Evidence for a Carbon−Carbon Coupling Reaction To Proceed through a Planar-Tetracoordinate Carbon Intermediate

Treatment of bis(propynyl)zirconocene with B(C6F5)3 results in a linear C−C coupling of
the alkynyl ligands to form the zwitterionic complex 3. Its treatment with excess RC⋮N
yields an organometallic methylenecyclopropene derivative (6). This reaction topologically
requires a very endothermic substituted butenyne to methylenecyclopropene cyclization to
become energetically feasible by suitable stabilization effects. A DFT study has revealed
that the 3 → 6 conversion is probably triggered by nitrile addition to the metal with formation
of a planar-tetracoordinate carbon intermediate, featuring coordination of the three-membered carbocycle through one of its carbon−carbon σ bonds.

对双(丙炔基)锆茂与B(C6F5)3的处理导致炔基配体的线性C−C偶联，形成两性离子复合物3。该复合物与过量的RC⋮N反应生成有机金属亚甲基环丙烯衍生物（6）。此反应在拓扑上需要一种非常吸热的取代丁二烯进行亚甲基环丙烯环化，通过适当的稳定化效应使其在能量上变得可行。密度泛函理论（DFT）研究表明，3 → 6的转化可能是由腈基向金属的添加所触发，形成平面四配位碳中间体，其中通过其碳−碳σ键之一进行三碳环的配位。