Carbon dioxide reduction by an Al–O–P frustrated Lewis pair

The reaction of tBu₂P(O)H with Bis₂AlH (Bis = CH(SiMe₃)₂) afforded the adduct tBu₂P(H)–O–Al(H)Bis₂ (3). It slowly releases H₂ to form the first oxygen-bridged geminal Al/P frustrated Lewis pair tBu₂P–O–AlBis₂. It is capable of reversibly binding molecular hydrogen to afford 3, shown by NMR and H/D scrambling experiments, and forms a 1,2-adduct with CO₂. Importantly, the H₂ adduct 3 reduces CO₂ in a stoichiometric reaction leading to the formic acid adduct tBu₂P(H)–O–Al(CO₂H)Bis₂. The formation of the different species was explored by density functional theory calculations which provide support for the experimental results. All products were characterized by NMR spectroscopy as well as X-ray diffraction experiments and elemental analyses.

Addition vs. reduction: the geminal FLP Bis₂Al–O–PtBu₂ can reversibly bind molecular hydrogen, it reacts with CO₂ to give an adduct, and its hydrogen adduct reduces CO₂ to an adduct of formic acid.     

Separation of Dihydro-Isocoumarins and Dihydro-Stilbenoids from Hydrangea macrophylla ssp. serrata by Use of Counter-Current Chromatography

Previously, different Hydrangea macrophylla ssp. serrata cultivars were investigated by untargeted LC-MS analysis. From this, a list of tentatively identified and unknown compounds that differ significantly between these cultivars was obtained. Due to the lack of reference compounds, especially for dihydro-isocoumarins, we aimed to isolate and structurally characterise these compounds from the cultivar ‘Yae-no-amacha’ using NMR and LC-MS methods. For purification and isolation, counter-current chromatography was used in combination with reversed-phase preparative HPLC as an orthogonal and enhanced purification workflow. Thirteen dihydro-isocoumarins in combination with other metabolites could be isolated and structurally identified. Particularly interesting was the clarification of dihydrostilbenoid glycosides, which were described for the first time in H. macrophylla ssp. serrata. These results will help us in further studies on the biological interpretation of our data.     

Geschwindigkeitsoszillationen beim Wachstum aus der Schmelze mit komplizierten Erstarrungsflächen

Basing on a formerly described model, the fluctuation of the growth velocity is computed for the growth of a crystal with rotating seed and a solidification interface, which has an maximum at r = r_c = 0. The distribution of the velocity and the pattern of the resulting striations is discussed.     

Fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane: Structure,Bonding, and Reactivity

In this contribution we report on fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane as a phosphorus based fluorinating reagent. Its solid state structure can be described as a trigonal bipyramid featuring elongated axial bonds due to the formation of a 3-center 4-electron bond. Abstraction of the fluoride ion leads to a shortening of the axial P–C bond. Thus the title compound can be utilized for substitution of bromine with fluorine and for the transfer of fluoride ions onto electrophilic compounds. Reaction with Sn(C₂F₅)₂Br₂ afforded salt [P(CH₃)₃(C₃F₅)]₂[Sn(C₂F₅)₂F₄]. When fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane was treated with P(C₂F₅)₂F the primarily produced anion is sufficiently nucleophilic to attack the propenyl group of the cation in β-position to the phosphorus atom to yield zwitterionic [Me₃PCF=C(CF₃)–PF₃(C₂F₅)₂].