Mechanosynthesis of polymeric and binuclear copper complexes via dehydrochlorination and their application in solvent-free C–S bond cross-coupling

Two copper complexes, [Cu(L1)Cl3·CH3OH]n (1′-Cu) and [Cu(L2)Cl3]2 (2′-Cu), are readily synthesized from their respective salts, [H2L1]3+·[CuCl4]2−·Cl− (1-Cu) and 2[H2L2]3+·3[CuCl4]2− (2-Cu), by dehydrochlorination reactions with KOtBu by liquid-assisted grinding; L1 = 1,3-bis(picolyl)imidazolium chloride, L2 = 1,3-bis(picolyl)benzimidazolium chloride. The single crystal structure determination revealed that 1′-Cu is a polymeric complex and 2′-Cu is a binuclear complex. Both copper complexes were subsequently used as catalysts for the cross-coupling of C–S bonds between 2-bromoacetophenone and 2-mercaptobenzothiazole. The results show that the bridged dinuclear complex [Cu(L2)Cl3]2 has a high catalytic efficiency and short reaction time compared to other catalysts under the same conditions. The green metrics, E-factor and EcoScale, were close to the ideal values, showing the eco-friendliness of the entire procedure.