Phosphonium Formation by Facile Carbon–Phosphorus Reductive Elimination from Gold(III)

A recent trend in homogeneous gold
catalysis has been the development of oxidative transformations relying
on Au­(I)/Au­(III) redox cycling. Typically, phosphine-supported Au­(I)
precatalysts are used in the presence of strong oxidants to presumably
generate phosphine Au­(III) intermediates. Herein, we disclose that
such Au­(III) complexes can undergo facile Caryl–P
reductive elimination to afford phosphonium salts, which have been
spectroscopically and crystallographically characterized. Mechanistic
studies indicate that this process occurs from cationic species at temperatures as low as −20 °C but can be accelerated
in the presence of nucleophiles, such as acetonitrile and phosphines,
via a five-coordinate intermediate. Importantly, this study highlights
that irreversible Caryl–P reductive elimination
is a feasible decomposition or activation pathway for phosphine-supported
Au­(III) catalysts and should not be ignored in future reaction development.