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)[subscript 6] with the pyridine-substituted PDI ligand, [superscript PyEtP]DI, resulted in carbonyl ligand substitution and formation of the respective bis(ligand) compound ([superscript PyEt]PDI)[subscript 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 π*-orbitals of the unreduced PDI ligands. Heating an equimolar solution of Mo(CO)[subscript 6] and the phosphine-substituted PDI ligand, [superscript Ph2PPr]PDI, to 120 °C allowed for the preparation of ([superscript Ph2PPr]PDI)Mo(CO) (2), which is supported by a κ5-N,N,N,P,P-[superscript Ph2PPr]PDI chelate. Notably, 1 and 2 have been found to catalyze the hydrosilylation of benzaldehyde at 90 °C, and the optimization of 2-catalyzed aldehyde hydrosilylation at this temperature afforded turnover frequencies of up to 330 h[superscript –1]. Considering additional experimental observations, the potential mechanism of 2-mediated carbonyl hydrosilylation is discussed.