Visible light-mediated intermolecular crossed [2+2] cycloadditions using a MOF-supported copper triplet photosensitizer

The photochemical [2+2] cycloaddition of styrenes provides a frequently used route for the synthesis of multi-substituted cyclobutanes. Despite the extensive studies in noble-metal and organo-photocatalysis, developing sustainable cycloaddition methods with copper photosensitizers is still in its infancy, largely owing to their low reactivity and photostability. Here we show that the introduction of a binap-ligated heteroleptic copper(I) complex to the linker of a microporous zirconium-based metal-organic framework produces a highly stable and reusable heterogeneous photocatalyst with an extended excited-state lifetime. Under visible light irradiation, this robust copper triplet photosensitizer efficiently promotes multiple intermolecular crossed [2+2] cycloadditions, including an underdeveloped cycloaddition reaction of simple styrenes with electron-deficient alkenes. Our findings suggest that metal-organic framework-based heterogenization strategies have the potential to advance copper photocatalysis and foster a variety of visible light-mediated energy-transfer processes. [Cu(phen)(binap)]+ features a relatively high photocatalytic activity, but its low photostability hinders its use in organic chemistry. Now immobilization of this motif on a metal-organic framework matrix enhances its stability and excited-state lifetime, enabling the promotion of [2+2] cycloadditions of styrenes with a variety of olefins, including electron-deficient alkenes.