Theoretical insight into decatungstate photocatalyzed alkylation of -tosylimine hydrogen atom transfer and proton-coupled electron transfer.

Decatungstate as a photocatalyst can activate various C(sp)-H bonds to successfully construct the C(sp)-C(sp) bond with -tosylimines. Herein density functional theory (DFT) calculations reveal a unique radical mechanism triggered by the reductive quenching cycle of decatungstate. First of all, photoexcited *[WO] activates the C(sp)-H bond of ether through the hydrogen atom transfer (HAT) mechanism to generate [HWO] and a C-centered radical species. Next, the C-centered radical will selectively attack the imine carbon of -tosylimine to provide the N-centered radical species containing the C(sp)-C(sp) bond. Finally, the C(sp)-C(sp) coupling product can be afforded by the stepwise proton-coupled electron transfer (PCET) process between [HWO] and the N-centered radical. Importantly, the bridging oxygen in the lateral position of [WO] is the most active. Intrinsic bond orbital (IBO) analysis confirms that *[WO] activates C(sp)-H through HAT instead of PCET. Furthermore, the origin of the regio-selectivity has been explored in depth. We hope that the reductive quenching cycle mechanism ([WO]-*[WO]-[HWO]-[WO]) can provide a clear understanding of the alkylation of -tosylimine.