Luminescent cyclometalated gold(iii) complexes covalently linked to metal–organic frameworks for heterogeneous photocatalysis

Abstract

Phosphorescent gold(III) complexes possess long-lived emissive excited states, making them ideal for use as molecular sensors and photosensitizers for organic transformations. Literature reports indicate that gold(III) emitters exhibit good catalytic activity in homogeneous photochemical reactions. Heterogeneous metal–organic framework (MOF)-supported gold(III) photocatalysts are considered to show high recyclability in photochemical reactions and potentially provide new selectivities. Here, we report the design and development of visible-light-absorbing MOF-covalently linked gold(III) photocatalysts. A MOF-supported gold(III) complex exhibits a longer phosphorescence lifetime than its homogeneous counterpart, reaching approximately 110 μs under argon and 12 μs under air when suspended in acetonitrile. This is attributed to the localization of the gold(III) complex within the MOF nano-cages. The MOF-derived gold(III) photosensitizer exhibits good catalytic performance in intramolecular and intermolecular [2 + 2] cycloaddition reactions to construct functionalized cyclobutanes and azetidines, both of which are important building blocks for pharmaceuticals. These photochemical [2 + 2] cycloaddition reactions catalyzed by the gold(III)-MOF are governed by an energy transfer mechanism and do not require redox modulators. Under similar reaction conditions, the crossed [2 + 2] photocycloaddition reaction of two activated alkenes proceeds smoothly, and the cyclobutane product is obtained within 3 hours of irradiation under dilute conditions (0.2 mol dm⁻³ of alkene).