Synergistic dimetallic effects in propargylic substitution reaction catalyzed by thiolate-bridged diruthenium complex
Synergistic dimetallic effects in propargylic substitution reaction catalyzed by thiolate-bridged diruthenium complex
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DOI：
10.1021/ja050298z
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发表时间：
2005-07-06
影响因子：
15
通讯作者：
Nakamura, E
中科院分区：
文献类型：
--
作者：
Ammal, SC;Yoshikai, N;Nakamura, E
利用密度泛函计算（B3LYP）研究了硫酸桥接的二钌配合物在丙炔醇亲核取代反应中独特催化活性的来源，该反应以二钌-烯基配合物为关键中间体。单钌和二钌体系的比较表明，刚性但相当灵活的Ru-Ru核心结构在催化剂周转步骤中起着关键作用（即产物t配合物与起始丙炔醇通过配位不饱和Ru配合物的解离配体交换）。在二钌体系中，由于配位不饱和造成的能量损失可以通过增强Ru-Ru键来补偿，而在单钌体系中则没有这种效果。二钌配合物较弱的回给能力也有利于t配合物的解离。因此，配体交换在二钌体系中顺利进行，以再生活性物质，而单钌反应在Ru产物pi络合物的死端停止。目前的研究也表明质子分子（如MeOH）在丙炔醇-烯丙二烯转化过程中介导平滑质子转移的重要作用。
The origin of unique catalytic activity of a thiolate-bridged diruthenium complex in nucleophilic substitution reactions of propargylic alcohols, which features a diruthenium-allenylidene complex as a key intermediate, was studied with the aid of density functional calculations (B3LYP). Comparison of mono- and diruthenium systems has shown that the rigid but reasonably flexible Ru-Ru core structure plays a critical role in the catalyst turnover step (i.e., dissociative ligand exchange of the product T-complex with the starting propargyl alcohol that goes through a coordinatively unsaturated Ru complex). In the diruthenium system, the energy loss due to coordinative unsaturation can be compensated by reinforcement of the Ru-Ru bond, while such an effect is unavailable in the monoruthenium counterpart. Weaker back-donation ability of the diruthenium complex is also advantageous for dissociation of the T-complex. Thus, ligand exchange takes place smoothly in the diruthenium system to regenerate the reactive species, while the monoruthenium reaction stops at a dead-end Ru product pi-complex. The present studies have also shown the important role of protic molecules (e.g., MeOH) that mediate smooth proton transfer in the propargyl alcohol-allenylidene transformation.