Modulating the coordinated microenvironments of single Co(II) sites in metal-organic frameworks for harnessing acyl radical

Abstract

There is always a challenge in activating abundantly available aliphatic aldehydes and generating stable acyl radical intermediates, which is a key step for further assembling functional molecules. Herein, we have fabricated a series of UiO-67-Ir-CoX2 (X = NO3, Cl, OAc, CF3SO3) frameworks, which feature different coordinating anions around the single Co sites. The resulting UiO-67-Ir-CoX2 materials demonstrate well catalytic activity in facilitating the photocatalytic synthesis of 4H-benzo[b]pyrans via harnessing acyl radical, exhibiting a broad substrate scope under mild conditions. Notably, the efficiency for aliphatic aldehyde activation exhibits 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 jointly 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 interaction with aliphatic aldehydes, can be finely modulated by the coordination environment of Co atoms. This modulation thereby 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.