Studies of reductive elimination reactions to form carbon-oxygen bonds from Pt(IV) complexes

The platinum(IV) complexes fac-L(2)PtMe3(OR) (L-2 = bis(diphenylphosphino)ethane, o-bis(diphenylphosphino)benzene, R = carboxyl, aryl; L = PMe3, R = aryl) undergo reductive elimination reactions to form carbon-oxygen bonds and/or carbon-carbon bonds. The carbon-oxygen reductive elimination reaction produces either methyl esters or methyl aryl ethers (anisoles) and L2PtMe2, while the carbon-carbon reductive elimination reaction affords ethane and L2PtMe(OR). Choice of reaction conditions allows the selection of either type of coupling over the other. A detailed mechanistic study of the reductive elimination reactions supports dissociation of the OR- ligand as the initial step for the C-O bond formation reaction. This is followed by a nucleophilic attack of OR- upon a methyl group bound to the PL(IV) cation to produce the products MeOR and L2PtMe2. C-C reductive elimination proceeds from L2PtMe3(OR) by initial L (L = PMe3) or OR- (L2 = dppe, dppbz) dissociation, followed by C-C coupling from the resulting five-coordinate intermediate. Our studies demonstrate that both C-C and C-O reductive elimination reactions from Pt(IV) are more facile in polar solvents, in the presence of Lewis acids, and for OR- groups that contain electron withdrawing substituents.