Preparation And Hydrosilylation Activity Of A Molybdenum Carbonyl Complex That Features A Pentadentate Bis(Imino)Pyridine Ligand

Attempts to prepare low-valent molybdenum complexes that feature a pentadentate 2,6-bis(imino)pyridine (or pyridine diimine, PDI) chelate allowed for the isolation of two different products. Refluxing Mo(CO)(6) with the pyridine-substituted PDI ligand, (PDI)-P-PyEt, resulted in carbonyl ligand substitution and formation of the respective bis(ligand) compound ((PDI)-P-PyEt)(2)Mo (1). This complex was investigated by single-crystal X-ray diffraction, and density functional theory calculations indicated that 1 possesses a Mo(0) center that back-bonds into the pi*-orbitals of the unreduced PDI ligands. Heating an equimolar solution of Mo(CO)(6) and the phosphine-substituted PDI ligand, (PDI)-P-Ph2PPr, to 120 degrees C allowed for the preparation of ((PDI)-P-Ph2PPr)Mo (CO) (2), which is supported by a kappa(5)-N,N,N,P,P-(PDI)-P-Ph2PPr chelate. Notably, 1 and 2 have been found to catalyze the hydrosilylation of benzaldehyde at 90 degrees C, and the optimization of 2-catalyzed aldehyde hydrosilylation at this temperature afforded turnover frequencies of up to 330 h(-1). Considering additional experimental observations, the potential mechanism of 2-mediated carbonyl hydrosilylation is discussed.