posted on 2021-02-22, 20:04authored byArun Dixith
Reddy Shada, Alexander J. M. Miller, Thomas J. Emge, Alan S. Goldman
Dehydrogenation
to give olefins offers the most broadly applicable
route to the chemical transformation of alkanes. Transition-metal-based
catalysts can selectively dehydrogenate alkanes using either olefinic
sacrificial acceptors or a purge mechanism to remove H2; both of these approaches have significant practical limitations.
Here, we report the use of pincer-ligated iridium complexes to achieve
alkane dehydrogenation by proton-coupled electron transfer, using
pairs of oxidants and bases as proton and electron acceptors. Up to
97% yield was achieved with respect to oxidant and base, and up to
15 catalytic turnovers with respect to iridium, using t-butoxide as base coupled with various oxidants, including oxidants
with very low reduction potentials. Mechanistic studies indicate that
(pincer)IrH2 complexes react with oxidants and base to
give the corresponding cationic (pincer)IrH+ complex, which
is subsequently deprotonated by a second equivalent of base; this
affords (pincer)Ir which is known to dehydrogenate alkanes and thereby
regenerates (pincer)IrH2.