Synthesis and characterization of primary cyclopentadienylphosphines and cyclopentadienylarsines

Primary cyclopentadienylphosphines and cyclopentadienylarsines have been pr epared by reduction of the corresponding dichloro derivatives and character ized by NMR and photoelectron spectroscopy and mass spectrometry. Their flu xional behavior has been established by both low-temperature NMR experiment s and theoretical (DFT) calculations. The structure and the possible pathwa ys to the circumambulatory rearrangement have been determined by quantum ch emical computations. The high rate of the 1,2-rearrangement which favors re tention of configuration at the migrating atom is explained by a low barrie r due to the aromaticity of the transition states. The NMR and photoelectro n spectra were assigned by making use of HF-GIAO and OVGF computations, res pectively. The observed splitting of the photoelectron bands, compared to t hose of cyclopentadiene and EX3 (E = P, As; X = H, Cl), was attributed to a hyperconjugative interaction between the cyclopentadienyl ring and the car bon-element bond.