Highly Stable COF‐Supported Co/Co(OH)₂ Nanoparticles Heterogeneous Catalyst for Reduction of Nitrile/Nitro Compounds under Mild Conditions

Abstract

Ordered nanoporosity in covalent organic framework (COF) offers excellent opportunity for property development. Loading nanoparticles (nPs) onto them is one approach to introducing tailor-made properties into a COF. Here, a COF-Co/Co(OH) composite containing about 16 wt% of <6 nm sized Co/Co(OH) nPs is prepared on a N-rich COF support that catalyzes the release of theoretical equivalence of H from readily available, safe, and cheap NaBH . Furthermore, the released H is utilized for the hydrogenation of nitrile and nitro compounds to amines under ambient conditions in a facile one-pot reaction. The COF "by choice" is built from "methoxy" functionalized dialdehydes which is crucial in enabling the complete retention of the COF structure under the conditions of the catalysis, where the regular Schiff bonds would have hydrolyzed. The N-rich binding pockets in the COF ensure strong nP-COF interactions, which provides stability and enables catalyst recycling. Modeling studies reveal the crucial role played by the COF in exposing the active facets and thereby in controlling the activation of the reducing agent. Additionally, via density functional theory, we provide a rational explanation for how these COFs can stabilize nanoparticles which grow beyond the limiting pore size of the COF and yet result in a truly stable heterogeneous catalyst - a ubiquitous observation. The study underscores the versatility of COF as a heterogeneous support for developing cheap and highly active nonnoble metal catalysts.

Nitrogen‐Doped Carbon‐Supported Nickel Nanoparticles: A Robust Catalyst to Bridge the Hydrogenation of Nitriles and the Reductive Amination of Carbonyl Compounds for the Synthesis of Primary Amines

“…These results suggested that nickel nanoparticles were the active sites for the hydrogenation of nitriles. Generally, metallic nanoparticles have the ability to activate molecular hydrogen in chemical reduction reactions …”

“…However, the hydrogenation of nitriles by homogeneous catalysts has distinct drawbacks in terms of the difficulty of recycling and reuse of the homogeneous catalysts as well as the contamination of the target products with trace amounts of metal from the homogeneous catalysts, which is detrimental to pharmaceuticals. To overcome the issues of homogeneous catalytic systems, a considerable effort has been devoted to the design of new heterogeneous catalytic systems for the hydrogenation of nitriles, which have been mainly based on precious metals. Undoubtedly, the use of expensive noble‐metal catalysts would result in high production costs in practical applications.…”

Ag Nanoparticles Supported on a Resorcinol‐Phenylenediamine‐Based Covalent Organic Framework for Chemical Fixation of CO2

“…However, the TON is not remarkably high because only certain facets of the Ag nPs are exposed to the surface for catalytic activity. Also, the atoms in the core of the cluster are not accessible to the reactants …”

Covalent Organic Frameworks: Chemical Approaches to Designer Structures and Built‐In Functions

“…[212] Similarly,C o@CTF with Co/ Co(OH) 2 nanoparticles catalyzes the reduction of arylnitrile and arylnitro compounds to arylamines in 87 %y ield. [213] Hydrazone-linked Ru@COF-ASB (Figure 49 g) promotes the solvent-free one-pot tandem oxidation-condensation between benzylic alcohols and arylamines in air to afford aw ide range of imines in yields of 70-91 %. [214] b-Ketoenamine-linked PtNPs@COF (Figure 49 h; NPs = nanoparticles) transforms 4-nitrophenol into 4-aminophenol, with 100 %c onversion within 8min, [215] which is faster than AuNPs-COF (13 min).…”