Copper-mediated C-H activation/C-S cross-coupling of heterocycles with thiols.

We report the synthesis of a series of aryl- or alkyl-substituted 2-mercaptobenzothiazoles by direct thiolation of benzothiazoles with aryl or alkyl thiols via copper-mediated aerobic C-H bond activation in the presence of stoichiometric CuI, 2,2'-bipyridine and Na(2)CO(3). We also show that the approach can be extended to thiazole, benzimidazole, and indole substrates. In addition, we present detailed mechanistic investigations on the Cu(I)-mediated direct thiolation reactions. Both computational studies and experimental results reveal that the copper-thiolate complex [(L)Cu(SR)] (L: nitrogen-based bidentate ligand such as 2,2'-bipyridine; R: aryl or alkyl group) is the first reactive intermediate responsible for the observed organic transformation. Furthermore, our computational studies suggest a stepwise reaction mechanism based on a hydrogen atom abstraction pathway, which is more energetically feasible than many other possible pathways including ß-hydride elimination, single electron transfer, hydrogen atom transfer, oxidative addition/reductive elimination, and σ-bond metathesis.

Electroreduction activity of hydrogen peroxide on Pt and Au electrodes.

Hydrogen peroxide electroreduction on both catalytically active Pt and inactive Au surfaces are studied by using both surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) calculations. SERS measurements on Pt show the presence of Pt-OH at negative potentials, which suggests that hydroxide is formed as an intermediate during the electroreduction process. Additionally, the O-O stretch mode of H(2)O(2) is observed on Pt, which shifts to lower energy as potential is swept negatively, indicating that the O-O bond is elongated. For comparison, there is no variation in the energy of the same O-O mode on Au surfaces, and there is no observation of Au-OH. DFT calculations show that H(2)O(2) adsorption on Pt(110) results in the dissociation of O-O bond and the formation of Pt-OH bond. On Au, O-O bond elongation is calculated to occur only on the (110) face. However, the magnitude of the elongation is much smaller than that found on Pt(110).