A cobalt-based metal–organic framework as a sustainable catalyst for base-free transfer hydrogenation of biomass-derived carbonyl compounds

Abstract

A bifunctional cobalt-based MOF 1, offering both Lewis acidic–basic (Co and –OH⁻) and Brønsted acidic (–COOH) sites, has been synthesized and characterized. MOF 1 presents a double-chain structure and, therefore, remarkably exposed Lewis acidic–basic and Brønsted acidic sites. MOF 1 acts as a remarkable heterogeneous catalyst for the transfer hydrogenation (TH) of carbonyl compounds using isopropanol as a green hydrogen source without the requirement of any base. MOF 1 exhibits excellent catalytic performance for the TH of assorted aldehydes and ketones, resulting in high yield and excellent selectivity. Notably, several biomass-derived substrates such as furfural, 5-methylfurfural, 5-hydroxymethylfurfural, and levulinic acid were successively converted to their corresponding products in high yield. The substrate scope further encompassed biologically relevant ones such as vanillin, cinnamaldehyde, perillaldehyde, and estrone. Subsequently, both poisoning experiments and temperature-programmed desorption studies were employed to elucidate the role of Lewis acidic–basic and Brønsted acidic sites in this MOF. To further evaluate the role of Brønsted acidic sites in TH, an ester derivative of MOF, 1-Et, was synthesized and utilized which exhibited a poor catalytic performance. Collectively, all experiments confirm a cooperative effect of Lewis acidic–basic (Co and –OH⁻) and Brønsted acidic (–COOH) sites in TH catalysis. The entire catalytic process encompassing reagents, solvents, and operating conditions, was assessed using the CHEM21 green metrics toolkit to highlight the environmental sustainability of the present catalytic method. The MOF 1 overcomes the limitations of conventional catalysts by excluding the need for a base, offering a broad substrate scope, and achieving high yield with excellent selectivity, thus acting as a more efficient and sustainable catalyst for TH reaction.