Conversion of CO2 into chemicals and fuels is one of the most desired technologies for mitigation of CO2 emission. Formic acid, which has a hydrogen content of 4.3 %, have recently attracted attention as a liquid-based hydrogen storage medium [1] as high-pressure gases of H2 and CO2 could be produced from formic acid.[2] For the reverse reaction of CO2 hydrogenation in water without any organic additives, we have developed several efficient catalysts having N,N-bidentate ligands , according to the following catalyst-design concepts: (i) enhancement by the electron donating effect, (ii) a strong electron-donating effect resulting from the oxyanion formed by deprotonation of a hydroxyl group,[3-4] and (iii) second coordination sphere interactions.[5] Here we describe highly efficient iridium catalysts having deprotonated picolinamide ligands providing strong electron donation.[6] The X-ray analysis indicated that the amide moieties were converted to anionic species by deprotonation through a resonance stabilization effect and functioned as anionic ligands, which exhibited strong electron donation to the Ir center. The in situ catalyst (1:1 mixture of [Cp*Ir(H2O)3][SO4] and picolinamide) showed excellent activity. The results prompted us to evaluate various picolinamide-based catalysts and we found that the picolinamde-based iridium catalyst, which incorporated a proton-responsive pyridinol moiety, achieved a TON of 14,700 (TOF: 167 h-1) and a formate concentration of 0.64 M under ambient conditions. These results represent the highest TON and formate concentration among the previous researches conducted under ambient conditions.[4] Furthermore, we describe the hydrogen production by dehydrogenation of formic acid using the iridium catalysts.[7]

CO2 hydrogenation for hydrogen storage using iridium catalysts with deprotonated picolinamide ligands

256th National Meeting (2018)

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