Highly active mesoionic chalcogenone zinc(ii) derivatives for C–S cross-coupling reactions†
The first mesoionic heavier chalcogenones, L1–L3 [L1 = 1-(2-mesitylene)-3-methyl-4-phenyltriazolin-5-selone; L2 = 1-(2-mesitylene)-3-methyl-4-phenyltriazolin-5-thione; L3 = 1-(benzyl)-2-3(methyl)-4-phenyltriazolin-5-selone], were isolated and characterised. Density functional theory was used to obtain insights into the σ donor and π accepting nature of mesoionic chalcogenones. Using these new ligands, a series of the first zinc(II) mesoionic chalcogenone complexes were isolated. Three mono nuclear zinc(II) chalcogenone complexes, [(L1)Zn(Cl)2(HOMe)] (1), [(L2)Zn(Cl)2(HOMe)] (3) and [(L2)Zn(Br)2(HOMe)] (4), and two dinuclear zinc complexes, [(L1)Zn(Br)(μ2-Br)]2 (2) and [(L3)Zn(Br)(μ2-Br)]2 (5), containing mesoionic thione and selone ligands were synthesized and characterised. These new complexes 1–5 represent the first structurally characterized mesoionic chalcogenone supported metal derivatives. Furthermore, all zinc complexes were characterized by thermogravimetric analysis and UV-vis spectroscopy. The solid-state structures of all zinc complexes were determined by single-crystal X-ray diffraction. The catalytic activities of the zinc(II) complexes in thioetherification reactions were investigated without scrubbing of oxygen. The scope of the catalytic reactions was explored with a wide range of thiophenols and aryl halides. The diaryl thioethers were obtained in very good yield under mild conditions. The present protocol furnishes a synthetic route for the C–S cross-coupling of thiophenols and aryl halides without scrubbing oxygen and moisture.