C−−H activation by acetate-assisted cyclometallation of a phenyl group with half-sandwich complexes [{MCl(2)Cp*}(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 cyclometallated complexes [MCl(C^N)(ring)] (HC^N = 2-phenylpyrazole, M = Ir, Rh ring = Cp*; M = Ru, ring = p-cymene) readily undergo insertion reactions with RC≡CR (R = CO(2)Me, Ph) to give mono insertion products, the rhodium complex also reacts with PhC≡CH regiospecifically to give an analogous product. The products of the reactions of the cyclometallated imine complexes [MCl(C^N)Cp*] (HC^N = PhCH=NR, R = Ph, CH(2)CH(2)OMe, Me; M = Ir, Rh) with PhC≡CPh depend on the substituent R; when R = CH(2)CH(2)OMe a monoinsertion is observed, however for R = Me the initial insertion product is unstable, undergoing reductive elimination with loss of the organic fragment, and for R = Ph no metal-containing product is isolated. With PhC≡CH the cyclometallated imine complexes can give mono or di-insertion products. The implications for catalytic synthesis of carbo- and heterocycles by a tandem C-H activation, alkyne insertion mechanism are discussed.

No abstract