Application of NHSi and NHGe supported Cu(I) halide complexes as efficient catalysts for A3 and KA2 coupling reaction: Solvent-free approach in a microwave reactor

Abstract

N-heterocyclic silylenes (NHSis), the heavier analogs of carbenes, have been demonstrated to possess strong σ-donation properties and, in some cases, π-acceptance properties as well. These highly reactive species have attracted significant interest due to their remarkable chemistry. Though the chemistry of NHSis has been well explored in metal complexation and small-molecule activation, their activity as catalytic agents has received less attention. The reaction between a carbonyl component, an alkyne, and a secondary amine, resulting in the formation of a propargylamines, is of wide-ranging importance due to its utility in drug discovery and pharmaceutical applications. Previous reports have explored the use of NHC-supported Cu(I) complexes for catalysis of the A3 and KA2 coupling reactions; however, there is no report on the catalytic activity of NHSi-supported Cu(I) complexes for the same reaction. In this thesis, we report a novel approach to the KA2 and A3 coupling reactions using an NHSi supported copper (I) catalyst. The catalyst incorporates an earth-abundant and nontoxic first-row transition coinage metal, copper(I), within a silylene ligand, and its use in the KA2 and A3 coupling reactions affords the corresponding propargylamines in excellent yield with low catalyst loading and fast reaction times. We have thoroughly expounded on the substrate scope of the reaction and tested the catalyst's reactivity with challenging substrates. In addition, we have also tested the catalytic activity of the corresponding N-heterocyclic germylene (NHGe) complexes and compared their utility as catalysts. The NHSi-based complex effectively catalyzes both the facile A3 reaction and the comparatively more challenging KA2 reaction with near quantitative yield.