Alkyne insertion into cyclometallated pyrazole and imine complexes of iridium, rhodium and ruthenium; relevance to catalytic formation of carbo- and heterocycles

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 RCCR (R = CO2Me, Ph) to give mono insertion products, the rhodium complex also reacts with PhCCH regiospecifically to give an analogous product. The products of the reactions of the cyclometallated imine complexes [MCl(C^N)Cp*] (HC⁁N = PhCHNR, R = Ph, CH2CH2OMe, Me; M = Ir, Rh) with PhCCPh depend on the substituent R; when R = CH2CH2OMe 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 PhCCH 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.