Formation and reactivity of the cyclometallated N-heterocyclic carbene complexes [Ru(NHC)′(dppe)(CO)H]

Abstract

Thermolysis of [Ru(PPh₃)(dppe)(CO)HCl] (dppe = 1,2-bis(diphenylphosphino)ethane) with the N-heterocyclic carbenes IⁱPr₂Me₂ (1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene), IEt₂Me₂ (1,3-diethyl-4,5-dimethyl-imidazol-2-ylidene) or ICy (1,3-dicyclohexylimidazol-2-ylidene) gave the cyclometallated carbene complexes [Ru(NHC)′(dppe)(CO)H] (NHC = IⁱPr₂Me₂, 4; IEt₂Me₂, 5; ICy, 6). Dissolution of 4 in CH₂Cl₂ or CHCl₃ gave the trans-Cl–Ru–P complex [Ru(IⁱPr₂Me₂)′(dppe)(CO)Cl] (7), which converted over hours at room temperature to the trans-Cl–Ru–CO isomer 7′. Chloride abstraction from 7 by NaBPh₄ under an atmosphere of H₂ produced the cationic mono-hydride complex [Ru(IⁱPr₂Me₂)(dppe)(CO)H][BPh₄] (9), which could also be formed by protonating 4 with 1 eq HBF₄·OEt₂. Treatment of 4 with excess HBF₄·OEt₂ followed by extraction into MeCN produced the dicationic acetonitrile complex [Ru(IⁱPr₂Me₂)(dppe)(CO)(NCMe)₂][BF₄]₂ (10). The structures of 6, 7, 7′ and 10 have been determined by X-ray crystallography.