Exclusive C–C Oxidative Addition in a Rhodium Thiophosphoryl Pincer Complex and Computational Evidence for an η3-C–C–H Agostic Intermediate

The room-temperature reaction between the Rh­(I) precursor [Rh­(COE)2(acetone)2]­BF4 (COE = cyclooctene) and a new thiophosphoryl-based SCS pincer ligand leads to oxidative addition of an sp2–sp3 C–C bond as the only observed outcome, despite the presence of accessible sp3 C–H bonds. A DFT study reveals that the chemistry of the SCS system is controlled by π repulsion between occupied rhodium d orbitals and the lone-pair electrons on the two sulfur atoms. This repulsion gives rise to the thermodynamic selectivity for C–C over C–H cleavage, as it is attributed to the higher electronegativity of a methyl versus hydride ligand, thereby allowing more effective release of excessive π electron density. It is also demonstrated that the observed C–C and unobserved C–H cleavage pathways originate from a common intermediate that features a novel η3-C–C–H agostic interaction. The COE ligand is shown to play an important role by greatly stabilizing this intermediate, making it the only available entry point to both reaction pathways.