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

Abstract

Decatungstate as a photocatalyst can activate various C(sp³)–H bonds to successfully construct the C(sp³)–C(sp²) bond with N-tosylimines. Herein density functional theory (DFT) calculations reveal a unique radical mechanism triggered by the reductive quenching cycle of decatungstate. First of all, photoexcited *[W₁₀O₃₂]⁴⁻ activates the C(sp³)–H bond of ether through the hydrogen atom transfer (HAT) mechanism to generate [HW₁₀O₃₂]⁴⁻ and a C-centered radical species. Next, the C-centered radical will selectively attack the imine carbon of N-tosylimine to provide the N-centered radical species containing the C(sp³)–C(sp²) bond. Finally, the C(sp³)–C(sp²) coupling product can be afforded by the stepwise proton-coupled electron transfer (PCET) process between [HW₁₀O₃₂]⁴⁻ and the N-centered radical. Importantly, the bridging oxygen in the lateral position of [W₁₀O₃₂]⁴⁻ is the most active. Intrinsic bond orbital (IBO) analysis confirms that *[W₁₀O₃₂]⁴⁻ activates C(sp³)–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 ([W₁₀O₃₂]⁴⁻–*[W₁₀O₃₂]⁴⁻–[HW₁₀O₃₂]⁴⁻–[W₁₀O₃₂]⁴⁻) can provide a clear understanding of the alkylation of N-tosylimine.