EPR and theoretical studies of the reduction product of the fulvenephosphaallene system

Fluoren-9-ylidenemethylene-(2,4,6-tri-tert-butyl-phenyl)phosphane (2), a ne w type of phosphaallene with the terminal carbone incorporated in a cyclope ntadienyl ring, has been synthesized and its crystal structure has been det ermined. The P-31 and C-13 (central carbon) hyperfine tensors of the reduct ion compound of this phosphaallene have been measured on the EPR spectra re corded after electrochemical reduction of a solution of 2 in THF. Structure s of the model molecules HP=C=Cp (where Cp is a cyclopentadienyl ring), [HP =C=Cp](.-) and [HP-CH=Cp](.) have been optimized by DFT and the hyperfine c ouplings of the paramagnetic species have been calculated by DFT and SO met hods. The comparison between the experimental and the theoretical results s hows that, in solution, the radical anion [2](.-) is readily protonated and that the EPR spectra are due to the phosphaallylic radical. (C) 2001 Publi shed by Elsevier Science B.V.