Ruthenium and osmium complexes of dihydroperimidine-based N-heterocyclic carbene pincer ligands

Abstract

The reactions of N,N′-bis(phosphinomethyl)dihydroperimidine pro-ligands H₂C(NCH₂PR₂)₂C₁₀H₆ (R = Cy 1a, R = Ph 1b) with [RuCl₂(PPh₃)₃] give markedly different products. Chelate-assisted double C–H activation in the former affords the perimidinylidene-based N-heterocyclic carbene (per-NHC) pincer complex [RuCl₂(OC₄H₈){κ³-P,C,P′-C(NCH₂PCy₂)₂C₁₀H₆}] (2), while the latter reaction provides the asymmetric PNP-coordinated complex [RuCl₂(PPh₃){κ³-P,N,P′-CH₂(NCH₂PPh₂)₂C₁₀H₆}] (3), in which no C–H activation has occurred. Subsequent reactions of the per-NHC complex 2 with carbon monoxide and mesityl isocyanide readily displaced the labile THF ligand to afford the complexes [RuCl₂(CA){κ³-P,C,P′-C(NCH₂PCy₂)₂C₁₀H₆}] (A = O 4, A = NC₆H₂Me₃5). Double C–H activation of 1a and 1b was significantly more facile on reaction with [OsCl₂(PPh₃)₃], providing the per-NHC complexes [OsHCl(PPh₃){κ³-P,C,P′-C(NCH₂PR₂)₂C₁₀H₆}] (R = Cy 7a, R = Ph 7b, respectively), each as two isomers. The reactions of 1b with [Ru₂(μ-Cl)₂Cl₂(η-C₆H₃Me₃)₂] or [AuCl(THT)] (THT = tetrahydrothiophene) provide the bimetallic complexes [Ru₂{μ-H₂C(NCH₂PPh₂)₂C₁₀H₆}Cl₄(η-C₆H₃Me₃)₂] (8) and [Au₂{μ-H₂C(NCH₂PPh₂)₂C₁₀H₆}Cl₂] (9) without C–H activation occurring.