Dynamic Pt-OH-•H2O-Ag Species Mediate Synergetic Electron and Proton Transfer for Catalytic Hydride Reduction of 4-Nitrophenol at Confined Nanoscale Interface

The nature of interfacial state and/or bonding at heterogeneous nanoscale surface of bimetals remains elusive. For very classical probe reaction of catalytic hydride catalytic reduction of –NO2 to NH2 (herein reduction of 4-NP to 4-AP as an example), three abnormal experimental phenomena cannot be elucidated as such: 1) the hydrogen source of final product of 4-AP is originated from water solvent, rather than NaBH4 reducer; 2) reverse electron transfer between bimetals was observed, which is resisted to the normal thermaldynamic law; 3) even in the absence of any metals, for example just using carbon nanodots as supports, the reaction occurs. These observations indicates that the reduction of –NO2 groups did not follow the classical metal-centered electron and hydride transfer mechanism, i.e., Langmuir-Hinshelwood (L-H) mechanism. We herein provide strong evidence that, the catalytic hydride reduction of 4-NP to 4-AP is though a completely new surface hydrous hydroxyl specie mediated concerted electron and proton transfer process, wherein owing to the space overlapping of p orbitals in hydrous hydroxyl intermediate, an ensemble of interface states are dynamically formed, which could be alternative channels for concerted electron and proton transfer. The main role of second metal of Pt is to regulate the density of surface hydrous hydroxyl intermediate and its interactive strength with metals. This new mechanism not only answers all the abnormal experimental observations above mentioned, but also provide some new insights to water and/or hydroxyl group promoted reaction involved the activation of small molecules (CO2, CO, N2, H2O etc.) in areas of electrochemistry, energy storage and metalloenzyme catalysis.

INFLUENCE OF ALLOYING Ti, Mo AND W ON THE KINETIC AND STRENGTH CHARACTERISTICS OF MEMBRANE ALLOYS BASED ON Nb AND V

Проведен анализ влияния Ti, Mo и W на характер аморфной нано- и кристаллической структуры на прочностные и кинетические характеристики - диффузии D и проницаемости Ф водорода в мембранных сплавах, созданных на основе бинарных Ni - Nb и V - Ni. Легирование сплавов Ni - V титаном, молибденом и вольфрамом ведет к постепенному замещению ими ниобия и ванадия и способствует образованию нескольких второстепенных фаз хотя и действующих как барьеры для диффузии водорода, но способствующих снижению процессов гидридообразования. Выявлена строгая зависимость кинетики водорода не только от термодинамических параметров -температуры и давления, но и от наличия свободного объема в формируемых аморфных, нано-кристаллических и кристаллических сплавов. Установлено, что процессы селективности, динамика водорода - его поток J, определяемый произведением диффузии и проницаемости (J = D×Ф), зависят от базового состава, выбора легирующих элементов (Ti,Mo и W ), а также формируемых структур - аморфной, нанокристаллической и полифазной дуплексной кристаллической микроструктурой. Установлено, что тщательно подобранный состав определяет производительность селективного процесса и способствует выделению высокочистого водорода с последующими его приложениями для зеленой энергетики. An analysis was carried out of influence of Ti, Mo and W on the nature of the amorphous nano- and crystalline structures on the strength and kinetic characteristics - diffusion D and permeability Ф of hydrogen in membrane alloys based on binary Nb - Ni, V - Ni. Doping with Nb - V alloys, titanium, molybdenum and tungsten leads to the gradual replacement of niobium and vanadium, and promotes the formation of several minor phases while acting as barriers for hydrogen diffusion, but contributing hydride reduction processes. A close dependence of the hydrogen kinetics was revealed not only on thermodynamic parameters - temperature and pressure, but also on the presence of free volume in the formed amorphous, nanocrystalline and crystalline alloys. So, the processes of selectivity, the dynamics of hydrogen - its flux J determined by the product of diffusion D and permeability Ф, J = D×Ф depend on the basic composition and the choice of alloying elements (Ti,Mo and W ), as well as the formed structures - amorphous, nanocrystalline and duplex, represented by multiphase crystalline microstructures. It was found that a carefully selected composition determines the productivity of the selective process and promotes the release of high-purity hydrogen with its subsequent applications for green energy.

Enantiodivergent Synthesis of Benzoquinolizidinones from L-Glutamic Acid

Benzoquinolizidinone systems were synthesized in both enantiomeric forms from L-glutamic acid. The key chiral arylethylglutarimide intermediate was synthesized from dibenzylamino-glutamate and homoveratrylamine. Aldol reaction of the glutarimide afforded a mixture of syn and anti-aldol adducts. Subsequent regioselective hydride reduction of the glutarimide carbonyl followed by N-acyliminium ion cyclization afforded a product with opposite absolute configurations at C3 and C11b. Cope elimination of the dibenzylamino group then converted the two diastereomers into enantiomers.

Surface Electronic State Mediates Proton Transfer at Metal Nanoscale Interface for Catalytic Hydride Reduction of −NO2 to −NH2

Concerted electron and proton transfer is a key step for the reversible conversion of molecular hydrogen in both heterogeneous nanocatalysis and metalloenzyme catalysis. (Gabor A. Somorjai, et al. PNAS, 2016, 113, 5159–5166) However, the activation mechanism involving electron and proton transfer dynamic remains elusive. (Starla D. Glover and Leif Hammarström et al., J. Am. Chem. Soc. 2021, 143, 560−576.) With the most widely used catalytic hydride reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction, we evaluate the catalytic activity of noble metal NPs trapped in porous silica in aqueous NaBH4 solution. By virtue of a novel combination of catalyst design, reaction kinetics, isotope labeling, and multiple spectroscopic techniques, we counter-intuitively demonstrates that, the hydrogen resource of the final product of 4-AP by hydride reduction is not originated from the NaBH4 reduced, and that metal NPs (Ag/Pt/Pd) is not a real catalytic active site for surface electron mediation. (Avelino Corma etal., Angew. Chem. Int. Ed. 2007, 46, 7266 –7269; ACS Catal. 2015, 5, 7114−7121.). A completely new ‘Surface Electronic State Mediated Proton Transfer’ mechanism was proposed to understand the catalytic hydride reduction of −NO2 to −NH2 at metal nanoscale interface. The similar concerted electron and proton transfer dynamic was only recently observed in the [FeFe]-hydrogenases for reversible proton reduction. (Gregory A. Voth et al., J. Phys. Chem. B 2013, 117, 4062−4071; J. Chem. Phys. 2014, 141, 22D527; Juan C. Fontecilla-Camps et al., Chem. Rev. 2007, 107, 4273-4303.) We believed that current research provide a completely new insights into the working mechanism of nanocatalysis and metalloenzyme catalysis involved by electron and proton transfer.

Surface Electronic State Mediates Proton Transfer at Metal Nanoscale Interface for Catalytic Hydride Reduction of −NO2 to −NH2

Concerted electron and proton transfer is a key step for the reversible conversion of molecular hydrogen in both heterogeneous nanocatalysis and metalloenzyme catalysis. (Gabor A. Somorjai, et al. PNAS, 2016, 113, 5159–5166) However, the activation mechanism involving electron and proton transfer dynamic remains elusive. (Starla D. Glover and Leif Hammarström et al., J. Am. Chem. Soc. 2021, 143, 560−576.) With the most widely used catalytic hydride reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction, we evaluate the catalytic activity of noble metal NPs trapped in porous silica in aqueous NaBH4 solution. By virtue of a novel combination of catalyst design, reaction kinetics, isotope labeling, and multiple spectroscopic techniques, we counter-intuitively demonstrates that, the hydrogen resource of the final product of 4-AP by hydride reduction is not originated from the NaBH4 reduced, and that metal NPs (Ag/Pt/Pd) is not a real catalytic active site for surface electron mediation. (Avelino Corma etal., Angew. Chem. Int. Ed. 2007, 46, 7266 –7269; ACS Catal. 2015, 5, 7114−7121.). A completely new ‘Surface Electronic State Mediated Proton Transfer’ mechanism was proposed to understand the catalytic hydride reduction of −NO2 to −NH2 at metal nanoscale interface. The similar concerted electron and proton transfer dynamic was only recently observed in the [FeFe]-hydrogenases for reversible proton reduction. (Gregory A. Voth et al., J. Phys. Chem. B 2013, 117, 4062−4071; J. Chem. Phys. 2014, 141, 22D527; Juan C. Fontecilla-Camps et al., Chem. Rev. 2007, 107, 4273-4303.) We believed that current research provide a completely new insights into the working mechanism of nanocatalysis and metalloenzyme catalysis involved by electron and proton transfer.

Au(III) complexes with tetradentate-cyclam-based ligands

Chiral cyclam (1,4,8,11-tetraazacyclotetradecane) derivatives were synthesized stepwise from chiral mono-Boc-1,2-diamines and (dialkyl)malonyl dichloride via open diamide-bis(N-Boc-amino) intermediates (65–91%). Deprotection and ring closure with a second malonyl unit afforded the cyclam tetraamide precursors (80–95%). The new protocol allowed the preparation of the target cyclam derivatives (53–59%) by a final optimized hydride reduction. Both the open tetraamine intermediates and the cyclam derivatives successfully coordinated with AuCl3 to give moderate to excellent yields (50–96%) of the corresponding novel tetra-coordinated N,N,N,N-Au(III) complexes with alternating five- and six-membered chelate rings. The testing of the catalytic ability of the cyclam-based N,N,N,N-Au(III) complexes demonstrated high catalytic activity of some complexes in selected test reactions (full conversion in 1–24 h, 62–97% product yields).

Studies on the Enantioselective Synthesis of E-Ethylidene-bearing Spiro[indolizidine-1,3′-oxindole] Alkaloids

A synthetic route for the enantioselective construction of the tetracyclic spiro[indolizidine-1,3′-oxindole] framework present in a large number of oxindole alkaloids, with a cis H-3/H-15 stereochemistry, a functionalized two-carbon substituent at C-15, and an E-ethylidene substituent at C-20, is reported. The key steps of the synthesis are the generation of the tetracyclic spirooxindole ring system by stereoselective spirocyclization from a tryptophanol-derived oxazolopiperidone lactam, the removal of the hydroxymethyl group, and the stereoselective introduction of the E-ethylidene substituent by acetylation at the α-position of the lactam carbonyl, followed by hydride reduction and elimination. Following this route, the 21-oxo derivative of the enantiomer of the alkaloid 7(S)-geissoschizol oxindole has been prepared.

Transfer hydrogenations catalyzed by streptavidin-hosted secondary amine organocatalysts

Streptavidin-based secondary amine enables organocatalytic hydride reduction.

Lithium aluminum hydride reduction of 1-phenylbutane-1,3-dione, and acetylation of the products: NMR and GC-MS analysis

Reduction of ?-diketones with lithium aluminum hydride (LiAlH4, LAH) can lead to different products, depending on the tautomeric equilibrium: the reduction of diketo forms gives the corresponding diols and the reduction of ketoenol forms yields elimination products, saturated and unsaturated ketones and alcohols. Here, we report on the results of LAH reduction of 1-phenylbutane-1,3-dione. The products of reduction were further acetylated and separated by dry flash chromatography. The obtained products, phenylbut(en)ols, phenylbut(en)ones and phenylbut(en)yl acetates, were characterized by spectral (1H and 13C NMR, MS) and retention index (RI) data. It can be concluded that LAH preferentially reduces the carbonyl group more distant from the phenyl group of 1-phenylbutane-1,3-dione. The structure-retention index relationships between isomers were discussed. Proton splitting patterns were resolved by proton NMR simulations.