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<p>The Pd-catalyzed cross-coupling of thiols
with aromatic electrophiles is a reliable method for the synthesis of aryl
thioethers, which are important compounds for pharmaceutical and agricultural
applications. Since thiols and thiolates strongly bind late transition metals,
previous research has focused on catalysts supported by chelating, bisphosphine
ligands, which were considered less likely to be displaced during the course of
the reaction. We show that by using monophosphine ligands instead, more effective
catalysis can be achieved. Notably, compared to previous methods, this
increased reactivity allows for the use of much lower reaction temperature,
soluble bases, and base-sensitive substrates. In contrast to conventional
wisdom, our mechanistic data suggest that the extent of displacement of
phosphine ligands by thiols is, firstly, not correlated with the ligand bulk or
thiol nucleophilicity, and secondly, not predictive of the effectiveness of a
given ligand in combination with palladium.</p>
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