Characterization of supported NiICO(TAP)n(n < 3) complexes by the CO stretching vibration. Electron-donating effect of trialkylphosphine ligands

Abstract

The i.r. characterization of supported Ni^I trialkylphosphine (TAP) complexes Ni^I(TAP)_n(n < 3) is performed using a CO probe molecule. The affinities of Ni^II and Ni^I ions for CO are compared. It is evidenced that TAP is a stronger ligand than CO: Ni^I(TAP)_n(n < 3) complexes cannot coordinate more than one CO ligand at low CO pressure, whereas phosphine-free Ni^I complexes can coordinate two CO molecules. The increase of electron density on the metal ion causes a shift downwards of the ν_co frequency, proportional to the number and to the basicity of TAP ligands. It also produce a weakening of the M—CO bond, resulting in the easier removal of CO.