Density functional theory investigation on Pd-catalyzed cross-coupling of azoles with aryl thioethers.
In the present study, a density functional theory (DFT) study has been carried out on the Pd-catalyzed coupling of azoles with aryl thioethers. Our effort is mainly put into identifying the most feasible catalytic cycle, and especially the origin of chemoselectivity for the exclusive aromatic Csp(2)-S bond activation (in the presence of an alkyl Csp(3)-S bond). The coupling mainly consists of three steps: C-S activation, NaO(t)Bu mediated C-H palladation, and reductive elimination. The Csp(2)-S activation is favored over Csp(3)-S activation, and thus di(hetero)aryls are the predicted products. This conclusion well reproduces Wang's recent experimental observations. The rate- and chemoselectivity determining steps of the C-H/Csp(2)-S activation mechanism are C-H palladation and C-S activation steps, respectively. Analyzing the origin of chemoselectivity, we found that the easiness of Pd catalyzed C-S activation is independent of the C-S bond strengths in thioether substrates. By contrast, d-π* backdonation in Csp(2)-S-Pd intermediates is the main driving force for the favorable Csp(2)-S activation (over the Csp(3)-S activation).
Department of Chemistry and Center for Atomic Engineering of Advanced Materials, Anhui University, Hefei, 230601, China. yuhaizhu@ahu.edu.cn and Department of Polymer Science and Engineering, University of Science and Technology Beijing, Beijing, 100083, China.
Yi-Meng
YM
Yang
Department of Polymer Science and Engineering, University of Science and Technology Beijing, Beijing, 100083, China.
Zhi-Min
ZM
Dang
Department of Chemistry and Center for Atomic Engineering of Advanced Materials, Anhui University, Hefei, 230601, China. yuhaizhu@ahu.edu.cn.
Hai-Zhu
HZ
Yu