A Recyclable Heterogeneous Palladium Catalyst Anchored to Modified Metal-Organic Framework for Hydrogenation of Styrene Oxide

A heterogeneous palladium(II) catalyst anchored to modified metal-organic framework has been synthesized and characterized. The performance of the catalyst has been tested for the hydrogenation of styrene oxide at ambient temperature and pressure. The catalyst showed an excellent activity and selectivity for the preparation of 2-phenylethanol from styrene oxide with 100% conversion and 98% selectivity. The catalyst is very stable and easily recyclable for several times without loss of activity.

     

Novel hydrido-ruthenium(II) complexes with histidine derivatives and their application in the hydrogenation of ketones

The complexes RuHCl((R)-binap)(L-NH2) with L-NH2 = (S)-histidine-Me-ester (1), histamine (3), (S)-histidinol (4) or 1-Me-(S)-histidine-Me-ester (5), and RuHCl((S)-binap)(L-NH(2)) with L-NH2 = (S)-histidine-Me-ester (2) have been prepared in 60-81% overall yields in a one-pot, three-step procedure from the precursor RuCl2(PPh3)3. Their octahedral structures with hydride trans to chloride were deduced from their NMR spectra and confirmed by the results of a single crystal X-ray diffraction study for complex 3. Under H2 and in the presence of KOtBu, complexes 1-5 in 2-propanol form moderately active catalyst precursors for the asymmetric hydrogenation of acetophenone to 1-phenylethanol. Complex 5 is more active and enantioselective than complexes 1-4, allowing complete conversion to 1-phenylethanol in 46% e.e. (R) in 72 h at 20 degrees C under 1 MPa of H2 with substrate : catalyst : base = 2000 : 1 : 30. Complex 5, when activated, also catalyzes the hydrogenation of trans-4-phenyl-3-buten-2-one to exclusively the allyl alcohol 4-phenyl-3-buten-2-ol under 2.7 MPa of H2 at 50 degrees C in 2-propanol. This selectivity for C=O versus C=C hydrogenation is consistent with a mechanism involving the outer sphere transfer of hydride and proton to the polar bond. Further extensions to complexes with peptides with N-terminal histidine groups appear feasible on the basis of the current work.     

Mechanism of the chemo–bio catalyzed cascade synthesis of <Emphasis Type="Italic">R</Emphasis>-1-phenylethyl acetate over Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, lipase,and Ru-catalysts

One-pot synthesis of R-1-phenylethyl acetate was investigated starting from acetophenone hydrogenation performed over Pd/Al₂O₃ and PdZn/Al₂O₃ catalysts followed by acylation of the intermediate secondary alcohol, R-1-phenylethanol, over an immobilized lipase. Furthermore, the performance of a third type of catalyst, Ru supported on hydroxyapatite (HAP) was evaluated for racemization of S-1-phenylethanol in one pot together with the two other catalysts. The main objectives of this work were to separate the effects of different catalysts and to reveal the reaction mechanism. For this purpose not only acetophenone, but also (R,S)-1-phenylethanol, S-1-phenylethanol, R-1-phenylethyl acetate, and styrene were used as reactants in combination with Pd/Al₂O₃, lipase and Ru/HAP as catalysts. The results revealed that the main side product, ethylbenzene, was formed in two different ways, via dehydration of (R,S)-1-phenylethanol to styrene, followed by its rapid hydrogenation to ethylbenzene, and via debenzylation of the desired product, R-1-phenylethyl acetate to ethylbenzene. The true one-pot synthesis, however, was demonstrated over Shvo’s catalyst, but Ru/HAP was not sufficiently active in the racemization step. Ru/Al₂O₃ was a promising catalyst for racemization of S-1-phenylethanol and for dynamic kinetic resolution of (R,S)-1-phenylethanol, when using only small amounts of the acyl donor ethyl acetate. The challenge in racemization is that the activity of heterogeneous Ru catalysts was inhibited by esters.     

Acetophenone hydrogenation over a Pd catalyst in the presence of H2O and CO2

The addition of carbon dioxide and water enhances acetophenone hydrogenation activity over an activated carbon-supported palladium catalyst, and 1-phenylethanol can be easily recovered without distillation and neutralization. Two liquid phases (water and acetophenone) are indispensable for enhancement of the hydrogenation rate.     

Microwave effect on the surface composition of the Urushibara Ni hydrogenation catalyst and improved reduction of acetophenone

The Urushibara Ni (U-Ni) hydrogenation catalyst and some modified forms, and for comparison Raney-Ni, were subjected to conventional (oil bath) and MW heating, and subsequently characterized by electron dispersive X-ray analysis (EDX), by BET surface area, and by scanning electron microscopy (SEM); yields of the catalyzed hydrogenation of acetophenone to 1-phenylethanol in 2-propanol by one of the modified forms (U-Ni-B) were greatly improved (from 68% to 95%).     

Chiral ruthenabicyclic complexes: precatalysts for rapid, enantioselective, and wide-scope hydrogenation of ketones

A novel ruthenabicyclic complex with base shows excellent catalytic activity in the asymmetric hydrogenation of ketones. The turnover frequency of the hydrogenation of acetophenone reaches about 35,000 min(-1) in the best case, affording 1-phenylethanol in >99% ee. Several aliphatic and base-labile ketones are smoothly converted to the corresponding alcohols in high enantioselectivity. The catalytic cycle for this hydrogenation, in which the ruthenabicyclic structure of the catalyst is maintained, is proposed on the basis of the deuteration experiment and spectroscopic analysis data.     

Hydrogenation of styrene oxide in the presence of supported platinum catalysts to produce 2-phenylethanol

Gas-phase hydrogenation of styrene oxide was investigated using platinum catalysts deposited on magnesia, γ-alumina and activated carbon (AC), at atmospheric pressure and within a wide range of temperature (348–398 K). In order to correlate the chemical and textural properties with the catalytic activity, all catalysts were characterized by several techniques such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), H₂-temperature-programmed desorption (TPD) N₂ physisorption and H₂ chemisorption. Obtained results indicate that the catalytic activity and the selectivity were affected by the nature of the support. In the presence of MgO or activated carbon, as supports, the main product was 2-phenylethanol (2-PEA). However, when the support was γ-alumina, the main product was phenylacetaldehyde (PAD). The basic character of the support led to the formation of the less substituted alcohol (2-PEA). This was obtained at high conversion (85%) with practically total selectivity (around 99%). However, more acid support such as γ-alumina led to the formation of the more substituted alcohol 1-phenylethanol (1-PEA) and phenylacetaldehyde, mainly due to the isomerisation of the epoxide. Consequently, the acid–base character of the support plays an important role in the selectivity of this reaction.     

Development of a new class of (1S,3R,4R)-2-azabicyclo[2.2.1]heptane-oxazoline ligands and their application in asymmetric transfer hydrogenation

New 2-aza-norbornane-oxazoline compounds were synthesized and evaluated as ligands in the transfer hydrogenation of acetophenone. The best catalyst prepared in situ from [IrCl₂(COD)]₂ and a ligand afforded 1-(S)-phenylethanol in good yields and 79% ee.     

Acylation of (<Emphasis Type="Italic">R,S</Emphasis>)-1-phenylethanol with ethyl acetate over an immobilized enzyme

Acylation of (R,S)-1-phenylethanol, which is a product of acetophenone hydrogenation, over a Pd-supported catalyst, was studied in ethyl acetate with an immobilized lipase. It was demonstrated that in the presence of hydrogen and Pd/C in the reaction medium the (R,S)-1-phenylethanol acylation rate is not hindered, whereas the selectivity was strongly altered in the latter case, leading to significant amounts of side products.     

Mechanistic investigations of the reaction network in chemo-bio catalyzed synthesis of R-1-phenylethyl acetate

The kinetics and reaction network of the one-pot synthesis of R-1-phenylethyl acetate was investigated at 70°C in toluene over a combination of three different catalysts: PdZn/Al₂O₃ as a catalyst for acetophenone hydrogenation, lipase as an enzymatic catalyst for R-1-phenylethanol acylation with ethyl acetate and Ru/Al₂O₃ as a racemization catalyst for S-1-phenylethanol. In addition to the desired reactions, other reactions, namely hydrogenolysis and dehydration of (R, S)-1-phenylethanol and debenzylation of (R, S)-1-phenylethyl acetate also occurred. The kinetic results revealed that ethylbenzene formation was enhanced with higher amounts of PdZn/Al₂O₃, whereas lipase did not catalyze ethylbenzene formation. Furthermore, ethylbenzene was formed in the hydrogenolysis of (R, S)-phenylethanol and in the debenzylation of (R, S)-1-phenyl-ethylacetate over Pd/Al₂O₃ catalyst. The presence of Ru/Al₂O₃ catalyst, in which Ru was in the oxidation state of 3⁺, enhanced the formation of R-1-phenylethyl acetate, although no clear racemization of S-1-phenylethanol during the one-pot synthesis of R-1-phenylethyl acetate was observed. Dynamic kinetic resolution of (R, S)-1-phenylethanol in toluene, was, however, demonstrated over Ru/Al₂O₃ and lipase.     

Microwave Induced Reaction of H-Dimethylphosphonate with Styrene Oxide

Microwave catalyzed reaction of a neat mixture of styrene oxide and H-dimethylphosphonate furnished dimethyl methylphosphonate, trimethylphosphate, phenylacetaldehyde, 1-methoxy-2-phenylethanol, 1-phenylethleneglycol, cis- and trans-1,3-diphenylcyclobutanes, hydrogen 1-(2-phenylethyl)methylphosphinate, (1-phenylethyl)dimethylphosphonate, and (1-phenylethyl)dimethylphosphonate via free radical processes.     

温控Noyori配体的合成及在苯乙酮不对称氢转移反应中的应用

设计并合成了一种新型的聚乙二醇单甲醚(MPEG)修饰的温控Noyori配体.将其与[RuCl2.(p-cymene)]2络合形成的催化剂用于水/环己烷两相体系中苯乙酮不对称氢转移反应.以甲酸钠为氢源,考察了反应温度、时间、甲酸钠用量、底物与催化剂摩尔比以及溶剂用量等因素对催化反应的影响.结果表明,反应体系中含催化剂的水相具有浊点,并且催化剂显示出良好的不对称催化性能,在甲酸钠/苯乙酮/催化剂的摩尔比为300:100:1、环己烷/水体积比1:1及30℃的反应条件下反应6h,苯乙酮的转化率为99.7%,产物α-苯乙醇的对映选择性(e.e.)为93.9%.催化剂相易与产物相分离并与直接循环使用,循环使用的催化剂活性明显下降,但产物对映选择性仍保持不变.     

新的双胺双膦钌配合物的合成、表征和催化性能

Polydentate ligands, N,N'-bis[o-(diphenylphosphino)benzylidene]-1,2-propane-diamine [P2N2Me for short] and N,N'-bis[o-(diphenylphosphino)benzy1]-1,2-propanediamine [P2N2 H4Me for short] have been synthesized. The interaction of RuCl2(DMSO)4 with one equivalent of P2N2Me or P2N2H4Me in refluxing toluene gave trans-RuCl2(P2N2Me) and trans-RuCl2(P2N4H4Me) in good yield, respectively. The ligands and the complexes have been fully characterized by elemental analysis and spectroscopic methods. The complexes act as an excellent catalyst precursor in hydrogen transfer hydrogenation of acetophenone in catalyst: acetophenone :iso-PrOK of 1: 100: 15, leading to 2-phenylethanol of 89-96% yield.     

Asymmetric hydrogenation of acetophenone catalyzed by cinchonidine stabilized Ir/SiO2

A series of silica (SiO₂) supported iridium catalysts stabilized by cinchona alkaloids was prepared and applied in the heterogeneous asymmetric hydrogenation of acetophenone. Cinchona alkaloids exhibited a marked ability to stabilize and disperse the Ir particles. In the presence of (1S,2S)-diphenylethylenediamine ((1S,2S)-DPEN)) as chiral modifier, the cinchonidine (CD) stabilized catalyst 5%Ir/2CD-SiO₂ exhibited excellent catalytic performance in the asymmetric hydrogenation of acetophenone in MeOH. Under the optimum conditions, the ee value of (R)-phenylethanol achieved 79.8% and no other product was produced, a higher enantioselectivity than that reported up to now for acetophenone hydrogenation catalyzed by the supported metal catalysts modified by chiral reagents. In particular, a synergistic effect between (1S,2S)-DPEN and CD was observed, which significantly accelerated the reaction rate and enhanced the enantioselectivity. The catalyst can be reused several times without a significant loss of activity and enantioselectivity.     

Asymmetric reduction and hydrogenation over heterogenous catalysts prepared by reacting nickel-boride with norephedrine

The reduction of acetophenone with borane–THF over heterogeneous catalysts prepared by reacting nickel-boride with (1R,2S)-(−)-norephedrine, afforded (R)-(+)-1-phenylethanol with high enantioselectivity (ee=90%). The catalysts can be recycled two times with little or no loss of performance. The excellent enantioselective properties resulted from the formation of 1,3,2-oxazaborolidine which is strongly anchored at the surface of the nickel-boride. Used for the hydrogenation of acetophenone, 4-methylpentan-2-one and isophorone, the catalyst hydrogenated with a slight predominance of the S configuration. The ee was poor but it remained constant when the catalyst was reused.     

RuCl2(BISBI)[(R,R)-DPEN]催化苯乙酮不对称加氢反应研究

报道了配合物RuCl₂(BISBI)[(R,R)-DPEN] [BISBI＝2,2'-二(二苯膦亚甲基)-1,1'-联苯, DPEN＝1,2-二苯基乙二胺]的合成和表征, 并研究了其在苯乙酮不对称加氢反应中的催化性能. 考察了底物/催化剂物质的量比、碱浓度、反应温度和氢气压力等对催化活性和对映选择性的影响, 在苯乙酮/KOH/催化剂的物质的量比为30000∶250∶1, 氢气压力为2 MPa, 反应温度为35 ℃时, 苯乙酮的转化率和生成α-苯乙醇的对映选择性分别达到了100%和65% ee.     

Employing the structural diversity of nature: development of modular dipeptide-analogue ligands for ruthenium-catalyzed enantioselective transfer hydrogenation of ketones

A library of novel dipeptide-analogue ligands based on the combination of tert-butoxycarbonyl(N-Boc)-protected alpha-amino acids and chiral vicinal amino alcohols were prepared. These highly modular ligands were combined with [[RuCl(2)(p-cymene)](2)] and the resulting metal complexes were screened as catalysts for the enantioselective reduction of acetophenone under transfer hydrogenation conditions using 2-propanol as the hydrogen donor. Excellent enantioselectivity of 1-phenylethanol (up to 98 % ee) was achieved with several of the novel catalysts. Although most of the ligands contained two stereocenters, it was demonstrated that the absolute configuration of the product alcohol was determined by the configuration of the amino acid part of the ligand. Employing ligands based on L-amino acids generated S-configured products, and catalysts based on D-amino acids favored the formation of the R-configured alcohol. The combination N-Boc-L-alanine and (R)-phenylglycinol (Boc-L-Ab) or its enantiomer (N-Boc-D-alanine and (S)-phenylglycinol, Boc-D-Aa) proved to be the best ligands for the reduction process. Transfer hydrogenation of a number of aryl alkyl ketones were evaluated and excellent enantioselectivity, up to 96 % ee, was obtained.     

Enantioselective hydrogenation of itaconate using rhodium bihelicenol phosphite complex. Matched/mismatched phenomena between helical and axial chirality

Phosphites prepared from bihelicenol, menthol (or 1-phenylethanol), and PCl₃ are effective ligands for the rhodium-catalyzed enantioselective hydrogenation of dimethyl itaconate. Stereochemistry of the helicene moiety plays an important role in the asymmetric induction, and matched/mismatched phenomena are observed between helical and axial chirality.     

A succession of isomers of ruthenium dihydride complexes. Which one is the ketone hydrogenation catalyst?

Reaction of RuHCl(PPh(3))(2)(diamine) (1a, diamine = (R,R)-1,2-diaminocyclohexane, (R,R)-dach; 1b, diamine = ethylenediamine, en) with KO(t)Bu in benzene quickly generates solutions of the amido-amine complexes RuH(PPh(3))(2)(NHC(6)H(10)NH(2)), (2a'), and RuH(PPh(3))(2)(NHCH(2)CH(2)NH(2)), (2b'), respectively. These solutions react with dihydrogen to first produce the trans-dihydrides (OC-6-22)-Ru(H)(2)(PPh(3))(2)(diamine) (t,c-3a, t,c-3b). Cold solutions (-20 degrees C) containing trans-dihydride t,c-3a react with acetophenone under Ar to give (S)-1-phenylethanol (63% ee). Complexes t,c-3 have lifetimes of less than 10 min at 20 degrees and then isomerize to the cis-dihydride, cis-bisphosphine isomers (OC-6-32)-Ru(H)(2)(PPh(3))(2)(diamine) (Delta/Lambda-c,c-3a, c,c-3b). A solution containing mainly Delta/Lambda-c,c-3a reacts with acetophenone under Ar to give (S)-1-phenylethanol in 20% ee, whereas it is an active precatalyst for its hydrogenation under 5 atm H(2) to give 1-phenylethanol with an ee of 50-60%. Complexes c,c-3 isomerize to the cis-dihydride, trans-bisphosphine complexes (OC-6-13)-Ru(H)(2)(PPh(3))(2)(diamine) (c,t-3a, c,t-3b) with half-lives of 40 min and 1 h, respectively. A mixture of Delta/Lambda-c,c-3a and c,t-3a can also be obtained by reaction of 1a with KBH(Bu(sec))(3). A solution of complex c,t-3a in benzene under Ar reacts very slowly with acetophenone. These results indicate that the trans-dihydrides t,c-3a or t,c-3b along with the corresponding amido-amine complexes 2a' or 2b' are the active hydrogenation catalysts in benzene, while the cis-dihydrides c,c-3a or c,c-3b serve as precatalysts. The complexes RuCl(2)(PPh(3))(2)((R,R)-dach) or 1a, when activated by KO(t)Bu, are also sources of the active catalysts. A study of the kinetics of the hydrogenation of acetophenone in benzene catalyzed by 3a indicates a rate law: rate = k[c,c-3a](initial)[H(2)] with k = 7.5 M(-1) s(-1). The turnover-limiting step appears to be the reaction of 2a' with dihydrogen as it is for RuH(NHCMe(2)CMe(2)NH(2))(PPh(3))(2) (2c'). The catalysts are more active in 2-propanol, even without added base, and the kinetic behavior is complicated. The basic cis-dihydride c,t-3a reacts with [NEt(3)H]BPh(4) to produce the dihydrogen complex (OC-14)-[Ru(eta(2)-H(2))(H)(PPh(3))(2)((R,R)-dach)]BPh(4) (4) and with diphenylphosphinic acid to give the complex RuH(O(2)PPh(2))(PPh(3))(2)((R,R)-dach) (5). The structure of 5 models aspects of the transition state structure for the ketone hydrogenation step. Complex 2b' decomposes rapidly under Ar to give dihydrides 3b along with a dinuclear complex (PPh(3))(2)HRu(mu-eta(2);eta(4)-NHCHCHNH)RuH(PPh(3))(2) (6) containing a rare, bridging 1,4-diazabutadiene group. The formation of an imine by beta-hydride elimination from the amido-amine ligand of 2a' under Ar might explain some loss of enantioselectivity of the catalyst. The structures of complexes 1a, 5, and 6 have been determined by single-crystal X-ray diffraction.     

多级孔TS-1用于油酸甲酯高效绿色环氧化

当今时代,资源短缺、环境污染等问题日益严峻,生物质资源化学转化利用成为各国研究重点,以生物质资源代替化石资源、以生物基材料代替石化材料,为发展绿色经济、循环经济奠定了基础.植物油资源由于其广泛的可获得性、固有的生物可降解性、低成本及突出的环境效益受到广泛关注.其中,环氧化的植物油作为可再生原材料应用于生产热塑材料的增塑剂和稳定剂、生物润滑油、涂料、粘合剂、化妆品及各种聚合物材料 (聚酯、聚氨酯、聚酰胺等).目前,工业上生产环氧化植物油通常采用 Prilezhaev 过程,即在无机强酸如 H2SO4,HCl,HNO3等的催化作用下,过氧化氢与甲酸或乙酸作用原位生成过氧甲酸或过氧乙酸作为环氧化试剂用于环氧化反应.但就该反应过程而言,强酸的存在会带来一系列问题:(1) 强酸的存在容易引发一系列副反应,如环氧环开环生成二醇、二聚物等; (2) 产物分离问题,反应完毕后产物需经碱洗、水洗和减压蒸馏才能得到最后产品,工艺过程复杂且可能造成环境污染,不符合绿色化学理念; (3) 强酸存在引起的设备腐蚀问题.因而开发新型高效的催化技术降低生产成本,解决生产过程中的污染问题,实现植物油的绿色高效利用,是我们当前迫切要解决的问题.寻找安全无污染且具有高效催化性能的非均相催化剂也迫在眉睫.因此,各过渡金属如 MoIV,WVI,NbV和 TiIV复合物催化剂得到广泛研究.其中,钛硅分子筛 TS-1 由于其良好的稳定性及优异的环氧化催化性能受到关注,然而其狭窄的孔道尺寸使得它在大分子反应物参与的反应中受到显著的扩散限制,因而需合成含有介孔及大孔的多级孔 TS-1 用于植物油环氧化反应中.本课题组多年从事钛硅分子筛的制备及催化氧化研究工作.本文以聚季铵盐-6 作为介孔模板剂合成了多级孔TS-1(HTS-1),将其作为催化剂,油酸甲酯作为模型化合物,H2O2作为氧化剂,系统研究了反应条件 (H2O2与双键摩尔比、氧化剂浓度与用量、反应温度与时间) 对油酸甲酯环氧化反应的影响.采用响应曲面分析法 (RSM) 优化反应条件,获取环氧化油酸甲酯的最大收率,并对各因素对油酸甲酯环氧化影响的显著性及各因素之间的交互作用进行探究.结果发现,H2O2与双键摩尔比及催化剂用量对油酸甲酯环氧化的影响较大,在优化的反应条件下环氧化产物的收率可高达 94.9%.而HTS-1 表现出的优异催化性能主要归结于其良好的疏水性能和高活性且可供大分子接触反应的钛物种.