The scope of ambiphilic acetate-assisted cyclometallation with half-sandwich complexes of iridium, rhodium and ruthenium

摘要

C-H activation by acetate-assisted cyclometallation of a phenyl group with half-sandwich complexes [{MCl_2Cp*}_2] (M=Ir, Rh) and [{RuCl_2(p-cymene)}_2] can be directed by a wide range of nitrogen donor ligands including pyrazole, oxazoline, oxime, imidazole and triazole, and X-ray structures of a number of complexes are reported. All the ligands tested cyclometallated at iridium, however ruthenium and rhodium fail to cause cyclometallation in some cases. As a result, the nitrogen donors have been categorised based on their reactivity with the three metals used. The relevance of these cyclometallation reactions to catalytic synthesis of carbocycles and heterocycles is discussed. The ease of cyclometallation at [{MCl_2Cp*}_2] (M=Ir, Rh) and [{RuCl _2(p-cymene)}_2] with different N-donor groups has been determined experimentally by using ambiphilic acetate-assisted C-H activation. Cp*Ir is more efficient than either Cp*Rh or (p-cymene)Ru at promoting cyclometallation. The implications for the catalytic synthesis of carbocycles and heterocycles are discussed.