Abstract
The photocatalytic CC coupling of benzyl alcohol (BA) into hydrobenzoin (HB), is appealing to obtain high-value chemicals. However, the selectivity of HB is still low due to the inevitable formation of benzaldehyde. Herein, we report In(OH)3-ZnS photocatalyst for CC coupling of BA into HB with very high selectivity (∼100 %). The introduction of In(OH)3 onto ZnS with stable interaction facilitates light harvesting and separation of photo-excited charges. As a result, BA conversion on optimized In(0.1)-ZnS catalyst (73 %) is much higher than ZnS (29 %). Besides, the surface hydroxyl groups derived from In(OH)3 enables the facile desorption of CH(OH)Ph radical. Therefore, the over oxidation of CH(OH)Ph radical into by-product of benzaldehyde can be effectively inhibited. More significantly, in-situ FTIR spectra and reduction of by-product manifest the instant reverse reduction process of benzaldehyde into CH(OH)Ph radical during CC coupling of BA, which is the key to realizing satisfied HB selectivity (100 %). Theoretical simulations reveal that the weak adsorption of CH(OH)Ph radical over catalyst and the high energy barrier of over-oxidation of CH(OH)Ph into benzaldehyde contributes to the formation of highly selective coupling products. This work will inspire new insights to design rational photoredox systems for organic transformations with high selectivity
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