Paradine Shauna M, Griffin Jennifer R, Zhao Jinpeng, Petronico Aaron L, Miller Shannon M, Christina White M
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
Nat Chem. 2015 Dec;7(12):987-94. doi: 10.1038/nchem.2366. Epub 2015 Oct 5.
C-H bond oxidation reactions underscore the existing paradigm wherein high reactivity and high selectivity are inversely correlated. The development of catalysts capable of oxidizing strong aliphatic C(sp(3))-H bonds while displaying chemoselectivity (that is, tolerance of more oxidizable functionality) remains an unsolved problem. Here, we describe a catalyst, manganese tert-butylphthalocyanine [Mn((t)BuPc)], that is an outlier to the reactivity-selectivity paradigm. It is unique in its capacity to functionalize all types of C(sp(3))-H bond intramolecularly, while displaying excellent chemoselectivity in the presence of π functionality. Mechanistic studies indicate that [Mn((t)BuPc)] transfers bound nitrenes to C(sp(3))-H bonds via a pathway that lies between concerted C-H insertion, observed with reactive noble metals such as rhodium, and stepwise radical C-H abstraction/rebound, as observed with chemoselective base metals such as iron. Rather than achieving a blending of effects, [Mn((t)BuPc)] aminates even 1° aliphatic and propargylic C-H bonds, demonstrating reactivity and selectivity unusual for previously known catalysts.
C-H键氧化反应凸显了现有范式，即高反应性和高选择性呈负相关。开发能够氧化强脂肪族C(sp(3))-H键同时展现化学选择性（即对更易氧化官能团的耐受性）的催化剂仍然是一个未解决的问题。在此，我们描述了一种催化剂，叔丁基锰酞菁[Mn((t)BuPc)]，它是反应性-选择性范式的一个异类。它在分子内官能团化所有类型的C(sp(3))-H键的能力方面独一无二，同时在存在π官能团的情况下展现出优异的化学选择性。机理研究表明，[Mn((t)BuPc)]通过一种介于协同C-H插入（如铑等活性贵金属所观察到的）和逐步自由基C-H夺取/回弹（如铁等化学选择性贱金属所观察到的）之间的途径，将结合的氮烯转移至C(sp(3))-H键。[Mn((t)BuPc)]并非实现效应的混合，甚至能胺化一级脂肪族和炔丙基C-H键，展现出对先前已知催化剂而言不同寻常的反应性和选择性。
