Multicenter Bonding in Wilkinson's Catalyst: A Theoretical Study from a Distorted Monomer to a Localized Dimer

In this work, we present a computational study of Wilkinson's catalyst, [Rh(PPh3)3Cl], focusing on the connection between geometric structure, electronic structure, and thermodynamics in its monomeric and dimeric forms, as well as the coordination of hydrogen atoms. Scalar-relativistic DFT with modern meta-GGA-based functionals, coupled-cluster benchmarks, and bonding analyses (NBO/NRT) show that steric effects and noncovalent interactions control deviations from ideal square-planar geometry in the metastable monomeric structure as well as affect dissociation and dimerization energetics, whereas electronic factors dominate the dimer structure and enthalpy. The monomer is characterized by intrinsically delocalized multicenter bonding, best described as two crossed three-center, four-electron (3c-4e) interactions spanning Rh, while entropy-controlled dimerization induces a qualitatively different and more localized bonding regime. In both species, Rh acts as an electron acceptor in donor-acceptor Rh-ligand interactions and remains consistent with a 16-electron configuration. Thermodynamic results support the experimentally observed tendency toward dimerization in solution, highlighting the importance of multicenter bonding, entropic factors, and steric control for interpreting the structure and reactivity of Wilkinson's catalyst.