Study of nano‐Cu/SiO2 catalysts for highly selective hydrogenation of acetophenone

Hydrogenation of acetophenone over nano‐Cu/SiO₂ catalysts was investigated. The catalysts, prepared by a liquid precipitation method using various precipitating agents, were characterized using low‐temperature nitrogen adsorption, X‐ray diffraction, temperature‐programmed desorption of ammonia, hydrogen temperature‐programmed reduction, transmission electron microscopy and X‐ray photoelectron spectroscopy. It was found that the catalysts prepared by a homogeneous precipitation method had better activity and stability than those prepared by a co‐precipitation method. The catalyst prepared using urea as precipitating agent had well‐dispersed copper species, high surface area and abundant pore structure. The catalytic performance and mechanism of the Cu/SiO₂ catalysts were further studied. It was found that the activity and stability of the catalysts could be improved by adjusting the proportion of Cu⁺/(Cu⁺ + Cu⁰). The sample prepared using urea as precipitating agent presented higher activity and selectivity. Also, the catalyst prepared using urea maintained a high catalytic performance while being continuously used for 150 h under the optimal reaction conditions.     

Atropselective Dibrominations of a 1,1′‐Disubstituted 2,2′‐Biindolyl with Diverging Point‐to‐Axial Asymmetric Inductions. Deriving 2,2′‐Biindolyl‐3,3′‐diphosphane Ligands for Asymmetric Catalysis

On the ¹H NMR timescale, 2,2′‐biindolyls with (R)‐configured (1‐alkoxyprop)‐2‐yl, (1‐hydroxyprop)‐2‐yl, or (1‐siloxyprop)‐2‐yl substituents at C‐1 and C‐1′ are atropisomerically stable at <0 °C and interconvert at >30 °C. A 2,2′‐biindolyl (R,R)‐ 17 a of that kind and achiral (!) brominating reagents gave the atropisomerically stable 3,3′‐dibromobiindolyls (M)‐ and/or (P)‐ 18 a at best atropselectively—because of point‐to‐axial asymmetric inductions—and atropdivergently, exhibiting up to 95 % (M)‐ and as much (P)‐atropselectivity. This route to atropisomerically pure biaryls is novel and should extend to other substrates and/or different functionalizations. The dibromobiindolyls (M)‐ and (P)‐ 18 a furnished the biindolyldiphosphanes (M)‐ and (P)‐ 14 without atropisomerization. These syntheses did not require the resolution of a racemic mixture, which distinguishes them from virtually all biaryldiphosphane syntheses known to date. (M)‐ and (P)‐ 14 acted as ligands in catalytic asymmetric allylations and hydrogenations. Remarkably, the β‐ketoester rac‐ 25 c was hydrogenated trans‐selectively with 98 % ee; this included a dynamic kinetic resolution.     

Tuning the phase behavior of semicrystalline hydrogenated polynorbornene via epimerization

Hydrogenated polynorbornene (hPN) synthesized by ring‐opening metathesis polymerization (ROMP) exhibits a thermoreversible change in crystal polymorph at a temperature T _cc below its melting point, T _m. The polymorphic transition corresponds to a sharp increase in rotational disorder around the chain axis as the temperature is increased above T _cc. Saturation of ROMP polynorbornene (PN) to hPN can be achieved through both catalytic and noncatalytic approaches. Here, three different hydrogenation routes were employed on the same precursor polymer: catalytic routes over either supported Pd⁰ or a Ni/Al complex, and noncatalytic saturation with diimide. The different hydrogenation routes result in hPNs with varying degrees of epimerization of the cyclopentylene ring (from cis to trans); these epimerized units are included in the hPN crystals. The crystal structure of the rotationally ordered hPN polymorph, observed below T _cc, changes sharply at low levels of epimerization and then is weakly influenced by further increases in trans content. The stability of the rotationally ordered hPN polymorph decreases with increasing epimerization, as reflected in a reduction of T _cc from 134 °C to 92 °C at 22% epimerization. T _cc is less affected by epimerization than by the inclusion of a similar content of 5‐methylnorbornene units, reflecting the smaller size of the trans defect. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1188–1195     

Hydrogenation of 3d-metal oxide clusters: Effects on the structure and magnetic properties

The geometrical structures and properties of the M₈O₁₂, M₈O₁₂H₈, and M₈O₁₂H₁₂ clusters are explored using density functional theory with the generalized gradient approximation for all 3d-metals M from Sc to Zn. It is found that the geometries and total spin magnetic moments of the clusters depended strongly on the 3d-atom type and the hydrogenation extent. More than the half of all of the 30 clusters had singlet lowest total energy states, which could be described as either nonmagnetic or antiferromagnetic. Hydrogenation increases the total spin magnetic moments of the M₈O₁₂H₁₂ clusters when MMn Ni, which become larger by four Bohr magneton than those of the corresponding unary clusters M₈. Hydrogenation substantially affects such properties as polarizability, forbidden band gaps, and dipole moments. Collective superexchange where the local total spin magnetic moments of two atom squads are coupled antiparallel was observed in antiferromagnetic singlet states of Fe₈O₁₂H₈ and Co₈O₁₂H₈, whereas the lowest total energy states of their neighbors Mn₈O₁₂H₈ and Ni₈O₁₂H₈ are ferrimagnetic and ferromagnetic, respectively. Hydrogenation leads to a decrease in the average binding energy per atom when moving across the 3d-metal atom series. © 2018 Wiley Periodicals, Inc.     

凹凸棒石负载Cu-Fe-Co基催化剂组合体系用于CO加氢制备低碳醇

采用浸渍法(IM)和浸渍燃烧法(IMSC)制备了凹凸棒石(ATP)及凹凸棒石-多孔硅胶微球混合物(ATPS)负载CuFe-Co基改性费托催化剂,通过N_2吸附-脱附、X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电镜(SEM)、透射电镜(TEM)、H_2-程序升温还原(H_2-TPR)和CO_2-程序升温脱附(CO_2-TPD)等手段对催化剂进行了表征,并将它们应用于CO加氢制备低碳醇反应。结果表明,IMSC较IM制备催化剂更有利于CuO的负载、分散和还原,促进H_2和CO与Cu活性位的接触,但两者的最佳低碳醇合成温度均为280℃。通过对ATP和ATPS负载Cu-Fe-Co基催化剂(CFCK/ATP、CFCK/ATPS)与Cu/ZnO/Al_2O_3(CZA)甲醇催化剂的组合体系的优化,获得较理想的低碳醇合成催化剂组合体系CZA║CFCK/ATPS-IMSC。利用它们之间的"产物转化耦合效应",实现CO转化率为46.3%,低碳醇选择性为39.6%,C_(2+)醇含量为22.7%。     

Bio‐Inspired Transition Metal–Organic Hydride Conjugates for Catalysis of Transfer Hydrogenation: Experiment and Theory

Taking inspiration from yeast alcohol dehydrogenase (yADH), a benzimidazolium (BI⁺) organic hydride‐acceptor domain has been coupled with a 1,10‐phenanthroline (phen) metal‐binding domain to afford a novel multifunctional ligand ( L ^BI+) with hydride‐carrier capacity ( L ^BI++H^?? L ^BIH). Complexes of the type [Cp*M( L ^BI)Cl][PF₆]₂ (M=Rh, Ir) have been made and fully characterised by cyclic voltammetry, UV/Vis spectroelectrochemistry, and, for the Ir^III congener, X‐ray crystallography. [Cp*Rh( L ^BI)Cl][PF₆]₂ catalyses the transfer hydrogenation of imines by formate ion in very goods yield under conditions where the corresponding [Cp*Ir( L ^BI)Cl][PF₆] and [Cp*M(phen)Cl][PF₆] (M=Rh, Ir) complexes are almost inert as catalysts. Possible alternatives for the catalysis pathway are canvassed, and the free energies of intermediates and transition states determined by DFT calculations. The DFT study supports a mechanism involving formate‐driven Rh?H formation (90 kJ mol^?1 free‐energy barrier), transfer of hydride between the Rh and BI⁺ centres to generate a tethered benzimidazoline (BIH) hydride donor, binding of imine substrate at Rh, back‐transfer of hydride from the BIH organic hydride donor to the Rh‐activated imine substrate (89 kJ mol^?1 barrier), and exergonic protonation of the metal‐bound amide by formic acid with release of amine product to close the catalytic cycle. Parallels with the mechanism of biological hydride transfer in yADH are discussed.     

Alkyne hydrogenation using Pd–Ag hybrid nanocatalysts in surface‐immobilized dendrimers

A series of Pd–Ag mixed‐metal nanocatalysts were prepared by reduction of Pd–Ag salts in the presence of poly(propylene imine) dendrimers, which were covalently bound to the surface of a silica polyamine composite, BP‐1 (polyallylamine covalently bound to a silanized amorphous silica gel). Three different Pd‐to‐Ag ratios were evaluated (50:50, catalyst 1 ; 40:60, catalyst 2 ; 60:40, catalyst 3 ) with the goal of determining how the amount of Ag effects selectivity, rate and conversion in the selective reduction of alkynes, such as phenylacetylene and 1‐ or 4‐octyne, to the corresponding alkenes. Conditions for the catalysis are reported where there is improved selectivity without a serious reduction in rate when compared with the analogous Pd‐only catalysts. Catalyst 2 worked best for phenylacetylene and catalyst 3 worked best for the octynes. The catalysts could be reused seven times without loss of activity. Copyright © 2015 John Wiley & Sons, Ltd.