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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >P-heterocyclic carbenes as potential ligands in the design of new metathesis catalysts. A computational study
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P-heterocyclic carbenes as potential ligands in the design of new metathesis catalysts. A computational study

机译：在新的复分解催化剂的设计中，P-杂环卡宾是潜在的配体。计算研究

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摘要

Density functional calculations are reported concerning the olefin metathesis characteristics of a variety of P-heterocyclic carbene (PHC) complexes. The calculations employ model catalysts of the type (PMe3)(PHC) Cl2Ru= CH2, the PHC ligands being 1,3-dihydro-1,3-diphosphol-2-ylidene PH, 1,3-diphenyl-1,3-diphosphol-2-ylidene PPh, and 1,4-dihydro-1,4-diphosphol-2-azol-5-ylidene PNH. Complexes with N-heterocyclic carbenes (NHC) are included for comparison. Associative and dissociative reaction pathways are considered, the latter ones representing the favored reaction mechanisms. Calculations show that the rate determining step is ring opening of a ruthena-cyclobutane intermediate. In comparison with NHC model catalysts, the PHC compounds have lower phosphine dissociation energies, and also form weaker pi-complexes with an olefinic substrate. Compared to the initially formed pi-complexes, the ruthena-cyclobutane is more stable for PHC- than for NHC-catalysts. The catalytic activity of model PHC- compounds in comparison with NHC-compounds is discussed on the basis of the calculated reaction profiles. In this context, different models for enhanced reactivity of NHC-based catalysts that have been proposed in the literature are considered as well. It is demonstrated that the nature of the substituent of the carbene phosphorus not only exhibits a steric influence on the course of the reaction, but a significant stereoelectronic effect as well. Further, agostic interactions in ruthena-cyclobutane intermediates are investigated.
机译：据报道有关各种P杂环卡宾（PHC）配合物的烯烃复分解特性的密度泛函计算。该计算使用类型为（PMe3）（PHC）Cl2Ru = CH2的模型催化剂，PHC配体为1,3-二氢-1,3-二磷酸-2-亚烷基PH，1,3-二苯基-1,3-二磷酸-2-亚烷基PPh和1，4-二氢-1,4-二膦基-2-氮杂-5-亚烷基PNH。包含与N-杂环卡宾（NHC）的配合物用于比较。考虑了缔合和解离的反应途径，后一种代表了有利的反应机理。计算表明，速率确定步骤是钌-环丁烷中间体的开环。与NHC模型催化剂相比，PHC化合物具有较低的膦离解能，并且还与烯烃底物形成较弱的pi络合物。与最初形成的pi络合物相比，钌-环丁烷对PHC-的稳定性高于对NHC催化剂的稳定性。根据计算得出的反应曲线，讨论了模型PHC化合物与NHC化合物的催化活性。在这种情况下，还考虑了文献中已经提出的用于增强基于NHC的催化剂的反应性的不同模型。已经证明，卡宾磷的取代基的性质不仅对反应过程表现出空间影响，而且还具有显着的立体电子效应。此外，研究了钌-环丁烷中间体中的有害相互作用。

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