Cyclotrimerization of acetylene by Grubbs first and second generation CC bond metathesis catalysts has been attempted by experimentalists with limited success and lack of reliable information about the mechanism of the reaction hinders further progress in the development of efficient catalysts. Herein, we describe a systematic density functional theory study on the probable mechanisms of this reaction and show that it proceeds through either a fully metathesis pathway (pathway 1) or through an alternate non-metathesis pathway (pathway 2). Pathway 1 consists of four metathesis steps characterized by the formation of metallacyclobutene-like intermediate in each step while pathway 2 passes through a metallacyclopentadiene intermediate. In metathesis pathway, the final ring closing metathesis step for benzene formation competes with another cross metathesis propagation step towards polyene chain expansion. Pathways 1 and 2 show a highly exothermic ∼120 kcal/mol reaction profile due to the tremendous energy gain in converting acetylene triple bonds to aromatic bonds. The reaction is highly influenced by the choice of ligands in the catalyst design, particularly, by reducing the steric influence of ligands, cyclotrimerization of acetylene to benzene appears as a feasible process by Grubbs-type catalysts.

实验者已经尝试了用Grubbs的第一代和第二代CC键复分解催化剂进行乙炔的环三聚反应，但成功的方法有限，缺乏有关反应机理的可靠信息，阻碍了有效催化剂的进一步发展。在这里，我们描述了对该反应的可能机理的系统密度泛函理论研究，并表明它通过完全复分解途径（途径1）或通过替代的非复分解途径（途径2）进行。途径1由四个复分解步骤组成，其特征在于在每个步骤中形成类似金属环丁烯的中间体，而途径2穿过金属环戊二烯中间体。在复分解途径中 苯形成的最后一个闭环复分解步骤与另一个朝着多烯链膨胀的交叉复分解传播步骤竞争。由于乙炔三键转化为芳族键的巨大能量增加，通道1和2显示出高放热的〜120 kcal / mol反应曲线。该反应在催化剂设计中受配体选择的影响很大，特别是通过减少配位体的空间影响，乙炔到苯的环三聚反应似乎是格鲁布斯型催化剂的可行方法。