Citation:
Abstract:
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.
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Times Cited: 25Chivers, T Eisler, DJ Fedorchuk, C Schatte, G Tuononen, HM Boere, RT