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

Abstract

FT-Raman spectroscopy and density functional theory (DFT) calculations have been used to study the trans influence of ligands L in complexes of the general composition trans-[RhX(L)(PiPr₃)₂], where X = F, Cl, Br, I, CH₃ and CCPh; L =  ¹³C¹³CH₂ , CCHPh and CO. For the vinylidene compounds 1–10, the sequence of the trans influence CCPh > CH₃ > I > Br > Cl > F has been derived from the order of the ν(RhC) wavenumbers. In the carbonyl halide complexes 11–14, the sequence of the trans influence for the halide ligands is the same as for the related vinylidene halide derivatives. The trans influence of the ligands X is discussed in terms of both the σ-donor capabilities of these ligands and the electronic repulsion between the d electrons of rhodium and the lone pairs of X.