Mechanism for Reduction Catalysis by Metal Oxo: Hydrosilation of Organic Carbonyl Groups Catalyzed by a Rhenium(V) Oxo Complex

摘要

High oxidation state oxo complexes are widely used in catalytic oxidations and oxygen atom transfer reactions.However,the use of such complexes in catalytic reductions is extremely rare.Few reports have appeared recently describing rhenium(V),rhenium-(VII),and molybdenum(VI) oxo catalysts for the hydrosilation of aldehydes and ketones.In their mechanistic interpretation of the rhenium dioxo system,Toste and co-workers proposed Si-H addition across the Re=O multiple bond to give a hydrido-oxorhenium(V) complex.The additional oxo ligand was hypothesized to stabilize the resulting oxo-hydrido,compensating for the loss of pi donation from one of the oxo ligands (eq 1).However,several mechanistic questions remain,including the role of the additional oxo ligand and if indeed a dioxo complex is needed.