In this work we lay out design guidelines for catalytically more efficient organic photocathodes achieving stable hydrogen production in neutral pH. We propose an organic photocathode architecture ...employing a NiO hole selective layer, a PCDTBT:PCBM bulk heterojunction, a compact TiO2 electron selective contact and a RuO2 nanoparticle catalyst. The role of each layer is discussed in terms of durability and function. With this strategically designed organic photocathode we obtain stable photocurrent densities for over 5 h and discuss routes for further performance improvement.
Here we report the use of 2-piperidino-1,2,2-triphenylethanol (5) as an outstanding catalyst for the ligand-catalyzed arylation of aldehydes. The use of 5 and a 2/1 mixture of Et2Zn/Ph2Zn provided ...the corresponding chiral diarylcarbinols with enantiomeric excess of up to 99% ee. The effect of temperature on the reaction enantioselectivity was studied and the inversion temperature (T inv) was determined to be 10 °C for reaction with p-tolylaldehyde. Most remarkably, lowering the amount of catalyst (5) to 0.5 mol % still afforded excellent levels of enantiocontrol (93.7% ee). Kinetics of the catalyzed and uncatalyzed arylation of aldehydes was studied by means of in situ FT-IR. The background uncatalyzed addition rates to p-tolylaldehyde when using pure Ph2Zn and Et2Zn/Ph2Zn (2/1) suggest that in the latter case a mixed zinc species forms (EtPhZn) minimizing the undesired nonselective addition. Formation of EtPhZn was modeled at the DFT calculation level. A four-center TS (TS - V) corresponding to the Et/Ph scrambling was localized along with two dimers (D-IV and D-VI). The model supports the hypothesis that Et/Ph exchange is a kinetically facile process. Gas evolution experiments during the formation of the active catalyst showed that the formation of an active site with a ONZn-Et (10) moiety is kinetically favored over ONZn-Ph (11). Finally, the phenyl transfer to benzaldehyde was modeled at the PM3(tm) level through anti and syn 5/4/4 tricyclic TS structures for both 10 and 11. The model could correctly predict the sense and selectivity of the overall process and predicted that 11 should be more selective than 10.
A functional polymer 4, obtained by reaction of (R)‐2‐(1‐piperazinyl)‐1,1,2‐triphenylethanol with a Merrifield resin, has been loaded in a packed bed reactor and used as catalyst for the continuous ...enantioselective production of 1‐arylpropanols by ethylation of aromatic aldehydes. The high catalytic activity depicted by 4 allows the complete conversion of the substrates with the use of stoichiometric reagent ratios and unprecedently short residence times (down to 2.8 min). In practice, a single‐pass operation can be used for all the studied aldehydes, and productions of up to 13.0 mol/g h are recorded. The sequential operation of the flow system for the uninterrupted synthesis of a small library of enantiopure 1‐arylpropanols is also reported.
Designing low cost, highly-active and stable oxygen evolution reaction (OER) catalysts for Proton Exchange Membrane Water Electrolysers (PEMWE) anodes is an important topic for industry and academia. ...A possible strategy to alleviate the cost of the anodic catalyst consists in synthesizing iridium oxide (IrOx) nanoparticles and dispersing them on an electron-conducting and highly-porous support such as SnO2 doped with hypervalent cations e.g. Sb(V) or Ta(V). Herein, we show the benefits of Sb- and Ta- doped SnO2 aerogels synthesized by a sol-gel route. The effect of the dopant nature on the aerogel's properties (as morphology, structure, conductivity, etc.) was investigated using a set of physical and chemical techniques. The electrocatalytic performance of the synthesized nanocatalysts towards the OER was also assessed in rotating disk electrode (RDE). Supported IrOx catalysts showed both higher specific and mass activity and stability than unsupported IrOx nanoparticles.
•Doped tin oxide aerogels with high specific surface area and enhanced electronic conductivity.•Ta-doped aerogel feature specific surface areas close to Sb-doped aerogels.•Deposition of IrOx nanoparticles on aerogels based supports.•Enhanced activity for OER and stability of supported vs. unsupported catalysts.
A series of enantiopure ligands based on the aminoindanol scaffold, but differing in regio‐ and stereochemistry has been synthesized. These ligands have been conveniently derivatized and their ...catalytic efficiency in different enantioselective reactions has been screened to determine privileged candidates with respect to regio‐ and stereochemistry for each considered process. The nature of the amino substituent has been optimized for specific applications and this has led to the development of an efficient method for the preparation of bulky bicyclic amines by reductive amination.
Advanced materials are needed to meet the requirements of devices designed for harvesting and storing renewable electricity. In particular, polymer electrolyte membrane water electrolyzers (PEMWEs) ...could benefit from a reduction in the size of the iridium oxide (IrO x ) particles used to electrocatalyze the sluggish oxygen evolution reaction (OER). To verify the validity of this approach, we built a library of 18 supported and unsupported IrO x catalysts and established their stability number (S-number) values using inductively coupled plasma mass spectrometry and electrochemistry. Our results provide quantitative evidence that (i) supported IrO x nanocatalysts are more active toward the OER but less stable than unsupported micrometer-sized catalysts, for example, commercial IrO2 or porous IrO x microparticles; (ii) tantalum-doped tin oxides (TaTO) used as supports for IrO x nanoparticles are more stable than antimony-doped tin oxides (ATO) and carbon black (Vulcan XC72); (iii) thermal annealing under air atmosphere yields depreciated OER activity but enhanced stability; (iv) the beneficial effect of thermal annealing holds both for micro- and nano-IrO x particles and leads to 1 order of magnitude lower Ir atom dissolution rate with respect to nonannealed catalysts; (v) the best compromise between OER activity and stability was obtained for unsupported porous IrO x microparticles after thermal annealing under air at 450 °C. These insights provide guidance on which material classes and strategies are the most likely to increase sustainably the OER efficiency while contributing to diminish the cost of PEMWE devices.
Two new highly pyramidalized tricyclo3.3.0.0
3,7oct-1(5)-ene derivatives containing ether and acetal functionalities have been generated, trapped as Diels–Alder adducts and dimerized. The initially ...obtained diene dimers were photochemically converted into cyclobutane derivatives. The thermal reversion of several cyclobutane derivatives to the corresponding dienes has been studied by
1H NMR, ab initio calculations and DSC. For the first time, transannular additions of bromine and iodine to a diene dimer of this series have been observed.
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A readily available chiral amino alcohol has been immobilized on silica by sol−gel synthesis and grafting. The solid prepared according to the latter method led to the best enantioselectivity (77% ...ee) described for the asymmetric addition of diethylzinc to benzaldehyde using inorganic solids.
A very active and highly enantioselective catalytic resin, designed for minimal perturbation of the catalytic center by the polymer matrix, has been assembled in two steps from (S)-triphenylethylene ...oxide, piperazine, and Merrifield resin and tested in the enantioselective ethylation of aldehydes. 1-Arylpropanols of 94−95% ee are obtained in high yield by the use of only 2 mol % of catalytic resin at 0 °C for 4 h.
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