Issue 29, 2022

A covalent organic framework with electrodeposited copper nanoparticles – a desirable catalyst for the Ullmann coupling reaction

Abstract

A covalent organic framework is a porous covalently-linked polymeric assembly built from molecular lego blocks, the monomers. A COF's high surface area, ordered pores, and intrinsic low density makes it a perfect heterogeneous catalyst component. Dispersing catalytic metal nanoparticles into the porous COF matrix in a ‘capping-agent-free’ manner can aid the maximal utilization of the active sites. To generate single-site catalysts, metals have been anchored to dense supports, or metal ions have been coordinated to the porous organic framework. The latter has superior atom efficiency and a substrate diffusion advantage. Stably nestling neutral metallic clusters into open-framework supports with no specifically strong binding groups requires a different approach. If infused from extremely dilute electrolytes, metal clusters can be nanoconfined into electrically activated COFs. At low-loadings, it can resemble a single-site catalyst with high atom efficiency. Herein, we report the larger scale synthesis of IISERP-COF15 and electrochemical loading of copper nanoparticles into its pores at loadings as low as 3.34 wt%. We employed classical Ullmann reactions to adjudge its activity. Typical turnover numbers for the catalysts reported in the literature are approximately 50–100. A Cu@COF shows high activity with a very low catalyst loading of 0.25 mol% (TON around ∼300–350 vs. 4 for neat CuCl2·2H2O (homogeneous catalyst) and turnover frequency (∼15–17 h−1)). We recycled it for up to 3 cycles. Furthermore, we report a multi-fold Ullmann reaction producing an unreported hexaaldehyde to demonstrate the latitude of the catalyst. Our work points to the potential of a dilutely loaded metal@COF as a mimic of the single-site catalyst for synthesizing valuable C–O linked molecules. Our findings from computational modeling shed light on the role of the COF as an active nanoporous support for Ullmann C–O coupling.

Graphical abstract: A covalent organic framework with electrodeposited copper nanoparticles – a desirable catalyst for the Ullmann coupling reaction

Supplementary files

Article information

Article type
Paper
Submitted
17 Nah 2022
Accepted
21 Qas 2022
First published
22 Qas 2022

J. Mater. Chem. A, 2022,10, 15647-15656

A covalent organic framework with electrodeposited copper nanoparticles – a desirable catalyst for the Ullmann coupling reaction

C. Chandran, H. D. Singh, L. S. Leo, P. Shekhar, D. Rase, D. Chakraborty, C. P. Vinod and R. Vaidhyanathan, J. Mater. Chem. A, 2022, 10, 15647 DOI: 10.1039/D2TA01326F

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