Theoretical Study of Reductive Functionalization of Methyl Ligands of Group 9 Complexes Supported by Two Bipyridyl Ligands: A Key Step in Catalytic Hydrocarbon Functionalization

A density functional theory (DFT) study was performed to understand the factors that control the reactivity of bipyridine (bpy)-ligated Rh­(III) methyl complexes toward nucleophiles to produce functionalized methane and Rh­(I) complexes. The effect of the structure of the complex, the nucleophile, the identity of the ancillary ligand, the electronic properties of the bipyridine ligand, and the identity of the metal were considered. Many similarities were found between the reaction of Rh­(III) methyl complexes supported by bipyridyl ligands and classic organic SN2 reactions, including a strong dependence of the reaction on the nucleophile identity and modifications to the complex that facilitate rhodium as a leaving group. Using these concepts, a comparison of reductive functionalization of Rh­(III) alkyl complexes supported by porphyrin versus two bipyridyl ligands was made, and modifications that could lead to more active complexes were proposed.