Origin and Regioselectivity of Direct Hydrogen Atom Transfer Mechanism of C(sp)-H Arylation by [WO]/Ni Metallaphotoredox Catalysis.

Polyoxometalates (POMs) have a broad array of applied platforms with well-characterized catalysis including photocatalysis to achieve aliphatic C(sp)-H bond functionalization. However, the reaction mechanism of POMs in organic transformation remains unknown due to the complexity of POM structures. Here, a challenging [WO]/Ni metallaphotoredox-catalyzed C(sp)-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 [WO] is responsible for the abstraction of a foreign hydrogen atom and the activation of a C(sp)-H bond. Furthermore, we discussed this activated process using the direct activation model of the C(sp)-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 Ni, Ni, and Ni to construct a C-C bond, the nickel catalytic cycle induced by the Ni active catalyst is profitable in kinetics and thermodynamics. Finally, a radical mechanism merging the ([WO]-[WO]-[HWO]-[WO]) decatungstate reductive quenching cycle, ([HWO]-[HWO]-[HWO]) electron relay, and (Ni-Ni-Ni-Ni-Ni) 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(sp)-H bond.