A metal-free porous organic polymer-based heterogeneous catalyst for the borrowing hydrogen-mediated N-alkylation of sulfonamides with alcohols†

Abstract

The development of green and sustainable borrowing hydrogen catalysis without using expensive and toxic metals is a challenging task. Herein, a highly stable, low-cost, metal-free heterogeneous carbocatalyst has been developed for the first time to mediate the N-alkylation of sulfonamides with alcohols via borrowing hydrogen catalysis. The designed 1,10-phenanthroline (Phen)-functionalized porous organic polymer-based carbocatalyst (Phen-POP) efficiently produces N-alkylated sulfonamides in good yields, performing on par with the transition-metal-based catalysts. Computational studies show that the electronegative N present in the Phen unit pulls the electron density from the adjacent C atom, making it more electron-deficient, which in turn boosts the transfer of hydride to the substrates. The prepared Phen-POP catalyst is highly robust and can be reused for at least five cycles without significant activity loss. Further, a scalable protocol has been successfully demonstrated at the gram-scale (5.0 g) with isolation of pure product without any chromatography. Therefore, this work provides a promising module to realize the synthesis of N-alkylated sulfonamides with alcohols on an industrial scale, and a design strategy to develop metal-free systems for many other borrowing hydrogen catalysis.