Catalytic Asymmetric Heterogeneous Aziridination Using CuHY/bis(oxazoline): Effect of Reaction Conditions on Enantioselectivity

The copper-catalyzed aziridination of styrene with copper-exchanged zeolite HY (CuHY) and copper(II) triflate (trifluoromethanesulfonate) (Cu(OTf)₂) as catalysts is described using N-(p-tolylsulfonyl)imino]phenyliodinane (PhI=NTs) as the nitrene donor. The effects on the ee and yield of the aziridine when the catalyst is modified by the presence of a chiral bis(oxazoline) are investigated in detail. The heterogeneously catalyzed reaction under these conditions shows a slight, but significant, enhancement in ee with increasing conversion at 25 °C. This is not observed in the more rapid homogeneously catalyzed reaction under identical reaction conditions using PhINTs as the nitrene donor. The enhancement in ee is proposed to result from the preferential reaction of the (S)-aziridine with the Cu²⁺:bis(oxazoline) complex in the presence of PhI=NTs, leading to an enhancement of the (R)-aziridine in the remaining aziridine product.     

Heterogeneous Catalytic Sulfimidation using Immobilized Cu(acac)2

The heterogeneous sulfimidation of various sulfides by microencapsulated copper(II) acetylacetonate, [MC‐Cu(acac)₂], and Cu(acac)₂ immobilized in ionic liquids using [N‐(p‐tolylsulfonyl)imino]phenyliodinane (PhINTs) as nitrene donor has been developed to afford the corresponding sulfimides in good to excellent yields. In the presence of a chiral bis(oxazoline) as ligand, asymmetric induction occurs to afford the chiral sulfimides (up to 50% ee). The ionic liquid containing the immobilized bis(oxazoline)‐copper catalyst can be reused for several cycles with consistent activity and enantioselectivity.     

Nanostructured biomimetic catalysts for asymmetric hydrogenation of enamides using molecular imprinting technology

A new class of heterogeneous catalysts for asymmetric hydrogenation of enamides was synthesized using molecular imprinting technology. These new catalysts are molecularly imprinted polymers (MIPs) made from rhodium (I) and copper (II) complexes with the bis(oxazoline) chiral ligands. One of the Rh-MIPs showed 87% ee toward L-enantiomeric product while the Cu-MIP showed 82% ee toward D-enantiomeric product. Both MIPs are easy to separate and reusable.     

新的手性膦配体的合成及其在苯乙烯不对称氢甲酰化反应中的应用

以甘露醇为原料合成了两个新的手性膦配体,并用这些新的手性膦配体和醋酸钯原位生成的催化剂体系催化苯乙烯的不对称氢甲酰化反应,当配体为手性膦氧配体(DDPPIO)时得到S构型的2-苯基丙醛的e.e.为21.9％,用手性膦硫配体(DDPPIS)作配体时得到S构型的2-苯基丙醛的e.e.11.2％。     

Remarkable Efficiency Improvement in the Preparation of Insoluble Polymer‐Bound (IPB) Enantioselective Catalytic Systems by the Use of Silicone Chemistry

The use of platinum‐catalyzed hydrosilylation chemistry of silicones greatly simplifies the preparation of bis‐oxazoline (box) ligands covalently bound to an insoluble polymeric support. The use of such immobilized chiral ligands in different copper‐catalyzed asymmetric transformations (carbonyl‐ene, Mukaiyama aldol and olefin cyclopropanation reactions) allows the attainment of high levels of enantioselectivity (91–99 % ee).     

Heterogeneous Enantioselective Synthesis of a Dihydropyran Using Cu-Exchanged Microporous and Mesoporous Materials Modified by Bis(oxazoline)

The formation of dihydropyran from the Diels–Alder reaction between E-ethyl-2-oxo-3-pentenonate and vinyl ethyl ether is investigated using copper (II) bis(oxazoline) as catalyst. The homogeneously and heterogeneously catalyzed reactions are contrasted. Immobilization using mesoporous materials (Cu-MCM-41, Cu-AlSBA-15, Cu-MSU-2) and zeolite Y is found to produce an effective heterogeneous catalyst. Although the level of enantioselection is not high in this initial study, the CuH-zeolite Y/bis(oxazoline) catalyst gives the highest ee (41% ee), which is significantly higher than that observed for the Cu(OTf)₂ homogeneous catalyst (20% ee) under comparable conditions. In addition, with the heterogeneously catalyzed reaction, the enantioselection changes from the initial 2R,4S product to the 2S,4R diastereoisomer. This behavior is not observed with the homogeneously catalyzed reaction, which always yields the 2R,4S product. These results are discussed in terms of the confinement of the catalyst complex within the pores of the heterogeneous catalyst.     

Organofunctionalized catalyst surfaces highly active and selective for carbon–carbon bond-forming reactions

This article illustrates two types of organofunctionalized heterogeneous catalysts for variety of organic carbon–carbon bond-forming reactions, summarizing our previous reports and also presenting new data. Organic amines with an alkoxysilane moiety were immobilized on inorganic silica-alumina surfaces (SA-NR₂) by simple silane-coupling reactions between the silica-alumina surface (SA) and the alkoxysilane. This SA-NR₂ acted as acid–base bifunctional heterogeneous catalysts for carbon–carbon bond-forming reactions, such as cyano-ethoxycarbonylation, Michael reaction of nitriles, and nitro-aldol reaction. These reactions did not occur with either SA or homogeneous amine compounds. In addition, the mixture of SA and homogeneous amine showed low catalytic activity due to undesirable acid–base neutralization reaction. Achiral organic silane-coupling reagents with a variety of functional groups were also immobilized on a SiO₂ surface that had been immobilized with chiral bis(oxazoline) (BOX), to which Cu ions were coordinated to make chiral Cu–BOX complexes on the SiO₂ surface. The SiO₂-supported Cu–BOX complex catalyst functionalized with achiral 3-methacryloxypropyltrimethoxysilane dramatically increased enantioselectivity in the asymmetric Diels–Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone. The organofunctionalized catalysts showed much better performances for the C–C bond-forming reactions compared to the corresponding homogeneous systems. The heterogeneous catalysts thus obtained were characterized by solid-state ¹³C and ²⁹Si MAS NMR, FT-IR, UV/vis, XAFS, ESR, XRF, and elemental analysis.     

脂肪二酸类手性双(口恶)唑啉配体的合成进展

总结了近年来用于不对称催化的脂肪二酸类手性双噁唑啉配体的合成方法,该类配体可由丙二酸、乙二酸与丁二酸的酰氯和二酯或二元腈与相应的氨基醇反应得到。     

Non-covalent immobilization of chiral copper complexes on Al-MCM41: Effect of the nature of the ligand

Cu-Al-MCM41, prepared by deposition of copper(II) triflate with incipient wetness impregnation and thermal treatment under air flow, can be modified with different chiral ligands of the bis(oxazoline) family. The efficiency of the supported chiral catalysts in the enantioselective cyclopropanation of styrenes with ethyl diazoacetate depends on the nature of the ligand. The azabis(oxazolines) perform much better than the bis(oxazolines) and give stable catalysts that can be used for at least five consecutive runs, with productivities that can reach values close to 1000 molecules of cyclopropane per copper site. The best enantioselectivities obtained with these catalysts are in the range of 60–70% ee in the reaction at 90 °C.     

Ethylene polymerization with homogeneous and heterogeneous catalysts based on bis(4‐fluorophenyl)methyl‐substituted bis(imino)pyridyliron complexes

A series of bis(4‐fluorophenyl)methyl‐substituted bis(imino)pyridyliron chloride complexes were immobilized on oxide supports. The kinetics of ethylene polymerization by both homogeneous and heterogeneous systems was followed, the catalysts mostly demonstrating high activities. The effect of the ligands nature and reaction conditions on the catalytic activities and molecular weights of the resultant polyethylenes was examined. In contrast to homogeneous systems, the supported iron complexes were found to exhibit high and stable activity upon activation with triisobutyl aluminium, producing high‐molecular‐weight polyethylene with good morphology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42674.     

Chiral bis(oxazoline) copper(II) complexes: versatile catalysts for enantioselective cycloaddition, Aldol, Michael, and carbonyl ene reactions

A bis(oxazoline) (box) copper(II) complex and its hydrated counterpart (1 and 2) function as enantioselective Lewis acid catalysts for carbocyclic and hetero Diels-Alder, aldol, Michael, ene, and amination reactions with substrates capable of chelation through six- and five-membered rings. X-ray crystallography of the chiral complexes reveals a propensity for the formation of distorted square planar or square pyramidal geometries. The sense of asymmetric induction is identical for all the processes catalyzed by [Cu((S,S)-t-Bu-box)](X)(2) complexes 1 and 2 (X = OTf and SbF) resulting from the intervention of a distorted square planar catalyst-substrate binary complex. These catalyzed processes exhibit excellent temperature-selectivity profiles. Reactions catalyzed by [Cu(S,S-Ph-pybox)](SbF(6))(2) and their derived chelation complexes are also discussed.     

Synthesis of condensation polymers catalyzed by palladium-graphite

Palladium-graphite (Pd---Gr) was applied to polycondensations as a heterogeneous palladium catalyst. Catalytic activities of Pd---Gr for the Heck reaction and a carbonyl insertion reaction were investigated using the model reactions. Polycinnamamide was synthesized through the Heck reaction of N, N′-(3,4′-oxydiphenylene)bis(acrylamide) and bis(4-iodophenyl) ether catalyzed by Pd---Gr. The polymerization proceeded efficiently in the presence of tributylamine, but required a long reaction time compared with the case of homogeneous catalysts. The resulting polymer was almost white in color, which means that it was less contaminated by palladium metal. The removal and recycling of Pd---Gr were much easier than the case of homogeneous catalysts. Aramid was also synthesized through the carbonyl insertion reaction of m-diiodobenzene and bis(4-aminophenyl) ether catalyzed by Pd---Gr. The rate of carbon monoxide consumption for the polymerization catalyzed by Pd---Gr was almost equal to that catalyzed by the homogeneous palladium catalyst. In both cases, the structures of the resulting polymers were identical to those prepared by homogeneous palladium catalysts.     

Self-supported chiral catalysts for heterogeneous asymmetric catalysis

A conceptually new strategy for chiral catalyst immobilization, self-supported catalysts, in heterogeneous asymmetric catalysis is highlighted in the present article. Various homochiral metal-organic polymers with diverse structures have been designed and readily prepared through coordination assembly of modular polytypic/polyfunctional ligands and metal ions without using any supports. These polymers have been successfully employed as chiral catalysts in a variety of heterogeneous asymmetric ractions, including hydrogenation, epoxidation, sulfoxidation, carbonyl-ene reactions, diethylzinc addition, and Michael addition. The self-supported heterogeneous chiral catalysts showed activity and enanioselectivity comparable or even superior to those obtained with their corresponding homogeneous counterparts, and could be readily recovered and reused several times without significant loss of activity or enantioslectivity.     

Chiral Bis(N‐sulfonylamino)phosphine‐ and TADDOL‐Phosphite‐Oxazoline Ligands: Synthesis and Application in Asymmetric Catalysis

A series of N,P‐ligands has been prepared, containing a chiral oxazoline ring and as a second chiral unit a bis(N‐sulfonylamino)phosphine group embedded in a diazaphospholidine ring or a cyclic phosphite group derived from TADDOL. These modular ligands are readily synthesized from chiral amino alcohols and chiral 1,2‐diamines or TADDOLs. Palladium and iridium complexes derived from these ligands were found to be efficient catalysts for enantioselective allylic alkylation and olefin hydrogenation, respectively.     

Titanium-catalyzed enantioselective additions of alkyl groups to aldehydes: mechanistic studies and new concepts in asymmetric catalysis

The catalytic asymmetric addition of alkyl groups to aldehydes is an important reaction in the enantioselective synthesis of secondary alcohols. This reaction can be catalyzed by zinc- or titanium-based catalysts. While the mechanism of the zinc/amino alcohol catalysts has received significant attention, the titanium-based catalysts have been less studied. This Account summarizes our mechanistic studies with bis(sulfonamide) and BINOL-derived titanium catalysts. It also describes our use of this reaction in the development of new approaches to asymmetric catalysis, including applications of diastereomeric catalysts and optimization of asymmetric catalysts with achiral and meso ligands.     

多相手性催化剂的制备及其对不对称加氢反应的催化作用

综述了不对称加氢反应中多相手性催化剂的研究进展,包括将均相手性催化剂固定到有机聚合物、磁性的Fe₃O₄纳米颗粒、功能化修饰的分子筛等载体上;直接利用有机金属配合物中的阳离子和分子筛骨架中的阴离子相互作用实现多相化;采用金鸡纳生物碱等手性小分子为修饰剂和天然高分子为手性源制备多相催化剂。同时对不同途径制备的多相手性催化剂的结构特性、催化性能和立体选择性进行了评价。     

Cobalt(II) and nickel(II) complexes bearing mono(imino)pyridyl and bis(imino)pyridyl ligands: preparation,structure and ethylene polymerization/oligomerization behaviors

BACKGROUND: Ethylene oligomerization is the major industrial process to produce linear α‐olefins. Recently much work has been devoted to late transition metal catalysts used in this process, especially those with 2,6‐bis(imino)pyridyl dihalide ligands. Considering that most work has focused on simple modification to the substituents in imino‐aryl rings based on the symmetric bis(imino)pyridyl framework, here we expand this work to the asymmetric mono(imino)pyridyl ligands. RESULTS: The preparation, structure and ethylene polymerization/oligomerization behavior of series of mono(imino) pyridyl–MCl₂ and bis(imino)pyridyl–MX_n complexes are presented. The systematic studies were focused on the relationship between the catalytic behavior of these complexes for ethylene polymerization/oligomerization and reaction conditions, ligand structures, metal centers and counter‐anions. The influence of the coordination environment on catalyst behavior is also discussed. CONCLUSION: For mono(imino)pyridyl–Co(II) and ? Ni(II) catalysts bearing the Cl^? counter‐anion, good activities ranging from 0.513 × 10⁵ to 1.58 × 10⁵ g polyethylene (mol metal)^?1 h^?1 atm^?1 are afforded, and the most active catalysts are those with methyl in both ortho‐ and para‐positions of the imine N‐aryl ring. For bis(imino)pyridyl–Co(II) and ? Ni(II) catalysts bearing the SO₄^2? and NO₃^? counter‐anions, the low activities for ethylene oligomerization are in sharp contrast to those of their chloride analogues. Copyright © 2009 Society of Chemical Industry     

Palladium Nanoparticles in Allylic Alkylations and Heck Reactions: The Molecular Nature of the Catalyst Studied in a Membrane Reactor

A series of palladium nanoparticles stabilized by five chiral sugar‐based oxazolinyl‐phosphite ligands, containing various substituents at the oxazoline and phosphite moieties has been synthesized. They were characterized by transmission electron microscopy (TEM), X‐ray powder diffraction (XRD), infrared spectroscopy (IR) and elemental analysis. These nanoparticles were applied in Pd‐catalyzed asymmetric allylic alkylation and Heck coupling reactions. A detailed study to elucidate the nature of the active species using a continuous‐flow membrane reactor (CFMR), accompanied by TEM observations, classical poisoning experiments, and kinetic measurements have been carried out. Conclusive evidence of the nature of the species involved in the use of PdNPs in asymmetric catalytic reactions has been obtained. The CFMR experiments proved the molecular nature of the true catalysts and all conversions can be justified by the amount of molecular palladium that leached as measured by ICP‐AES.     

Immobilization of new Mn(salen) complex over MCM-41 and its activity in asymmetric epoxidation of styrene

New tetradentate chelates of bis-Schiff bases were synthesized and then these chiral salen ligands were immobilized over mesoporous MCM-41 by using the ion-exchange method. The efficiency of the chiral catalyst was examined in the asymmetric epoxidation of styrene. Chiral Mn(salen) complexes immobilized onto mesoporous MCM-41 were stable during the reaction without any leaching and exhibited relatively high enantioselectivity for epoxidation as compared with homogeneous complexes. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Development of the Asymmetric Nozaki–Hiyama–Kishi Reaction

This review collates the literature to date on the development of the Nozaki–Hiyama–Kishi (NHK) reaction into an important chromium‐mediated, carbon‐carbon bond forming process. The initial research employed stoichiometric quantities of chromium and this was exploited in the key steps of a range of total syntheses. Thereafter, the NHK reaction was further developed with the discovery of the catalytic variant. The focus of recent investigations is on the application of this reaction in asymmetric synthesis. The asymmetric NHK typically employed a range of salen‐ and oxazoline‐derived chiral ligands and tethered bis(8‐quinolinato)‐chromium complexes. To date, good to high enantioselectivities have been obtained in a variety of NHK‐type processes, including allylation, crotylation, methallylation, allenylation, propargylation and vinylation of a range of aldehydes, with limited examples employing ketones as substrates. Selected examples of the asymmetric NHK in total synthesis will also be described.