UV-PE Spectra and DV-Xa Calculations of Some Phosphido-Bridged Dimers

Phosphido-bridged transition-metal complexes of the type [(CO)4M(ti-PR2)]2 (M = V, Cr, Mo, W, Mn) have been investigated by means of gas-phase ultraviolet (UV)-photoelectron (PE) spectroscopy and first-principle DV-Xa quantum mechanical calculations. The attention was focused on the variation of the metal-metal bond multiplicity along the series and on the changes in the whole electronic structure, with particular emphasis on the metal-bridge interactions. The increase in the metal-metal distance observed on going from the V to the Mn complex reflects the progressive occupation of antibonding metal-metal MOs. In agreement with such considerations, difference density maps for the V and Mn complexes show an evident charge accumulation between the two V atoms in contrast with a saddle point along the Mn-Mn axis. However, the large M-M lengthening observed on passing from Cr to Mn is more easily understood if the occupation of a M-bridge antibonding orbital is also taken into account. The UV-PE data and the theoretical results both demonstrate the existence of through-space interactions between the phosphorus bridging atoms, maximized in the Mn complex where the P-P distance takes the minimum value. © 1987, American Chemical Society. All rights reserved.