Ruthenium Phosphinimine Complex as a Fast-Initiating Olefin Metathesis Catalyst with Competing Catalytic Cycles
Ruthenium Phosphinimine Complex as a Fast-Initiating Olefin Metathesis Catalyst with Competing Catalytic Cycles
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DOI：
10.1021/acs.organomet.2c00487
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发表时间：
2022-10
期刊：
影响因子：
2.8
通讯作者：
S. Saha;B. Averkiev;Peter E. Sues
中科院分区：
文献类型：
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作者：
S. Saha;B. Averkiev;Peter E. Sues
合成并表征了带有单齿三苯基膦亚胺配体Ru1的钌基烯烃复分解（OM）催化剂，并研究了其对末端烯烃自偶联的活性。利用 1-己烯作为模型底物，发现 Ru1 的经验速率定律在烯烃和络合物中是一阶的（表明两种物质都参与限速步骤），速率常数为 0.697 ± 0.050 M–1s–1。此外，实验确定的活化参数ΔS⧧和ΔH⧧（分别为-48.7±5.1eu和3.19±0.15kcal/mol）与缔合或缔合互换配体取代反应一致。当考虑到 17.7 kcal/mol 的 ΔG⧧(298 K) 值时，Ru1 跻身文献报道的最快引发钌基 OM 催化剂之列。还进行了密度泛函理论（DFT）计算以探索潜在的催化机制。考虑了两种途径：膦亚胺配体脱配的传统机制和膦供体脱配的替代机制。尽管两条途径之间的能量差异通常相当小（1.4-3.5 kcal/mol），但磷化氢脱配的替代途径在能量上更有利。然而，预计两个循环在催化反应期间同时进行。除了动力学研究之外，还使用 1-己烯作为模型底物探索了 Ru1 的稳定性。发现膦亚胺催化剂具有轻度氧敏感性和耐湿性。此外，通过关键降解产物的晶体学表征，Ru1 被确定易于双分子分解。还有强有力的证据表明三环己基膦和三苯基膦亚胺部分之间存在 NH 交换。最后探讨了Ru1对于α-烯烃的底物范围。催化效率随着缺电子烯烃的增加以及基材上空间体积的增加而下降，这与所提出的催化机制一致。
A ruthenium-based olefin metathesis (OM) catalyst bearing a monodentate triphenylphosphinimine ligand,Ru1, was synthesized, characterized, and its activity for the homocoupling of terminal alkenes was investigated. Utilizing 1-hexene as a model substrate, the empirical rate law forRu1was found to be first-order in alkene and complex (indicating that both species were involved in the rate-limiting step), with a rate constant of 0.697 ± 0.050 M–1s–1. Moreover, the experimentally determined activation parameters ΔS⧧and ΔH⧧(−48.7 ± 5.1 eu and 3.19 ± 0.15 kcal/mol, respectively) were consistent with an associative or associative interchange ligand substitution reaction. When considering the ΔG⧧(298 K) value of 17.7 kcal/mol,Ru1ranked among the fastest initiating ruthenium-based OM catalysts reported in the literature. Density functional theory (DFT) calculations were also performed to explore potential catalytic mechanisms. Two pathways were considered: a traditional mechanism where the phosphinimine ligand de-coordinated and an alternative mechanism where the phosphine donor de-coordinated. Although the energy differences between the two pathways were typically fairly small (1.4–3.5 kcal/mol), the alternative pathway with phosphine de-coordination was energetically more favorable. It is anticipated, however, that both cycles are working in tandem during the catalytic reaction. In addition to kinetic studies, the stability ofRu1was explored using 1-hexene as a model substrate. The phosphinimine catalyst was found to be mildly oxygen-sensitive and moisture-tolerant. Furthermore,Ru1was determined to be prone to bimolecular decomposition, through the crystallographic characterization of a key degradation product. There was also strong evidence for NH exchange between the tricyclohexylphosphine and triphenylphosphinimine moieties. Lastly, the substrate scope ofRu1in regard to α-olefins was explored. Catalytic efficiency dropped with more electron-deficient alkenes, as well as with increasing steric bulk on the substrate, which was consistent with the proposed catalytic mechanism.