Computational insight into ¹⁰³Rh chemical shift-structure correlations in rhodium bis(phosphine) complexes

¹⁰³Rh NMR chemical shifts have been computed at the GIAO-B3LYP level of density functional theory (DFT) for a number of [Rh(COD)(PP)] ⁺ complexes [COD = 1,5-cyclooctadiene, PP = chelating bis(phosphine) including bis(dimethylphosphino)ethane (dmpe), bis(diphenylphosphino)ethane (dmpe), MeDUPHOS, DIOP, BINAP, and others]. Structures have been optimized using PBE0 and M06 functionals in the gas phase, in a continuum modeling the solvent, and with [PF₆]^- counteranion included explicitly. Observed trends in δ(¹⁰³Rh) are well reproduced for pristine PBE0-optimized cations in the gas phase or for ion pairs optimized in a continuum with M06. While there is no overall trend between computed δ(¹⁰³Rh) values and complex stabilities (evaluated through isodesmic ligand exchange reactions), there is a linear relationship between the ¹⁰³Rh chemical shifts and the mean Rh-P bond distances. This relationship appears to be remarkably general, encompassing various chelating ring sizes and substituents at P, including remote electron-donating and -withdrawing substituents that are characterized through their Hammett constants. The combination of ¹⁰³Rh NMR and DFT computations emerges as a useful tool for structure elucidation of Rh-phosphine complexes.