N-Heterocyclic carbene-containing ruthenium difluoro complexes and their reactivity towards BF3

Abstract

Treatment of tetranuclear [RuF(μ-F)(CO)₃]₄ (1) with the free N-heterocyclic carbenes (NHCs), IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), followed by work-up in carbon tetrachloride leads to fluoride-bridge cleavage in 1 and the formation of the mononuclear octahedral complexes cis,cis,trans-[RuF₂(CO)₂(NHC)₂] [NHC = IMes (2a), IPr (2b)], respectively. Complexes 2a and 2b can also be obtained by interaction of 1 with the corresponding imidazolium chloride, [-N(Ar)CHN(Ar)CHCH-]Cl (Ar = 2,4,6-Me₃C₆H₂, 2,6-i-Pr₂C₆H₃), in the presence of KO^tBu. However, extension of this latter base-assisted approach to [-N(Ar)CHN(Ar)CHCH-]Cl (Ar = 2,6-Me₂C₆H₃, 2,4,6-i-Pr₃C₆H₂) results in halide exchange with the work-up solvent (CCl₄) to generate cis,cis,trans-[RuCl₂(CO)₂(IMe)₂] (3) and dinuclear [RuCl(μ-Cl)(CO)₂(ITPr)]₂ (4), respectively. Reaction of 2a with gaseous BF₃ in dichloromethane and subsequent carbonylation affords in high yield monocationic [Ru(FBF₃)(CO)₃(IMes)₂](BF₄) (5), while with 2b, BF₃ addition alone results in solvent exchange to yield dinuclear monocationic [Ru₂(μ-Cl)₃(CO)₄(IPr)₂](BF₄)/(F) (6). Conversely, interaction of 2a and 2b with BF₃·OEt₂ in acetonitrile furnishes dicationic cis,cis,trans-[Ru(CO)₂(NCMe)₂(NHC)₂](BF₄)₂ [NHC = IMes (7a), IPr (7b)]; in the case of 7acarbonylation gives [Ru(CO)₄(IMes)₂](B₂F₇)₂ (8). Single crystal X-ray structures are presented for 3, 4, 5, 6 and 8.