Modulating the coordinated microenvironments of single Co(ii) sites in metal–organic frameworks for harnessing acyl radicals

Abstract

There is always a challenge in activating abundantly available aliphatic aldehydes and producing stable acyl radical intermediates, which are key steps in the assembly of functional molecules. Herein, we have fabricated a series of UiO-67-Ir-CoX₂ (X = NO₃, Cl, OAc, CF₃SO₃) frameworks that feature different coordinating anions around single Co sites. The resulting UiO-67-Ir-CoX₂ materials demonstrate good catalytic activity and facilitate the photocatalytic synthesis of 4H-benzo[b]pyrans by harnessing acyl radical, exhibiting a broad substrate scope under mild conditions. Notably, the efficiency for aliphatic aldehyde activation has a strong correlation with the coordination environment of Co sites, among which, UiO-67-Ir-Co(NO₃)₂ demonstrates superior photocatalytic performance, outperforming other counterparts. Experimental investigations and theoretical calculations have revealed that the aliphatic acyl radical is involved in the photocatalytic reaction. Importantly, the electronic structure of Co sites, as well as their adsorption and electronic interactions with aliphatic aldehydes, can be finely modulated by the coordination environment of Co atoms. This modulation facilitates the activation of aliphatic aldehydes, accounting for the boosted catalytic efficiency. Our work provides critical insights into the precise modulation of coordination environments around single-metal sites in MOFs, significantly enhancing their capability to harness acyl radicals.