Rhodium and Iridium Complexes of N-Heterocyclic Carbenes via Transmetalation:  Structure and Dynamics

Rhodium and iridium complexes of N-heterocyclic carbenes (3ac and 4ac) were obtained by transmetalation from the corresponding Ag(I) complexes. The structure of 3b was verified by X-ray diffraction. The compounds display restricted rotation about the metal−carbene bond, the rate of which can be controlled by altering the steric bulk of the auxiliary ligands. Infrared spectroscopy provides an estimate of the electron-donor power of the carbene ligands from ν(CO) of the carbonyl derivatives.