Formic Acid Dehydrogenation Catalysis Using Novel Pyridyl-Formamidine Half-Sandwich Ruthenium(II) Complexes

Abstract

The reaction of N,N′-bidentate chelating ligands with [Ru(p-cymene)Cl₂]₂ in methanol resulted in six-membered Ru complexes with tshe general formula [RuCl(p-cymene)L]Cl exhibiting a pseudo-octahedral piano-stool geometry. The combination of NMR, MS, FTIR and SCXRD techniques confirmed the successful synthesis of the reported compounds. The prepared complexes were all active in formic acid dehydrogenation (FADH) catalysis, producing an equimolar mixture of H₂ and CO₂ gases with no detectable amount of CO. Establishing thermodynamic and kinetic parameters provided evidence for the role of pre-catalyst and FA during catalysis. Reactivity studies between C6 and HCOOK revealed complex equilibria and allowed for the detection of the key monohydride species involved in catalysis. Remarkably, C6 proved to be robust at 100°C, resulting in approximately 98% substrate conversion with a total TON of about 7892 and TOF close to 300 h⁻¹ after 35 h.