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Symmetrical and Non‐symmetrical Pd (II) Pincer Complexes Bearing Mesoionic N‐heterocyclic Thiones: Synthesis, Characterizations and Catalytic Properties
Applied Organometallic Chemistry ( IF 3.9 ) Pub Date : 2020-07-10 , DOI: 10.1002/aoc.5885
Xuechao Yan 1 , Bo Zhang 1 , Xin Zhang 1 , Haiying Wang 1 , Yu‐Ai Duan 1 , Shuai Guo 1
Affiliation  

In contrast to well‐established symmetrical pincer complexes, non‐symmetrical metal pincers with the loss of C2v symmetry are much less studied. In this work, mesoionic NHTs (NHTs = N‐heterocyclic thiones), which can be viewed as the sulfur adducts of mesoionic carbenes, are incorporated into pincer complexes for the first time. Two symmetrical and non‐symmetrical phenylene‐bridged bis (NHT) compounds 3a/3b were synthesized as proligands via a “cycloaddition‐alkylation‐thionation” reaction sequence. In a case to access bis (NHT) compound 3c, N‐dealkylation reactions occurred. The carbene NMR signals of NHTs are only partially correlated to the π‐accepting abilities of carbenes, which is different from Bertrand's carbene‐phosphinidene system. The structural analysis of 3a/3b indicates that they possess C‐S partial double bonds. 3a and 3b served as the precursors to access two aryl anion‐linked [SCS/S′] pincer complexes 6a/6b. An external base proved to be essential for this cyclopalladation process. The catalytic properties of 6a/6b in the cycloisomerizations of alkynoic acids have been examined. Finally, non‐symmetrical complex 6a shows superior catalytic performance in such transformations contrasting to its symmetrical counterpart 6b.

中文翻译:

带有中性N-杂环亚砜的对称和非对称Pd(II)钳形配合物:合成,表征和催化性能

与已建立的对称钳形复合体相比,缺少C 2v对称性的非对称金属钳形结构研究较少。在这项工作中,中性NHT(NHTs = N-杂环硫酮),可以看作是中性卡宾的硫加成物,首次被引入到钳形配合物中。通过“环加成-烷基化-硫代”反应序列合成了两个对称和不对称的亚苯基桥双(NHT)化合物3a / 3b。在使用双(NHT)化合物3c的情况下,发生了N-脱烷基反应。NHT的卡宾NMR信号仅与部分碳烯的π接受能力相关,这与Bertrand的卡宾-次膦系统不同。3a / 3b的结构分析表明它们具有C-S部分双键。3a3b作为进入两个芳基阴离子连接的[SCS / S']钳络合物6a / 6b的前体。事实证明,外部基础对于该环palpalladation过程至关重要。研究了6a / 6b在炔酸环异构化中的催化性能。最后,非对称复合体6a与对称的对应物6b相比,在此类转化中显示出优异的催化性能。
更新日期:2020-09-14
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