Major-auxiliary cooperative metal pairs in MOFs enable cascade oxidation of KA oil to ε-caprolactone.

Xue, Guangxin; Liu, Hanlin; Liu, Wei; Yang, Caoyu; Ban, Zhiyong; An, Pengfei; Chen, Wenxing; Zheng, Lirong et al. · Nat Commun · 2024

basic_science · Level V

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Abstract

Direct oxidation of KA oil (the mixture of cyclohexanone and cyclohexanol) toward ε-caprolactone is in high demand yet hard to implement in need of juggling the activation of both methyne C-H bond of cyclohexanol and α-C-C bond of cyclohexanone. Here we demonstrate that in situ formed Cu<sup>1+δ</sup>-O<sup>δ-•</sup> active site, which originates from relay reaction at Ni(II) and Cu(I) pairs in a metal-organic framework (known as NiCu-MOF-74) with O<sub>2</sub> and benzaldehyde (PhCHO), efficiently oxidizes KA oil toward ɛ-caprolactone along with good stability. Mechanism investigation discloses that the auxiliary Ni(II) site first adsorbs O<sub>2</sub> for abstracting formyl hydrogen in PhCHO followed by transfer of PhCO· to react with another O<sub>2</sub> over the major Cu(I) site, leading to formation of Cu<sup>1+δ</sup>-O<sup>δ-•</sup> and PhCOOH. This major-auxiliary cooperative strategy will be particularly suitable for multivariate MOFs as next generation catalysts towards complex reactions.