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.