HINDERED ROTATION AROUND A C-(PH)-P-CENTER-DOT BOND - A SINGLE-CRYSTAL EPR STUDY OF THE DIPHENYLDIBENZOBARRELENEPHOSPHINYL RADICAL

A new phosphine, the diphenyldibenzobarrelenephosphine 2, was designed to study the barrier to rotation of the P-H group around the C-P-. bo nd. After homolytic scission of a P-H bond by radiolysis, the EPR spec trum of the resulting phosphinyl radical, trapped in a single crystal of 2, was studied at 77 K and at room temperature. The directions of t he P-31 hyperfine eigenvectors were compared with the bond orientation s of the undamaged compound as determined from its crystal structure. The temperature dependence of the EPR spectrum was analyzed by using t he density matrix formalism; this showed that interaction between the phosphinyl hydrogen and the phenyl ring bound to the ethylenic bond is determinant for explaining the potential energy profile. DFT investig ations are consistent with these experimental results.