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.