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

Abstract

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).