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

Abstract

Treatment of tetranuclear [RuF(-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 KOtBu. 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(mu-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(mu-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 7a carbonylation gives [Ru(CO)4(IMes)2](B2F7)2 (8). Single crystal X-ray structures are presented for 3, 4, 5, 6 and 8.