An investigation into the relative influence of alkoxide and thiolate ligands on the metal–carbon triple bond in X 3MCH compounds, where M=Cr, Mo and W and X=OH, SH, OCH 3, SCH 3, OCF 3 and SCF 3 from electronic structure calculations

Abstract

Electronic structure calculations using density functional theory with the aid of the gaussian-98 package have been employed on the model Group 6 metal alkylidyne complexes X 3MCH, where M=Cr, Mo and W and X=OH, SH, OCH 3, SCH 3, OCF 3 and SCF 3. Collectively, these calculations reveal that the relative energies of the metal–carbon π-bonding molecular orbitals are greatly influenced by the metal and the ancillary ligand X. In comparing the bonding in related O and S containing molecules, the effect of oxygen is to increase the relative energy of the M–C π bond by approximately 1 eV as a result of M–O π antibonding interactions. In contrast, the ligand-based lone-pair orbitals lie higher in energy for sulfur and for the series where X=SH, SCH 3 and SCF 3, the HOMO is a sulfur lone-pair combination of a 2 symmetry in the C 3 v point group. The relative influence of H, CH 3 and CF 3 within each series is as expected based on their electron releasing properties. A comparison is made with related compounds having metal to metal or metal to nitrogen triple bonds.