The
potential safety hazards associated with Pd-catalyzed cross-coupling
reactions have been underappreciated and inadequately discussed. These
hazards have not been universally recognized in the past decades,
perhaps overshadowed by the ubiquity of this class of chemistry and
the desire to pursue new scientific advancements. The awareness of
these hazards is further limited by the fact that synthetic chemists
who develop these types of reactions on small scales are not typically
trained in reactive chemistry hazard evaluation, and existing studies
from industrial chemists and chemical engineers are often not published in journals that are
commonly read by academic groups and synthetic chemists that typically
work on small scales. This review summarizes observations of the exothermic
behavior associated with the Pd-catalyzed α-arylation, Buchwald–Hartwig
amination, Kumada–Corriu, Mizoroki–Heck, Negishi, Sonogashira,
and Suzuki–Miyaura cross-coupling reactions. This exothermic
behavior is consistently observed across each subset of cross-coupling
reactions and appears to be relatively independent of the nucleophile,
electrophile, base, solvent, and catalyst system employed. The magnitude
of the exotherms poses potential safety hazards that could result
in runaway scenarios in cases where the maximum temperature of a synthesis
reaction (MTSR) exceeds the solvent boiling point and/or the onset
temperature for reaction mixture decomposition. This contribution
will serve as an educational resource to encourage researchers to
conduct reaction safety evaluations and to develop control strategies
accordingly to mitigate such potential safety risks prior to practicing
Pd-catalyzed cross-coupling as well as other transition-metal-catalyzed
cross-coupling reactions.