Ring-opening and double-metallation reactions of the N-Heterocyclic carbene ligand in Cp^∗(IXy)Ru (IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene) complexes. Access to an anionic fischer-type carbene complex of ruthenium This paper is dedicated to John Bercaw on the occasion of his 70th birthday

An N-heterocylic carbene (NHC) ring-opening reaction was observed upon treatment of the silyl complex Cp^∗(IXy-H)(H)RuSiH₂Mes [1; IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene; IXy-H = 1-(2-CH₂C₆H₃-6-methyl)-3-(2,6-dimethylphenyl)imidazol-2-ylidene-1-yl (the deprotonated form of IXy); Cp^∗ = η⁵-C₅Me₅] with LiCH₂SiMe₃. This reaction results in formation of a novel, anionic Fischer-type carbene complex Cp^∗(H)Ru{κ²-CHN(Xyl)CH[Si(CH₂SiMe₃)Mes]N(Xyl)Li} (4). This ring-opening reaction demonstrates a new pathway for NHC degradation via the cooperation of ruthenium, silicon, and lithium. Additionally, treatment of the dinitrogen complex Cp^∗(IXy-H)Ru(N₂) with LiCH₂SiMe₃ led to the doubly-metallated complex [Cp^∗(IXy-2H)Ru]Li (5), which exhibits a solid-state polymeric structure and metallation of both xylyl groups of the IXy ligand. Finally, removal of a hydride from 4, achieved with two equiv of B(C₆F₅)₃, led to C-H activation of the Cp^∗ ligand and formation of an unusual, formally dianionic η⁵-Me₄C₅CH₂B(C₆F₅)₃ ligand in a ruthenium carbene complex [η⁵-Me₅C₅CH₂B(C₆F₅)₃](H)Ru{κ³-CHN(Xyl)CH[SiH(CH₂SiMe₃)Mes]N(Xyl)} (7).