Porous organic polymer with free carboxylic acids (Carboxy-POP) as an expedient heterogeneous catalyst for transamidation/transimidation of multifarious amides, thioamides, imides and urea

Abstract

The exceptional attributes of porous organic polymers (POPs) such as high physicochemical stability, intrinsic microporosity, and customised access from simple organic building blocks render them highly suitable as catalytic nanosized reactors. These materials can be engineered in a ‘bottom-up’ fashion by integrating catalytic components into the polymeric structures through facile synthesis based on rationally designed building blocks and judicious selection of the polymerization reactions. Herein, we report that a POP adorned by free carboxylic acid functionalities (Carboxy-POP) on its surface works remarkably as a heterogeneous catalyst for metal-free transamidation, a fundamentally important transformation, of diverse unactivated carboxamides and thiocarboxamides with aliphatic, aromatic and cyclic amines. The protocol is also shown to be applicable for the transimidation of challenging substrates such as phthalimides and the transamidation of urea, providing the corresponding products in good to excellent isolated yields. The significant highlights of this methodology include efficiency, ease of workup, facile separation, and recyclability of the catalyst; the latter is demonstrated up to 12 cycles.