Polyoxometalate-Embedded Metal–Organic Framework as an Efficient Copper-Based Monooxygenase for C(sp³)–H Bond Oxidation via Multiphoton Excitation

Abstract

The complex and precise structure of natural monooxygenases makes it difficult to clone their structure and activity, and the reported artificial copper-based monooxygenase catalysts for the oxidation of inert C(sp 3 )–H bonds exhibit limited catalytic activities. Inspired by monooxygenases, we report a metal–organic framework ( SiW 12 @CuMOF-1 ) comprising a binuclear copper HAT catalyst, photosensitizing nicotinamide adenine dinucleotide (NAD + ) mimic bridging ligand, and embedded polyoxometalate. SiW 12 @CuMOF-1 accelerates the oxidative dehydrogenation of 3,5-DTBC with a catalytic efficiency comparable to that of natural polyphenol oxidase. In the presence of pyridine hydrochloride, irradiation of SiW 12 @CuMOF-1 afforded the highly active chlorine radical and Cu I species via a ligand-to-metal charge transfer process. The chlorine radical abstracts a hydrogen atom selectively from C(sp 3 )–H bonds to generate the radical intermediate. The Cu I species interacted with the active oxygen species 1 O 2 that formed from the photoinduced energy transfer from the excited state of the NAD + mimics, giving the active oxygen species O 2 •– for further oxidization. The well-modified binuclear copper sites cleave the O–O bond to give the final products selectively. Meanwhile, the embedded polyoxometalates interacted with the alcohol substrates via hydrogen bonding interactions to help the catalytic conversion with high efficiency. The well-defined structural characters, the finely modified catalytic properties, and the sustainable multiphoton excitation photocatalytic processes provide a new avenue to develop robust artificial enzymes with uniform active sites and improved catalytic performances.