Recent progress in molecular transition metal catalysts for hydrogen production from methanol and formaldehyde.

Hydrogen is considered as a potential alternative and sustainable energy carrier, but its safe storage and transportation are still challenging due to its low volumetric energy density. Notably, C1-based substrates, methanol and formaldehyde, containing high hydrogen contents of 12.5 wt% and 6.7 wt%, respectively, can release hydrogen on demand in the presence of a suitable catalyst. Advantageously, both methanol and aqueous formaldehyde are liquid at room temperature, and hence can be stored and transported considerably more safely than hydrogen gas. Moreover, these C1-based substrates can be produced from biomass waste and can also be regenerated from CO2, a greenhouse gas. In this review, the recent progress in hydrogen production from methanol and formaldehyde over noble to non-noble metal complex-based molecular transition metal catalysts is extensively reviewed. This review also focuses on the critical role of the structure-activity relationship of the catalyst in the dehydrogenation pathway.

Ruthenium Catalyzed Dehydrogenation of Alcohols and Mechanistic Study.

We synthesized pyridylamine ligated arene-Ru(II) complexes and employed these complexes for the catalytic acceptorless dehydrogenation of primary alcohols to carboxylic acids. All the synthesized complexes [Ru]-1-[Ru]-10 are characterized using several spectro-analytical techniques, and the structures of complexes [Ru]-1, [Ru]-2, and [Ru]-5 are determined using single crystal X-ray crystallography. Efficient catalytic conversion of primary alcohols to potassium carboxylates or carboxylic acids is achieved in toluene with the quantitative release of hydrogen gas. The studied protocol for carboxylic acid synthesis with hydrogen generation is also employed for a wide range of substrates, including aliphatic alcohols, aromatic alcohols, and heteroaromatic alcohols, to obtain respective carboxylic acids in good yields (up to 86%). The studied arene-Ru catalysts also exhibit superior catalytic activity for the bulk reaction to achieve a turnover number of 1378. Moreover, extensive mass investigations are also performed to elucidate the mechanistic pathway by identifying the crucial catalytic intermediates, including aldehyde and diol coordinated Ru species under the catalytic and controlled reaction conditions.