Photoinduced Mechanisms of C–S Borylation of Methyldiboron: A Density Functional Theory Investigation

The reaction mechanisms of C–S borylation of aryl sulfides catalyzed with 1,4-benzoquinone (BQ) were investigated by employing the M06-2X-D3/ma-def2-SVP method and basis set. In this study, the SMD model was taken to simulate the solvent effect of 1,4-dioxane. Also, TD-DFT calculations of BQ and methyl(p-tolyl)sulfane were performed in an SMD solvent model. The computational results indicated that BQ and methyl(p-tolyl)sulfane, serving as a photo-catalyst, would be excited under a blue LED of 450 nm, aligning well with experimental observations. Additionally, the role of [sup.3]O[sub.2] was investigated, revealing that it could be activated into [sup.1]O[sub.2] from the released energy of [sup.1][BQ + methyl(p-tolyl)sulfane]* or [sup.3][BQ + methyl(p-tolyl)sulfane]*→BQ + methyl(p-tolyl)sulfane process. Then, [sup.1]O[sub.2], bis(pinacolato)diboron, and methyl(p-tolyl)sulfane would, through a series of reactions, yield the final product, P. The Gibbs free energy surface shows that path a2-2 is optimal, and this path has fewer steps and a lower energy barrier. Electron spin density isosurface graphs were employed to analyze the structures and elucidate the single electron distribution. These computational results offer valuable insights into the studied interactions and related processes and shed light on the mechanisms governing C–S borylation from aryl sulfides and b[sub.2]pin[sub.2] catalyzed with BQ and methyl(p-tolyl)sulfane.