Multifunctional porous organic polymers (POPs): Inverse adsorption of hydrogen over nitrogen, stabilization of Pd(0) nanoparticles, and catalytic cross-coupling reactions and reductions

Abstract

In spite of the fact that a variety of reactions have been exploited for creation of innumerable porous organic polymers (POPs), aldol condensation reactions between aldehydes and ketones leading to enones remain unutilized quite inexplicably. We surmised that the enone functionality can be exploited for stabilization of Pd akin to the manner of Pd(0) in Pd2(dba)3 by developing POPs based on aldol condensation reactions of polycarbonyl compounds with dialdehydes, and that such materials can be employed for catalytic transformations. By subjecting rationally designed tri-/tetraacetyl-functionalized aryl amines to aldol condensations with terephthalaldehyde, three different POPs, i.e., TPAPOPs 1–3, that feature enone functionalities have been synthesized and shown to exhibit palpable gas sorption properties. Remarkably, inverse uptake for sorption of H2 over N2 was observed for all POPs. As surmised, the representative POP, i.e., TPAPOP-1, was found to stabilize in situ-generated Pd(0) nanoparticles to enable application of the resultant material, i.e., Pd@TPAPOP-1, as a recyclable heterogeneous catalyst for a number of organic transformations. It is shown that coupling reactions such as Suzuki and Heck, and reductions such as nitro-to-amine and hydrogenation of olefins can be accomplished in a facile manner by employing Pd@TPAPOP-1 as a heterogeneous recyclable catalyst; the aforementioned transformations have been demonstrated on a broad set of substrates for each type.