Rhodium and iridium complexes of N-heterocyclic carbenes (3a−c and 4a−c) were obtainedby transmetalation from the corresponding Ag(I) complexes. The structure of 3b was verifiedby X-ray diffraction. The compounds display restricted rotation about the metal−carbenebond, 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 ligandsfrom ν(CO) of the carbonyl derivatives.
Rhodium and iridium complexes of N-heterocyclic carbenes were obtained by transmetalation from silver. Metal−carbene bond rotation and the electron-donor power of the carbene ligands were examined.