Nickel-Catalyzed Hydroimination of Alkynes

A modular
and atom-efficient synthesis of 2-aza-1,3-butadiene derivatives
has been developed via nickel-catalyzed intermolecular coupling between
internal alkynes and aromatic N–H ketimines. This novel alkyne
hydroimination process is promoted by a catalyst system of a Ni(0)
precursor ([Ni­(cod)2]), N-heterocyclic carbene (NHC) ligand
(IPr), and Cs2CO3 additive. The exclusive formation
of (Z)-enamine stereoisomers is consistent with a proposed anti-iminometalation of alkyne by π-complexation with
Ni(0) and subsequent attack by the N–H ketimine nucleophile.
An NHC-ligated Ni(0) π-imine complex, [(IPr)­Ni­(η1-HNCPh2)­(η2-HNCPh2)], was independently synthesized and displayed improved reactivity
as the catalyst precursor.

本研究开发了一种兼具模块化与原子经济性的2-氮杂-1,3-丁二烯（2-aza-1,3-butadiene）衍生物合成策略，该策略通过镍催化内炔烃与芳香族N-H酮亚胺的分子间偶联反应实现。该新型炔烃氢亚胺化（alkyne hydroimination）反应采用零价镍（Ni(0)）前驱体[Ni(cod)₂]、氮杂环卡宾（N-heterocyclic carbene, NHC）配体IPr与碳酸铯（Cs₂CO₃）作为催化体系，实现反应的高效推进。反应专一性生成(Z)-型烯胺立体异构体，该结果与所提出的反应机理相符：零价镍通过π配位与炔烃形成配合物，随后N-H酮亚胺亲核试剂发起进攻，完成炔烃的反式亚胺金属化过程。研究人员独立合成了氮杂环卡宾配位的零价镍π-亚胺配合物[(IPr)Ni(η¹-HN=CPh₂)(η²-HN=CPh₂)]，该配合物作为催化前驱体时展现出更优异的反应活性。