Influence of metal to di-imine π-backbonding on the resonance-Raman spectra of [M(CO)4L], fac-[Re(CO)3LCl], and [Ru(CO)3L] complexes (M = Mo or W; L = di-imine)

Abstract

The resonance-Raman (r.R.) spectra of complexes [M(CO)₄L], fac-[Re(CO)₃LCl], and [Ru(CO)₃L][M = Mo or W; L = 1,2-bis(arylimino)ethane or 1,2-bis(i-propylimino)ethane] obtained by excitation into the lowest-energy absorption band are reported. An increase of π-backbonding from the metal to the di-imine ligand appears to be accompanied by a decrease of the r.R. effect for the symmetrical stretching modes of the ligand with respect to the symmetrical metal–ligand stretching modes. At the same time, an increase of the r.R. effect is observed for vibrations of the aryl rings which are virtually inactive in the Raman spectra of the free ligands. This latter result is interpreted in terms of a distortion of the aryl rings in the metal-to-ligand charge transfer excited state.