Leveraging Metallotropism-Enabled Substrate Activation in Cobalt-Catalyzed Annulation Chemistry: Protic NHC Template Is the Key

This
study introduces the access of protic NHC
(pNHC) complexes with Cp*Co­(III) species via metallotropism-triggered
activation of ubiquitous azole substrates. These “CoIII-pNHC” templates were further explored in
catalytic annulative functionalization of azoles with internal alkynes,
providing a variety of π-extended polycyclic heteroarene compounds.
Mechanistic investigations via isolation and structure elucidation
of the key pNHC-Co intermediates followed by control
stoichiometric and catalytic reactions highlighted the crucial electronic
control on the azole C–H activation, alkyne insertion, and
regiodivergent annulation steps involved in this catalytic protocol.
These results demonstrate that the cobalt-based metallotropism can
act as a potentially useful platform toward earth-abundant first-row
transition metal-catalyzed C–H functionalization, complementary
to the dominant noble metal-based strategies.

本研究通过金属趋变触发的普遍性唑类底物的活化，引入了质子化 NHC (pNHC) 复合物对 Cp*Co­(III) 物种的可及性。这些“CoIII-pNHC”模板在催化内炔基唑类化合物中进一步进行了功能化研究，从而得到了一系列π-扩展的多环杂环化合物。通过分离和结构解析关键 pNHC-Co 中间体，随后进行控制化学计量和催化反应的机理研究，强调了在该催化过程中唑类 C-H 活化、炔基插入和区域选择性闭环步骤中的关键电子控制。这些研究结果证明了基于钴的金属趋变可能作为地球丰饶的第一行过渡金属催化的 C-H 功能化的一种潜在有用的平台，与占主导地位的高贵金属基策略相辅相成。