Monitoring of the Phosphine Role in the Mechanism of Palladium-Catalyzed Benzosilole Formation from Aryloxyethynyl Silanes

Understanding
the formation of benzosiloles by the intramolecular
palladium-catalyzed annulation of alkynyl­(aryl)­silanes is crucial
for achieving synthetic diversity toward the enhancement of the chemistry
of siloles. By a combination of density functional theory calculations
and experiments, we describe not only the whole mechanism of reaction
but also the drawbacks that block this type of reaction. We also unravel
the role of the phosphine ligand, without which the reactions could
not go forward. Moreover, in silico predictive catalysis is presented
here since the substitution of the phosphine ligand by an N-heterocyclic
carbene (NHC) promises milder experimental conditions. A screening
of substrates with different electronic properties was carried out
to further understand the two fundamental steps of the reaction: stereoisomerization
and concerted metalation–deprotonation.