Issue 2, 2008

Photophysical, dynamic and redox behavior of tris(2,6-diisopropylphenyl)phosphine

Abstract

The title phosphine, Dipp3P, was synthesized using an aryl copper reagent and the structure determined by X-ray crystallography (R = 2.94%): d(P–C) = 1.852(1) Å, ∠C–P–C = 111.88(5)°. In hexane solution, the electronic spectrum displays 3 bands [326 (9.3), 254 (8.7), 205 (11.4) nm (log|ε|)] and the fluorescence spectrum has a Stokes shift of 129 kJ mol−1. NMR: (δ) 31P = −49.7 ppm in solution and −49.5 in the solid (CP-MAS). Room temperature 1H and 13C spectra reflect D3 symmetry, changing below −30 °C to C3. A variable temperature NMR study provided an activation enthalpy of 49(±1) kJ mol−1 and entropy of 24–27(±5) J mol−1K−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 Dipp3P to Dipp3P+˙ at +0.18 (CH3CN–nBu4NPF6) and +0.09 (CH2Cl2nBu4NPF6) V vs. Fc+/0 (Fc = ferrocene). The diffusion coefficient for Dipp3P is 1.0–1.2 × 105 cm2 s−1. The electrode process displays quasi-reversible electron transfer kinetics [ks ≈ 0.01 (CH2Cl2) to 0.08 (CH3CN) cm s−1]. Optically transparent thin layer electrolysis reversibly generates Dipp3P+˙ in CH2Cl2nBu4NPF6 [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|ε|)]. The EPR spectrum of Dipp3P+˙ in solution is a doublet (a(P) = 23.9 mT, g = 2.008), and in frozen solution is axial (a = 42.6 mT, g = 2.0045; a = 12.7 mT, g = 2.0085 mT).

Graphical abstract: Photophysical, dynamic and redox behavior of tris(2,6-diisopropylphenyl)phosphine

Supplementary files

Article information

Article type
Paper
Submitted
27 Jun 2007
Accepted
14 Sep 2007
First published
04 Oct 2007

New J. Chem., 2008,32, 214-231

Photophysical, dynamic and redox behavior of tris(2,6-diisopropylphenyl)phosphine

R. T. Boeré, A. M. Bond, S. Cronin, N. W. Duffy, P. Hazendonk, J. D. Masuda, K. Pollard, T. L. Roemmele, P. Tran and Y. Zhang, New J. Chem., 2008, 32, 214 DOI: 10.1039/B709602J

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