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.