Synthesis, photophysical properties and catalytic activity of Ƙ3-SCS pincer palladium (II) complex of N,N'-di-tert-butylbenzene-1,3-dicarbothioamide supported by DFT analysis

Abstract

The title complex [PdCl(L)] (1), is obtained from the reaction of SCS pincer ligand HL (where, HL = N,N'-di-tert-butylbenzene-1,3-dicarbothioamide) with lithium tetrachloropalladate (II) in methanol. The compound 1 is characterized by elemental analysis, FTIR, 1H, and 13C NMR spectroscopy, UV–Vis spectroscopy, and X-ray crystallographic techniques. At room temperature, 1 emits luminescence light of wavelength 460 nm in the solid state upon excitation by UV light of wavelength 280 nm. The average emission lifetime indicates that, both the ligand and complex emission is fluorescence in nature and involves mainly ligand centers π-π* deexcitation. It also shows good catalytic activity towards Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions of aryl bromides with tert-butyl acrylate and p-tolylboronic acid respectively. For both type of reactions, >99% conversion of the substrates is found to occur for electronically activated p-nitro bromobenzene using 1 mol % of 1. Further, modern DFT calculations are performed to decipher the mechanistic insight on the preferable pathways of the Mizoroki-Heck cross-coupling reaction. Stepwise free energy of reactions for various probable reaction pathways suggest that the catalytic route has profound preference for Pd(0)-Pd(II) over Pd(II)-Pd(IV) pathway.