Akihiro Tsurusaki

Carbon Dioxide to Methanol: The Aqueous Catalytic Way at Room Temperature

Carbon dioxide may constitute a source of chemicals and fuels if efficient and renewable processes are developed that directly utilize it as feedstock. Two of its reduction products are formic acid and methanol, which have also been proposed as liquid organic chemical carriers in sustainable hydrogen storage. Here we report that both the hydrogenation of carbon dioxide to formic acid and the disproportionation of formic acid into methanol can be realized at ambient temperature and in aqueous, acidic solution, with an iridium catalyst. The formic acid yield is maximized in water without additives, while acidification results in complete (98 %) and selective (96 %) formic acid disproportionation into methanol. These promising features in combination with the low reaction temperatures and the absence of organic solvents and additives are relevant for a sustainable hydrogen/methanol economy.

Direction to practical production of hydrogen by formic acid dehydrogenation with Cp*Ir complexes bearing imidazoline ligands

A Cp*Ir complex with a bidentate pyridyl-imidazoline ligand achieved the evolution of 1.02 m3 of H2/CO2 gases by formic acid dehydrogenation without any additives or adjustments in the solution system. The pyridyl-imidazoline moieties provided the optimum pH to be 1.7, resulting in high activity and stability even at very acidic conditions.

Synthesis, Structures, and Properties of Hexapole Helicenes: Assembling Six [5]Helicene Substructures into Highly Twisted Aromatic Systems

Hexapole helicenes 1, which contain six [5]helicene substructures, were synthesized by Pd-catalyzed [2+2+2]cycloadditions of aryne precursor 6. Among the possible 20 stereoisomers, which include ten pairs of enantiomers, HH-1 was obtained selectively. Density functional theory (DFT) calculations identified HH-1 as the second most stable isomer that quantitatively isomerizes under thermal conditions into the most stable isomer (HH-2). Both enantiomers of HH-2 can be separated by chiral HPLC. Single-crystal X-ray diffraction analyses revealed a saddle-like structure for (P,M,P,P,M,P) HH-1 and a propeller-like structure for (P,M,P,M,P,M) HH-2. Because of the helical assembly and the resulting steric repulsion, the structure of HH-1 is significantly distorted and exhibits the largest twisting angle reported so far (up to 35.7° per benzene unit). Electrochemical studies and DFT calculations indicated a narrow HOMO-LUMO gap on account of the extended π-system. Kinetic studies of the isomerization from HH-1 to HH-2 and the racemization of enantiomerically pure HH-2 were conducted based on 1H NMR spectroscopy, HPLC analysis, and DFT calculations.

Tetrasilane-Bridged Bicyclo[4.1.0]heptasil-1(6)-ene

Tetrasilane-bridged bicyclo[4.1.0]heptasil-1(6)-ene 1 was synthesized by the reduction of 1,1,2,2-tetrachlorocyclohexasilane 2 in 12% yield as red-orange crystals. The structure and properties of 1 were studied by spectroscopy, X-ray crystallography, and theoretical calculations. The linkage of the cyclotrisilene moiety with two tetrasilane chains with tert-butyl groups remarkably affects its structure and (29)Si NMR spectrum.

Aqueous phase homogeneous formic acid disproportionation into methanol

The catalytic activity of a homogeneous iridium complex in formic acid disproportionation into methanol was explored. Formic acid reduction to methanol proceeds efficiently in aqueous media with the methanol yield depending on the nature of the solvent, substrate concentration, applied H2 pressure and reaction temperature. The methanol yield peaked at 75% when D2O was used as a solvent at 50 °C. Increasing the reaction temperature to 80 °C and doubling the substrate concentration led to an improved methanol concentration, even though the corresponding yield dropped to 59%. Initial H2 pressures further enhanced methanol formation, affording a highly concentrated 9.8 m methanol solution or a TON of 1260 upon in situ catalyst recycling under aerobic conditions. No catalyst deactivation was observed for five cycles.

A Unique Thermal Reaction of 9-Anthryldiphosphene Leading to the Formation of a Triphosphirane Derivative

Heating of a 9-anthryldiphosphene kinetically stabilized by 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl substituent (denoted as Bbt) group, BbtP ═ P(9-Anth) (9-Anth = 9-anthryl), with (n-Bu)3P═Te afforded 1,2-bis(9-Anth)-3-Bbt-triphosphirane in moderate yield. The structural parameters and physical properties of the isolated triphosphirane were determined by spectroscopic and X-ray crystallographic analyses.

The Radical Anion of Cyclopentasilane‐Fused Hexasilabenzvalene

The radical anion of cyclopentasilane-fused hexasilabenzvalene was synthesized by the reduction of the corresponding neutral compound. X-ray crystallographic analysis showed a more trans-bent structure of the disilene moiety than the neutral compound. Theoretical calculations showed that the highly trans-bent structure is attributed to the hexasilabenzvalene structure. The EPR spectrum showed that an unpaired electron exists mainly at the disilene moiety. In the UV/Vis spectrum, a large bathochromic shift was observed compared with the neutral compound.

Decasilahexahydrotriquinacene and Decasilaisotwistane: σ Conjugation on a Bowl Surface

The first bowl-shaped oligosilane, hexadecamethyldecasilahexahydrotriquinacene (1), and a related oligosilane, hexadecamethyldecasilaisotwistane (2), were synthesized, and their structures and properties were studied. The results revealed importance of σ conjugation on a bowl surface: the HOMOs of 1 are σ orbitals delocalized on the bowl surface, whereas the LUMO is a pseudo π* orbital on the convex and concave sides of the bowl surface.

Selenization and Tellurization Reactions of Kinetically Stabilized Dipnictenes

The kinetically stabilized heavier dipnictenes, diphosphene, distibene, and dibismuthene, bearing 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)]methylphenyl (Bbt groups were found to undergo selenization and tellurization reactions leading to the formation of the corresponding three-membered ring hetercycles, chalcogenadipnictiranes. The structural parameters and spectroscopic data of the isolated chalcogenadipnictiranes will be described.