Interaction of a Bulky <i>N</i>-Heterocyclic Carbene Ligand with Rh(I) and Ir(I). Double C−H Activation and Isolation of Bare 14-Electron Rh(III) and Ir(III) Complexes

Reactivity and structural studies of unusual rhodium and iridium systems bearing two N-heterocyclic carbene (NHC) ligands are presented. These systems are capable of intramolecular C−H bond activation and lead to coordinatively unsaturated 16-electron complexes. The resulting complexes can be further unsaturated by simple halide abstraction, leading to 14-electron species bearing an all-carbon environment. Saturation of the vacant sites in the 16- and 14-electron complexes with carbon monoxide permits a structural comparison. DFT calculations show that these electrophilic metal centers are stabilized by π-donation of the NHC ligands.