The Uncommon Reactivity of Dihapto-Coordinated Nitrile, Ketone, and Alkene Ligands When Bound to a Powerful π-Base

A series of complexes of the form TpM(NO)(L‘)(η2-L) are prepared (where L is a nitrile, ketone, or alkene, M = W or Mo, L‘ = PMe3, MeIm, Tp = hydridotris(pyrazolyl)borate). These complexes are subjected to various electrophiles (e.g., alkyl halides, Brønsted acids) to systematically probe the ability of the π-basic transition metal to affect the reactivity of the dihapto-coordinated ligand. Alkylation is observed at the heteroatom of the ketone and the nitrile, but depending on the reagent, alkylation of the nitrosyl ligand or addition to the complexed π-bond also occurs. The structures of several nitrilium complexes and a rare example of an η2-acetonium complex are also reported.