Origin and Regioselectivity of Direct Hydrogen Atom Transfer Mechanism of C(sp<sup>3</sup>)–H Arylation by [W<sub>10</sub>O<sub>32</sub>]<sup>4–</sup>/Ni Metallaphotoredox Catalysis
Yujiao Dong, Bo Zhu, Yu-Jie Liang, Wei Guan, Zhong‐Min Su
Abstract
Polyoxometalates (POMs) have a broad array of applied platforms with well-characterized catalysis including photocatalysis to achieve aliphatic C(sp3)–H bond functionalization. However, the reaction mechanism of POMs in organic transformation remains unknown due to the complexity of POM structures. Here, a challenging [W10O32]4–/Ni metallaphotoredox-catalyzed C(sp3)–H arylation of alkane has been investigated by density functional theory (DFT) calculations. The calculation revealed that the superficial active center located in bridged oxygen of *[W10O32]4– is responsible for the abstraction of a foreign hydrogen atom and the activation of a C(sp3)–H bond. Furthermore, we discussed this activated process using the direct activation model of the C(sp3)–H σ-bond to deepen our mechanistic understanding of POM mediated C–H bond activation via the hydrogen atom transfer (HAT) pathway. Specifically, comparing three common mechanisms for nickel catalysis inducing by Ni0, NiI, and NiII to construct a C–C bond, the nickel catalytic cycle induced by the NiI active catalyst is profitable in kinetics and thermodynamics. Finally, a radical mechanism merging the ([W10O32]4––*[W10O32]4––[HW10O32]4––[W10O32]4–) decatungstate reductive quenching cycle, ([HW10O32]4––[H2W10O32]4––[HW10O32]4–) electron relay, and (NiI–NiII–NiI–NiIII–NiI) nickel catalytic cycle is proposed to be favorable. We hope that this work would provide a better understanding of the unique catalytic activity of decatungstate anions for the direct functionalization of the C(sp3)–H bond.