Metal-carbon vibrational modes as a probe of the trans influence in vinylidene and carbonyl rhodium(I) complexes

FT-Raman spectroscopy and density functional theory (DFT) calculations have been used to study the trans influence of ligands L in complexes of the ge neral composition trans-[RhX(L)(PiPr(3))(2)] where X=F, Cl, Br, I, CH3 and C drop CPh; L=C-13=(CH2)-C-13, C=CHPh and CO. For the vinylidene compounds 1-10, the sequence of the trans influence C drop CPh > CH3 > I > Br > Cl > F has been derived from the order of the v(Rh=C) wavenumbers. In the carbon yl halide complexes 11-14, the sequence of the trans influence for the hali de ligands is the same as for the related vinylidene halide derivatives. Th e trans influence of the ligands X is discussed in terms of both the sigma -donor capabilities of these ligands and the electronic repulsion between t he d electrons of rhodium and the lone pairs of X.