Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

Bearing the versatility of N-heterocyclic carbene (NHC) ligands, here density functional theory (DFT) calculations unravel the capacity of coordination of a deprotonated NHC ligand (pNHC) to generate a doubly C2,N3-bridged dinuclear complex. Here, in particular the discussion is based on the combination of the deprotonated 1-arylimidazol (aryl = mesityl (Mes)) with [M(cod)(μ-Cl)] (M = Ir, Rh) generated two geometrical isomers of complex [M(cod){µ-C(3)H(2)N(2)(Mes)-κC2,κN3}](2)). The latter two isomers display conformations head-to-head (H-H) and head-to-tail (H-T) of C(S) and C(2) symmetry, respectively. The isomerization from the H-H to the H-T conformation is feasible, whereas next substitutions of the cod ligand by CO first, and PMe(3) later confirm the H-T coordination as the thermodynamically preferred. It is envisaged the exchange of the metal, from iridium to rhodium, confirming here the innocence of the nature of the metal for such arrangements of the bridging ligands.