Base-Free Methanol Dehydrogenation Using a Pincer-Supported Iron Compound and Lewis Acid Co-catalyst

Hydrogen is an attractive alternative
energy vector to fossil fuels
if effective methods for its storage and release can be developed.
In particular, methanol, with a gravimetric hydrogen content of 12.6%,
is a promising target for chemical hydrogen storage. To date, there
are relatively few homogeneous transition metal compounds that catalyze
the aqueous phase dehydrogenation of methanol to release hydrogen
and carbon dioxide. In general, these catalysts utilize expensive
precious metals and require a strong base. This paper shows that a
pincer-supported Fe compound and a co-catalytic amount of a Lewis
acid are capable of catalyzing base-free aqueous phase methanol dehydrogenation
with turnover numbers up to 51 000. This is the highest turnover
number reported for either a first-row transition metal or a base-free
system. Additionally, this paper describes preliminary mechanistic
experiments to understand the reaction pathway and propose a stepwise
process, which requires metal–ligand cooperativity. This pathway
is supported by DFT calculations and explains the role of the Lewis
acid co-catalyst.