Dual-Excitation Polyoxometalate-Based Frameworks for One-Pot Light-Driven Hydrogen Evolution and Oxidative Dehydrogenation

Dehydrogenation
of the tetrahydroisoquinoline derivatives coupled with hydrogen production
is important for hydrogen storage applications. Herein, we formulated
a new system that embedded Dawson-type polyoxometalates as efficient
photosensitizers into the pores of redox-active coordination polymers
for the light-driven photocatalytic oxidative Mannich reaction and
hydrogen evolution. In the designed Co-POM polymer, UV light excitation
gives the excited state of the Dawson-type polyoxometalate first to
oxidize electron donors or substrates; the reduced form (i.e., heteropolyblue)
adsorbs visible light to achieve a new excited state, which reduced
the cobalt redox sites and facilitates hydrogen evolution reaction.
The photosensitizer recovered to the ground state, completing the
catalytic cycle. Under the optimized conditions, Co-POM enabled the
hydrogen evolution and dehydrogenation of tetrahydroisoquinoline without
the presence of any other additives. The high catalytic efficiency
and robustness indicated the advantages of the combining functional
polyoxometalate-based catalysts and porous characters of the coordination
polymers for the development of highly active heterogeneous catalysts.