Facile reversible hydrogenation of a poly(6-vinyl-2,3-dimethyl-1,2,3,4-tetrahydroquinoxaline) gel-like solid

Polymers bearing hydrogen storage units store hydrogen gas via chemical bond formation, and have inherent advantages as quasi-solid polymeric hydrogen carriers, such as handling easiness and high safety. A recent study demonstrated that a poly(6-vinyl-1,2,3,4-tetrahydroquinoxaline) gel-like solid was dehydrogenated over 5 h under 120°C and air, and then the material was reversibly hydrogenated under 60°C and ambient hydrogen pressure in the presence of an iridium complex catalyst. The present work aimed to improve the dehydrogenation rate via the substitution of methyl groups for hydrogen atoms on carbon atoms adjacent to the nitrogen atoms in the quinoxaline unit. The dramatic improvement was attributed to the electron donating property of methyl group, and stabilization of the dehydrogenated state. The poly(6-vinyl-2,3-dimethyl-1,2,3,4-tetrahydroquinoxaline) gel-like solid was rapidly dehydrogenated within 2 h under the same mild conditions. This article provides a guideline for the molecular design of nitrogen heterocyclic compounds for rapid dehydrogenation.