Bottom-Up De Novo Synthesis of Porous Organic Polymers with Enone Functionalities as Supports for Pd and Cu Nanoparticles for Catalytic Tandem Synthesis

Two porous organic polymers (POPs), namely, ANT and NAP based on N,N,N′,N′-tetrakis(4-acetylphenyl)anthracene-9,10-diamine and N,N,N′,N′-tetrakis(4-acetylphenyl)naphthalene-1,4-diamine, respectively, as core scaffolds and enone functionalities as the connecting backbones, were synthesized using an aldol condensation reaction. The enone backbones of the POPs mimic α,β-unsaturated ketone functionalities of dibenzylideneacetone (dba), which is frequently employed to stabilize Pd(0), e.g., Pd2(dba)3, for effective utilization in the catalysis of a myriad of organic transformations. We have thus leveraged the chalcone motifs inherent to ANT and NAP for stabilization of Pd(0) or Cu(0) nanoparticles (NPs) to provide access to POPs embedded with Pd(0) and Cu(0) nanoparticles, i.e., Pd@ANT, Pd@NAP, Cu@ANT, and Cu@NAP. Pd@POPs are shown to be applicable to facile synthesis of therapeutically useful N-arenesulfonylindoles and 2-arylbenzofurans by tandem Songashira coupling–cyclization reactions in a recyclable manner without any perceptible loss of their catalytic efficiency for up to 15 catalytic cycles. In a similar manner, Cu@POPs are shown to serve for expedient synthesis of (i) 1-aryl-1H-indazoles by tandem imine formation–Ullmann coupling, and (ii) unsymmetrical diaryl selenides by tandem activation of diphenyl diselenide–coupling with arylboronic acids in a recyclable fashion for up to eight catalytic cycles. The results thus attest to the fact that mechanisms that allow stabilization of nanoparticles can be built into the design of building blocks to develop, in a bottom-up fashion, robust POPs as supports, which obviate leaching issues and permit recyclability by precluding any loss in the catalytic efficacy of the catalysts. Furthermore, it is shown that POPs exhibit selective adsorption of clean and green fuel, namely, hydrogen gas over nitrogen, with a very high selectivity factor.