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 H NMR spectroscopy, HPLC analysis, and DFT calculations.

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.

A Cp*Ir complex with pyridyl-imidazoline achieved the quantity production of 1 m3 of H2/CO2 gases from only HCO2H in water without any additives.

Production of methanol (MeOH) from CO 2 is strongly desired as a key chemical feedstock and a fuel. However, the conventional process requires elevated temperature and pressure, and high temperature restricts the productivity of MeOH due to equilibrium limitations between CO 2 and MeOH. This paper describes the efficient hydrogenation/disproportionation of formic acid (FA) to MeOH by using iridium catalysts with electronically tuned ligands and by optimizing reaction conditions. An iridium complex bearing 5,5′-dimethyl-2,2′bipyridine in FA hydrogenation achieved MeOH selectivity with H 2 of up to 47.1% for FA hydrogenation under 4.5 MPa of H 2 in the presence of H 2 SO 4 . The final concentration of MeOH of 3.9 M and a TON of 1314 were obtained in 12 M FA aqueous solution including 10 mol % of H 2 SO 4 at 60 °C under 5.2 MPa of H 2 . Even under atmospheric pressure without introduction of external hydrogen gas, the FA disproportionation under deuterated conditions produced MeOH with 15.4% selectivity. Furthermore, the isotope effect and NMR studies revealed mechanistic insight into the catalytic hydrogenation of FA to MeOH.

Cyclopentasilane-fused hexasilabenzvalene 1 was synthesized by the reduction of tetrachlorocyclopentasilane 6 in 19% yield as a green powder. The molecular structure and properties of 1 were studied by spectroscopic and X-ray crystallographic analyses. Theoretical calculations of the model and real molecules of 1 and their structural isomers 12–16 suggest that the linkage of the central hexasilabenzvalene moiety with trisilane chains and the introduction of tert-butyl groups affect their relative energies.

Optically active triple helicenes (TH-1) were prepared via a palladium-catalyzed enantioselective cross-cyclotrimerization of two helicenyl arynes 5, which are generated in situ from 3, with dialkyl acetylenedicarboxylate 4. Enantiomeric ratios of up to 98:2 were obtained when using 4a and (S)-QUINAP as the alkyne and chiral ligand, respectively. The absolute stereochemistry of TH-1a was revealed to be (M,P,M) by a single-crystal X-ray diffraction analysis. Kinetic studies of the racemization of enantiomerically pure TH-1a at elevated temperatures were conducted based on a high-performance liquid chromatography analysis. The activation energy for the racemization was found to be 29.1 kcal mol −1 . Density functional theory calculations revealed that the palladium-catalyzed enantioselective cross-cyclotrimerization reactions proceed via the dynamic kinetic resolution of a five-membered palladacycle 6a with two [5]helicenes. Several initially formed stereoisomers of 6a eventually isomerize into the most thermodynamically stable palladacycle intermediate (M,P,M)-6a by inversion of the [5]helicenyl moiety. Then, the insertion of 4 into 6a to form (M,P,M)-12a, followed by a reductive elimination, leads to the formation of (M,P,M)-TH-1a in a stereoselective manner. The optical properties of TH-1a were studied by circular dichroism and circularly polarized luminescence.

On the move: The title compounds 1, which are unique heterocyclic systems containing a PB bond, have been synthesized by the reduction of 1‐diarylboryl‐8‐dichlorophosphinonaphthalene derivatives (see scheme). Both experimental and theoretical results for 1 revealed an effective interaction between the phosphorus atom, boron atom, and naphthyl moiety. Furthermore, 1 exhibits orange fluorescence in solution.

We report newly developed iridium catalysts with electrondonating imidazoline moieties as ligands for CO2 hydrogenation to formate in aqueous solution. Interestingly, these new complexes promote CO2 hydrogenation much more effectively than their imidazole analogues, exhibiting the turnover frequency (TOF) of 1290 h-1 for the bisimidazoline complex compared to that of 20 h-1 for