刚性大环格拉布斯配合物:内外异构体在催化反应性上表现出巨大差异的罕见实例

IF 2.5 3区 化学 Q2 CHEMISTRY, INORGANIC & NUCLEAR Organometallics Pub Date : 2024-09-03 DOI:10.1021/acs.organomet.4c0033110.1021/acs.organomet.4c00331
Anibal R. Davalos-Morinigo, Srini Vemulapalli, Travis Dudding* and Steven T. Diver*, 
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引用次数: 0

摘要

通过设计一种刚性大环 N-heterocyclic carbene(NHC)配体,形成了碳内和碳外钌(in-and-out-Ru carbene)配合物,并确定了其结构特征。在这项研究中,通过引入构象锁使杂芳基-芳基键刚性化,从而使二面角更加垂直。要形成异构的碳化 Ru 复合物(Grubbs 复合物),需要一个强制金属化步骤。主要异构体的碳化 Ru 片段位于大环之外,而次要异构体的碳化 Ru 位于大环之内。这两种新的碳化 Ru 复合物是格拉布斯型复合物的内异构体和外异构体的首例。通过 X 射线衍射(XRD)研究确定了每种碳化钌异构体配合物的固态结构。在基准底物二烯丙基丙二酸二乙酯的闭环缩合反应(RCM)中,两种 Ru 复合物显示出明显不同的催化反应活性。我们进行了计算研究,以确定旋转障碍;发现非金属 NHC 配体中存在可扩展的能量障碍,有利于内向异构体 2.4 kcal/mol。这些计算结果以及尝试进行的异构体相互转化支持了一种机制,即在金属化之前的预平衡步骤中,NHC 亲核体发生旋转异构化。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

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A Rigidified Macrocyclic Grubbs Complex: A Rare Example of In- and Out-Isomers that Show a Dramatic Difference in Catalytic Reactivity

The design of a rigidified macrocyclic N-heterocyclic carbene (NHC) ligand led to the formation and structural characterization of in- and out-Ru carbene complexes. In this study, the introduction of a conformational lock was used to rigidify heteroaryl–aryl bonds and thereby enforce a more perpendicular dihedral angle. A forcing metalation step was needed to form the isomeric Ru carbene complexes (Grubbs complexes). The major isomer had the Ru carbene fragment located outside the macrocyclic ring, whereas the minor isomer had the Ru carbene inside the macrocyclic ring. The two new Ru carbene complexes are the first examples of in- and out-isomers of a Grubbs-type complex. The solid-state structures of each isomeric ruthenium carbene complex were determined by X-ray diffraction (XRD) studies. The two Ru complexes showed significantly different catalytic reactivities in the ring-closing metathesis (RCM) of the benchmark substrate, diethyl diallylmalonate. We performed computational studies to determine rotational barriers; scalable energetic barriers were found in the unmetalated NHC ligand, favoring the in-isomer by 2.4 kcal/mol. These calculations, coupled with the attempted interconversion of isomers, support a mechanism featuring rotational isomerization of the NHC nucleophile in a pre-equilibrium step before metalation.

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来源期刊
Organometallics
Organometallics 化学-无机化学与核化学
CiteScore
5.60
自引率
7.10%
发文量
382
审稿时长
1.7 months
期刊介绍: Organometallics is the flagship journal of organometallic chemistry and records progress in one of the most active fields of science, bridging organic and inorganic chemistry. The journal publishes Articles, Communications, Reviews, and Tutorials (instructional overviews) that depict research on the synthesis, structure, bonding, chemical reactivity, and reaction mechanisms for a variety of applications, including catalyst design and catalytic processes; main-group, transition-metal, and lanthanide and actinide metal chemistry; synthetic aspects of polymer science and materials science; and bioorganometallic chemistry.
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