Mn2+ and [Ru(bpy)3]2+ in UiO-67 metal organic frameworks enhance photocatalytic oxidation of benzylamine via an electron transfer pathway

Abstract

The selective oxidation of amines to imines is an essential transformation in many chemical syntheses. Driving such reactions with light and earth abundant catalysts is highly interesting in the context of solar light energy conversion and broadening the reaction scope in organic synthesis. The here reported bimetallic metal–organic framework (MOF), UiO-67 Ru₅₀-Mn₁₀, allows oxidation of benzylamine under ambient conditions via dual electron and energy transfer with oxygen. UiO-67 Ru₅₀-Mn₁₀ integrates [Mn(bpy)₂(Cl)₂] active sites and light-active [Ru(bpy)₃]²⁺ photosensitizers at the linkers of the UiO-67 scaffold. The spatial organisation of photo and redox-active centres enables efficient charge separation and mass transport. Under 460 nm LED irradiation for 24 h and ambient aerobic conditions, UiO-67 Ru₅₀-Mn₁₀ catalyses the oxidation of benzylamine to N-benzylidene-1-phenylmethanamine with turnover numbers up to 634, which is 1.6 to 1.8 times higher than homogeneous analogues and the Mn-free UiO-67 Ru₅₀. Structural and spectroscopic studies confirm successful incorporation of both metals, while mechanistic analyses reveal dual electron and energy transfer pathways, influenced by the solvent environment. This work highlights the potential of heterometallic MOFs with earth-abundant catalytic sites as efficient platforms for photocatalytic oxidative transformations.