The Mechanism of Photocatalytic C(sp 3 )-H Activation by Decatungstate Anion: CPET or HAT?

The decatungstate anion ([W 10 O 32 ] 4– ) has demonstrated remarkable success in photocatalytic C(sp 3 )–H activation under mild conditions, however, its photocatalytic mechanism remains elusive. This work systematically studies the photocatalytic C(sp 3 )–H activation of [W 10 O 32 ] 4– through combined theoretical calculations and known experimental evidence. Specifically, upon light irradiation, [W 10 O 32 ] 4– undergoes excitation to its first singlet excited state (S 1, 1 A 2u ), followed by intersystem crossing (ISC) to populate the second triplet excited state (T 2, 3 A 1u ). The T 2 state was first identified as the reactive electronic state, characterized by both a distinct long-range ligand to metal charge transfer ( l -LMCT) and a rare nonradiative anti-Kasha behavior, which facilitates C(sp 3 )–H bond activation. Importantly, the block localized wave function (BLW) calculations prove that the photocatalytic C(sp 3 )–H activation proceeds via a concerted proton–electron transfer (CPET) mechanism: the σ(C–H) bonding electron of alkane mainly transfers to the p-orbital of inner-shell oxygen atoms in [W 10 O 32 ] 4–, while the proton adsorbs the bridging oxygen site on the surface of [W 10 O 32 ] 4– . This finding fundamentally challenges the conventional hydrogen atom transfer (HAT) mechanism paradigm for the activation C(sp 3 )-H bond by [W 10 O 32 ] 4– .