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The Ligand-Based Quintuple Bond-Shortening Concept and Some of Its Limitations

机译：基于配体的五元键缩短概念及其局限性

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摘要

Herein, the ligand-based concept of shortening quintuple bonds and some of its limitations are reported. In dichromium-diguanidinato complexes, the length of the quintuple bond can be influenced by the substituent at the central carbon atom of the used ligand. The guanidinato ligand with a 2,6-dimethylpiperidine backbone was found to be the optimal ligand. The reduction of its chromium(II) chloride-ate complex gave a quintuply bonded bimetallic complex with a Cr-Cr distance of 1.7056 (12)?. Its metal-metal distance, the shortest observed in any stable compound yet, is of essentially the same length as that of the longest alkane C-C bond (1.704 (4)?). Both molecules, the alkane and the Cr complex, are of remarkable stability. Furthermore, an unsupported Cr~I dimer with an effective bond order (EBO) of 1.25 between the two metal atoms, indicated by CASSCF/CASPT2 calculations, was isolated as a by-product. The formation of this by-product indicates that with a certain bulk of the guanidinato ligand, other coordination isomers become relevant. Over-reduction takes place, and a chromium-arene sandwich complex structurally related to the classic dibenzene chromium complex was observed, even when bulkier substituents are introduced at the central carbon atom of the used guanidinato ligand.
机译：在本文中，报道了缩短五重键的基于配体的概念及其一些局限性。在双铬-双胍基络合物中，五元键的长度会受到所用配体中心碳原子上取代基的影响。发现具有2，6-二甲基哌啶骨架的胍基配体是最佳配体。还原其氯化铬（Ⅱ）配合物，得到五重键合的双金属配合物，其Cr-Cr距离为1.7056（12）?。它在任何稳定化合物中观察到的最短金属-金属距离与最长的烷烃C-C键（1.704（4）？）的长度基本相同。烷烃和Cr络合物这两个分子都具有显着的稳定性。此外，通过副产物CASSCF / CASPT2计算表明，两个金属原子之间的有效键序（EBO）为1.25的无支撑Cr〜I二聚体被分离出来。该副产物的形成表明，对于一定量的胍基配体，其他配位异构体变得重要。发生过度还原，即使在使用的胍基配体的中心碳原子上引入了更大的取代基，也观察到了与经典二苯铬配合物在结构上相关的铬-芳烃三明治配合物。

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