Design of an efficient new catalyst that can mimic the enzymatic pathway for catalytic dehydrogenation of liquid fuels like alcohols is described in this report. The catalyst is a nickel(II) complex of 2,6-bis(phenylazo)pyridine ligand (L), which possesses the above requisite with excellent catalytic efficiencies for controlled dehydrogenation of alcohols using ligand-based redox couple. Mechanistic studies supported by density functional theory calculations revealed that the catalytic cycle involves hydrogen atom transfer via quantum mechanical tunneling with significant k/k isotope effect of 12.2 ± 0.1 at 300 K. A hydrogenated intermediate compound, [NiCl(HL)], is isolated and characterized. The results are promising in the context of design of cheap and efficient earth-abundant metal catalyst for alcohol oxidation and hydrogen storage.

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Electroprotic storage materials, though invaluable in energy-related research, are scanty among non-natural compounds. Herein, we report a zinc(II) complex of the ligand 2,6-bis(phenylazo)pyridine (L), which acts as a multiple electron and proton reservoir during catalytic dehydrogenation of alcohols to aldehydes/ketones. The redox-inactive metal ion Zn(II) serves as an oxophilic Lewis acid, while the ligand behaves as efficient storage of electron and proton. Synthesis, X-ray structure, and spectral characterizations of the catalyst, ZnLCl (1a) along with the two hydrogenated complexes of 1a, ZnHLCl (1b), and ZnHLCl (1c) are reported. It has been argued that the reversible azo-hydrazo redox couple of 1a controls aerobic dehydrogenation of alcohols. Hydrogenated complexes are hyper-reactive and quantitatively reduce O and para-benzoquinone to HO and para-hydroquinone, respectively. Plausible mechanistic pathways for alcohol oxidation are discussed based on controlled experiments, isotope labeling, and spectral analysis of intermediates.

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