Iridium complexes of perimidine-based N-heterocyclic carbene pincer ligands via aminal C–H activation

Abstract

The reactions of N,N′-bis(phosphinomethyl)dihydroperimidine pro-ligands H2C(NCH2PR2)2C10H6-1,8 (R = Ph 1a, R = Cy 1b) with iridium(I) substrates have been investigated and shown to readily result in chelate-assisted C–H activation processes. The reaction of 1b with [Ir2Cl2(COE)4] (COE = cyclo-octene) affords the 18-electron iridium(III) dihydrido complex [IrH2Cl{κ3-C,P,P′-C(NCH2PCy2)2C10H6}], which forms [IrHCl2{κ3-C,P,P′-C(NCH2PCy2)2C10H6}] under acidic (HCl) conditions. In contrast, reaction of 1a with [Ir2Cl2(COD)2] (COD = 1,5-cyclo-octadiene) affords the complex [IrCl(COD){κ2-P,P′-H2C(NCH2PPh2)2C10H6}], thermolysis of which affords cyclo-octene and the pincer-NHC complex [IrCl{κ3-C,P,P′-C(NCH2PPh2)2C10H6}]. The reaction of 1a with two equivalents of [Ir2Cl2(COD)2] provides the binuclear complex [Ir2{μ-H2C(NCH2PPh2)2C10H6}Cl2(COD)2] which is also observed to accumulate and then dissipate during the preceding thermolysis. Related binuclear complexes [M2{μ-H2C(NCH2PPh2)2C10H6}Cl4(η-C5Me5)2] (M = Ir, Rh) which obviate C–H activation were similarly synthesised.