Noninnocent Ligands for Efficient Dehydrogenation of Aqueous and Neat Formic Acid under Base-Free Conditions

Formic acid could play an important role in energy transition
if
robust catalysts for its efficient dehydrogenation are developed.
Most importantly, additive-free protocols are sought to reduce the
cost and simplify the dehydrogenation process. Ideally, the highest
energy concentration requires the use of neat formic acid for which
only a few catalysts, active under additive-free conditions, have
been reported. We prepared several new ruthenium and iridium complexes
incorporating dipyridylamine ligands with various electronic and steric
properties. Among all these complexes, the air-stable Ir8 bearing a bis-dimethylamino-substituted dipyridylamine ligand displayed
the best performances in the dehydrogenation of aqueous solutions
of formic acid in the absence of any additives. The same catalyst
could also dehydrogenate neat formic acid with a TOF of 11,373 h–1 at 80 °C. High H2/CO2 pressure,
CO- free gas stream, and catalyst latency enabling storage and further
use of FA/catalyst premix have been achieved. Experimental and theoretical
studies have highlighted the roles of dipyridylamine and the SO42- ligand in the dehydrogenation process.