RC6H4CN4S3NPR'3]-. radical anions (R'=4-CH3OC6H4, R=4-CH3O, 4-H, 4-CF3) were detected at -50 °C in CH2Cl2 by using in situ electrolysis and simultaneous ESR spectroscopy: [4-RC6H4CN4S3NP(4-CH3OC6H4)3]-., estd. a(31P)=0.078 mT, a(14N1)=0.031 mT, a(14N2,3)=0.256 mT, a(14N4,5)=0.341 mT.  The signals decay rapidly, but after the electrolysis is ended, a persistent EPR signal is always obtained with EPR parameters that match known 4-aryl-1,2,3,5-dithiadiazolyls, i.e., a(N)=0.51 mT and g=2.0105, which are consistent with the prodn. of [4-CF3-C6H4CN2S2]..

The crystal structures of tris(3,5-dimethylphenyl)phosphine (C24H27P), (I), tris(3,5-dimethylphenyl)phosphine oxide (C24H27OP), (II), tris(4-methoxy-3,5-dimethylphenyl)phosphine (C27H33O3P), (III), and tris(4-methoxy-3,5-dimethylphenyl)phosphine oxide (C27H33O4P), (IV), are reported.  The strucure of (III) has been described before [Romain et al. (2000). Organometallics, 19, 2047-2050], but it is rereported here on the basis of modern area-detector data and to facilitate comparison with the other structures reported here.  Compds. (I) and (II) crystallize isostructurally in P21/c.  Similarly, (III) and (IV) crystallize isostructurally in Pbca.  The conformations of (I) and (II) in the solid state deviate strongly from helical, whereas those of (III) and (IV) are found to be closer to an ideal threefold rotational symmetry.  The pyramidality indexes, ∑(C-P-C), are 305.35 (16), 317.23 (15), 307.2 (4) and 318.67 (18)° for (I), (II), (III) and (IV), resp.  Each is found to be more pyramidal than Ph3P or Ph3PO.  Hybrid DFT calcns. incorporating terms for dispersion provide evidence that the causes of the increased pyramidality, despite the 3,5-di-Me group substitution, include dispersion interactions.  The calcd. ∑(C-P-C) values are 304.8° for both (I) and (III) and 317.4° for both (II) and (IV), with no difference arising from the substitution at ring position 4.

The preparation and crystal structures of four beta-ketoimines with bulky aryl nitrogen substituents (2,6-diisopropylphenyl and 2,4,6-trimethylphenyl) and varying degrees of backbone methyl substitution are reported. Backbone substitution ``pinches'' the chelate ring. Deprotonation with n-butyllithium leads to dimeric Li2O2 clusters, as primary laddered units, with an open transoid geometry as shown by crystal structures of three examples. The coordination sphere of each lithium is completed by one tetrahydrofuran ligand. NMR spectra undertaken in either C6D6 or 1:1 C6D6/d(8)-THF show free THF in solution and the chemical shifts of ligand methyl groups experience significant ring-shielding which can only occur from aryl rings on adjacent ligands. Both features point to conversion to higher-order aggregates when the THF concentration is reduced. Recrystallization of the materials from hydrocarbon solutions results in secondary laddering as tetrameric Li4O4 clusters with a cuboidal core, three examples of which have been crystallographically characterised. These clusters are relatively insoluble and melt up to 250 degrees C; a consideration of the solid-state structures indicates that the clusters with 2,6-diisopropylphenyl substituents form very uniform ball-like molecular structures that will only be weakly solvated.

Crystals of 4-[3-(trifluoromethyl) phenyl]-3H-1,2,3,5-dithiadiazol-3-yl grown by slow sublimation in a three-zone furnace form in P (1) over bar with Z = 12. The six independent molecules combine into two cis-oid and one twisted dimer, which arrange in a layer structure as two elegant clusters, with non-crystallographic fourfold and two-fold symmetry, respectively. Crystals of 4-(3-cyano-5-tertbutyl-phenyl)-3H-1,2,3,5-diselenadiazol- 3-yl, formed from decomposition of a bis-diselenadiazolyl, grow in two forms under different sublimation conditions using the same furnace. The alpha form crystallizes in P (1) over bar with Z = 6 and the beta in P2(1)/c with Z = 20. The a polymorph consists of a distorted cis-oid dimer linked electrostatically to a monomer in the asymmetric unit. These cluster with a second unit to a centrosymmetric aggregate of six heterocycles. The beta polymorph consists of clusters of four cis-oid dimers that link into chains along the b axis, whereas the fifth molecule links via -C equivalent to N center dot center dot center dot Se supramolecular synthons into an infinite chain of monomers also along the b axis but out-of-register with the dimer chain. A carefully curated compilation of all 83 distinct 1,2,3,5-dithiadiazolyl and of all 24 distinct 1,2,3,5-diselenadiazolyl crystal structures reveals an extraordinarily large number of structures with Z' > 1 (72%) and also those with Z' >= 3 (24%), compared to the average for organic molecules over the whole collection in the Cambridge Structure Database. This high incidence is analyzed and attributed to competing intermolecular synthons.

The first lanthanide complexes with a redox-active sulfur diimide ligand, [LnCp*(2)(Me3SiN=)(2)S] (Ln= Sm, Eu, Yb; Cp*=eta(5)-C5Me5), are reported. The complexes were synthesized by using [LnCp*(2)(THF)(2)] and (Me3SiN=)(2)S and have been thoroughly characterized by single-crystal X-ray diffraction, EPR spectroscopy, UV/Vis/NIR electronic absorption spectroscopy and SQUID magnetometry. The results, as in-terpreted by CASSCF/SOC-RASSI calculations providing a non-perturbative treatment of spin-orbit coupling, indicate that these paramagnetic complexes are best described as Ln3+ and [( Me3SiN=)(2)S]-(center dot) adducts. As such, these complexes contain the first isolated and structurally characterized acyclic [(RN=)(2)S](-center dot) radical anions.

An arene-ruthenium (II) complex - [Ru(eta(6)-p-cymene)(ampy)Cl]PF6, where ampy is 2-(aminomethyl) pyridine -was synthesized and used in the construction of a modified carbon ceramic electrode (Ru-CCE) for determining paracetamol (PCT) by square wave voltammetry (SWV). The modified electrode, constructed by sol-gel methods, provides a considerable enhancement of PCT oxidation. Under the optimized working conditions, the peak current is linear to the PCT concentration in the ranges of 1.99 x 10(-6) - 3.10 x 10(-5) mol L-1 with a detection limit of 5.83 x 10(-7) mol L-1. The Ru-CCE showed good repeatability and reproducibility (RSD < 4%), long-term stability (> 12 months). Lastly, the proposed sensor was used for the determination of PCT in pharmaceutical formulations, offering a promising tool for quality control. (C) 2017 The Electrochemical Society. All rights reserved.

The solid-state structure of a dimeric beta diketiminate magnesium(II) complex is discussed. The compound, di-mu-iodido-bis[(\4-amino-1,5-bis[2,6-bis(propan-2-yl) phenyl] pent-3-en-2-ylidene\ azanido-kappa N-2,N') magnesium(II)] toluene sesquisolvate, [Mg-2(C29H41N2)(2)I-2]center dot 1.5C(7)H(8), crystallizes as two independent molecules, each with 2/m crystallographic site symmetry, located at Wyckoff sites 2c and 2d. These have symmetry-equivalent magnesium atoms bridged by mu-iodide ligands with very similar Mg-I distances. The two Mg atoms are located slightly below (similar to 0.5 angstrom) the least-squares plane defined by N-C-C-N atoms in the ligand scaffold, and are approximately tetrahedrally coordinated. One and one-half toluene solvent molecules are disordered with respect to mirror-site symmetry at Wyckoff sites 4i and 2a, respectively. In the former case, two toluene molecules interact in an off-center parallel stacking arrangement; the shortest C to C' (pi-pi) distance of 3.72 (1) angstrom angstrom was measured for this interaction.

4,7-dicyano-2,1,3-benzothiadiazole, L1, and diethyl-4,7-dicarboxylato-2,1,3-benzothiadiazole, L2, form coordination polymers with silver(I) salts of weakly coordinating anions. Synthesis was achieved by the slow diffusion of benzene solutions of silver salts into dichloromethane solutions of L1 or L2. Slow growth of crystals occurred with partial evaporation of the solvent, leading to a number of different crystalline coordination polymers. For L1, both nitrile and ring N atoms can coordinate with great variability of structural motifs, whereas for L2 a chelating geometry is always found in which each Ag+ is coordinated by two N and two carbonyl O from different ligands. The resulting coordination polymers form layer structures that tend to fill with solvent benzene molecules in a stoichiometric fashion; the benzenes are found to -coordinate to silver.

The title compound Dipp(H) P-P(H)Dipp where Dipp = 2,6-diisopropylyphenyl has been prepared starting from DippPH(2) via DippPHLi reacting 2:1 with BrCH2CH2Br. A high-resolution single-crystal X-ray diffraction study at 153 +/- 2 K provides an accurate description of the structure in the solid state, only the fourth dihydro diorganophosphane to have been so characterized. The Raman spectrum of the solid shows an intense, broad peak for P-H stretching at 2314 cm(-1) and two peaks at 460 and 450 cm(-1) for P-P stretching, assignments confirmed by RHF/6-31G+(3d,2p) frequency calculations undertaken on the anti conformers. P-31, P-31\H-1\, H-1\P-31\, and C-13\H-1\ solution NMR spectra in CDCl3 are consistent with the presence of 58% meso and 42% rac diastereomers. Analysis of their AA'XX' spin systems enabled calculation of (1)J(PP') values of (-)189 and (-)205 Hz, respectively. A B3LYP/6-31G(d,p) computational analysis of the energetics of rotation about the P-P bond in both diastereomers shows that the anti and two gauche conformers are likely to be populated approximately equally in each. The resulting average phi angles (torsions of the phosphorus lone pairs) are 110 degrees for meso and 103 degrees for rac; the smaller phi angle fits with the larger (1)J(PP') value for the rac isomer.

The crystal structure of [Ph3PH](2)[Ga2Br6], previously described as having a disordered anion in the space group R (3) over bar, has been re-determined in the correct space group P (3) over bar, where it is fully ordered. Interestingly, two-thirds of the [Ga2Br6](2-) dianions have an intermediate conformation with a Br-Ga-Ga-Br torsion angle of 36.91 (1)degrees, while the remaining is staggered as required from adopting a site with inversion symmetry. In the lattice, [Ph3PH](+) ions lie along the same threefold axes as the dianions and are oriented such that the P-H bond is directed towards a gallium atom. The phosphonium ions lie back-to-back and interact with relatively strong T-interactions between phenyl rings on adjacent cations. DFT calculations at the B3LYP/6-311+ G(fd,) level have been used to determine the barriers to rotation in [Ga2X6](2-) ions. For X = Cl and X = Br, the barriers are found to be very small, with values of 4.3 and 5.1 kJ mol(-1) for the two halogens.

Metal(0) complexes L(Cr, Mo, W)(CO)(5) have been prepared from 1,3-bis(2,6-diisopropylphenyl)-2-(4-methylphenyl)-3-aza-1(lambda(3),sigm a(2))-phosphapropene and 1,3-bis(2,6-diisopropylphenyl)-2-(4-methoxy-phenyl)-3-aza-1(lambda(3),si gma(2))-phosphapropene using standard methods. Full characterization of four products and crystal structures of these complexes as well as the methoxyphenyl-phosphapropene are reported. The ligands coordinate kappa P, common for simple phosphaalkenes, despite the strongly-perturbing amino substitution at the double bond C atoms. Analyses of the NMR and vibrational spectroscopic data reveal that the complexes have very similar character to similarly-coordinated phosphaalkenes, with strong sigma-donor character. The presence of some net pi-interactions (acceptor or donor) is indicated by structures in which the ligands coordinate fully eclipsed with the M-CO groups. The synthetic and structural results have been augmented by B3PW91/LANL2DZ calculations that reproduce the structures of the Cr complexes accurately. The calculated vibrational spectra are used to confirm the assignment of the nu(C=O) vibrational data. Detailed orbital interaction diagrams based on DFT calculations are reported for the title complexes as well as for the Cr(CO)(5) complex of Mes-P-CPh2. The electronic absorption spectra of the title complexes have intense low-energy absorptions ranging from 24 500 to 25 300 cm(-1), which can be interpreted qualitatively using the DFT results.

The structure of dimeric 2,7-bis[4-(trifluoromethyl)phenyl]-4 lambda(4),5 lambda(4),9 lambda(4),10 lambda(4)-tetrathieto[1,2-a:3,4-a']bis[1,2,3,5]dithiadiazole (C8H4F3N2S2)(2) and its adduct with triphenylstibine, (C8H4F3N2S2)(2)center dot C18H15Sb, both have triclinic (P (1) over bar) symmetry. They crystallize in layers containing centrosymmetric clusters consisting of four dithiadiazolyl dimers in the parent compound and two such dimers paired with two triphenylstibine units in the aromatic co-crystal. In the co-crystal, the Ph3Sb molecules associate with an equivalent moiety from a neighbouring cluster in a geometry that is very reminiscent of other Ph3Sb-containing structures. Thus, the adduct combines structural elements from those of its component parts. Key interactions between molecules in the pure dithiadiazolyl (S to S) and the co-crystal (S to C) are significantly shorter than the sums of atom van der Waals radii.

The title compound has been prepared from 1,5-dibromonaphthalene (obtained from 1,5-diaminonaphthalene) using Suzuki-Miyaura cross-coupling to 4-pyridylboronic acid. The crystal and molecular structure was determined by single-crystal X-ray diffraction.

{{The reaction of [3,5-Ph-2-C2N3S](2) with [CpCr(CO)(3)](2) in toluene at room temperature forms an adduct via a Cr-S bond, formulated as CpCr(CO)(3)SN3C2Ph2, which has fitting NMR, IR, and combustion analysis data. The structure was determined by a single-crystal X-ray structure diffraction study (P2(1)/n

The reactions of dipyridylmethane (dpma) with group 13 trichlorides were investigated in 1 : 1 and 1 : 2 molar ratios using NMR spectroscopy and X-ray crystallography. With 1 : 1 stoichiometry and Et2O as solvent, reactions employing AlCl3 or GaCl3 gave mixtures of products with the salt [(dpma)(2)MCl2](+)[MCl4](-) (M = Al, Ga) as the main species. The corresponding reactions in 1 : 2 molar ratio gave similar mixtures but with [(dpma) MCl2](+)[MCl4](-) as the primary product. Pure salts [(dpma) AlCl2](+)[Cl](-) and [(dpma) AlCl2](+)[AlCl4](-) could be obtained by performing the reactions in CH3CN. In the case of InCl3, a neutral monoadduct (dpma) InCl3 formed regardless of the stoichiometry employed. A neutral adduct (dpma)(BCl3)(2) was obtained from the reaction between dpma and BCl3 in Et2O using 1 : 2 stoichiometry. With 1 : 1 molar ratio of reagents, a mixture of products and deprotonation of the methylene bridge in [(dpma) BCl2](+) was observed. The experimental data showed that the structural flexibility of the dpma ligand results in more diverse coordination chemistry with group 13 elements than that observed for bipyridine (bpy), while computational investigations indicated that the investigated metal-ligand interactions are, to a first approximation, independent of the ligand type. Electrochemical and chemical attempts to reduce the cations [(dpma)MCl2](+) showed that, in stark contrast to the chemistry of the related [(bpy) BCl2](+) cation, the neutral radicals [(dpma)MCl2](center dot) are extremely unstable. Differences in the redox behaviour of dpma and bpy could be rationalized with the electronic structure of the ligand and that of the methylene bridge in particular. As a whole, the facile reactivity of the methylene bridge in the dpma ligand renders it amenable to further reactivity and functionalization that is not possible in the case of bpy.

Density functional theory (DFT) calculations for the six-membered ring 1,4-(CH2)(2)((PBu)-Bu-t)(4) (1), the dimer ((PBu2)-Bu-t)(2) (2) and the 2,5-chalcogenated derivatives of 1, 3a (E = S) and 3b (E = Se), and the corresponding cation radicals and dications predict significant structural changes upon oxidation. The formation of a transannular P-P single bond (ca. 2.25 angstrom) in the three cyclic dications 1(2+), 3a(2+), and 3b(2+) is indicated by geometry and consideration of the frontier orbitals. The calculations also indicate a weak transannular interaction in the cyclic cation radicals. The nature of these transannular P-P bonding interactions is analyzed through a consideration of the molecular orbitals involved. Cyclic Voltammetry studies of 1 and 2 reveal two well-separated oxidation processes. Both processes are irreversible for 1 at normal scan rates, whereas for 2 the first process is quasi-reversible. The cation radical 1(+center dot) could not be detected by in situ electron paramagnetic resonance studies of the first electrochemical oxidation, but a spectrum for the radical cation 2(+center dot) could be observed. The difference in the redox behavior of 1 and 2 is considered with respect to the structural parameters and DFT calculations. Chemical oxidation of 1 with NO+[Al(ORF)(4)]-(R-F = C(CF3)(3)) in CH2Cl2 led to a complex mixture; the protonated cation H1(+) (1,4-(CH2)(2)((PBu)-Bu-t)(3)((HPBu)-Bu-t)(+)) was identified as one of the major products on the basis of multinuclear (C) 2014 Wiley Periodicals, Inc.

The first preparation and full characterization of highly insoluble [\eta(5)-Cp\CoS2N2H][BF4] is reported. Proof of structure and composition is established from a single-crystal X-ray diffraction experiment at 173 K, which determined a crystal structure containing two independent cations and two independent anions in the asymmetric unit. The site of protonation is the terminal N of the S-N-S-N2- ligand which is coordinated to cobalt in the metallacycle. The crystal lattice contains numerous interatomic interactions, of which the most important are formed from multiple hydrogen bonds that link four [\eta(5)-Cp\CoS2N2H](+) ions and two [BF4](-) ions into a tetrameric cluster. The second kind of [BF4](-) is not involved in intermolecular bonding. Short S center dot center dot center dot S' interactions link such tetramers into planes; the resulting double-layer planes are described by the (101) Miller planes. DFT calculations using the B3PW91/6-311+G(3df)(2p) and B3LYP/6-311+G(3df)(2p) methods are in excellent agreement with the structure of the title cation from crystallography. Comparison to newly calculated and literature-reported DFT calculations on the neutral starting material [\eta(5)-Cp\CoS2N2] and to a recent low-temperature crystal structure of the latter shows that there are only minor changes (<= 3%) in the bond lengths within the CoS2N2 ring upon protonation, whereas the bond angles change by up to 9%. The B3PW91 functional is shown to be superior to B3LYP for computing the molecular structures of these formally Co-III metallacycles.

The title salt, triphenyl(P,P,P-triphenylphosphineimidato-kappa N)-phosphorus(1+) 1,3,5,7-tetrathia(1,5-S-IV)-2,4,6,8,9-pentaazabicyclo[3.3.1]nona-1,4,6 ,7-tetraene(1-), CAS [48236-06-2], prepared by the literature method, is found by crystallography to be a 1: 1 CH3CN solvate. Disorder exists for the N atoms of the anion. A VT crystal structure study was conducted at 100 K, 120 K, 140 K, 172 K, 200 K, 240 K and 280 K. The 100 K structure is superior, with only 10% of a second anion position oppositely-oriented w.r.t the diad axis of point group 2mm. At 120 K, an adjacent two-site disorder is encountered, but at higher temperatures three-site disorder with both opposite and adjacent placements of S4N5- ions is required w.r.t. the primary component. At 240 and especially 280 K, the anion nitrogen atoms appear fully scrambled amongst the six possible sites on the edges of an S-4 tetrahedron with 83.3% occupancy for each. The PPN+ geometry does not show strong cation-cation interactions. However, there are numerous supramolecular contacts corresponding mostly to non-classical H-bonds between PPN+ ions and S4N5- as well as CH3CN. The geometry of the anion is corroborated from B3LYP/6-311++G(3df) DFT calculations, and the infra-red spectrum was assigned with excellent agreement between experimental and calculated frequencies.

The perhalogenated closo-dodecaborate dianions [B12X12](2-) (X=H, F, Cl, Br, I) are three-dimensional counterparts to the two-dimensional aromatics C6X6 (X=H, F, Cl, Br, I). Whereas oxidation of the parent compounds [B12H12](2-) and benzene does not lead to isolable radicals, the perhalogenated analogues can be oxidized by chemical or electrochemical methods to give stable radicals. The chemical oxidation of the closo-dodecaborate dianions [B12X12](2-) with the strong oxidizer AsF5 in liquid sulfur dioxide (lSO(2)) yielded the corresponding radical anions [B12X12](-) (X=F, Cl, Br). The presence of radical ions was proven by EPR and UV/Vis spectroscopy and supported by quantum chemical calculations. Use of an excess amount of the oxidizing agent allowed the synthesis of the neutral perhalogenated hypercloso-boranes B12X12 (X=Cl, Br). These compounds were characterized by single-crystal X-ray diffraction of dark blue B12Cl12 and [Na(SO2)(6)][B12Br12]B12Br12. Sublimation of the crude reaction products that contained B12X12 (X=Cl, Br) resulted in pure dark blue B12Cl12 or decomposition to red B9Br9, respectively. The energetics of the oxidation processes in the gas phase were calculated by DFT methods at the PBE0/def2-TZVPP level of theory. They revealed the trend of increasing ionization potentials of the [B12X12](2-) dianions by going from fluorine to bromine as halogen substituent. The oxidation of all [B12X12](2-) dianions was also studied in the gas phase by mass spectrometry in an ion trap. The electrochemical oxidation of the closo-dodecaborate dianions [B12X12](2-) (X=F, Cl, Br, I) by cyclic and Osteryoung square-wave voltammetry in liquid sulfur dioxide or acetonitrile showed very good agreement with quantum chemical calculations in the gas phase. For [B12X12](2-) (X=F, Cl, Br) the first and second oxidation processes are detected. Whereas the first process is quasi-reversible (with oxidation potentials in the range between +1.68 and +2.29V (lSO(2), versus ferrocene/ferrocenium (Fc(0/+)))), the second process is irreversible (with oxidation potentials ranging from +2.63 to +2.71V (lSO(2), versus Fc(0/+))). [B12I12](2-) showed a complex oxidation behavior in cyclic voltammetry experiments, presumably owing to decomposition of the cluster anion under release of iodide, which also explains the failure to isolate the respective radical by chemical oxidation.

The title compound, C45H70P+center dot ClO4-or [Tripp(3)PH(+)][ClO4-], was produced from the perchlorate salt of the corresponding radical cation Tripp(3)P.(+) through very slow H-atom abstraction reactions in a solution of 1,2-dimethoxyethane (Tripp is 2,4,6triisopropylphenyl). The H atom on the P atom was located in a difference map and was freely refined with an isotropic displacement consistent with full occupancy [P-H = 1.37 (3) A]. It is the most sterically congested triarylphosphonium salt yet to be reported and has a ` propeller' arrangement of the three Tripp groups around the P atom, with the protonation site located along the molecular threefold axis. There are short contacts between the flanking isopropyl methine H atoms and the P atom [Ph3H = 1.99 (2)2.17 (2) A]. The sum of the angles around the P atom [Sigma(C-P-C) = 349.9 (6) angstrom] is a convenient index of pyramidality for tricoordinate centres. This value is significantly larger than in analogous Mes3PH + salts (Mes is mesityl or 2,4,6trimethylphenyl), for which the average of the three reported structures in the literature is Sigma (C-P-C) = 345.3 (6) . For comparison, in the ubiquitous Ph3PH+ salts, this parameter has a typical average value of only 333.3 (9)degrees. The value of Sigma (CP- C) in the title compound is midway between that of the neutral phosphane Tripp3P [334.4 (6)degrees] and the phosphoniumyl radical cation Tripp3P(+) [359.8 (2)degrees]. This geometrical feature provides additional support for the assignment as a phosphonium salt.

The crystal structure of the spirobicyclic phosphorane 3,3'-dimethyl-2 lambda(5)-2,2'(3H,3'H)-spirobi[1,3,2-benzoxazaphosphole], [HP(OC6H4NCH3)(2)] (1) has been determined. Crystals of C14H15N2O2P are monoclinic, a = 8.483(2), b = 7.616(2), c = 19.805(6) , Z = 4, space group P2(1)/c. Compound 1 was also characterized by C-13{H-1} and H-1 NMR. The crystal structure along with DFT B3LYP (6-311++G(2df,2p)) calculations, both suggest significant pi-overlap between the equatorial nitrogen atoms and the phosphorus center. The crystal structure and DFT B3LYP (6-311++G(2df,2p)) calculations of the spirobicyclic phosphorane 3,3'-dimethyl-2 lambda(5)-2,2'(3H,3'H)-spirobi[1,3,2-benzoxazaphosphole], [HP(OC6H4NCH3)(2)] is reported.

(1RS,3RS,4RS,10SR)-2,2,3,10-Tetrabromo-1,2,3,4-tetrahydro-1,4-ethanonaphthalene, C12H10Br4, (I), is the first structure to be reported with four Br atoms bound to a 1,4-ethanonaphthalene framework and also the first which possesses three Br atoms in exo positions. Interactions between the Br atoms [three short intramolecular Br center dot center dot center dot Br distances of 3.1094 (4), 3.2669 (4) and 3.4415 (5) angstrom] have little effect on the C-C bond lengths but lead to significant twisting of the cage structure compared with the parent hydrocarbon, which is expected to be fully eclipsed at the two saturated C2H4 bridge positions. Chemically related (1SR,4RS)-2,3-dibromo-1,4-ethenonaphthalene, C12H8Br2, (II), obtained by double dehydrobromination of (I), represents the first structure of any halogen-substituted benzobarrelene. This cis-dibromide shows little evidence of steric congestion at the double bond [Br center dot center dot center dot Br = 3.5276 (8) angstrom] as a consequence of the large C-C-Br angles [average C=C-Br angle = 126.15 (10)degrees].

Activation barriers to the electrochemical oxidation for the series PPh3-n(dipp)(n) (dipp = 2,6-diisopropylphenyl) in CH2Cl2/Bu4NPF6 were measured using large amplitude FT ac voltammetry. Increasing substitution across this series, which offers the widest range of steric requirements across any analogous series of triarylphosphines reported to date, increases the energetic barrier to electron transfer; values of 18, 24, and 25 kJ mol(-1) were found for compounds with n = 1, 2, and 3, respectively. These values are significantly greater than those calculated for outer sphere activation barriers, with deviations between observed and calculated values increasing with the number of dipp ligands. This suggests that the steric congestion afforded by these bulky substituents imposes significant reorganizational energy on the electron transfer processes. This is the first investigation of the effect of sterics on the kinetics of heterogeneous electron transfer across a structurally homologous series. Increased alkyl substitution across the series also increases the chemical reversibility of the oxidations and decreases the oxidation peak potentials. As the compounds for which n = 1 and 2 are novel, the synthetic strategies employed in their preparation are described, along with their full spectroscopic, physical, and crystallographic characterization. Optimal synthesis when n = 1 is via a Grignard reagent, whereas when n = 2 an aryl copper reagent must be employed, as use of a Grignard results in reductive coupling. Chemical oxidation studies were performed to augment the electrochemical work; the O, S, and Se oxidation products for the parent triarylphosphines for which n = 1 and 2 were isolated and characterized.

The range of electrochemical stability of a series of weakly coordinating halogenated (Hal=F, Cl, Br, I) 1-carba-closo-dodecaborate anions, [1-R-CB11X5Y6]- (R=H, Me; X=H, Hal, Me; Y=Hal), has been established by using quantum chemical calculations and electrochemical methods. The structures of the neutral and dianionic radicals, as well as the anions, have been optimized by using DFT calculations at the PBE0/def2-TZVPP level. The calculated structures are in good agreement with existing experimental data and with previous calculations. Their gas-phase ionization energies and electron affinities were calculated based on their optimized structures and were compared with experimental (cyclic and square-wave) voltammetry data. Electrochemical oxidation was performed in MeCN at room temperature and in liquid sulfur dioxide at lower temperatures. All of the anions show a very high resistance to the onset of oxidation (2.152.85 V versus Fc0/+), with only a minor dependence of the oxidation potential on the different halogen substituents. In contrast, the reduction potentials in MeCN are strongly substituent dependent (-1.93 to -3.32 V versus Fc0/+). The calculated ionization energies and electron affinities correlate well with the experimental redox potentials, which provide important verification of the thermodynamic validity of the mostly irreversible redox processes that are observed for this series. The large electrochemical windows that are afforded by these anions indicate their suitability for electrochemical applications, for example, as supporting electrolytes.

The synthesis, NMR spectroscopy, single-crystal X-ray structure, and solution electrochemistry of the new compound [2,6-\CH(CH3)\(2)C6H3](3) As, abbreviated as Dipp(3)As, is reported. The molecule, prepared by reaction of AsCl3 with a preformed aryl copper reagent, Dipp(4)Cu(4), crystallizes in the hexagonal space group R3 as a racemic twin. The sum of angles around As, Sigma angle\CAsC\, is 329.13(3)degrees in the X-ray structure and 329.17 degrees from an R-B3LYP/6-31G(d,p) hybrid density functional theory calculation. The aromatic rings are quite distorted with both the ipso carbon and especially the As atom significantly out of plane by 0.503(3) angstrom . The ambient temperature NMR spectrum fits for C-3 symmetry implying that inversion is slow on the NMR timescale. Cyclic voltammetry on a glassy carbon electrode in CH2Cl2 with 0.4 M [(Bu4N)-Bu-n][PF6] over scan rates of 0.05-0.8V s(-1) and temperatures of 22 +/- 28 degrees C produced one quasi-reversible process with E-m1 = +0.43V at a scan rate of 0.20 V s(-1) and a second irreversible process with a peak potential of +1.45 V (v. Fc(+/0)). The diffusion coefficient has been measured as 3.3 +/- 0.1 x 10(-6) cm(2) s(-1) in CH2Cl2 solution containing 0.4 M [(Bu4N)-Bu-n][PF6]. Chemical oxidation with AgPF6 in CH2Cl2 in degassed solutions in sealed vessels allowed for recording of characteristic EPR spectra; at 293 K, a (As-75) = 26.1 mT and g = 2.021. In frozen solution, an almost isotropic spectrum is obtained (g(parallel to) - 2.000 mT and g(perpendicular to) - 2.003 mT) and the hyperfine splitting constants are a(parallel to) - 47.9 and a(perpendicular to) - 19.0 mT, leading to an estimate for the structure being slightly pyramidal with Sigma angle\CAsC\ approximate to 351 degrees.

In the structure of the title compd., C12H8Br2, the two Br substituents are oriented exo to the boat-shaped cyclooctatetraene at the two ring sites that are β to the ring fusion positions.  The av. Br-C bond distance is 1.919(2) Å, the av. distance for C=C double bonds that are Br substituted is 1.328(2) Å, while the other two double-bond distances are 1.327(2) and 1.398(2) Å for the nonfused and fused bonds, resp.  Each type of ring interat. distance is within s.u. of the av. values for the four known structures, including the title compd., of benzo-fused cycloocatatetraenes that are not coordinated to a metal atom.  The crystal structure features short Br···Br [3.6620(3) Å] and C···H [2.834(2) and 2.841(2) Å] contacts.  Crystallog. data and at. coordinates are given.

The cation of the title salt, (C14H10NS2)[FeBr4], contains a flat central NC2S2 ring (r.m.s. deviation = 0.005 A), with two attached phenyl rings that are almost coplanar [the dihedral angles between the mean planes are 2.4 (1) and 7.7 (1)degrees for the two phenyl rings]. The [FeBr4]- anion makes short Br...S contacts [Br...S = 3.4819 (8), 3.6327 (9) and 3.5925 (9) A] and also bridges by way of short contacts to ring H atoms of a second cation held parallel to the first by [pi]-stacking, with a separation between the mean 1,2,4-dithiazolium rings of 3.409 A. The closest contacts are between a phenyl ring centroid of one cation and the ipso C atom of the phenyl ring of another cation, for which the distance is 3.489 A. The discrete dimers are linked laterally by further Br...H short contacts, resulting in double sheets located parallel to the b axis and to the bisector of a and c.

The title compound, C24H47PSi2, is the first organophosphane bearing two tert-butyldimethylsilyl ( TBDMS) groups to be crystallographically characterized, even though TBDMS is a very popular bulky silyl group. The structure is a considerably flattened trigonal pyramid, with the sum of the C/Si-P-C/Si angles being 333.35 (6)degrees, which can be attributed to the steric pressure from the three bulky groups. The P-Si distances [2.2605 (6) and 2.2631 (6) angstrom] are normal, while the P-C distance [1.8646 (12) angstrom] is long (outside the s.u. values) compared with related structures. The plane of the aryl ring approximately bisects the Si-P-Si angle, quite unlike the secondary (tert-butyldimethylsilyl)(2,6-diisopropylphenyl)phosphane bearing only one TBDMS group, in which the single Si atom is perpendicular to the aryl ring. The title structure conforms closely to that predicted from B3LYP/6-31G(d) calculations, although the calculations overestimate the degree of planarity. The compound crystallizes centrosymmetrically in the space group P (1) over bar as isolated molecules.

In the structure of the title compound [systematic name: 1-(naphthalen-2-yl)ethanone], C12H10O, the acetyl group is approximately coplanar with the naphthalene ring with a Car-Car-C=O torsion angle of 5.8 (2)degrees. In the crystal, the molecules are packed in a classic herringbone arrangement typical for aromatic polycycles such as pentacene. They are also linked by weak end-to-end C-H...O interactions along the ac diagonal.

The title compound, C17H16O5, is a previously unreported substituted semibulvalene cage compound (that is, a tricyclic hydrocarbon formed from one cyclopropane and two cyclopentene rings which also has one double bond fused to a benzene ring). It has one methoxy substituent attached to the bridgehead C atom that links only the two cyclopentene rings and two methyl carboxylate groups located on the C atom shared by all three non-benzene rings and that shared only between the cyclopropane and the cyclopentene rings. The stereochemistry of the two enantiomers (racemate) that assemble in each unit cell is RRRS and SSSR. In the crystal, molecules are linked via C-H...O hydrogen bonds and C-H...[pi] interactions, forming double-layered sheets lying perpendicular to the a axis.

In the title compound, C16H26NO+.Cl-.0.5H2O, the asymmetric unit consists of two independent cations, their respective chloride anions and a solvent water molecule. Together they form a discrete crescent-shaped entity linked by hydrogen bonds from the central water atom to two Cl- ions and from the latter to two protonated imine groups. The geometries of the two independent cations are essentially the same. The planar N=C(O)CH3 groups in each (r.m.s. deviations = 0.0011 and 0.0026 A) form dihedral angles of 75.28 (5) and 79.10 (4)degrees with the benzene rings. In one cation, the methyl atoms of one of the isopropyl groups were modeled as disordered over two sets of sites, with refined occupancies of 0.589 (17) and 0.411 (17).

The title compound, C12H10Br2, is a bridged ring system based on a homobenzonorbornadiene framework. The exo configuration of one of the Br atoms was previously assigned via NMR correlations and has now been confirmed by the geometry of the solid-state structure. The compound features a Br-C-C-Br torsion angle of 66.68 (12)degrees, whereby the C atoms in the calculation are respectively sp(3)- and sp(2)-hybridized.

A general synthetic route to 3-trifluoromethyl-5-aryl-1 lambda(3)-1,2,4,6-thiatriazinyl radicals was developed. X-ray structures were obtained for all five neutral radicals and show that they exist in the solid state as cofacial dimers linked by S center dot center dot center dot S contacts. X-ray structures were also obtained for two of the precursor chlorothiatriazines along with several aryl N-imidoylamidines, p-methoxybenzamidine, and N-chlorosulfonyl-N,N'-benzamidine. Cyclic voltammetric studies were performed on the [R2C2N3S](center dot) radicals in CH3CN and CH2Cl2 with ["Bu4N][PF6] as the supporting electrolyte under vacuum conditions in an all-glass electrochemical cell. The results provide quasi-reversible formal potentials for the [R2C2N3S](-/0) process in the range of 0.61 to 0.47 V, irreversible peak potentials for the [R2C2N3S](0/+) process from 0.59 to 0.91 V at lower concentrations, and the appearance of a second, reversible oxidation process from 0.69 to 0.94 V at higher concentrations (versus the Fc(0/+). couple; Fc = ferrocene). This behavior was indicative of monomer dimer equilibrium in solution, as ascertained from digital models of the voltammograms. There is a small but measurable trend in both the oxidation and reduction potentials with varying remote aryl substituents. EPR spectra were obtained for all five neutral radicals in CH2Cl2 solutions, which confirm the concentration of the unpaired electron density on the heterocyclic core. Trends were also seen in the hyperfine splitting constants a(N) with varying remote aryl substituents. Calculations were performed for all three oxidation states of the [R2C2N3S](-/center dot/+) monomeric rings; the resulting theoretical redox energies correlate well with solution phase voltammetric data.

In the title compound, [Mo(C37H53N3)(CO)(3)], the Mo atom to ring-centroid distance in the eta(6)-coordinated tricarbonyl-molybdenum group is 1.958 (1) angstrom. The three C O groups are pseudo-octahedrally disposed with C-Mo-C angles ranging from 80.7 (1) to 87.4 (1)degrees. The two uncoordinated 2,6-diisopropylphenyl-substituted benzene rings form dihedral angles of 75.96 (8) and 78.01 (9)degrees with the mean plane of the guanidine group. The coordinated benzene ring is in a slight sofa conformation with the N-substituted C atom and the bonded N atom dispaced by 0.090 (3) and 0.458 (4) angstrom, respectively, from the mean plane of the remaining ring atoms. In the crystal, despite there being two N-H donor groups, no conventional hydrogen bonds are present. This may be because of the steric effects of the bulky diisopropylphenyl groups.

The title compound, C(10)H(10)Cl(3)N(3), features a delocalized unsaturated N - C - N - C - N chain and strong intramolecular N-H center dot center dot center dot N hydrogen bonding across the chelate ring and also intramolecular N-H center dot center dot center dot Cl contacts to a CCl(3)-group Cl atom. The only intermolecular contacts in the lattice are non-classical hydrogen bonds between methyl and CCl(3) groups. The pseudo-six-membered ring is distinctly non-planar by virtue of rotation about the N-C bond between the carboximidamide and imine components [C-N-C-N torsion angle = -23.6 (2)degrees].

In the solid state, 4-methoxy-N'-(2,2,2-trichloroethanimidoyl)benzene-1-carboximidamide, C10H10Cl3N3O, (I), N'-(2,2,2-trichloroethanimidoyl) benzene-1-carboximidamide, C9H8Cl3N3, (II), 4-chloro-N'-(2,2,2-trichloroethanimidoyl) benzene-1-carboximidamide, C9H7Cl4N3, (III), 4-bromo-N'-(2,2,2-trichloroethanimidoyl) benzene-1-carboximidamide, C9H7BrCl3N3, (IV), and 4-trifluoromethyl-N'-(2,2,2-trichloroethanimidoyl) benzene-1-carboximidamide, C10H7Cl3F3N3, (V), display strong intramolecular N-H center dot center dot center dot N hydrogen bonding across the chelate ring and also intramolecular N-H center dot center dot center dot Cl contacts. Additional intermolecular hydrogen bonds link the molecules into chains, double chains or sheets in all cases except for compound (V). For compound (II), there are three independent molecules per asymmetric unit.

The prototypal 1,5,2,4,6,8-dithiatetrazocine has been synthesized for the first time by two routes: reaction of 1,2,3,5-dithiadiazolium chloride with N, N, N'-tris(trimethylsilyl) formamidine in acetonitrile and reaction of 1,2,3,5-dithiadiazolyl radical with dioxygen in solution. Yields are low but single crystals could be obtained for an X-ray crystal structure determination which shows it to have the planar delocalized structure predicted by B3LYP/6-311+G(2d,p) hybrid DFT calculations. The crystal structure is strongly reminiscent of that of benzene in the same Pbca space group. Aromaticity is demonstrated by a H-1 NMR chemical shift of +9.70 ppm indicative of diamagnetic ring shielding and an intense low-energy optical absorption with lambda(max) = 349 nm (MeOH). The voltammetric behaviour of the title compound is compared with that of 1,3 lambda(4)delta(2),5,2,4-trithiadiazepine; both resist electrochemical oxidation and reduction over a wide potential range as is typical for aromatic heterocycles.

n/a

The Pd-3(dppm*)(3)(CO)(n+) enantiomers (n = 2 (2), 1 (3)) were prepared either from (R, R)-or (S, S)-P-chirogenic bis(phenyl-m-xylylphosphino) methane (dppm*; 1) and Pd(OAc) 2 in the presence of CF3CO2H, CO and water (n = 2), and then by reductive electrolysis (n = 1). The stable enantiomeric [Pd-3((S,S)-dppm*)(3)(CO)](+center dot) (3), is the first C-3-symmetry radical-cation M-M bonded cluster, therefore the odd electron is delocalized onto the Pd-3 frame within this symmetry. The novel chiral species have been characterized by circular dichroism (CD) of both enantiomers of the Pd-3(dppm*)(3)(CO)(2+) clusters (2) and by EPR spectroscopy for the Pd-3((S, S)-dppm*)(3)(CO)(+center dot) paramagnetic compounds (3, g = 2.041). Evidence for reduced symmetry with respect to the achiral cluster was also obvious from the hyperfine splittings of the EPR signal which display three different hyperfine coupling values: 3 A(31P) = 83.9 10(-4) cm(-1), 3 X A(P-31) = 69.7 10(-4) cm(-1), 3 A(Pd-105) = 12.5 10(-4) cm(-1). In the absence of an X-ray structure for the paramagnetic clusters, DFT computations were performed to address the geometry. The optimized geometry of the Pd-3((S, S)-dppm*)(3)(CO)(+center dot) radicals (3) exhibits three phosphorus atoms placed well above the Pd-3 plane, while the three others are located below the trimetallic frame within C-3-symmetry due to intramolecular steric hindrance. This makes them chemically different with respect to the carbonyl group and explains the experimental EPR spectrum well. Consequently this C-3-symmetry deformation also induces a change in the shape of the SOMO (semi-occupied molecular orbital) towards this same symmetry compared to the corresponding achiral C-3v species.

The structure of the title compound, [Mg-2(C4H9)(C14H18NO)(3)], contains two Mg atoms bridged by two mu(2)-O atoms from two of the three ketiminate ligands, while the third ketiminate is strictly chelating to one of the Mg atoms, which is thereby five-coordinate. In place of a chelating ligand, the second Mg atom is ligated by a single terminal n-butyl group and thus is four-coordinate. This is, so far, the only structurally characterized mixed magnesium ketiminate-alkyl cluster. The geometry at the first Mg atom is close to trigonal-bipyramidal with one chelating and one bridging O atom in the axial positions and two chelating N and one bridging O atom in the equatorial positions. The geometry at the second Mg atom is very distorted from tetrahedral, with an O-Mg-C angle of 131.0 (1)degrees.

The title compound, C3H2Cl3N3, crystallizes as the Z isomer with respect to the C=N bond. The -C(NH2)=NCN functional group is effectively planar (r.m.s. deviation = 0.016 angstrom), with only the three Cl atoms out of the molecular plane. A strong network of N-H center dot center dot center dot N hydrogen bonds forms dimers which are associated into ribbons in the crystal structure. Hydrogen bonding is suspected to be the cause of the near-equivalence of the formal C-N and C=N bonds (Delta(CN) = 0.008 angstrom)

Voltammetric studies of S2N2 employing both cyclic voltammetry (CV) and rotating disk electrode (RDE) methods on GC electrodes at room temperature (RT) revealed two irreversible reduction processes at about -1.4 V and -2.2 V in CH3CN, CH2Cl2, and tetrahydrofuran (vs ferrocene) and no observable oxidation processes up to the solvent limit when the scan is initially anodic. However, aftercycling the potential through -1.4 V, two new couples appear near -0.3 V and -1.0 V due to [S3N3](-/0) and [S4N4](-/0) respectively. The diffusion coefficient D for S2N2 was determined to be 9.13 x 10(-6) cm(2) s(-1) in CH2Cl2 and 7.65 x 10(-6) cm(2) s(-1) in CH3CN. Digital modeling of CVs fits well to a mechanism in which [S2N2](-center dot) couples rapidly with S2N2 to form [S4N4](-center dot), which then decomposes to [S3N3](-). In situ electron paramagnetic resonance (EPR) spectroelectrochemical studies of S2N2 in both CH2Cl2 and CH3CN resulted in the detection of strong EPR signals from [S4N4](-center dot) when electrolysis is conducted at -1.4 V; at more negative voltages, spectra from transient adsorbed radicals are observed. In moist solvent or with added HBF4, a longer-lived spectrum is obtained due to the neutral radical [S2N2H](-)center dot, identified by simulation of the EPR spectrum and density functional theory (DFT) calculations. The chemical reduction Of S2N2 with Na[C10H8] or Na[Ph2CO] produces [Na(15-crown-5)][S3N3], while reduction with cobaftocene gives [Cp2Co][S3N3]. The X-ray structure of the former reveals a strong interaction (Na center dot center dot center dot N = 2,388(5) angstrom) between the crown ether-encapsulated Na+ caton and one of the nitrogen atoms of the essentially planar six-membered cyclic anion [S3N3](-).

Isobenzofurans (IBF)s have seen widespread use in the synthesis of both natural products and polycyclic aromatic hydrocarbons. There are few examples that have two IBF entities linked in a fused aromatic ring system. Here we present the synthesis and characterization of a bis(IBF), 2,7-di(tert-butyl)pyreno[4,5-c:9,10-c']difuran. Reaction with bis(maleimide) dienophiles gives pyrenophanes. The solid-state structures of the bis(IBF) and two cyclophanes are discussed.

A series of phenyl-substituted bis(isobenzofuran)s in which the furan moieties are linked by 1,3-phenylene, 1,4-phenylene, or 4,4'-biphenylene linkers have been prepared in only two steps. They are comparable to diphenylisobenzofuran in their absorption and luminescent properties, their electrochemistry, and their reactivity. Their degree of similarity to diphenylisobenzofuran was found to depend significantly on the nature of the linking group. Diels-Alder reaction of the title compounds and subsequent aromatization gave very rapid access to penta- or hexa-aryl products.

The unsaturated redox-active cluster [Pd(3)(dppm)(3)(CO)](n+) (n = 0,1, or 2) reacts with ethylene dicarboxylic esters and a variety of terminal acetylenes (but not PhC CPh) in all three charge states. In particular, the radical cations [Pd(3)(dppm)(3)(CO)(RC CR')](+) can be produced by several routes: one-electron electrochemical reduction of the dication adducts, comproportionation of the neutral and dicationic adducts, as well as the direct complexation of alkyne to the known radical cation [Pd(3)(dppm)(3)(CO)](+). Compared with the latter, each of the adducts have significantly extended lifetimes and classify as persistent radicals in solution. The alkyne adducts have been characterized by voltammetry (cyclic and rotating disk electrode), by UV-vis titrations and by MALDI-TOF mass spectra from dithranol matrices. Isotropic solution EPR spectra of the adducts with R = R' = MeOC(O) and EtOC(O), as well as those with R' = H and R = C(6)H(5), FC(6)H(4), HC CC(6)H(4), and EtO have been obtained. Full line shape fitting simulations demonstrate that all display coupling to six different (31)P (I = 1/2) and to one to three (106)Pd (I = 5/2) nuclei. The A((31)P) values range from a low of 3.0 x 10(4) to a high of 180.5 x 10(4) cm(-1); this variation is caused by changes in the contribution of P s orbitals to the SOMO resulting from structural distortions of the Pd(3)P(6) core upon alkyne coordination.

In the title compound, C5H8N3+center dot Cl-, the cation and the anion lie on a mirror plane and are hydrogen bonded in a three-dimensional network via the H atoms of the two hydrazine N atoms. The pyridine N atom is protonated and hydrogen bonded to the terminal hydrazine N atom.

Voltammetric studies Of S4N4 employing both cyclic (CV) and rotating disk (RDE) methods in CH2Cl2 at a glassy carbon electrode reveal a one-electron reduction at -1.00 V (versus ferrocene/ferrocenium), which produces a second redox couple at -0.33 V, confirmed to be the electrochemically generated [S3N3](-) by CV studies on its salts. Diffusion coefficients (CH2Cl2/0.4 M [(Bu4N)-Bu-n][PF6]) estimated by RDE methods: S4N4, 1.17 x 10(-5) cm(2) s(-1); [S3N3](-), 4.00 x 10(-6) cm(2) s(-1). Digital simulations of the CVs detected slow rates of electron transfer for both couples and allowed for a determination of rate constants for homogeneous chemical reaction steps subsequent to electron transfer. The common parameters (k(f1) = 2.0 +/- 0.5 s(-1), k(s1), = 0.034 +/- 0.004 cm s(-1) for [S4N4](-/0); k(f2) = 0.4 +/- 0.2 s(-1), k(s2) = 0.022 +/- 0.005 cm s(-1) for [S3N3](-/0) at T= 21 +/- 2 degrees C) fit well to a "square-scheme" mechanism over the entire range of data with first order decay of both redox products. An alternate model could also be fit wherein [NS](center dot) liberated in the first step reacts with formed [S3N3](center dot) to reproduce S4N4 with an apparent second order rate constant k(f2)' = 1.1 +/- 0.3 x 10(3) M-1 s(-1). The crystal structure of [PPN][S3N3] was determined by X-ray crystallography indicating the solvation of the anion by 1 equiv of methanol. The generated [S4N4](-center dot) radical anion was detected by the Simultaneous Electrochemical Electron Paramagnetic Resonance (SEEPR) method to give: (a) [S-32(4) N-14(4)](-center dot), 9 lines, a(N-14) = 0.118 mT; (b) [(S4N4)-S-32-N-15](-center dot), 5 lines, a(N-15) = 0.164 mT; (C) [(S4N4)-S-33-N-14](-center dot), estimated a(N-14) = 0.118, a(S-13 = 0.2 mT); g = 2.0008(1). Equivalence of S-33 hyperfine splittings is consistent with dynamic averaging of the C-2v geometry in solution. High-level electronic structure calculations provide evidence for an open-shell doublet triradicaloid character to the ground state wave function Of [S3N3](center dot).

A silylated derivative of naphtho[1,2-c:5,6-c]difuran, 1,3,6,8-tetrakis(tert-butyldimethylsilyl)naphtho[1,2-c:5,6-c]difuran, has been isolated and its X-ray crystal structure determined. Bond localization confirms the polyene character of this isobenzofuran ring system. This molecule undergoes two successive Diels-Alder reactions with second-order rate constants differing by over 2 orders of magnitude, consistent with predictions based on their structure-count ratios and with the reactivity of the novel 1,3-bis(tert-butyldimethylsilyl)isobenzofuran. Crystal structures of two cyclophanes derived from the reaction of naphtho[1,2-c:5,6-c]difuran and bis(imide) or bis(ester) dienophiles show marked differences in the conformation of the aliphatic chain found in the solid state.

The heterotrinuclear complexes, [(CpTiCl(2)Cp-PPh(2))(2)Cu](+) (2) (as PF(6)(-) salt) and [CpTiCl(2)Cp-PPh(2)](2)CuCl (3), containing two electron-poor Ti(IV) fragments and one electron-rich Cu(I) center, and a tetrametallic species, [(CpTiCl(2)Cp-PPh(2))Cu(mu-Cl)](2) (4), were synthesized and characterized. The trinuclear nature of 2 and 3 was demonstrated by X-ray crystallography for which the three metallic centers are held together by two CpPPh(2) ligands. Weak Cl center dot center dot center dot Cu interactions are noted in 3, whereas two stronger Cl-Cu bridges are depicted in the cationic complex 2. The tetranuclear complex 4 contains two Cu atoms bridged together by two chloride ligands and connected to one Ti atom by one CpPPh(2) ligand and one mu-Cl ligand. Despite the short distances in the Ti-Cl-Cu bridges, notably in 2 and 4, the NMR spectra reveals evidence of fluxion in solution attributed to the lability of the mu-Cl ligands. Electrochemical experiments performed on 2 (rotating disk electrode and cyclic voltammograms) demonstrated the presences of two successive 1-electron reductions generating a first structurally unsymmetrical paramagnetic species [(CpTiCl(2)CP-PPh(2))(2)Cu](0) (2') confidently characterized by electron paramagnetic resonance (EPR) as a Ti(III)-Cu(I)-Ti(IV) system, and a second one, which is tentatively assigned to a symmetric neutral complex formulated as [CpTiClCp-PPh(2)](2)CuCl (5) with an EPR signature indistinguishable from that of 2' (i.e., Ti(III)-Cu(I)-Ti(III) system with a similar electronic environment). Density functional theory (DFT) computations examining the nature of the frontier orbitals and the geometry confirmed the presence and lack of symmetry in 2 and 2', respectively. The detection of chemical/electrochemical mechanisms in the electrochemical studies provides a clear explanation for the stepwise reduction behavior in these systems through chloride ligand transfer from Ti to Cu prior to the first reduction step. This transfer process is fully reversible upon re-oxidation. The electrochemical properties of complexes 3 and 4 are also reported.

A straightforward and efficient synthetic route to thiazolyl phosphines is reported. Moreover, the first application of these molecules in catalysis is described. These phosphines are excellent ligands in the copper-catalyzed arylation and vinylation of nucleophiles. The reactions could be performed in acetonitrile and various mixed aqueous/organic solvents and even in pure water in the presence of a phase transfer catalyst. In each case, coupling products are obtained with high yields at very mild temperatures.

DFT calculations for the group 15 radicals [PhB(mu-(NBu)-Bu-t)(2)](2)M-center dot (M = P, As, Sb, Bi) predict a pnictogen-centered SOMO with smaller contributions to the unpaired spin density arising from the nitrogen and boron atoms. The reactions of Li-2[PhB(mu-NR)(2)] (R = Bu-t, Dipp) with PCl3 afforded the unsolvated complex LiP[PhB(mu-(NBu)-Bu-t)(2)](2) (1a) in low yield and CIP[PhB(mu-NDiPP)(2)] (2), both of which were structurally characterized. Efforts to produce the arsenic-centered neutral radical, [PhB(mu-(NBu)-Bu-t)(2)](2)As-center dot, via oxidation of LiAs[PhB(mu-(NBu)-Bu-t)(2)](2) with one-half equivalent of SO2Cl2, yielded the Zwitterionic compound [PhB(mu-(NBu)-Bu-t)(2)As(mu-(NBu)-Bu-t)(2)B(Cl)Ph] (3) containing one four-coordinate boron center with a B-Cl bond. The reaction of 3 with GaCl3 produced the ion-separated salt, [PhB(mu-(NBu)-Bu-t)(2)](2)As+GaCl4- (4), which was characterized by X-ray crystallography. The reduction of 3 with sodium naphthalenide occurred by a two-electron process to give the corresponding anion [{PhB(mu-(NBu)-Bu-t)(2)}(2)As](-) as the sodium salt. Voltammetric investigations of 4 and LiAs[PhB(mu-(NBu)-Bu-t)(2)](2) (1b) revealed irreversible processes. Attempts to generate the neutral radical [PhB(mu-(NBu)-Bu-t)(2)](2)As-center dot from these ionic complexes via in situ electrolysis did not produce an EPR-active species.

The reaction of the 1,2,3,5-dithiadiazolyls (4-R-C6H4CN2S2)(2) (R = Me, 2a; Cl, 2b; OMe, 2c; and CF3, 2d) and (3-NC-5-(BU)-B-t-C6H3CN2S2)(2) (2e) with [CpCr(CO)(3)](2) (CP = eta(5)-C5H5) (1) at ambient temperature respectively yielded the complexes CpCr(CO)(2)(eta(2)-S2N2CC6H4R) (R = 4-Me, 3a; 4-Cl, 3b; 4-OMe, 3c; and 4-CF3, 3d) and CpCr(CO)(2)-(eta(2) -S2N2CC6H3-3-(CN)-5-(Bu-t)) (3e) in 35-72% yields. The complexes 3c and 3d were also synthesized via a salt metathesis method from the reaction of NaCpCr(CO)(3) (1B) and the 1,2,3,5-dithiadiazolium chlorides 4-R-C6H4-CN2S2Cl (R = OMe, 8c; CF3, 8d) with much lower yields of 6 and 20%, respectively. The complexes were characterized spectroscopically and also by single-crystal X-ray diffraction analysis. Cyclic voltammetry experiments were conducted on 3a-e, EPR spectra were obtained of one-electron-reduced forms of 3a-e, and variable temperature H-1 NMR studies were carried out on complex 3d. Hybrid DFT calculations were performed on the model system [CpCr(CO)(2)S2N2CH] and comparisons are made with the reported CpCr(CO)(2)(pi-allyl) complexes.

In the structure of the title compound, C16H14Br2, the central C=C bond length is 1.329 (4) angstrom and the two benzene rings are approximately coplanar with the double bond, with twist angles of 7.5 (2) and 13.6 (2)degrees.

The structure of the title compound, 1,3-diphenyl-2-benzofuran, C20H14O, exhibits a distinct alternation of short [mean 1.361 (3) angstrom] and long [ mean 1.431 (3) angstrom] C-C bonds around the benzofuran ring system, indicating a predominantly polyene character. Over 60 Diels-Alder adducts of this commercially available furan have been structurally characterized, but this is the first report of the structure of the parent compound.

The title phosphine, Dipp(3)P, was synthesized using an aryl copper reagent and the structure determined by X-ray crystallography (R=2.94%): d(P - C)=1.852(1) angstrom, angle C - P - C=111.88(5)degrees. In hexane solution, the electronic spectrum displays 3 bands [326 (9.3), 254 (8.7), 205 (11.4) nm (log|epsilon|)] and the fluorescence spectrum has a Stokes shift of 129 kJ mol(-1). NMR: ( d) P-31= - 49.7 ppm in solution and - 49.5 in the solid (CP-MAS). Room temperature 1 H and 13 C spectra reflect D-3 symmetry, changing below - 30 degrees C to C-3. A variable temperature NMR study provided an activation enthalpy of 49(+/- 1) kJ mol(-1) and entropy of 24 - 27(+/- 5) J mol(-1) K-1. An energy surface calculation using HF/3-21G theory discovered a single low-energy path describing pyramidal inversion through a transition state that is close to D3 geometry. The B3LYP/6-31G(d) calculated barrier to planarization is 37.5 kJ mol(-1). Voltammetric studies employing cyclic, rotating disk, steady state and Fourier Transform ac methods confirm a fully chemically reversible one-electron oxidation of Dipp(3)P to Dipp(3)P(+center dot) at +0.18 (CH3CN - (Bu4NPF6)-Bu-n) and +0.09 (CH2Cl2 - (Bu4NPF6)-Bu-n) V vs. Fc(+/0) (Fc=ferrocene). The diffusion coefficient for Dipp(3)P is 1.0 - 1.2 x 10(5) cm(2) s(-1). The electrode process displays quasi-reversible electron transfer kinetics [k(s)approximate to 0.01 (CH2Cl2) to 0.08 (CH3CN) cm s(-1)]. Optically transparent thin layer electrolysis reversibly generates Dipp(3)P(+center dot) in CH2Cl2 - (Bu4NPF6)-Bu-n [UV- Vis: 498 (3.31), 456 (3.29), 373 (4.04), 357 (3.84), 341 (3.49), 296 (3.78), 385 (3.91), 251 (3.99) nm (log|epsilon|)]. The EPR spectrum of Dipp(3)P(+center dot) in solution is a doublet (a(P)=23.9 mT, g=2.008), and in frozen solution is axial (a(parallel to)=42.6 mT, g(parallel to)=2.0045; a(perpendicular to)=12.7 mT, g(perpendicular to)=2.0085 mT).

The highly reactive palladium-centered radical cluster [Pd-3(dpPM)(3)(CO)](center dot+) exhibits only a limited stability in solution at room temperature (about an hour). This stability can be extended significantly to several hours by adding organic substrates such as the symmetric and asymmetric alkynes Ph-C C-H and MeO2C-C C-CO2Me, which reversibly bind to the Pd-3 triangle. The presence of the substrate inside the cavity protects the palladium centers from reacting with the "outside world", hence enhancing the stability. Both adducts are stable as the cluster is always totally recovered. The paramagnetic complexes along with their corresponding dications were characterized by EPR, variable-temperature P-31 NMR, UV-vis and MALDI-TOF spectroscopy, and electrochemistry. For the MeO2C-C C-CO2Me/[Pd-3-(dppm)(3)(CO)](2+) complex, the analysis of the low-temperature P-31 NMR spectra strongly suggests a major structure modification of the ligand and substrate with respect to the starting materials.

The combined use of theoretical and mathematical methods in the analysis of electron paramagnetic resonance data has greatly increased the ability to interpret even the most complex spectra reported for doublet state inorganic main group radicals. This personal account summarizes the theoretical basis of such an approach and provides an in-depth discussion of some recent illustrative examples of the utilization of this methodology in practical applications. The emphasis is on displaying the enormous potential embodied within the approach. (c) 2006 Elsevier B.V. All rights reserved.

The scattered electron paramagnetic resonance (EPR) spectroscopic data for binary sulfur-nitrogen (S,N) radicals have been compiled and critically assessed. Many of these are inorganic rings or cages. For each species, possible equilibrium structures in the gas phase and the EPR hyperfine coupling (hfc) constants have been calculated with DFT using the B3LYP functional and basis sets of triple-zeta (or better) quality. Good agreement is obtained between calculated and measured values for the well characterized [S(3)N(2)](+), a planar pi-radical for which the s-component of the orbitals is likely to be reasonably independent of minor geometrical changes between gas-phase and condensed-phase states. The cage compounds [S(4)N(4)](-.) and [S(4)N(5)](-2), for which reliable experimental EPR spectra have been reported, show larger variation between calculated and measured hfc, as a consequence of the dependence of the s orbital content of the molecular orbitals on small structural changes. The very large disagreements between the DFT calculated and experimentally claimed hfc constants for [NS](-), [SNS](-) and [S(4)N(4)](-3), in condensed phases lead us to question their assignment. Among binary S,N radicals, (33)S hfc data has only been reported for [S(3)N(2)](+.) (through isotopic enrichment). These values were essential for the correct identification of the EPR spectra of this important radical, which previously was misassigned to other species. Our results suggest that (33)S data will be equally important for the correct identification of the EPR spectra of other binary S,N species, many of which are cyclic systems, e.g. [S(3)N(3)](.), [S(4)N(3)](.) and [S(4)N(5)]. (c) 2006 Elsevier B.V. All rights reserved.

A rational synthesis for 5-tert-butyl-3-cyano-1-(1,2,3,5-dithiadiazolyl) benzene; which was first observed from thermal cleavage of the bis-dithiadiazolyl, has been developed. Voltammetry and electron paramagnetic resonance (EPR) spectra for this radical are reported and its X-ray structure is described. Despite the bulky Bu-t substituent, the cyano supramolecular synthon is still able to maintain links to a single neighbouring sulfur atom of the S-2 unit, as previously observed in cyano-substituted dithiadiazolyls. In the eta(2) complex with CpCr(CO)(2), no such interactions are observed; the nitrile group forms a centrosymmetric dimer through weak contacts with the para H atom on the aryl ring of the partner molecule. This behaviour is contrasted to similar complexes of less bulky dithiadiazolyls, where intermolecular interactions are retained in the crystalline lattice. (c) 2006 Elsevier B.V. All rights reserved.

The 2:1 adduct of benzyne with 2-methylanisole is shown to have the bisbenzotricyclic structure 6,6a,11,11a-tetrahydro-5-methoxy-6-methyl-5,6,11-metheno-5H-benzo[a]fluorene by a single-crystal X-ray diffraction study (C20H18O: Pca2(1), a = 15.0497(17), b = 9.87783(11), c = 9.6846(11); Z = 4; 1672 data points, R, = 0.0325). This structure is compared to an unpublished crystal structure of the parent hydrocarbon 6,6a, 11, 11a-tetrahydro-5,6,11-metheno-5H-benzo[a]fluorene, C18H14. Both structures have also been computed by DFT methods at the B3LYP/6-311 (d,p) level of theory. Bond distances and angles between the solid-state measurements and gas-phase calculations are found to agree well; average deviations are well below 1%. The H-1 NMR spectra show surprisingly small (3)J(HH) couplings in the central tricyclic cage, but can be assigned using 2D spectroscopy.

The previously unknown radical anions of unsaturated E2N4S2 ring systems (E = RC, R2NC, R2P) can be generated voltammetrically by the one-electron reduction of the neutral species and, despite half-lives on the order of a few seconds, have been unambiguously characterized by electron paramagnetic resonance (EPR) spectroelectrochemistry using a highly sensitive in situ electrolysis cell. Cyclic voltammetric studies using a glassy-carbon working electrode in CH3CN and CH2Cl2 with [(Bu4N)-Bu-n][PF6] as the supporting electrolyte gave reversible formal potentials for the [E2N4S2](0/-) process in the range of -1.25 to -1.77 V and irreversible peak potentials for oxidation in the range of 0.66 to 1.60 V (vs the Fc(+/0) couple; Fc = ferrocene). Reduction of the neutral compound undergoes an electrochemically reversible one-electron transfer, followed by the decay of the anion to an unknown species via a first-order (chemical) reaction pathway. The values of the first-order rate constant, k(f), for the decay of all the radical anions in CH2Cl2 have been estimated from the decay of the EPR signals for (X-C6H4CN2S)(2)(center dot-), where X = 4-OCH3 (k(f) = 0.04 s(-1)), 4-CH3 (k(f) = 0.02 s(-1)), 4-H (k(f) = 0.08 s(-1)), 4-Cl (k(f) = 0.05 s(-1)), 4-CF3 (k(f) = 0.05 s(-1)), or 3-CF3 (k(f) = 0.07 s(-1)), and for [(CH3)(3)CCN2S](2)(center dot-) (k(f) = 0.02 s(-1)), [(CH3)(2)NCN2S](2)(center dot-) (k(f) = 0.05 s(-1)), and [(C6H5)(2)PN2S](2)(center dot-) (k(f) = 0.7 s(-1)). Values of k(f) for X = 4-H and for [(CH3)(2)NCN2S](2)(center dot-) were also determined from the cyclic voltammetric responses (in CH2Cl2) and were both found to be 0.05 s(-1). Possible pathways for the first-order anion decomposition that are consistent with the experimental observations are discussed. Density functional theory calculations at the UB3LYP/6-31G(d) level of theory predict the structures of the radical anions as either planar (D-2h) or folded (C-2v) species; the calculated hyperfine coupling constants are in excellent agreement with experimental results. Linear correlations were observed between the voltammetrically determined potentials and both the orbital energies and Hammett coefficients for the neutral aryl-substituted rings.

The title compound, C5H12N+center dot Cl-, contains [Et2N = CH2](+) and Cl- ions. The C = N double-bond distance is 1.2729 (13) angstrom and the sum of the angles around the central N atom is 359.92 degrees. There are short contacts [2.973 (1) angstrom] between the iminium C atom and the Cl- ion and between five of the C-H H atoms and the Cl- ion, of which the shortest is 2.623 (11) angstrom.

The first magnesium and zinc boraamidinate(bam) complexes have been synthesized via metathetical reactions between dilithio, bams and Grignard reagents or MCl2 (M = Mg, Zn). The following new classes of bam complexes have been structurally characterized: heterobimetallic spirocycles {(L)mu-Li[PhB(mu-(NBu)-Bu-t)(2)]}(2)M (6a, b, M = Mg, L = Et2O, THF; 6c, M = Zn, L = Et2O); bis(organomagnesium) complexes {[PhB(mu(3)-(NBu)-Bu-t)(2)]((MgBu)-Bu-t)(2)(mu(3)-Cl)Li(OEt2)(3)} (8) and {[PhB(mu(3)-(NBu)-Bu-t)(2)](MgR)(2)(THF)(2)} (9a, R = Pr-i; 9b, R = Ph); mononuclear complex {[PhB(mu-NDiPP)(2)]Mg-(OEt2)(2)} (10). Oxidation of 6a or 6c with iodine produces persistent pink (16a, M = Mg) or purple (16b, M = Zn) neutral radicals {L-x-mu-Li[PhB(mu-(NBu)-Bu-t)(2)](2)M}(circle) (L = solvent molecule), which are shown by EPR spectra supported by DFT calculations to be C-s-symmetric species with spin density localized on one of the bam ligands, In contrast, characterization of the intensely colored neutral radicals {[PhB(mu-(NBu)-Bu-t)(2)](2)M}(circle) (5c, M = In, dark green; 5d, M = B, dark purple) reveals that the spin density is equally delocalized over all four nitrogen atoms in these D-2d(-) symmetric spirocyclic systems. Oxidation of the dimeric dilithio complex {Li-2[PhB(mu(4)-(NBu)-Bu-t)(2)]}(2) with iodine produces the monomeric neutral radical {[PhB(mu-(NBu)-Bu-t)(2)]Li(OEt2)(x)}(circle) (17), characterized by EPR spectra and DFT calculations. These findings establish that the bam anionic radical [PhB((NBu)-Bu-t)(2)](circle-) can be stabilized by coordination to a variety of early main-group metal centers to give neutral radicals whose relative stabilities are compared and discussed.

The homoleptic aryl copper reagent [Cu(4)Dipp(4)] (Dipp=2,6-diisopropylphenyl) has been prepared and structurally characterized by a single-crystal X-ray diffraction study. Its tetrameric structure differs in significant details from that of the previously reported [Cu(4)Tripp(4)] (Tripp=2,4,6-triisopropylphenyl). The electronic structure of the cluster has been probed through B3LYP/6311G(2d,p)//B3LYP/6-31G calculations on [Cu4Ph4] constrained to D-2d symmetry. The utility of the new copper reagent is demonstrated by the preparation of pure DippPCl(2), for which the crystal structure is also reported. (c) 2006 Elsevier B.V. All rights reserved.

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Stable and persistent phosphorus-containing radicals can be divided into five general categories: phosphinyl, diphosphanyl, 1,3-diphosphaallyl, lithiated tetrakisimidophosphates, and phosphaverdazyl systems. The syntheses, structures, EPR spectroscopic characterization, and sources of stability of these neutral radicals are presented and compared.

The title heterocyclic radicals coordinate to either 17e CpCr(CO)(3) or 15e CpCr(CO)(2) moieties as one-electron or as three-electron donors, respectively; in the former the bonding is via the perpendicular p orbital of the sulfur atom, while in the latter bonding is via p(pi) orbitals on both sulfur and nitrogen.

The reaction of Cl3PNSiMe3 with 3 equiv of LiHNR (R = Pr-i, Cy, Bu-t, Ad) in diethyl ether produces the corresponding tris(amino)(imino)phosphoranes (RNH)(3)PNSiMe3 (1a, R = Pr-i; 1b, R = Cy; 1c, R = Bu-t; 1d, R = Ad); subsequent reactions of 1b-d with (BuLi)-Bu-n yield the trilithiated tetraimidophosphates {Li-3[P(NR)(3)(NSiMe3)]} (2a, R = Cy; 2b, R = Bu-t; 2c, R = Ad). The reaction of [((BuNH)-Bu-t)(4)P]Cl With 1 equiv of (BuLi)-Bu-n results in the isolation of ((BuNH)-Bu-t)(3)(PNBu)-Bu-t (1e); treatment of le with additional nBuLi generates the symmetrical tetraimidophosphate {Li-3[P(NtBu)(4)]} (2d). Compounds 1 and 2 have been characterized by multinuclear (H-1, C-13, and P-31) NMR spectroscopy; X-ray structures of 1b,c were also obtained. Oxidations of 2a-c with iodine, bromine, or sulfuryl chloride produces transient radicals in the case of 2a or stable radicals of the formula {Li-2[P(NR)(3)(NSiMe3)]LiX center dot 3THF}(center dot) (X = Cl, Br, I; R = Bu-t, Ad). The stable radicals exhibit C3 symmetry and are thought to exist in a cubic arrangement, with the monomeric LiX unit bonded to the neutral radical {Li-2[P(NR)(3)(NSiMe3)]}(center dot) to complete the Li3N3PX cube. Reactions of solvent-separated ion pair {[Li(THF)(4)]{Li(THF)(2)[(mu-(NBu)-Bu-t)(2)P(mu-(NBu)-Bu-t)(2)]Li(THF)(2)} (6) with I-2 or SO2Cl2 produce the persistent spirocyclic radical {(THF)(2)Li mu-(NBu)-Bu-t)(2)P(mu-(NBu)-Bu-t)Li(THF)(2)}(center dot) (10a); all radicals have been characterized by a combination of variable concentration EPR experiments and DFT calculations.

The geometry of 15 triarylphosphines which differ in the nature of the substituents at the 2 and 6 positions of one or more phenyl rings are compared. The sum of angles around phosphorus, Sigma{angle CPC}, is used as the primary measure of steric bulk. The roles of substituents, which act as steric shields surrounding the phosphine lone pair and of those which generate steric pressure and cause flattening of the C3P pyramid are identified. Both crystallographic and computational (HF 6-31G(d)) structures are used to assess Sigma{angle CPC}, the pyramidalization angle alpha, the average C-P distance, and the helical twist angle of the aryl rings beta. All of these parameters confirm that ortho-2,6-diisopropyl substituted aryl groups generate the most sterically congested triarylphosphines. Comparison to Tolman cone angles are made where these are available. (c) 2004 Elsevier B.V. All rights reserved.

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Detailed electrochemical studies in dichloromethane (0.1 M BU4NPF6) on the oxidation of the half-lantern [Pt-2-((KAs)-As-2,C -C6H3-5-Me-2-AsPh2)(2)(mu-KAS,KC-C6H3-5-Me-2-AsPh2)(2)] (1) and full-lantern [Pt-2(mu-KAS,KC-C6H3-5-Me-2-AsPh2)(4)] (2) complexes reveal the presence of an exceptionally stable dinuclear Pt cation 2(+). Thus, oxidation of 1 occurs on the voltammetric time scale via a ladder-square scheme to give 2(+), whereas 2 is directly converted to 2(+). Electrochemically informed chemical synthesis enabled the isolation of solid [2(+)][BF4-] to be achieved. Single-crystal X-ray structural analysis showed that 2(+) also has a lantern structure but with a shorter separation between the Pt centers [2.7069(3) angstrom (2(+)), 2.8955(4) angstrom (2)]. EPR spectra of 2(+) provide unequivocal evidence for axial symmetry of the complex and are noteworthy because of an exceptionally large, nearly isotropic hyperfine coupling constant of about 0.1 cm(-1). Spectroscopic data support the conclusion that the unpaired electron in the 2(+) cation is distributed equally between the two Pt nuclei and imply that oxidation of 2 to 2(+) leads to the establishment of the metal-tometal hemibond. Results of extended Huckel molecular orbital and density functional calculations on 2 and 2(+) lead to the conclusions that s, p, d2/z mixing of orbitals contributes to the large EPR Pt hyperfine coupling and also that the structural adjustments that occur upon removal of an electron from 2 are driven by the metal-metal bonding character present in 2(+).

Stable dark red (M = Al) or dark green (M = Ga) neutral radicals {[PhB(mu-(NBu)-Bu-t)(2)](2)M}(center dot) are obtained by the oxidation of their corresponding anions with iodine, and EPR spectra supported by DFT calculations show that the spin density is equally delocalized over all four nitrogen atoms in these spiroconjugated systems.

The stoichiometric reaction of the bulky benzamidine N, N'-bis(2,6-diisopropylphenyl)-4-toluamidine (HDippAm) with the metal alkyls (BuLi)-Li-n (1 : 1 in THF), Bu2Mg (2 : 1 in THF) and Me3Al (1 : 1 in Et2O) is presented. This provides the mononuclear dihapto benzamidinate compounds [Li(DippAm)(THF)(2)] (1), [Mg(DippAm)(2)] (2) and [Al(DippAm)Me-2] (3), respectively. Compound 3 was also obtained by salt elimination using dimethylaluminium chloride and 1. All three compounds exhibit sterically strained geometries that are maintained in solution at increased temperatures. Compound 3 displays exceptional thermal and aerobic stability, while 2 constitutes a rare example of non-porphyrin supported square planar magnesium.

The reaction of ((BuNH)-Bu-1)(3)PNSiMe3 (1) with 1 equiV of (BuLi)-Bu-n results in the formation of Li[P((NHBU)-B-1)(2)((NBu)-Bu-t)(NSiMe3)] (2); treatment of 2 with a second equivalent of nBuLi produces the dilithium salt Li-2[P((NHBu)-Bu-t)((NBU)-B-t)(2)(NSiMe3)] (3). Similarly, the reaction of 1 and (BuLi)-Bu-n in a 1:3 stoichiometry produces the trilithiated species Li-3[P((NBU)-B-t)(3)(NSiMe3)] (4). These three complexes represent imido analogues of dihydrogen phosphate [H2PO4](-), hydrogen phosphate [HPO4](2-), and orthophosphate [PO4](3-), respectively, Reaction of 4 with alkali metal alkoxides MOR (M = Li, R = SiMe3; M = K, R = Bu-t) generates the imiclo-alkoxy complexes {Li-3[P((NBU)-B-t)(3)(NSiMe3)](MOR)(3)} (8, M = Li; 9, M = K). These compounds were characterized by multinuclear (H-1, Li-7, C-13, and P-31) NMR spectroscopy and, in the cases of 2, 8, and 9-3THF(1) by X-ray crystallography. In the solid state, 2 exists as a dimer with Li-N contacts serving to link the two Li[P((NHBu)-Bu-t)(2)((NBu)-Bu-t)(NSiMe3)] units. The monomeric compounds 8 and 9-3THF consist of a rare M3O3 ring coordinated to the (LiN)(3) unit of 4. The unexpected formation of the stable radical {(Me3SiN)P(mu(3)-(NBU)-B-t)(3)[mu(3)-Li(THF)](3)((OBu)-Bu-t)} (10) is also reported. X-ray crystallography indicated that 10 has a distorted cubic structure consisting of the radical dianion [P((NBU)-B-t)(3)(NSiMe3)](*2-), two lithium cations, and a molecule of (LiOBu)-Bu-t in the solid state. In dilute THF solution, the cube is disrupted to give the radical monoanion [(Me3SiN)((BuN)-Bu-t)P-(mu-(NBu)-Bu-t)(2)Li(THF)(2)](*-), which was identified by EPR spectroscopy.

The EPR spectra of six 1,2,4,6-thiatriazinyls have been redetermined and simulated using modern computer simulation programs. The hyperfine coupling (hfc) constants determined from the simulations differ in some cases significantly from those reported previously. The presence of unresolved coupling also can be detected in some of the spectra. The hfc values to the two kinds of nitrogen atoms in the ring vary in a systematic fashion with the relative electron-withdrawing character of the substituents attached to the ring carbon atoms at the 3 and 5 positions.

The reaction of DippPH(2) ( Dipp = 2,6-(Pr2C6H3)-Pr-i) with DippN=C(p-CH3C6H4)Cl in refluxing xylenes affords DippP=C(p-CH3C6H4)N(H) Dipp; deprotonation with alkali metal reagents produces unique lithium and potassium complexes with the ligand in a different geometry to that of the free phosphaamidine.

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The bulky primary phosphane 2,6-diisopropylphenylphosphane, DipPH(2), has been prepared from 1-bromo-2,6-diisopropylbenzene via the reaction of the Grignard reagent with PCl3. The resulting mixed phosphonous dihalides DipP(Cl,Br)(2) are reduced with LiAlH4 to yield the title compound in reasonable yield and on a synthetically useful scale. DipPH(2) is also used to prepare the monosilylated derivatives DipPHSi(CH3)(3) and DipPH{Si(CH3)(2)-t-Bu} as well as the disilylated compounds DipP{Si(CH3)(3)}(2) and DipP{Si(CH3)(2)-t-Bu}(2). All products have been fully characterized by IR, mass, and NMR spectroscopy. The crystal structure of DipPH{Si(CH3)(2)-t-Bu} was determined from single-crystal diffraction data: C18H33PSi, P2(1)/c, Z = 4, a = 8.5768(10), b = 28.104(3), c = 8.1102(4) Angstrom, beta = 93.341(3)degrees (R = 0.0518). Changes in the NMR spectrum of DipPH{Si(CH3)(2)-t-Bu} were observed over the temperature range 178-380 K. Barrier heights were determined from the peak separation at low temperature and the coalescence points: DeltaG(double dagger) approximately equal to 40 kJ mol(-1) for C(aryl)-P bond rotation and approximately equal to 72 kJ mol(-1) for pyramidal inversion at phosphorus.

This review is a critical overview of the literature on electrochemistry of unsaturated ring-compounds containing bonds between Group 15 and Group 16 elements (principally S and N), including metallacycles. It contains a detailed compilation of measured redox potentials and the conditions under which these were obtained for over 200 compounds. An introduction to the application of solution electrochemistry to this class of compounds is provided, and the relevance of such measurements to materials design is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

The reaction of N,N'-bis(2,6-diisopropylphenyl)carbodiimide with lithium 2,6-diisopropylanilide, quenching with water and recrystallization from heptane produces the symmetric guanidine [DipNH](2)C=NDip which crystallizes in the triclinic system, space group P(1) over bar, a = 10.6513(11), b = 10.8997(11), c = 16.2961(17) Angstrom, alpha = 80.524(12), beta = 78.921(13), gamma = 70.060(12)degrees, V = 1735.2(3) Angstrom (3), Z = 2. The molecule crystallizes with three perpendicular 2,6-diisopropylphenyl groups, which surround and shield the central CN3 unit, and provide (almost) three-fold symmetry around the central atom. Its dynamic solution behaviour has been studied by VT NMR between -90 and +180 degreesC, and is consistent with three distinct barriers to N-C-Ar rotation. Preliminary estimates of the Gibbs free energy of activation for the lower two barriers are 56 +/- 2 and 73 +/- 2 kJ mol(-1). Reaction of the title compound with Mo(CO)(6) in refluxing n-heptane produces [DipNH](2)C=NDip.Mo(CO)(3), a complex in which Mo(CO)(3) is eta (6)-coordinated to one of the diisopropylphenyl rings.

N,N'-bis-(2,6-diisopropylphenyl)trifluoroacetamidine has been prepared for the first time from 2,6-diisopropylaniline and the trifluoroacylation reagent TFAP via the imidoylchloride. The crystal structure of the amidine was determined, indicating that it crystallizes in the Z-anti tautomer, in contrast to the nonfluorinated analogue, which is Z-anti in the solid state. In solution, as indicated by NMR spectroscopy, it exists in two isomeric forms. The amidine reacts with Mo(CO)(6) to produce a coordination complex with Mo(CO)(3) in which the ligand is also in the Z-anti geometry, the metal is eta(6)-coordinated to the imino-2,6-diisopropylphenyl ring, and the amino N-H unit is directed towards the metal, as determined by a single-crystal X-ray structure. Unlike the analogous nonfluorinated acetamidine, there is no indication of an intermediate in which the neutral amidine is coordinated in a monodentate fashion to an Mo(CO)(5) unit, which we now attribute to the predominant geometry of the ligand, both in the solid state and in solution, being Z-anti. The high steric bulk of this superamidine ligand apparently prevents the formation of a metal-metal bonded Mo-2(amidinate)(4) as observed previously in a redox reaction between N,N'-diphenylbenzamidine and Mo(CO)(6) under similar thermal reaction conditions.

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The rotationally resolved infrared spectrum of the nu(1) band of the long-lived (a) over tilde(1)Delta electronic state of the CCO radical has been observed between 1918 and 1970 cm(-1) using a tunable diode laser spectrometer. Metastable CCO was produced in a discharge through a flowing mixture of carbon suboxide and helium. Fifty eight rovibrational transitions in the P and IZ branches and the five lowest J lines in the Q branch were measured. The band origin was determined to be 1942.8515(19) cm(-1). This is in close agreement to the values determined previously from photoelectron spectroscopy of CCO-. (C) 1999 American Institute of Physics. [S0021-9606(99)00902-2].

The air oxidation of the cluster compounds [Li2E((NBu)-Bu-t)(3)](2) (E = S, Se) in toluene produces deep blue (E = S) or green (E = Se) solutions. The ESR spectra of these solutions consist of a septet (1:3:6:7:6:3:1) of decuplets. The simulation of these spectra shows that the secondary hyperfine splitting results from interaction of the unpaired electron with three equivalent Li-7 ions consistent with the formation of the neutral radicals {Li-3[E((NBu)-Bu-t)(3)](2)}(.) (4a, E = S, g = 2.0039, a(N-14)= 5.69 G, a(Li-7) = 0.82 G; 4b, E = Se, g = 2.00652, a(N-14) = 5.41 G, a(Li-7) = 0.79 G). Over a period of 25 h the seven line pattern of 4b is replaced first by a five line (1:2:3:2:1) spectrum (g = 2.009, a(N-14) = 13.4 G) and, subsequently, by a three line (1:1:1) spectrum (g = 2.00946, a(N-14) = 15.4 G, a(Se-77) = 3.3 G), neither of which exhibit 7Li hyperfine splitting. These spectra are tentatively assigned to the radical anions SeO((NBu)-Bu-t)2(.-) and SeO2((NBu)-Bu-t)(.-), respectively. The cluster (Li-2[O2S((NBu)-Bu-t)]), (3) is prepared by the reaction of sulfur dioxide with 2 equiv of (LiNHBu)-Bu-t in toluene. The air oxidation of toluene solutions of {Li-2[OS((NBu)-Bu-t)(2)]}(6) (2a) or 3 produces deep blue species. In the former case the initial ESR spectrum is a 1:2: 3:2:1 quintet (g = 2.009, a(N-14) = 13.3 G) which, after 16 h, evolves into a 1:1:1 triplet (g = 2.008X, a(N-14) = 15.9 G). The same triplet is observed in the ESR spectrum of oxidized solutions of 3 leading to the assignments OS((NBu)-Bu-t)(2)(.-) and O2S((NBu)-Bu-t)(.-) for the quintet and triplet, respectively. The disproportionation 2OS((NBu)-Bu-t)(2)(.-) --> OS((NBu)-Bu-t)(.-) + S((NBu)-Bu-t)(3)(.-) is indicated by the changes observed for the ESR spectra of oxidized solutions of 2a.

The crystal structure of the title compound was determined at 250 K in space group I (4) over bar 2m, a = 20.661(5) Angstrom, c = = 6.764(7) Angstrom, Z = 8. The individual dithiadiazole rings form two sets of contrarotatory 4-member pinwheels clustered around a 4-fold rotation-inversion axis located halfway along the unit cell edges, describing an infinite channel lined with sulfur atoms but in which there are short intra-stack contacts through only one S atom of each CN(2)S(2) group. The double-layer stacking occurs in order to accommodate the bulk of the (t)Bu group, and the spacing between layers is very regular, with short and long S ... S contacts of 3.48(2) and 3.61(2) Angstrom and considerable thermal motion in the c direction. The title compound and its SbF(6)(-) salt are oxidized at +0.81 V (in CH(2)Cl(2)) and at +0.61 V (in CH(3)CN), while a reduction process is observed only in CH(2)Cl(2) at -0.73 V vs. SCE. Magnetic susceptibility data between 5 and 400 K demonstrate at very low temperature that the sample follows the Curie-Weiss law, theta = 0 K, and chi(0) =-156 ppm emu mol(-1). The free-spin concentration at T = 0 K is approximate to 1.3%, due to paramagnetic defects in an essentially diamagnetic structure. The diamagnetism starts to lift above 210 K; above 260 K, a strong antiferromagnetic exchange is operative. These results are consistent with the lifting of the Peierls distortion in this structure, starting above approximate to 200 K. The crystal structure of the parent diamidine 5-tert-butyl-1,3-[(Me(3)Si)(2)NCNSiMe(3)](2)C(6)H(3) was determined in C2/c with a = 10.0788(3), b = 21.328(5), c = 20.876(5) Angstrom, beta = 99.41(2)degrees, Z = 4. The two amidine functional groups are equivalent by crystal symmetry.

\N,N'-Bis(2,6-diisopropylphenyl)-4-toluamidine, -4-anisylamidine and -acetamidine have been prepared for the first time from 2,6-diisopropylaniline and the acid chlorides via the: corresponding imidoyl chlorides. The crystal structures of all three amidines were determined, indicating that the first is a disordered mixture of Z-anti and E-syn tautomeric forms, the second Z-anti, and the third E-anti in the solid state. Despite these differences, all three form identical coordination complexes with Mo(CO), in which the ligand is in the Z-anti geometry, and the metal is pi-coordinated to the imino 2,6-diisopropylphenyl ring, and the amino N-H unit is directed towards metal. The coordination mode was confirmed by single-crystal X-ray structure determination of the toluamidine and methylamidine complexes with Mo(CO),. In the case only of the methylamidine, an isolable intermediate is first formed in which the neutral amidine is coordinated in a monodentate fashion to an Mo(CO)(5) unit. The crystal structure of this complex shows that the ligand is in the E-anti geometry, with the imino nitrogen coordinated to Mo, d(Mo-N) = 2.352(2) Angstrom. The structures are closely related in that the initial Mo(CO)(5) N-coordination sets up the metal for conversion to the more thermodynamically stable pi-coordinated Mo(CO)(3) complex. The high steric bulk of these superamidine ligands is seen in the failure of any of them to form the metal-metal bonded Mo-2(amidinate)(4) complexes typically prepared using common, less bulky, amidines.

The 2 nu(1) - nu(1) and nu(1) + nu(3) - nu(3) difference bands of the CCO radical in the gas phase have been studied using a tunable infrared diode laser spectrometer. The CCO radical was produced using a flowing mixture of carbon suboxide and helium subjected to a hollow-cathode discharge. The spectral region between 1920-1960 cm(-1) was probed. Ninety and seventy-five rovibrational transitions were measured in the 2 nu(1) - nu(1) and nu(1) + nu(3) - nu(3) bands, respectively. The analyses of these bands yielded spectroscopic constants for the (001), (200), and (101) vibrational states. The band origins for 2 nu(1) - nu(1) and nu(1) + nu(3) - nu(3) determined to be 1941.85761(54) cm(-1) and 1936.79402(56) cm(-1), respectively. (C) 1998 American Institute of Physics.

The infrared absorption spectrum of the CCO radical has been studied in an extension of the original observation of the C-O stretching vibration by Yamada et al. [J. Chem. Phys. 84 (1985) 2573]. The CCO radical was generated using a flowing mixture of carbon suboxide and helium subjected to a hollow-cathode discharge. The spectral region between 1930-1990 cm(-1) was probed using a tunable diode laser spectrometer. Transitions with N-values up to 40 were measured for the nu(1) fundamental and nu(1) + nu(2) - nu(2) sequence bands. Their analysis yielded band origins, rotational, centrifugal distortion, spin-spin interaction, and spin-orbit interaction parameters for the lower and upper vibrational states, and l-doubling parameters for the degenerate bending states upsilon(2) = 1 and (upsilon(1) = 1, upsilon(2) = 1). In particular, the band origins for nu(1) and nu(1) + nu(2) - nu(2) were determined to be 1970.86332(41) cm(-1) and 1960.13093(37) cm(-1), respectively. (C) 1997 Published by Elsevier Science B.V.

Molybdenum and tungsten chlorides, chloride oxides and chloride nitrides as well as thiazene and phosphazene metallacycles were studied by electrochemical methods in CH2Cl2. The different ligand systems have a profound influence on the redox potentials. The stabilization of high valency increases from the hexachloro to pentachlorooxo to chloronitrido complexes and the metallacycles. There is a systematic difference in the electrode potentials between molybdenum and tungsten redox couples. The geometries of the d(1) and d(0) species, optimized using density functional methods, are in good agreement with the available experimental data and trends in redox data are reproduced by the computed energy difference between the appropriate d(1)/d(0) pair. The relative stability of the higher oxidation state is directly linked to the donor properties of the ligands present, and increases in the order: Cl-6 < F-6 < Cl5O < Cl-4(N3S2) < Cl-N?3P?2 < Cl4N.

The title compounds have been studied in CH2Cl2 by cyclic voltammetry. Nonacarbonyldi(mu(3)-methylidyne)triiron, [Fe-3(CO)(9)(mu(3)-CX)(2)] (X = F, Cl, Br, H), undergo chemically reversible 1e(-) reduction (-0.72 to -0.88 V vs. SCE) and irreversible oxidation (+1.59 to +1.72 V); the compound for which X = F displays a second, irreversible reduction (-1.96 V). Using reduction potentials of comparable mu(3)-E (E = S, Se, NPh, PPh) clusters, mu(3)-methylidyne ligands are shown to be strongly basic, comparable to PPh and NPh and more basic than S or Se. The methylidyne clusters are both more difficult to oxidize and reduce than isomeric alkyne clusters [Fe-3(CO)(9)(C(2)R(2))], indicative of greater thermodynamic stability. The complexes previously formulated as [Fe-2(CO)(6)(S(2)N(2)CC(6)H(4)X)] (X = H, CF3, OCH3) are reversibly reduced (-1.59 to -1.70 V) and irreversibly oxidized (+1.0 to 1.3 V), unlike free dithiadiazole radicals, which are reversibly oxidized around +0.8 V. This behaviour is not consistent with the ring-centered free radical claimed for the case where X = H; instead we find conclusive evidence that these are diamagnetic complexes of the 3-H-1,2,3,5-dithiadiazolines, [Fe-2(CO)(6)(S2N{NH}CC(6)H(4)X)] (nu(NH) = 3376-3381 cm(-1); delta(NH) = 6.55-7.1 ppm). Dicyclopentadienyl-dithiadiazoledinickel, [Ni(2)Cp(2)(S2N2CC6H5)], is both reversibly reduced (-0.79 V) and oxidized (+0.45 V); and irreversibly oxidized at +1.9 V. This is consistent with an unpaired electron, and only the nickel cluster has an ESR signal (g = 2.0410, no resolved hyperfine splitting). Extended Huckel theory locates the free electron in a SOMO restricted to Ni, C, and S atoms.

The eight-membered ring in the title compound, C10H18N4S2, lies about an inversion centre and is essentially planar with normal bond lengths and angles [mean c-s 1.569 (2) and mean c-N 1.326 (3) Angstrom].

The analysis of the title compound, C8H7N2OSe2, shows that its crystals are composed of weakly linked dimers, with intramolecular Se-Se distances of 2.343(3) and 2.345(2)Angstrom, intermolecular Se ... Se distances of 3.193(3) and 3.316(3)Angstrom and lateral Se ... Se interactions of 3.514(2) and 3.579 (3) Angstrom.

Cyclic and ac voltammetry were carried out on 17 different 1,2,3,5-dithia- or diselenadiazole radicals under vacuum in CH2Cl2 and CH3CN solutions containing NBu(4)PF(6) electrolyte. The redox potentials for the oxidation and reduction processes are reported, referenced to SCE using ferrocene as a secondary standard. The oxidation process for five of the dithiadiazole radicals correlates linearly with the gas-phase ionization energies previously obtained from UV-PES, and the damping influence of the solvent medium is evident. Disproportionation energies defined as E(cell) = -{E(oxid) - E(reduc)} were calculated: (E = S, -1.43 +/- 0.06 V in CH3CN and -1.61 +/- 0.06 V in CH2Cl2 (average of 11 compounds); E = Se, -1.25 +/- 0.03 in CH3CN and -1.39 +/- 0.05 V in CH2Cl2 (average of six compounds)) and compared to the enthalpies of the same process in the gas phase obtained from MNDO calculations (E(cell)(gas) = -6.5 V). Both calculation and experiment show that the title compounds, by comparison with TTF+, TCNQ(-), and other related compounds, have higher than desirable disproportionation energies which is a disadvantage for their use in constructing molecular metals. The electrochemistry of 1,4-bis(dithia- and diselenadiazolyl)benzene has also been investigated by voltammetry and coulometry. These bifunctional diradicals undergo independent redox chemistry in each CN(2)E(2) ring, and the ''oxidation'' process involves a two-electron transfer confirmed by coulometry. The disproportionation energies of these compounds are shown to be similar to those of the monofunctional radicals; by implication the same limitations apply to their solid-state properties.

The preparation and isolation in the solid state of five aryl 1,2,3,5-dithia- and diselenadiazolyls is reported. The structure of the dimer of 4-Cl-C6H4-CN2S2 in the solid state was obtained: monoclinic, C2/c with Z = 8, a = 20.982(10), b = 10.058(3), c = 15.867(6) angstrom, beta = 93.34(4)-degrees, R = 0.066, R(w) = 0.053 for 1099 data. Cyclic voltammetry shows reversible oxidation to a 6 pi cation for all 10 compounds in both CH2Cl2 and CH3CN; reversible reduction to an 8pi anion is observed in CH2Cl2 for all except X = CF3, E = S. The reductions are only quasi-reversible in CH3CN for E = Se. The oxidation process is independent of chalcogen type; the reduction process is found to be about 0.2 V more negative for E = S vs E = Se.

The reactions of S4N4 with CpM(CO)x and Cp*M(CO)x (M = Mn, Fe, Co, Ni and Rh) result in tractable products only when M = Co. The electrochemical behaviour of the previously known complexes CPCoS2N2 and Cp*CoS2N2 has been investigated by DC and AC cyclic voltammetry. Each has a single one-electron reduction process occurring at -0.65 V (Cp) and -0.99 V (Cp*). vs. SCE, in CH2Cl2 solution. For the Cp complex, chemical reduction using cobaltocene has also been achieved. 15N NMR spectra were recorded for 99% N-15 enriched samples: 550 (broad singlet) and 431 (singlet) for Cp, 518 (broad singlet) and 404 ppm (singlet) for Cp*, referenced to liquid NH3. The electronic absorption spectra are also reported, and interpreted in the light of EHMO calculations.

The reduction processes of the volatile hexafluorides TeF6 and SeF6 have been studied in CH2Cl2 using electrochemical methods with a vacuum-tight electrochemical cell. At -78-degrees-C the half-wave potential for the [TeF6]0/2- step occurs at - 0.88 V vs. SCE, while the less reversible [SeF6]0/2- reduction is observed at the more positive potential, E1/2 = - 0.1 V. The complex ion [TeF7]- is irreversibly reduced in MeCN at - 0.7 V. These results are interpreted using an orbital framework. The results of Extended Huckel calculations on model systems are discussed. In each case, reduction results in the population of a metal-ligand antibonding orbital which is dominated by the metal valence s orbital.

4-CF3-C6H4-CN3S2, 1, forms symmetrical sulfur-bound adducts with norbornene (NBE), norbornadiene (NBD), and 1-heptene (C7H14), which were studied by H-1, C-13, COSY-45, and HETCORR NMR. 1NBE exists in solution in a single isomeric form which corresponds to that found in the solid state for 4-CH3O-C6H4-CN3S2.NBE by single-crystal X-ray diffraction: orthorhombic, P2(1)2(1)2(1) with Z = 4, a = 10.224(3), b = 10.369(5), c = 14.075(5). R = 0.0475 and R(w) = 0.0492 for 634 data. 1 NBD exists in solution in two isomeric forms which are not interchangeable. One of these corresponds to that found in the NBE adduct, i.e. exo addition; the other is the first example of endo addition. Two bis adducts of stoichiometry NBD.21 have been prepared and separated. They are isomers exhibiting eno-exo and exo-endo addition. The structure of the latter was confirmed by X-ray diffraction: orthorhombic, Pcab with Z = 8, a = 7.816(2), b = 17.264(3), c = 36.842(5). R = 0.068 and R(w) = 0.106 for 1506 data. 1.C7H14 exists as a mixture of syn and anti isomers. NMR structure parameters derived here have been applied to published data on over 15 thiazene NBE and NBD adducts.

Electrochemical studies of 5, 6, 7 and 8-membered rings containing catenated C-N-S and C-N-Se groups have been undertaken using cyclic and a.c. voltammetry. The results find a satisfying interpretation using semi-empirical MO theory. The results provide an important insight into the utility of such ring systems for the design of molecular metals.

The metallacycles [NPPh(2)NPPh(2)NMCl(3)], M=Mo, W have been studied in CH2Cl2 using cyclic voltammetry. The observed redox potentials indicate that the cyclic pi-base ligand, [NPPh(2)NPPh(2)N](3-), is capable of stabilising high oxidation states in both molybdenum and tungsten complexes. Empirical MO calculations are presented which rationalize the electronic structure of the metallacycles.

Electrochemical studies of 1,2,3,5-dithiadiazole complexes with iron carbonyl and nickel cyclopentadienide are reported. These are consistent with paramagnetism only in the latter. The former are in fact complexes of the dithiadiazole imine. Initial investigation of routes to ferrocene-linked dithiadiazoles are described. Electrochemistry of cyanoferrocene and ferrocene-1H-tetrazole is reported.

New preparative routes to the title compounds are reported in which the yields are substantially improved over previous methods. In one method, reaction of O2 With a mixture of XC6H4CN2S2+Cl- and Ph3Sb leads to the products in 40-60% yield. In another, the reaction of the same salts with silylated amidines XC6H4C{NSiMe3}N(SiMe3)2 in a 1:1 mol ratio leads to the same compounds in 18-65% yield. The syntheses of 3,7-(XC6H4)2{CN2S2N2C}, X = H, 4-CH3, 4-CH3O, 4-Cl, 4-CF3, and 3-CF3, are reported. Mixed derivatives were also prepared, but not isolated as pure compounds. The crystal structure of the 4-CF3 compound has been determined by X-ray diffraction; triclinic, P1BAR with Z = 1; cell dimensions: a = 6.835(2), b = 9.936(3), c = 6.320(2) angstrom, alpha = 96.44(3)degrees, beta = 102.88(3)degrees, gamma = 88.42(3)degrees. R = 3.4%, R(w) = 3.5% for 1100 data. The eight-membered ring is flat with equivalent bond lengths between any two types of atoms, indicative of a delocalized electron distribution. The 10pi central aromatic rings have been oxidized and reduced in CH2Cl2 using voltammetric methods. The reversible one-electron reduction step gives stable 11pi species. The resistance to oxidation of the title compounds is contrasted to the ease of oxidizing 3,7-[(CH3)2N]2{CN2S2N2C}, in accordance with earlier chemical studies.

The synthesis of XC6H4CN5S3, XC6H4CN3S2Cl2, {XC6H4CN3S2}2, and XC6H4CN3S2.C7H10 (X = 4-CH3, 4-Cl, 3-CF3, 4-CF3, 4-CH3O, 4-C6H5) is reported. The crystal structure of {4-ClC6H4CN3S2}2 was determined by a single-crystal X-ray diffraction study. The compound crystallizes in the triclinic space group P1BAR with Z = 2 in a cell of dimensions a = 6.107 (1) angstrom, b = 12.070 (2) angstrom, c = 13.206 angstrom, alpha = 113.73 (1)-degrees, beta = 99.04 (2)-degrees, and gamma = 97.53 (2)-degrees. The least-squares refinement with anisotropic thermal parameters for all non-hydrogen atoms converged at R = 0.084 for 1480 unique reflections. The structure is a cofacial dimer of 4-ClC6H4CN3S2 units, with short S...S contacts of 2.509 (4) and 2.534 (4) angstrom. Dimer units are stacked head-to-tail in the crystal along the bc diagonal. H-1-NMR studies of the more soluble compounds show significant shielding of the aromatic protons (0.3-0.6 ppm) attributable to ring currents of adjacent aromatic rings. This is consistent with the preservation in solution of the wedge-shaped dimeric structure found in the solid state.

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