SYNTHESIS OF ALKENYL SULFIDES CATALYZED BY CuNPS/TiO₂. A THEORETICAL-COMPUTATIONAL ANALYSIS

The alkyne hydrothiolation (thiol-yne click “TYC” reaction), is a simple approach to produce alkenyl sulfides from thiols and alkynes. In our research group, it has been reported a procedure for the synthesis of catechols with thiol pendant groups, interesting for the fabrication of novel materials. Besides, in the last years, we have been working in the development of methodologies based on the use of supported copper nanocatalysts. On this basis, we report our results about the TYC reaction between alkynes and catechol-thiol derivatives catalysed by CuNPs supported on TiO₂ in 1,2-dichloroethane (DCE) at 80 °C.

Activated alkynes bearing an adjacent electron-withdrawing group gave conversions from good to excellent of anti-Markovnikov Z-alkenyl sulfides, while the unactivated alkynes did not react. To explain this, we calculated and compared different methods for deriving partial atomic charges (Mulliken, CHELPG, Hirshfield, NBO) for all the alkynes. Furthermore, since we assumed that the reaction starts when the alkyne is activated by the copper, we modelled the nanocatalyst to find the most simple and representative structure. Computational results allowed us to assume that copper would be attached to a TiO₂ dimer through the oxygen atoms. DFT methods with the Gaussian09 and Orca software were used, applying different functionals (M06, M06-L, M06-2X, B3LYP) and basis set (TZVP, 6-311+G*). Moreover, the solvent effect (DCE) was evaluated with the CPCM model.