Achour Sofiene, Hosni Zied, Tangour Bahoueddine
University of Tunis El Manar, Research Unit of Modeling in Fundamental Sciences and Didactics, IPEIEM, PO Box 254, El Manar 2, 2096, Tunis, Tunisia.
Strathclyde Institute of Pharmacy and Biomedical Sciences (SIPBS), University of Strathclyde, 161 Cathedral Street, Glasgow, G4 0RE, UK.
J Mol Graph Model. 2020 Jul;98:107583. doi: 10.1016/j.jmgm.2020.107583. Epub 2020 Mar 13.
A DFT study was conducted to elucidate the mechanism of hexene hydrogenation catalysed by a series of ruthenium (II) monohydride catalysts: RuH(CO)(Cl)(LL') where L and L' represent C(cyclohexyl), Me (methyl) and IMe (N, N '-bis (mesityl) imidazole-2-ylidene). This investigation explores the feasibility of two different proposed mechanisms: the first describes the dissociated pathway and exploits a single phosphine complex. The second is the associative one and uses a two phosphines complex. The detailed pathways have been explored for the catalyst model with L = L' = Me. Three possibilities have been supported for the dissociative route. Pathway (A) begins with a phosphine release. The initial addition of hexane or a dihydrogen molecule on the ruthenium catalyst generates the pathways (B) and (C), respectively. Pathways (B) and (C) merge with the pathway (A) before and after the first proton transfer, respectively. Activation energies in the first hydrogen migration (the key-step of the mechanism) are close. Therefore, both mechanisms (A) and (B) are possible but the former is more probable. The substitution of the catalyst model RuHCl(CO)(PMe) by the real catalysts RuHCl(CO)(PCy) or RuHCl(CO)(IMes)(PMe) shows no significant influence on the energetic barriers of hexene hydrogenation mechanism. The energy profile of the first hydrogen migration for the catalyst RuHCl(CO)(PCy) is characteristic of a concerted asynchronous mechanism while our calculation led to two separated synchronous steps when the model catalyst is used. The associative pathway (D) integrates the two experimentally detected intermediates and generates activation energies close to those of dissociative pathways (A) and (B). The rationale to explain the experimentally detected species is achieved by considering the four proposed mechanisms where they occur simultaneously and with different rates (ie. The dissociative mechanism has the highest rate).
进行了一项密度泛函理论（DFT）研究，以阐明一系列氢化钌（II）催化剂RuH(CO)(Cl)(LL')催化己烯加氢的机理，其中L和L'分别代表C(环己基)、Me（甲基）和IMe（N,N'-双（均三甲苯基）咪唑-2-亚基）。本研究探讨了两种不同提出机制的可行性：第一种描述了离解途径，并利用了单膦配合物。第二种是缔合途径，使用了双膦配合物。已对L = L' = Me的催化剂模型的详细途径进行了探索。离解途径支持三种可能性。途径（A）始于膦的释放。己烷或二氢分子最初在钌催化剂上的加成分别产生途径（B）和（C）。途径（B）和（C）分别在第一次质子转移之前和之后与途径（A）合并。第一次氢迁移（该机理的关键步骤）中的活化能相近。因此，机制（A）和（B）都是可能的，但前者更有可能。用实际催化剂RuHCl(CO)(PCy)或RuHCl(CO)(IMes)(PMe)替代催化剂模型RuHCl(CO)(PMe)对己烯加氢机理的能量势垒没有显著影响。催化剂RuHCl(CO)(PCy)的第一次氢迁移的能量分布具有协同异步机理的特征，而当使用模型催化剂时，我们的计算得出了两个分开的同步步骤。缔合途径（D）整合了两个实验检测到的中间体，并产生了与离解途径（A）和（B）相近的活化能。通过考虑四种提出的机制来实现对实验检测到的物种的解释，其中它们同时以不同的速率发生（即离解机制具有最高的速率）。
