金属有机协同催化在C-H和C-C键活化及其同步回收中的应用
Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.
作者信息
Park Young Jun, Park Jung-Woo, Jun Chul-Ho
机构信息
Department of Chemistry and Center for Bioactive Molecular Hybrid, Yonsei University, Seoul 120-749.
出版信息
Acc Chem Res. 2008 Feb;41(2):222-34. doi: 10.1021/ar700133y. Epub 2008 Feb 2.
The development of an efficient catalytic activation (cleavage) system for C-H and C-C bonds is an important challenge in organic synthesis, because these bonds comprise a variety of organic molecules such as natural products, petroleum oils, and polymers on the earth. Among many elegant approaches utilizing transition metals to activate C-H and C-C bonds facilely, chelation-assisted protocols based on the coordinating ability of an organic moiety have attracted great attention, though they have often suffered from the need for an intact coordinating group in a substrate. In this Account, we describe our entire efforts to activate C-H or C-C bonds adjacent to carbonyl groups by employing a new concept of metal-organic cooperative catalysis (MOCC), which enables the temporal installation of a 2-aminopyridyl group into common aldehydes or ketones in a catalytic way. Consequently, a series of new catalytic reactions such as alcohol hydroacylation, oxo-ester synthesis, C-C triple bond cleavage, hydrative dimerization of alkynes, and skeletal rearrangements of cyclic ketones was realized through MOCC. In particular, in the quest for an optimized MOCC system composed of a Wilkinson's catalyst (Ph 3P) 3RhCl and an organic catalyst (2-amino-3-picoline), surprising efficiency enhancements could be achieved when benzoic acid and aniline were introduced as promoters for the aldimine formation process. Furthermore, a notable accomplishment of C-C bond activation has been made using 2-amino-3-picoline as a temporary chelating auxiliary in the reactions of unstrained ketones with various terminal olefins and Wilkinson's catalyst. In the case of seven-membered cyclic ketones, an interesting ring contraction to five- or six-membered ones takes place through skeletal rearrangements initiated by the C-C bond activation of MOCC. On the other hand, the fundamental advances of these catalytic systems into recyclable processes could be achieved by immobilizing both metal and organic components using a hydrogen-bonded self-assembled system as a catalyst support. This catalyst-recovery system provides a homogeneous phase at high temperature during the reaction and a heterogeneous phase at room temperature after the reaction. The product could be separated conveniently from the self-assembly support system by decanting the upper layer. The immobilized catalysts of both 2-aminopyridine and rhodium metal species sustained high catalytic activity for up to the eight catalytic reactions. In conclusion, the successful incorporation of an organocatalytic cycle into a transition metal catalyzed reaction led us to find MOCC for C-H and C-C bond activation. In addition, the hydrogen-bonded self-assembled support has been developed for an efficient and effective recovery system of homogeneous catalysts and could be successful in immobilizing both metal and organic catalysts.
开发一种用于碳氢键和碳碳键的高效催化活化(裂解)体系是有机合成中的一项重要挑战,因为这些键构成了地球上各种有机分子,如天然产物、石油和聚合物。在众多利用过渡金属轻松活化碳氢键和碳碳键的精妙方法中,基于有机部分配位能力的螯合辅助方案引起了极大关注,尽管它们常常因底物中需要完整的配位基团而受限。在本综述中,我们描述了通过采用金属 - 有机协同催化(MOCC)的新概念来活化羰基相邻的碳氢键或碳碳键的全部努力,该概念能够以催化方式将2 - 氨基吡啶基团暂时引入常见的醛或酮中。因此,通过MOCC实现了一系列新的催化反应,如醇氢酰化反应、氧代酯合成、碳碳三键裂解、炔烃的水合二聚反应以及环酮的骨架重排。特别地,在探索由威尔金森催化剂(三苯基膦)₃RhCl和有机催化剂(2 - 氨基 - 3 - 甲基吡啶)组成的优化MOCC体系时,当引入苯甲酸和苯胺作为醛亚胺形成过程的促进剂时,可以实现惊人的效率提升。此外,在无张力酮与各种末端烯烃以及威尔金森催化剂的反应中,使用2 - 氨基 - 3 - 甲基吡啶作为临时螯合助剂在碳碳键活化方面取得了显著成果。对于七元环酮,通过MOCC的碳碳键活化引发的骨架重排会发生有趣的环收缩,形成五元或六元环酮。另一方面,通过使用氢键自组装体系作为催化剂载体固定金属和有机组分,可以实现这些催化体系向可回收过程的根本进展。该催化剂回收体系在反应期间在高温下提供均相,在反应后在室温下提供非均相。通过倾析上层可以方便地将产物与自组装载体体系分离。2 - 氨基吡啶和铑金属物种的固定化催化剂在多达八次催化反应中都保持了高催化活性。总之,将有机催化循环成功纳入过渡金属催化反应使我们找到了用于碳氢键和碳碳键活化的MOCC。此外,已经开发出氢键自组装载体用于高效且有效的均相催化剂回收体系,并且能够成功固定金属和有机催化剂。