Kirchner Karl, Calhorda Maria José, Schmid Roland, Veiros Luís F
Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria.
J Am Chem Soc. 2003 Sep 24;125(38):11721-9. doi: 10.1021/ja035137e.
A complete catalytic cycle for the cyclotrimerization of acetylene with the CpRuCl fragment has been proposed and discussed based on DFT/B3LYP calculations, which revealed a couple of uncommon intermediates. The first is a metallacyclopentatriene complex RuCp(Cl)(C(4)H(4)) (B), generated through oxidative coupling of two alkyne ligands. It adds another alkyne in eta(2) fashion to give an alkyne complex (C). No less than three successive intermediates could be located for the subsequent arene formation. The first, an unusual five- and four-membered bicyclic ring system (D), rearranges to a very unsymmetrical metallaheptatetraene complex (E), which in turn provides CpRuCl(eta(2)-C(6)H(6)) (F) via a reductive elimination step. The asymmetry of E, including Cp ring slippage, removes the symmetry-forbidden character from this final step. Completion of the cycle is achieved by an exothermic displacement (21.4 kcal mol(-)(1)) of the arene by two acetylene molecules regenerating A. In addition to acetylene, the reaction of B with ethylene and carbon disulfide, the latter taken as a model for a molecule lacking hydrogen atoms, has also been investigated, and several parallels noted. In the case of the coordinated alkene, facile C-C coupling to the alpha carbon of the metallacycle is feasible due to an agostic assistance, which tends to counterbalance the reduced degree of unsaturation. Carbon disulfide, on the other hand, does not coordinate to ruthenium, but a C=S bond adds instead directly to the Ru=C bond. The final products of the reactions of B with acetylene, ethylene, and carbon disulfide are, respectively, benzene, cyclohexadiene, and thiopyrane-2-thione, the activation energies being lower for acetylene.
基于密度泛函理论/ B3LYP计算，已经提出并讨论了用CpRuCl片段使乙炔环三聚的完整催化循环，该计算揭示了一些不常见的中间体。第一个是金属环戊三烯配合物RuCp(Cl)(C(4)H(4)) (B)，它是通过两个炔烃配体的氧化偶联生成的。它以η(2)方式与另一个炔烃加成，生成炔烃配合物(C)。对于随后的芳烃形成，可以找到不少于三个连续的中间体。第一个是不寻常的五元环和四元环双环体系(D)，重排为非常不对称的金属七烯配合物(E)，后者通过还原消除步骤生成CpRuCl(η(2)-C(6)H(6)) (F)。E的不对称性，包括Cp环滑移，消除了这最后一步的对称性禁阻特征。通过芳烃被两个乙炔分子进行的放热取代反应(21.4千卡摩尔(-)(1))使A再生，从而完成循环。除了乙炔，还研究了B与乙烯和二硫化碳的反应，后者被用作缺乏氢原子的分子的模型，并注意到了一些相似之处。在配位烯烃的情况下，由于agostic辅助，金属环的α碳与C-C的容易偶联是可行的，这倾向于抵消不饱和程度的降低。另一方面，二硫化碳不与钌配位，而是一个C=S键直接加到Ru=C键上。B与乙炔、乙烯和二硫化碳反应的最终产物分别是苯、环己二烯和硫代吡喃-2-硫酮，乙炔的活化能较低。
