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.