Reactivity of carbon monoxide towards high valent molybdenum complexes

Article abstract of DOI:10.1016/0022-328X(91)83007-Q

Reaction of carbon monoxide (3 atm) with Mo(O)2(mes)2 (mes = mesityl = C6H2Me3-2,4,6) in pyridine at room temperature affords dimesityl ketone 1 (5percent) and 1,1'-bis(mesitoyl)-1,1',4,4'-tetrahydro-4,4'-bipyridine 2 (25percent), the molecular structure of which has been determined by an X-ray diffraction study.The formation of 2 represents the first example of N-acylation of a pyridine by CO mediated by a transition metal complex.It has been shown that the relative ratio of 1 and 2 is dependent on the reaction conditions and that the presence of pyridine is essential for the formation of 1.Reactions of CO with the isoelectronic complex Mo(N^tBu)2mes2 contrast sharply with Mo(O)2mes2 and, under the same conditions, no dihydropyridine is formed, the sole identified products being 1 (60percent) and mesityltertiobutyl amide HN(1Bu)COmes (40percent).In light of the experimental results and of extended Hueckel calculations on dioxo and diimido d⁰ molybdenum complexes, a tentative mechanism for the formation of 2 is proposed which involves oxycarbene-like intermediates in the case of the more electrophilic dioxo molybdenum species.