To shed light on the mechanism of this reaction, several mechanistic studies were performed (Scheme 3). initially, stoichiometric radical scavenger 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) was introduced into the system of cyclohexane 1a with α-trifluoromethyl styrene 2a under the standard reaction conditions. As shown in Scheme 3a, upon TEMPO introduction, the reaction was completely impeded and TEMPOtrapped intermediate 5 was detected by HRMS, implying the involvement of a radical pathway for this reaction. Light on/off experiment was also conducted, demonstrating that light is necessary throughout this reaction (Scheme 3b). Furthermore, we found that the reaction yield of cyclohexane 1a and α-trifluoromethyl styrene 2a decreased gradually as the amount of water present increased (Scheme 3c). This result implies that excess water was deleterious to this transformation. Subsequently, the reaction between TBADT and CrCl3 was investigated by UV-vis spectroscopy (Scheme 3d). When CrCl3 was added to a TBADT solution, the UV-vis spectrum of the reaction mixture was almost the same as that of TBADT, and no signal of CrCl2 was observed, thus suggesting that the redox reaction between TBADT and CrCl3 is unfavorable. Finally, a cyclic voltammetry experiment was carried out to investigate whether the two catalysts (W and Cr) could realize a closed catalytic cycle with each other. As shown in Scheme 3e, the cyclic voltammetry experiment indicated that the reduction of TBADT occurred at a more negative position (Ered = -0.96 V vs Ag/AgCl) than CrCl3 (Ered = -0.94 V vs Ag/AgCl), implying that the reduction of Cr(Ⅲ) to Cr(Ⅱ) by W10O32-was thermodynamically favorable. Scheme 3. Mechanistic studies Scheme 4. Proposed reaction mechanism.