Ligand influences on hydrogen migration in transition metal hydrido–carbyne complexes

Density Functional BP86 calculations are reported for the interconversion reactions of WH(CH)(CO)(PH3)3 and WH(CH)(CO)2(PH3)2 to the corresponding five-coordinated carbene complexes W(CH2)(CO)(PH3)3 and W(CH2)(CO)2(PH3)2, respectively. Transition states have been calculated to be 9.9 and 0.7 kcal mol−1 higher in energy than the carbynes. A comparison with the isoelectronic osmium system OsHCl2(CMe)(PH3)2 with a transition state for interconversion 27.2 kcal mol−1 above the carbyne leads to the conclusion that additional π-acceptors competing with the carbyne or carbene ligand for back donation facilitate the interconversion reaction, whereas additional π-donors undergoing synergic push–pull interactions impede the interconversion reaction.