Mechanistic Insight into Catalytic Redox-Neutral C-H Bond Activation Involving Manganese(I) Carbonyls: Catalyst Activation, Turnover, and Deactivation Pathways Reveal an Intricate Network of Steps
Mechanistic Insight into Catalytic Redox-Neutral C-H Bond Activation Involving Manganese(I) Carbonyls: Catalyst Activation, Turnover, and Deactivation Pathways Reveal an Intricate Network of Steps
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DOI：
10.1021/jacs.8b09095
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发表时间：
2019-02-13
影响因子：
15
通讯作者：
Fairlamb, Ian J. S.
中科院分区：
文献类型：
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作者：
Hammarback, L. Anders;Robinson, Alan;Fairlamb, Ian J. S.
锰（I）羰基催化的2-苯基吡啶和含有合适的金属导向基团的相关化合物的C-H键官能化最近已成为用于将各种基团引入苯环邻位的潜在有用的合成方法。初步的机理研究已经强调，这些反应可以通过许多不同的物种和步骤进行，此外，可能不同的催化循环。对于通常为10 mol %催化剂（通常为普遍存在的前体催化剂BrMn（CO）（5））的主要要求尚未受到质疑，也未得到显著改进，这表明催化失活可能是需要理解和解决的严重问题。负责在乙烯基-锰（I）羰基中间体的质子化中提供质子源的物种进一步提出了几个关键问题。在这项研究中，使用实验和理论相结合的方法，我们提供了全面的答案的关键机制问题有关锰（I）羰基催化的C-H键功能化的2-苯基吡啶和相关化合物。我们的结果能够解释炔底物依赖性，即，内炔与末端炔。我们发现BrMn（CO）（5）有不同的催化剂活化途径，例如，末端炔导致Mn-I-乙炔化物物质的产生，其形成使人想起在Sonogashira交叉偶联过程中被认为是至关重要的Cu-I-乙炔化物物质。我们已经明确地确定，炔，2-苯基吡啶，和水可以促进氢转移的质子化步骤，导致质子化烯烃产品的解放。
Manganese(I) carbonyl-catalyzed C-H bond functionalization of 2-phenylpyridine and related compounds containing suitable metal directing groups has recently emerged as a potentially useful synthetic methodology for the introduction of various groups to the ortho position of a benzene ring. Preliminary mechanistic studies have highlighted that these reactions could proceed via numerous different species and steps and, moreover, potentially different catalytic cycles. The primary requirement for typically 10 mol % catalyst, oftentimes the ubiquitous precursor catalyst, BrMn(CO)(5), has not yet been questioned nor significantly improved upon, suggesting catalytic deactivation may be a serious issue to be understood and resolved. Several critical questions are further raised by the species responsible for providing a source of protons in the protonation of vinyl-manganese(I) carbonyl intermediates. In this study, using a combination of experimental and theoretical methods, we provide comprehensive answers to the key mechanistic questions concerning the Mn(I) carbonyl-catalyzed C-H bond functionalization of 2-phenylpyridine and related compounds. Our results enable the explanation of alkyne substrate dependencies, i.e., internal versus terminal alkynes. We found that there are different catalyst activation pathways for BrMn(CO)(5), e.g., terminal alkynes lead to the generation of Mn-I-acetylide species, whose formation is reminiscent of Cu-I-acetylide species proposed to be of critical importance in Sonogashira cross-coupling processes. We have unequivocally established that alkyne, 2-phenylpyridine, and water can facilitate hydrogen transfer in the protonation step, leading to the liberation of protonated alkene products.