Catalysis of cyclohexane oxidation with air using various chitosan-supported metallotetraphenylporphyrin complexes

Three types of chitosan-supported metallotetraphenylporphyrins were prepared at room temperature by loading iron, cobalt and manganese tetraphenylporphyrins (TPP) onto chitosan. These were employed as catalysts for the aerobic oxidation of cyclohexane in the absence of additives and solvents. Three chitosan-supported and three simple metallotetraphenylporphyrins (MTPPs) showed different catalytic activity for the oxidation of cyclohexane. Under optimum reaction conditions of 418 K and 0.8 MPa, both the cobalt TPP and the corresponding chitosan-supported complex showed the highest catalytic activity, but lower ketone and alcohol selectivity. The reverse situation was observed for the iron TPP and the corresponding chitosan-supported complex. For cyclohexane oxidation, there was a difference in catalytic activity and ketone and alcohol selectivity between the simple MTTPs or the corresponding chitosan-supported complexes. These differences in catalysis probably result from two factors: the potential for O₂ activation of the different bivalent metal ions, which affects the activity of the corresponding chitosan-supported MTPPs and chitosan assistance of the MTPP catalysis.     

Hydrogenation of imines by rhodium-phosphine complexes

The hydrogenation of imines using RhCl(PPh₃)₃ and [Rh(PPh₃)₂(diene)]PF₆ as catalyst precursors is effective at room temperature under 1 atm of hydrogen, using alcohols as solvents. A water-diethylether phase-transfer system has been used for a solid imine. A catalytic cycle featuring hydrogen bonding between a coordinated alcohol and an imine, and involving a dialkylamido intermediate, is proposed.     

Pt-Sn/γ-Al2O3-catalyzed highly efficient direct synthesis of secondary and tertiary amines and imines

Versatile syntheses of secondary and tertiary amines by highly efficient direct N‐alkylation of primary and secondary amines with alcohols or by deaminative self‐coupling of primary amines have been successfully realized by means of a heterogeneous bimetallic Pt–Sn/γ‐Al₂O₃ catalyst (0.5 wt % Pt, Pt/Sn molar ratio=1:3) through a borrowing‐hydrogen strategy. In the presence of oxygen, imines were also efficiently prepared from the tandem reactions of amines with alcohols or between two primary amines. The proposed mechanism reveals that an alcohol or amine substrate is initially dehydrogenated to an aldehyde/ketone or NH‐imine with concomitant formation of a [PtSn] hydride. Condensation of the aldehyde/ketone species or deamination of the NH‐imine intermediate with another molecule of amine forms an N‐substituted imine which is then reduced to a new amine product by the in‐situ generated [PtSn] hydride under a nitrogen atmosphere or remains unchanged as the final product under an oxygen atmosphere. The Pt–Sn/γ‐Al₂O₃ catalyst can be easily recycled without Pt metal leaching and has exhibited very high catalytic activity toward a wide range of amine and alcohol substrates, which suggests potential for application in the direct production of secondary and tertiary amines and N‐substituted imines.     

Imine-bridged periodic mesoporous organosilica as stable high-activity catalytic for Knoevenagel reaction in aqueous medium

An imine-functionalized mesoporous solid base catalyst (BA@BE-PMO) was prepared by template agent-directed self-assembly condensation of bis[3-(triethoxysilyl)propyl]amine and 1,2-bis(triethoxysilyl)ethane in acid solution. The imine groups with catalytic activity were integrally embedded into mesopore walls of as-made BA@BE-PMO. In Knoevenagel reactions in aqueous medium, the BA@BE-PMO catalyst exhibited better catalytic activity than imine-functionalized SBA-15 catalyst synthesized using the traditional co-condensation method, which can be attributed to the pore surface with strong hydrophobicity originating from –CH₂CH₂– group fragments incorporated into pore walls. The strong hydrophobicity of the surface facilitates adsorption and diffusion of organic compounds on the catalyst surface in reactions in aqueous medium. Moreover, it exhibited comparable catalytic activity to dipropylamine homogeneous base catalyst because of the uniform dispersion of imine group active sites. The BA@BE-PMO catalyst could also be recovered and reused in up to five runs without significant loss in activity without any negative environmental impact.

     

A computational investigation of the hydrogenation of imines catalyzed by rhodium thiolate complexes

The mechanism of imine hydrogenation catalyzed by thiolate complexes of Rh(III) bearing a hydrotris(3,5‐dimethylpyrazolyl)borato ligand has been investigated via the density functional theory calculations. The overall catalytic cycle for heterolytic cleavage of H₂ and hydrogenation of N‐benzylidenemethylamine by the model catalyst [TpRh(bdt)MeCN)] is presented in detail. The results show that the reaction proceeds via an ionic mechanism through three steps: formation of dihydrogen complex, protonation of imine and the hydride transfer process. Protonation of imine occurs after the formation of Rh(H)‐S(H) moiety. For the whole catalytic cycle, the heterolytic splitting of dihydrogen is the step with the highest free energy barrier. © 2014 Wiley Periodicals, Inc.     

The Aza‐Morita–Baylis–Hillman Reaction: A Mechanistic and Kinetic Study

The aza‐Morita‐Baylis–Hillman (aza‐MBH) reaction has been studied in a variety of solvents, a selection of imine substrates and with various combinations of PPh₃ and para‐nitrophenol as the catalyst system. The measured kinetic data indicates that the effects of solvent and protic co‐catalyst are strongly interdependent. These results are most easily reconciled with a mechanistic model involving the reversible protonation of zwitterionic intermediates in the catalytic cycle, which is also supported by ³¹P NMR spectroscopy and quantum chemical studies.     

羧基亚胺配体的合成及其促进Suzuki偶联反应的研究

合成了4种羧基亚胺配体并将其用于促进Suzuki偶联反应。通过考察配体结构、溶剂极性、碱强度和温度等因素对反应产率的影响,确定了羧基亚胺配体参与的钯催化Suzuki偶联反应的最佳条件为:催化剂的量为0.001(mol)%的Pd Cl2和0.002(mol)%的配体,以碳酸钾作碱,4m L乙醇水溶液(1∶1,体积比)作溶剂,反应温度为60℃,在空气条件下反应。结果表明,羧基亚胺配体能够有效促进Suzuki偶联反应;在合成的配体L1~L4中,具有适当的位阻和给电子基团的L2的催化活性最高,能够高效催化合成一系列联芳类化合物。     

Preparation,characterization and catalytic application of PdPt bimetallic nanoparticles stabilized by 15‐membered triolefinic macrocycle‐terminated poly(propylene imine) dendrimer

PdPt bimetallic nanoparticles stabilized by 15‐membered triolefinic macrocycle‐stabilized poly(propylene imine) dendrimer (G3‐M(Pd_x Pt_10−x ) DSNs) have been prepared via synthesis of a 15‐membered triolefinic macrocycle‐modified third‐generation poly(propylene imine) dendrimer (G3‐M) and then synchronous ligand exchange with Pd(PPh₃)₄/Pt(PPh₃)₄ complexes. The structure and catalytic activity of the DSNs were characterized using Fourier transform infrared, ¹H NMR, transmission electron microscopy, energy‐dispersive X‐ray and X‐ray photoelectron analyses. As a novel catalyst system, it can be concluded that the composition of the bimetallic nanoparticles has an influence on the catalytic activity of the hydrogenation reaction of acrylonitrile–butadiene rubber, which can be related to synergistic effect. Furthermore, the selectivity and recyclability of G3‐M(Pd_x Pt_10−x ) DSN catalyst are also discussed.     

Pd/C促进的四氢异喹啉高选择性部分脱氢(英文)

采用K3PO4?3H2O修饰的Pd/C为催化剂实现了取代四氢异喹啉高选择性部分脱氢,并成功地避免了当量有害氧化剂的使用.多相催化剂Pd/C对四氢异喹啉化合物具有催化脱氢活性,但反应选择性较差,同时产生完全脱氢的芳构化产物异喹啉.而K3PO4?3H2O修饰的Pd/C催化剂能有效提高脱氢反应的化学选择性,在最优条件下可获得最高89%的分离收率.这为取代3,4-二氢异喹啉的合成提供了一种简便、高原子经济性和高化学选择性的反应途径.此外,该多相催化剂可回收循环使用多次,且活性和选择性基本保持不变.     

“One pot” synthesis of tertiary amines: Ru(II) catalyzed direct reductive N-benzylation of imines with benzyl bromide derivatives

The direct reductive N-benzylation of imines by reaction with benzyl bromide derivatives, in the presence of [RuCl₂(p-cymene)]₂ catalyst and PhSiH₃, is performed under mild conditions without additional base. This reaction proceeds by a tandem imine hydrosilylation/nucleophilic substitution with benzyl bromide derivatives to result the tertiary amines.     

Cationic Aluminium Complexes as Catalysts for Imine Hydrogenation

Strongly Lewis acidic cationic aluminium complexes, stabilized by β–diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C₆F₅)₄⁻ salts and were investigated for catalytic activity in imine hydrogenation. The backbone (R1) and N (R2) substituents on the ^R1,R2BDI ligand (^R1,R2BDI=HC[C(R1)N(R2)]₂) influence sterics and Lewis acidity. Ligand bulk increases along the row ^Me,DIPPBDI<^Me,DIPePBDI≈^tBu,DIPPBDI<^tBu,DIPePBDI; DIPP=2,6-C(H)Me₂-phenyl, DIPeP=2,6-C(H)Et₂-phenyl. The Gutmann-Beckett test showed acceptor numbers of: (^tBu,DIPPBDI)AlMe⁺ 85.6, (^tBu,DIPePBDI)AlMe⁺ 85.9, (^Me,DIPPBDI)AlMe⁺ 89.7, (^Me,DIPePBDI)AlMe⁺ 90.8, (^Me,DIPPBDI)AlH⁺ 95.3. Steric and electronic factors need to be balanced for catalytic activity in imine hydrogenation. Open, highly Lewis acidic, cations strongly coordinate imine rendering it inactive as a Frustrated Lewis Pair (FLP). The bulkiest cations do not coordinate imine but its combination is also not an active catalyst. The cation (^tBu,DIPPBDI)AlMe⁺ shows the best catalytic activity for various imines and is also an active catalyst for the Tishchenko reaction of benzaldehyde to benzylbenzoate. DFT calculations on the mechanism of imine hydrogenation catalysed by cationic Al complexes reveal two interconnected catalytic cycles operating in concert. Hydrogen is activated either by FLP reactivity of an Al⋅⋅⋅imine couple or, after formation of significant quantities of amine, by reaction with an Al⋅⋅⋅amine couple. The latter autocatalytic Al⋅⋅⋅amine cycle is energetically favoured.     

Chitosan-supported palladium(0) catalyst for microwave-prompted Suzuki cross-coupling reaction in water

A chitosan-supported palladium (Pd) (0) catalyst was prepared by simple adsorption of palladium(II) ion onto chitosan beads and a subsequent reduction process. To maintain mechanical stability, the chitosan-supported palladium(0) catalyst was cross-linked with either glutaraldehyde or diglycidyl ether polyethylene glycol. The catalysts were utilized for the Suzuki cross-coupling reaction in water. The catalyst, in the presence of a tetrabutylammonium bromide (TBAB) additive, showed excellent catalytic activity in microwave-prompted Suzuki cross-coupling reactions using various aryl halides and boronic acids. In addition, the catalyst was successfully reused up to five times without significant loss of catalytic activity.     

The study of Friedel-Crafts alkylation reaction of thiophenes with glyoxylate imine catalyzed by Fe(III): an easy access to α-aminoesters

A Friedel-Crafts alkylation reaction of thiophenes with glyoxylate imine was developed to give α-aminoesters. In the presence of FeCl₃·6H₂O as the catalyst, various α-aminoesters were prepared with moderate to high yields (up to 95%) except for some special substrates.     

Imine hydrosilylation using an iron complex catalyst: A computational study

The reaction mechanism for imine hydrosilylation in the presence of an iron methyl complex and hydrosilane was studied using density functional theory at the M06/6-311G(d,p) level of theory. Benzylidenemethylamine (PhCH = NMe) and trimethylhydrosilane (HSiMe₃) were employed as the model imine and hydrosilane, respectively. Hydrosilylation has been experimentally proposed to occur in two stages. In the first stage, the active catalyst (CpFe(CO)SiMe₃, 1 ) is formed from the reaction of pre-catalyst, CpFe(CO)₂Me, and hydrosilane through CO migratory insertion into the Fe Me bond and the reaction of the resulting acetyl complex intermediate with hydrosilane. In the second stage, 1 catalyzes the reaction of imine with hydrosilane. Calculations for the first stage showed that the most favorable pathway for CO insertion involved a spin state change, that is, two-state reactivity mechanism through a triplet state intermediate, and the acetyl complex reaction with HSiMe₃ follows a σ-bond metathesis pathway. The calculations also showed that, in the catalytic cycle, the imine coordinates to 1 to form an Fe C N three-membered ring intermediate accompanied by silyl group migration. This intermediate then reacts with HSiMe₃ to yield the hydrosilylated product through a σ-bond metathesis and regenerate 1 . The rate-determining step in the catalytic cycle was the coordination of HSiMe₃ to the three-membered ring intermediate, with an activation energy of 23.1 kcal/mol. Imine hydrosilylation in the absence of an iron complex through a [2 + 2] cycloaddition mechanism requires much higher activation energies. © 2018 Wiley Periodicals, Inc.     

Syntheése d′Imines Polyfluorées (R) (RF) C = NR′

Primary amines R′eNH₂ react with hemifluorinated ketones R-CO-R_F to give the corresponding polyfluorinated imines (R) (RF) C - NR′ in good yields. By means of ¹⁹F NMR, it is shown that the imine formation involves a gem-aminoalcohol intermediate, which spontaneously dehydrates without any catalyst.     

Insights into LiAlH4 Catalyzed Imine Hydrogenation

Commercial LiAlH₄ can be used in catalytic quantities in the hydrogenation of imines to amines with H₂. Combined experimental and theoretical investigations give deeper insight in the mechanism and identifies the most likely catalytic cycle. Activity is lost when Li in LiAlH₄ is exchanged for Na or K. Exchanging Al for B or Ga also led to dramatically reduced activities. This indicates a heterobimetallic mechanism in which cooperation between Li and Al is crucial. Potential intermediates on the catalytic pathway have been isolated from reactions of MAlH₄ (M=Li, Na, K) and different imines. Depending on the imine, double, triple or quadruple imine insertion has been observed. Prolonged reaction of LiAlH₄ with PhC(H)=NtBu led to a side-reaction and gave the double insertion product LiAlH₂[N]₂ ([N]=N(tBu)CH₂Ph) which at higher temperature reacts further by ortho-metallation of the Ph ring. A DFT study led to a number of conclusions. The most likely catalyst for hydrogenation of PhC(H)=NtBu with LiAlH₄ is LiAlH₂[N]₂. Insertion of a third imine via a heterobimetallic transition state has a barrier of +23.2 kcal mol⁻¹ (ΔH). The rate-determining step is hydrogenolysis of LiAlH[N]₃ with H₂ with a barrier of +29.2 kcal mol⁻¹. In agreement with experiment, replacing Li for Na (or K) and Al for B (or Ga) led to higher calculated barriers. Also, the AlH₄⁻ anion showed very high barriers. Calculations support the experimentally observed effects of the imine substituents at C and N: the lowest barriers are calculated for imines with aryl-substituents at C and alkyl-substituents at N.     

氧化铝负载的银纳米颗粒高选择性催化合成亚胺(英)

The oxidative dehydrogenation of alcohols to aldehydes catalyzed by Ag nanoparticles supported on Al₂O₃ was studied.The catalyst promoted the direct formation of imines by tandem oxidative dehydrogenation and condensation of alcohols and amines.The reactions were performed under mild conditions and afforded the imines in high yield（up to 99%） without any byproducts other than H₂O.The highest activity was obtained over 5 wt%Ag/Al₂O₃ in toluene with air as oxidant.The reactions were also performed under oxidant-free conditions where the reaction was driven to the product side by the production of H₂ in the gas phase.The use of an efficient and selective Ag catalyst for the oxidative dehydrogenation of alcohol in the presence of amines gives a new green reaction protocol for imine synthesis.     

Selective Production of Secondary Amine by the Photocatalytic Cascade Reaction Between Nitrobenzene and Benzyl Alcohol over Nanostructured Bi2MoO6 and Pd Nanoparticles Decorated with Bi2MoO6

The synthesis of secondary amine by the photoalkylation of nitrobenzene with benzyl alcohol using a simple light source and sunlight is a challenging task. Herein, a one-pot cascade protocol is employed to synthesize secondary amine by the reaction between nitrobenzene and benzyl alcohol. The one-pot cascade protocol involves four reactions: (a) photocatalytic reduction of nitrobenzene to aniline, (b) photocatalytic oxidation of benzyl alcohol to benzaldehyde, (c) reaction between aniline and benzaldehyde to form imine, and (d) photocatalytic reduction of imine to a secondary amine. The cascade protocol to synthesize secondary amine is accomplished using Bi₂MoO₆ and Pd nanoparticles decorated Bi₂MoO₆ catalysts. The surface characteristics, oxidation states, and elemental compositions of the materials are characterized by several physicochemical characterization techniques. Optoelectronic and photoelectrochemical measurements are carried out to determine the bandgap, band edge potentials, photocurrents, charge carrier's separation, etc. An excellent yield of secondary amine is achieved with simple household white LED bulbs. The catalyst also exhibits similar or even better activity in sunlight. The structure-activity relationship is established using catalytic activity data, control reactions, physicochemical, optoelectronic characteristics, and scavenging studies. Bi₂MoO₆ and Pd nanoparticles decorated Bi₂MoO₆ exhibit excellent photostability and recyclability. The simple catalyst design with a sustainable and economical light source for the synthesis of useful secondary amine from the nitrobenzene and benzyl alcohol would attract the researchers to develop similar catalytic protocols for other industrially important chemicals.     

Low density polyethylene by tandem catalysis with single site Ti(IV)/Co(II) catalysts

A variety of branched polyethylenes (PE), ranging from semicrystalline linear low density polyethylene to completely amorphous low density polyethylene and rubbery PE, can be produced from ethylene alone by tandem catalysis using as oligomerization catalysts the (imino)pyridyl Co(II) complexes N^BTCoCl₂ (1) ({6-(benzo[b]thiophen-2-yl)-2-(imine)pyridyl)}CoCl₂), N^ETCoCl₂ (2) ({6-(4-ethylthiophen-2-yl)-2-(imine)pyridyl)}CoCl₂), or N^PhCoCl₂ (3) ({6-(phenyl)-2-(imine)pyridyl)}CoCl₂) and as a copolymerization catalyst [η⁵-C₅Me₄)SiMe₂(t-BuN)]TiCl₂ (4). The catalytic activity of the systems 1/4/MAO, 2/4/MAO, and 3/4/MAO has been evaluated under comparable experimental conditions (T = 30°C, [ethylene] = 0.35 mol/l), varying the molar fraction of the cobalt precursors. A positive comonomer effect was observed for all the systems investigated. The maximum productivity (4570 kg PE (mol Ti)⁻¹ h⁻¹) was obtained for the benzothiophenyl-substituted cobalt complex. An effective control of the branching in the polymer backbone was achieved by varying either the oligomerization catalyst or its molar fraction. Completely amorphous materials with T _g as low as-60°C could be obtained. The text was submitted by the authors in English.     

Production of Primary Amines by Reductive Amination of Biomass‐Derived Aldehydes/Ketones

Transformation of biomass into valuable nitrogen‐containing compounds is highly desired, yet limited success has been achieved. Here we report an efficient catalyst system, partially reduced Ru/ZrO₂, which could catalyze the reductive amination of a variety of biomass‐derived aldehydes/ketones in aqueous ammonia. With this approach, a spectrum of renewable primary amines was produced in good to excellent yields. Moreover, we have demonstrated a two‐step approach for production of ethanolamine, a large‐market nitrogen‐containing chemical, from lignocellulose in an overall yield of 10 %. Extensive characterizations showed that Ru/ZrO₂‐containing multivalence Ru association species worked as a bifunctional catalyst, with RuO₂ as acidic promoter to facilitate the activation of carbonyl groups and Ru as active sites for the subsequent imine hydrogenation.