Citation:
Abstract:
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).
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Times Cited: 8Boere, Rene T. Bond, Alan M. Cronin, Steve Duffy, Noel W. Hazendonk, Paul Masuda, Jason D. Pollard, Kyle Roemmele, Tracey L. Tran, Peter Zhang, Yuankui