First use of a palladium complex with a thiosemicarbazone ligand as catalyst precursor for the Heck reaction

A novel palladium complex with salicylaldehyde N(4)-ethylthiosemicarbazone has been synthesized and according to its crystal structure the ligand is bound to the metal in an O, N, S-terdentate coordination mode. This phosphorus-free system efficiently catalyzes the Heck reaction of aryl bromides (from electron-rich to electron-poor) with styrene under argon, with turnover numbers of up to 43,000, at 150 °C after 24 h, and with a selectivity toward trans-stilbenes ranging from 92 to 96%. In air, for activated aryl bromides and for a palladium concentration of 1 mM, the yields are essentially the same as those obtained when the reaction was performed under argon.