Copper-cationic salphen catalysts for the oxidation of cyclohexene by oxygen

The modified copper-cationic salphen catalysts were synthesized and used in the allylic oxidation of cyclohexene to 2-cyclohexen-1-ol and 2-cyclohexen-1-one with oxygen under mild conditions. Compared with their unmodified counterpart, the catalytic activities of modified catalysts are improved. The type of counteranion could affect the reactivity of catalyst, which offers an opportunity to improve the catalysts via changing counteranions to optimize the selectivity. The cation–anion interaction can be adjusted by different solvents, which in turn influences the catalyst reactivity. Furthermore, these novel catalysts can be reused without sacrificing the activity.     

Salicylidene‐imine–zirconium(IV) complexes in combination with methylalumoxane as catalysts for the conversion of hexa‐1,5‐diene: adjusting of the catalytic activity

A variety of substituted schiff base complexes of the composition (“salen”)ZrCl₂(thf) ( 1 – 21 ) were synthesized, with methylalumoxane (“MAO”) activated and used for a systematic study of their catalytic activity towards hexa‐1,5‐diene (“salen”: substituted salicylidene–ethylene‐iminato ligands). Main product of the catalytic cycle is methylenecyclopentane. Dimers are only formed in minor amounts. The catalytic activity and selectivity of the Ziegler–Natta systems strongly depend on the nature and the position of the peripheric substituents in the Schiff base ligands. Electron‐withdrawing substituents in para‐position to the phenolato oxygen (5‐position) decrease the catalytic activity. Improved activity and selectivity were obtained with electron‐donating substituents in 5‐position. Altering the ethylene bridge causes a lowering of the activity or inactivation. According to the x‐ray analysis the metal center in the related complex (L)ZrCl₂ ( 22 ) (L: N′,N′‐bis(ethylene)‐N′‐methyl‐N,N′′‐bis(benzoylacetonato‐imine) has a pentagonal‐bipyramidal environment. The pentadentate schiff base ligand lies in the plane, and both chloro groups occupy the axial positions. In contrast to the catalytically active salene complexes 22 can not rearrange to form a species in which the both chlorides are cis to each other. Consequently 22 is catalytically inactive.     

Komplexkatalyse. XV. Kationische η3-Allyl-bis(triorganylphosphit)nickel(II)-Komplexe als Katalysatoren für die stereoreguläre Butadienpolymerisation

Complex Catalysis. XV. Cationic η³-Allyl-bis(triorganylphosphite)nickel(II) Complexes as Catalysts for the Stereoregular Butadiene Polymerisation Synthesis and catalytic properties of [C₃H₅NiL₂]PF₆ complexes 1a –f with L = tri-ethyl-, -isopropyl-, -phenyl-, -o-tolyl-, -thymyl- and o-biphenylylphosphite are described. It is shown how electronic and steric effects of the phosphite ligands in these complexes control their catalytic activity and selectivity in 1,4-polymerization of butadiene.     

锡卟啉的合成及其绿色催化氧气氧化环己烯

考察催化剂金属锡次卟啉二甲酯催化氧化环己烯的反应性能。探讨了在催化氧化过程中,反应温度、压力、时间、催化剂用量等因素对环己烯转化率和产物选择性的影响,并结合GC-MS在线分析检测。结果表明,当温度100℃、压力0.8 MPa、时间7 h、催化剂用量0.5 mg(7.6×10-4mmol)、环己烯10 mL(98 mmol)的条件下,环己烯的转化率达84%,相应产物2-环己烯-1-醇和2-环己烯-1-酮的总选择性为94%,并对该反应的催化氧化反应机理进行了初步研究。     

Oxidation of 2,6-di-tert-butylphenols to Diphenoquinones Catalysed by Schiff Base-Cu(II) Systems Immobilized on Polymer Support

Benzoquinone, diphenoquinones and its derivatives are important intermediates for industrial synthesis of a wide variety of special chemicals, such as pharmaceuticals, dyes and agricultural chemicals. The useful catalyst were obtained by aminolysis of vinylbenzyl chloride/divinylbenzene copolymer with ethylenediamine (1) or urotropine (2) and then modification by salicylaldehyde (1A, 2A) or picolinaldehyde (1B, 2B). The catalytic activity of Cu(II) complexes with Schiff base immobilized on the synthesized supports were tested in the oxidation reaction of 2,6-di-tert-butylphenol (DTBP) to diphenoquinone (PQ) with tert-butylhydroperoxide. The best oxidation degree of DTBP (60-70%) and the selectivity towards PQ (80%) is revealed by Cu(II) complexes with long Schiff base ligands derived from salicylaldimine (1A), which have CuL structure (EPR measurement).     

Selective oxidation of cyclohexene catalyzed by polymer-bound ruthenium–2,2′-bipyridine complexes

Cyclohexene was oxidized to 2-cyclohexen-1-ol and 2-cyclohexen-1-one by atmospheric pressure of molecular oxygen in the presence of linear polystyrene-bound-2,2′-bipyridine–ruthenium complexes in the absence of solvent at 70±5°C selectively. The alcohol/ketone molar ratio of the products can be adjusted by employing different additives or by varying the reaction pH.     

聚酰胺-胺树状分子锡配合物催化性能研究

通过固相合成的方法将聚酰胺-胺树状大分子PAMAM担载于大孔硅胶上,并对其外围分别用对羟基苯甲醛、2,4-二羟基苯甲醛和邻羟基苯甲醛进行修饰,再与SnCl2.2H2O反应形成三类共计9种不同代数树状高分子锡配合物。将该类配合物用作质量分数30%双氧水氧化酮的Baeyer-Villiger(B-V)反应的催化剂,考察其催化活性,结果表明,在该类配合物作用下,2-金刚烷酮、环戊酮、环己酮、4-甲基环己酮、4-叔丁基环己酮、3-甲基-2-戊酮和4-甲基-2-戊酮都可以发生B-V氧化反应而转化为相应的酯和内酯,底物的转化率(75%～99%)和产物选择性(95%～100%)都较高。比较了不同载体(氯球、纤维素、壳聚糖、硅胶)、不同配体的金属锡配合物对B-V催氧化反应的催化效果,研究发现,载体、配体和金属担载量对配合物的催化活性均有不同程度的影响。其中,硅胶为最好的载体,而邻羟基苯甲醛为最好的配体。     

原子转移自由基聚合中过渡金属催化剂的研究进展

综述了正向、反向原子转移自由基聚合(ATRP)中不同种类过渡金属催化剂的特点和进展以及配体对催化剂催化活性和选择性的影响。     

Chromium modified silica from rice husk as an oxidative catalyst

RH-Cr and RH-Cr500 were synthesized from rice husk by solvent extraction and gel precipitation technique. The specific surface area of RH-Cr and RH-Cr500 were found to be 0.542 and 1.20 m² g⁻¹ respectively. Energy dispersive X-ray (EDX) analysis showed that Cr(III) was homogenously incorporated in the matrix of both samples to a maximum of ca. 16% in RH-Cr500. Elemental analysis showed that RH-Cr contained ca. 15% carbon, while RH-Cr500 contained negligible amounts. FTIR analysis showed the extracted solid contained silanol (Si–OH) and siloxane (Si–O–Si) groups. Catalytic oxidation of cyclohexane with H₂O₂ using RH-Cr as the catalyst showed a 27.13% conversion to cyclohexanone and cyclohexanol with a selectivity of 57.37% and 42.63% respectively. However, RH-Cr500 showed only 14.01% conversion but with a selectivity of 64.83% of cyclohexanone and 35.17% of cyclohexanol. Epoxidation of cyclohexene using H₂O₂ with RH-Cr as the catalyst gave a conversion rate of 30.17% with a selectivity of 11.51% towards cyclohexene oxide, 63.21% 2-cyclohexen-1-one and 25.29% 2-cyclohexen-1-ol. The same reaction with RH-Cr500 as the catalyst showed 21.28% conversion with 14.65% cyclohexene oxide, 68.71% 2-cyclohexen-1-one and 16.64% 2-cyclohexen-1-ol. In the catalytic oxidation of cyclohexanol to cyclohexanone, RH-Cr showed a conversion of 12.25% while RH-Cr500 showed a conversion of 13.52%. No others products were detected in the conversion. Comparison with published catalytic systems showed that RH-Cr and RH-Cr500 to be a better catalyst even though the surface area of these catalysts were low.     

EDTA双酰胺Cu(Ⅱ)配合物的合成与催化性能研究

EDTA二酐分别与α-萘胺、β-萘胺反应得两种配体,继而与Cu(Ⅱ)配位得到两种配合物。通过红外光谱、核磁共振氢谱、元素分析和电导测定等手段对配体和配合物进行了表征。并研究了它们在苯羟基化为苯酚反应中的催化性能,在反应温度为80℃时,配合物1和配合物2催化苯的羟基化的转化率分别为9.0%、9.1%,苯酚的选择性分别为88.9%、90.1%。     

Dendronized polyamides supports for Mo catalysts

Dendronized polyamides of generations 1 and 2 were grafted with ethylenediamine (en) ligands at their peripheries by the condensation of chloromethyl groups and en molecules. The obtained dendronized complexes were further equipped with MoO₂acac₂ to form the catalysts PGn‐en‐Mo. The results of FT‐IR and thiocyanate photometric analysis confirmed the successful immobilization of Mo catalysts on dendronized polyamides. The catalytic properties of PGn‐en‐Mo were first studied in the epoxidation of cyclohexene with tert‐butyl hydroperoxide and exhibited high catalytic activity and selectivity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Highly Selective Cobalt‐Catalyzed Hydrovinylation of Styrene

Phosphine complexes of cobalt halide salts activated by diethylaluminum chloride are shown to yield highly active catalysts in the hydrovinylation of styrene, with unprecedented high selectivity to the desired product 3‐phenyl‐1‐butene (3P1B). Double‐bond isomerization, a common problem in codimerization reactions, only occurs after full conversion with these catalyst systems, even at elevated temperature. The most active catalysts are based on cobalt halide species combined with either C₁‐ or C₂‐bridged diphosphines, heterodonor P,N or P,O ligands, flexible bidentate phosphine ligands or monodentate phosphine ligands. Kinetic investigations show an order >1 in catalyst, which indicates either the involvement of dinuclear species in the catalytic cycle or partial catalyst decomposition via a bimolecular pathway.     

Oxidation of styrene over polymer‐ and nonpolymer‐anchored Cu(II) and Mn(II) complex catalysts

Catalytic oxidation of styrene was investigated over polymer‐ and nonpolymer‐anchored Cu(II) and Mn(II) complex catalysts prepared by schiff base tridentate ligands. The effect of temperature, styrene to H₂O₂ mole ratio and catalyst amount on the catalytic activity and product selectivity was investigated. Further, the catalysts were characterized by various techniques, such as elemental analysis, atomic absorption spectroscopy (AAS), FTIR, FE‐SEM, EDAX, TGA, and UV–vis spectrophotometer. The elemental analysis, EDAX and AAS results confirmed the formation of Cu(II) and Mn(II) complexes, and it was found that the metal loading in the polymer‐anchored complex catalysts were in the range of 0.53–3.74 %. FTIR results showed the co‐ordination bond formation between the polymer ligands and metal ion. The catalytic data showed that, over all the catalysts, the main reaction products were benzaldehyde, styrene oxide, and benzoic acid. The polymer‐anchored complex catalysts were found to be much more active when compared with nonpolymer‐anchored catalysts. The maximum conversion of styrene (92.3%) was obtained over PS‐[Cu(Hfsal‐aepy)Cl] catalyst with benzaldehyde selectivity to 69% at the styrene to H₂O₂ mole ratio of 1 : 4 at 75°C. Although the PS‐[Mn(Hfsal‐aepy)Cl] catalyst was less active, it was highly selective to benzaldehyde. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Covalent anchoring of Mo(VI) Schiff base complex into SBA-15 as a novel heterogeneous catalyst for enhanced alkene epoxidation

Molybdenum(VI) Schiff base complexes modified mesoporous SBA-15 hybrid heterogeneous catalysts were synthesized by the reaction of MoO₂(acac)₂ with mesoporous SBA-15 functionalized by grafting procedures of 3-aminopropyl-triethoxysilane and salicylaldehyde, respectively. The physico-chemical properties of the as-synthesized catalysts were analyzed by ICP-AES, XRD, N₂ adsorption–desorption, FT-IR, SEM, TEM and EDX. The as-synthesized catalysts were effective in the catalytic epoxidation of cyclohexene. The catalytic activity can be further enhanced by silylation of the residual Si–OH groups using Me₃SiCl, which was largely due to the higher content of Mo active sites. The conversion and selectivity reached to 97.78 and 93.99 % using tert-butyl hydroperoxide as oxidant for Mo–CH₃–SA–NH₂–SBA-15, while 81.97 and 89.41 % in conversion and selectivity for Mo–SA–NH₂–SBA-15. At the same time, the catalytic performances of the hybrid materials were further systematically investigated under various reaction conditions (solvent, oxidants and alkenes, etc.). Mo–CH₃–SA–NH₂–SBA-15 catalyst can be recycled effectively and reused four cycles with little loss in activity. In addition, the results from hot filtration demonstrated that the catalytic activity mostly resulted from the heterogeneous catalytic process.     

Cationic Ruthenium‐Cyclopentadienyl‐Diphosphine Complexes as Catalysts for the Allylation of Phenols with Allyl Alcohol; Relation between Structure and Catalytic Performance in O‐ vs. C‐Allylation

A new catalytic method has been investigated to obtain either O‐ or C‐allylated phenolic products using allyl alcohol or diallyl ether as the allyl donor. With the use of new cationic ruthenium(II) complexes as catalyst, both reactions can be performed with good selectivity. Active cationic Ru(II) complexes, having cyclopentadienyl and bidentate phosphine ligands are generated from the corresponding Ru(II) chloride complexes with a silver salt. The structures of three novel (diphosphine)Ru(II)CpCl catalyst precursor complexes are reported. It appears that the structure of the bidentate ligand has a major influence on catalytic activity as well as chemoselectivity. In addition, a strong cocatalytic effect of small amounts of acid is revealed. Model experiments are described that have been used to build a reaction network that explains the origin and evolution in time of both O‐allylated and C‐allylated phenolic products. Some mechanistic implications of the observed structure vs. performance relation of the [(diphosphine)RuCp]⁺ complexes and the cocatalytic role of added protons are discussed.     

Baeyer–Villiger oxidation of ketones with hydrogen peroxide catalyzed by cellulose-supported dendritic Sn complexes

Cellulose supported dendritic Sn complexes were prepared by solid phase synthetic methodology. A series of cycloketones and acyclic ketones including 2-andamantanone, cyclohexanone, 4-methylcyclohexanone, 4-tert-butylcyclohexanone, 3-methyl-2-pentanone, 4-methyl-2-pentanone and cyclopentanone were oxidized by hydrogen peroxide in a reaction catalyzed by cellulose-supported dendritic Sn complexes, affording the corresponding lactones or esters with the conversion of 70–99% and the product selectivity of 100%. The catalysts can be recycled for several times without any significant decline in catalytic activity.     

Polymer-supported molybdenum and vanadium catalysts for epoxidation of alkenes by alkyl hydroperoxides

Polymer-supported molybdenum and vanadium catalysts were synthesized using gel-type crosslinked copolymers with microheterogeneous structure. The supports were composed of inert ethylene–propylene rubber and crosslinked high molecular weight poly(ethylene oxide) matrices and polymeric ligands grafted or forming interpenetrating networks: poly(acrylic acid), poly(methacrylic acid), poly(4-vinylpyridine), and polyvinyl alcohol. Catalytic activity and selectivity of some of these complexes were tested in epoxidation of styrene by ethylbenzene hydroperoxide. Molybdenyl cations are strongly coordinated with pyridine-containing copolymers giving catalysts of high activity and selectivity. They provide conversion and selectivity above 70%. Because of the microheterogeneous mosaic-like structure of the supports, better accessibility of the active sites is achieved.     

Cobalt Schiff base complexes: Synthesis characterization and catalytic application in Suzuki–Miyaura reaction

3-Methoxysalicylaldehyde was condensed with the amines 4-aminoacetophenone and 2-amino-5-bromopyridine to obtain Schiff base ligands, 1 and 2, which were coordinated to cobalt salts as complex 1 and complex 2, respectively. The synthesized ligands and complexes were characterized by spectroscopic (FT-IR, UV-Vis, ¹H-NMR and mass spectrometry), thermal (TGA) and elemental analysis. The structures of the complexes were verified by evaluating their magnetic susceptibility and spectroscopic evidences. Synthesized complexes were studied for their catalytic activity in the Suzuki-Miyaura cross-coupling of aryl halides with phenylboronic acid. Optimized reaction yields 90% of the cyanobiphenyl for complex 1 and 91% for complex 2 with 0.1 mmol of catalyst loading thereby substantiating the C-C coupling efficiency of the synthesized complexes, 1 and 2.     

Beneficial influence of nanocarbon on the aryliminopyridylnickel chloride catalyzed ethylene polymerization

A series of 1-aryliminoethylpyridine ligands (L1―L3) was synthesized by condensation of 2-acetylpyridine with 1-aminonaphthalene, 2-aminoanthracene or 1-aminopyrene, respectively. Reaction with nickel dichloride afforded the corresponding nickel (II) chloride complexes (Ni1–Ni3). All compounds were fully characterized and the molecular structures of Ni1 and Ni3 are reported. Upon activation with methylaluminoxane (MAO), all nickel complexes exhibit high activities for ethylene polymerization, producing waxes of low molecular weight and narrow polydispersity. The presence of multi-walled carbon nanotubes (MWCNTs) or few layer graphene (FLG) in the catalytic medium can lead to an increase of productivity associated to a modification of the polymer structure.     

Catalyst Stability Determines the Catalytic Activity of Non‐Heme Iron Catalysts in the Oxidation of Alkanes

A series of iron(II) bis(triflate) complexes [Fe(L)(OTf)₂] containing linear tetradentate bis(pyridylmethyl)diamine ligands with a range of ligand backbones has been prepared. The backbone of the ligand series has been varied from a two‐carbon linkage [ethylene ( 1 ), 4,5‐dichlorophenylene ( 2 ) and cyclohexyl ( 3 )] to a three‐carbon [propyl ( 4 )) and a four‐carbon linkage (butyl ( 5 )]. The coordination geometries of these complexes have been investigated in the solid state by X‐ray crystallography and in solution by ¹H and ¹⁹F NMR spectroscopy. Due to the labile nature of high‐spin iron(II) complexes in solution, dynamic equilibria of complexes with different coordination geometries (cis‐α, cis‐β and trans) are observed with ligands 2 – 5 . In these cases, the geometry observed in the solid state does not necessarily represent the only or even the major geometry present in solution. The ligand field strength in the various complexes has been investigated by variable temperature magnetic moment measurements and UV‐vis spectroscopy. The strongest ligand field is observed with the most rigid ligands 1 and 2 , which generate complexes [Fe(L)(OTf)₂] with a cis‐α coordination geometry and the corresponding complexes [Fe(L)(CH₃CN)₂]²⁺ display spin crossover behaviour. The catalytic properties of the complexes for the oxidation of cyclohexane, using hydrogen peroxide as the oxidant, have been investigated. An increased flexibility in the ligand results in a weaker ligand field, which increases the lability of the complexes. The activity and selectivity of the catalysts appear to be related to the strength of the ligand field and the stability of the catalyst in the oxidising environment.