Reduction of Carbon Dioxide Promoted by a Dinuclear Tantalum Tetrahydride Complex

The reaction of 1 equiv of carbon dioxide with the dinuclear tetrahydride complex ([NPN]­Ta)2(μ-H)4 [where NPN = PhP­(CH2SiMe2NPh)2] results in the formation of ([NPN]­Ta)2(μ-OCH2O)­(μ-H)2 via a combination of migratory insertion and reductive elimination. The identity of the ditantalum complex containing a methylene diolate fragment was confirmed by single-crystal X-ray analysis, NMR analysis, and isotopic labeling studies. Density functional theory calculations were performed to provide information on the structure of the initial adduct formed and likely transition states and intermediates for the process.