[(IPent)PdCl2(morpholine)]: A Readily Activated Precatalyst for Room‐Temperature, Additive‐Free Carbon–Sulfur Coupling

A series of new, easily activated NHC–PdII precatalysts featuring a trans-oriented morpholine ligand were prepared and evaluated for activity in carbon-sulfur cross-coupling chemistry. [(IPent)PdCl2(morpholine)] (IPent=1,3-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene) was identified as the most active precatalyst and was shown to effectively couple a wide variety of deactivated aryl halides with both aryl and alkyl thiols at or near ambient temperature, without the need for additives, external activators, or pre-activation steps. Mechanistic studies revealed that, in contrast to other common NHC–PdII precatalysts, these complexes are rapidly reduced to the active NHC–Pd0 species at ambient temperature in the presence of KOtBu, thus avoiding the formation of deleterious off-cycle PdII–thiolate resting states.