Reversible Insertion of Carbenes into Ruthenium–Silicon Bonds

The five-coordinate carbene complexes [Ru­{κP,P,Si-Si­(Me)­(C6H4-2-PiPr2)2}­Cl­(CHR)] (2, R = Ph; 3, R = SiMe3), analogues of the Grubbs catalyst, were prepared from the dimer [Ru­(μ-Cl)­{κP,P,Si-Si­(Me)­(C6H4-2-PiPr2)2}]2 (1) and the corresponding diazoalkane N2CHR. The particular structural features that result from the presence of a strongly trans directing silyl group at the pincer ligand of these complexes are discussed on the basis of NMR information and the crystal structure of the vinylidene analogue [Ru­{κP,P,Si-Si­(Me)­(C6H4-2-PiPr2)2}­Cl­(CCHPh)] (4), which was also obtained from 1 and phenylacetylene. The reactions of 3 with reagents such as P­(OMe)3, CO, NCMe, and K­(acac) illustrate that the first response of these carbene complexes to an increase of the coordination number around ruthenium is the insertion of the carbene ligand into the Ru–Si bond. These reactions also indicate that the insertion process is reversible and allows typical transformations of carbene ligands such as C–H functionalizations via carbene insertion (in the acac ligand) or the formation of ketene from CO. In addition, the reactions of 3 with terminal alkynes such as phenylacetylene or 3,3-dimethyl-1-butyne show that the inserted carbenes can also undergo reactions typical of metal-bound alkyls such as alkyne insertion and C–H reductive elimination.

五配位卡宾配合物[Ru­{κP,P,Si-Si­(Me)­(C6H4-2-PiPr2)2}­Cl­(CHR)]（2中R=Ph；3中R=SiMe3）作为格拉布催化剂(Grubbs catalyst)的类似物，是以二聚体[Ru­(μ-Cl)­{κP,P,Si-Si­(Me)­(C6H4-2-PiPr2)2}]2（1）与相应的重氮烷烃N2CHR为原料制备得到的。本文基于核磁共振(NMR)谱学信息以及亚乙烯基配合物[Ru­{κP,P,Si-Si­(Me)­(C6H4-2-PiPr2)2}­Cl­(CCHPh)]（4）的晶体结构，讨论了这类配合物钳形配体(pincer ligand)上强反位导向硅基所带来的独特结构特征；该亚乙烯基配合物4同样可由1与苯乙炔反应制得。配合物3与三甲氧基膦P(OMe)3、一氧化碳CO、乙腈NCMe以及乙酰丙酮钾K(acac)等试剂的反应表明，当这类卡宾配合物中心钌的配位数升高时，其首要响应为卡宾配体插入钌-硅(Ru–Si)键内。这些反应同时证实，该插入过程具备可逆性，且可实现卡宾配体的典型转化：例如通过卡宾插入（在乙酰丙酮根(acac)配体中）完成C–H官能化，或是由CO反应生成烯酮。此外，配合物3与端炔（如苯乙炔或3,3-二甲基-1-丁炔）的反应显示，插入后的卡宾配体还可发生金属键合烷基的典型反应，包括炔烃插入反应与C–H还原消除反应。