Comparison of the photochemistry of organometallic N-heterocyclic carbene and phosphine complexes of manganese

Time-resolved IR (TRIR) studies on (eta(5)-C5H4Me)Mn(L)(CO) (L = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene, PPh3) indicate that the rate of reaction with CO is ca. 10(2) slower for the N-heterocyclic carbene intermediate, which DFT calculations suggest is due to the presence of a strong Mn center dot center dot center dot H-C agostic bond. The reactivity of these intermediates in alkane solvents is governed by such interactions rather than solvent coordination to the unsaturated metal centre.