Synthesis of Mixed NHC/L Platinum(II) Complexes: Restricted Rotation of the NHC Group

The use of (NHC)AgX salts as transmetallating agents for platinum can be tuned to introduce either one or two NHC ligands per platinum in high yield. Complexes with a single NHC ligand are prepared with an additional DMSO ligand, which can conveniently be replaced by other ligands such as phosphines to give mixed cis NHC/phosphine complexes. Variable-temperature NMR and DFT have been used to probe the nature of the restricted rotation of the NHC ligand about the square planar platinum center: experimentally, the barrier has been established as at least 85 kJ mol-1, and the computational value has been determined to be 92 kJ mol-1.