Photocatalytic C–H activation for C–C/CN/C–S bond formation over CdS: effect of morphological regulation and S vacancies

Abstract

The construction of C–X (X = C, N, S) bonds through C–H activation is one of the most challenging, important and rapidly developing fields in recent years. Herein, CdS with different morphologies (nanorods, nanospheres, nanosheets) was prepared by a thermal solvent method, and CdS enriched with S vacancies was constructed through simple calcination. The as-prepared heterogeneous CdS catalytic materials were utilized to fabricate C–C, CN and C–S bonds for the manufacture of drug intermediates or other value-added products through high bond energy, low polarity and strong inertia C–H bond activation. For example, the direct activation of sp³ C–H chemical bonds of tetrahydrofuran (THF) to form THF free radical and the free radical addition with olefins/alkynes could be achieved with various CdS catalytic materials without a base additive and oxidant. The CdS morphology improved the photocatalytic performance through the effective photogenerated carrier separation and transformation enhancement caused by the formation of hexagonal-phase CdS along with a certain degree of lattice distortion induced polarization dipole moment and internal polarization electric field. Furthermore, the S-vacancy-enriched CdS nanorods provided more active sites for THF capture and tetrahydrofuran free radical generation, so that the THF sp³ C–H direct activation to construct C–C bonds became more feasible. DMF and toluene sp³ C–H could also be activated to form C–C bonds; benzylamine sp³ C–H could be activated to construct CN bonds accompanied by H₂ generation; benzyl mercaptan S–H bonds and phenylacetylene/styrene C–H bonds could be activated to build C–S bonds; and benzene/toluene C–H bonds could be activated in the presence of CO₂ to produce carboxylic acid. Compared with the method requiring a stoichiometric oxidant in previous studies, the C–H activation of THF and the construction of other inert chemical structures could be mildly realized over S-vacancy-enriched hexagonal CdS nanorods.