Chiral self-dimerization of vanadium complexes on a SiO2 surface: the first heterogeneous catalyst for asymmetric 2-naphthol coupling

The self-dimerized chiral assembly of vanadium-Schiff-base complexes was found to occur on a SiO2 surface and to be the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol with 100% selectivity and 90% enantioselectivity.     

A novel type of catalysts for asymmetric oxidative coupling of 2-naphthol

Stereochemically inert, positively charged chiral octahedral complexes of Co^III and Cr^III were used as catalysts for asymmetric oxidative coupling of 2-naphthol. The reaction product 1,1´-bi-2-naphthol was produced with a yield of up to 74% and enantiomeric excess of up to 22%. The reduction and oxidation potentials of a series of Co^III and Cr^III cationic complexes were measured.     

Studies on the structure and catalytic performance of S and P promoted Na-W-Mn-Zr/SiO2 catalyst for oxidative coupling of methane

A series of Na-W-Mn-Zr/SiO2 catalysts promoted by different contents of S or/and P were prepared and their catalytic performance for oxidative coupling of methane was investigated to clarify the effect of S and P on the Na-W-Mn-Zr/SiO2 catalyst. The catalysts were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). From the characterization results, it is found that the addition of S and P to the Na-W-Mn-Zr/SiO2 catalyst helps the formation of active phases, such as α-cristo...     

Effect of the structure of copper(II) complexes, adsorbed on the surface of SiO2, on their catalytic activity in ozone decomposition

We describe the composition, structure, and catalytic activity in the reaction of ozone decomposition for copper(II) complexes with acido ligands and immobilized Schiff’s bases (propyl benzaldimine derivatives) that are anchored on silica (silica gel, aerosil). We demonstrate methods for controlling their catalytic activity. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 55–60, January–February, 2006.     

Chiral dinuclear vanadium(v) catalysts for oxidative coupling of 2-naphthols

Preparation and structural analysis of chiral dinuclear vanadium(v) catalysts with high catalytic activity for the oxidative coupling of 2-naphthols are described.     

Chiral copper-bipyridine complexes: Synthesis, characterization and mechanistic studies on asymmetric cyclopropanation

Chiral bipyridine ligands of different steric properties when reacted with CuCl₂ formed orange, yellow or green solids of new copper(II) complexes, [Cu(L)Cl₂] (L = L2-6), in good yield. Together with [Cu(L1)Cl₂], these complexes were characterized in solution by UV-Vis spectroscopy and cyclic voltammetry. The complexes give d-d transitions between 860 and 970 nm, and exhibit one quasi-reversible Cu(II)/Cu(I) couple between +0.405 V and +0.516 V versus NHE. Two of the copper(II) complexes, [Cu(L5)Cl₂] and [Cu(L6)Cl₂], and a copper(I) complex of L1, [Cu(L1)Cl], were characterized by X-ray crystallography. The triflate derivatives of both the Cu(I) and Cu(II) complexes are active catalysts towards the cyclopropanation of ethyl diazoacetate with styrene. The asymmetric induction suffers when the size difference between the alkyl and alkoxyl groups was minimized. The mechanism of the cyclopropanation was studied with kinetic and competition experiments. The rate is first order in catalyst and ethyl diazoacetate, inverse order with styrene and is strongly affected by the counterion.     

Chiral pyridylamino-ruthenium(II) complexes: synthesis, structure and catalytic properties in Diels-Alder reactions

Half-sandwich complexes [(eta(6)-arene)RuCl(pyam)][SbF(6)] (pyam = L(n) = N-(2-pyridylmethyl)-(R)-1-phenylethylamine (L(1)), N-(2-pyridylmethyl)-(R)-1-naphthylethylamine (L(2)), N-(2-quinolylmethyl)-(R)-1-naphthylethylamine (L(3)), N-(2-pyridylmethyl)-(R)-1-cyclohexylethylamine (L(4)), N-(2-pyridylmethyl)-(1R,2S,4R)-1-bornylamine (L(5))) have been synthetised and characterised. Treatment of these compounds with AgSbF(6) generates dicationic complexes [(eta(6)-arene)Ru(pyam)(H(2)O)](2+) which act as enantioselective catalysts for the Diels-Alder reactions of methacrolein and cyclopentadiene. The catalytic reactions occur quickly at room temperature with good exo : endo selectivity (from 84 : 16 to 98 : 2) and moderate enantioselectivity (up to 74% ee). The molecular structures of the chloride complexes (R(Ru),S(N),R(C))-[(eta(6)-p-MeC(6)H(4)iPr)RuClL(1)][SbF(6)], (R(Ru),S(N),S(C2))-[(eta(6)-p-MeC(6)H(4)iPr)RuClL(5)][SbF(6)], and that of the aqua complex (R(Ru),S(N),S(C2))-[(eta(6)-p-MeC(6)H(4)iPr)RuL(5)(H(2)O)][SbF(6)](2), were determined by X-ray diffractometric methods. The distinctive variations observed in the molecular structures of these complexes only concern the puckering parameters of the metallacycle and the relative disposition of substituents within this ring. A clear trend to localise the most steric demanding substituents at equatorial positions is evident from the structural study.     

Chiral pyranoside phosphite-oxazolines: a new class of ligand for asymmetric catalytic hydrogenation of alkenes

We have described the first successful application of a phosphite-oxazoline ligand library in the asymmetric Ir-catalyzed hydrogenation of several unfunctionalized olefins. The introduction of a bulky biaryl phosphite moiety in the ligand design is highly adventitious in the product outcome. By carefully selecting the ligand components, we obtained high activities (TOFs up to >1500 mol x (mol x h)(-1) at 1 bar of H2) and enantioselectivities (ee values up to >99%) and, at the same time, show a broad scope for different substrate types. So, this is an exceptional ligand class that competes favorably with a few other ligand series that also provide high ee values for tri- and disubstituted substrate types.     

Chiral ansa-bridged η-cyclopentadienyl molybdenum complexes: Synthesis, structure and application in asymmetric olefin epoxidation

Ansa-bridged η⁵-cyclopentadienyl carbonyl molybdenum complexes were synthesized with stereogenic centers located in the side chain. An exemplary X-ray crystal structure and the catalytic activity for asymmetric olefin epoxidation are reported. In non-chiral epoxidation the compounds show a good catalytic activity, comparable to activities observed for the related non-chiral complexes of composition CpMo(CO)₃X (X = Cl, CH₃). For the asymmetric epoxidation of trans-β-methylstyrene the chiral induction is up to ca. 20%. The high ring strain of the ansa-bridged system hampers, unfortunately, its stability under oxidative condition.     

Dinuclear chiral vanadium catalysts for oxidative coupling of 2-naphthols via a dual activation mechanism

This review describes our recent efforts in the development of chiral dinuclear vanadium complexes that work as dual activation catalysts for the oxidative coupling of 2-naphthols. The dinuclear vanadium(iv) complex (R(a),S,S)- was prepared by complexation of VOSO(4) with the Schiff base derived from (R)-3,3'-diformyl-2,2'-dihydroxy-1,1'-binaphthyl () and (S)-tert-leucine. Since the dinuclear vanadium(iv) complex was found to be readily oxidized to afford a corresponding vanadium(v) species during preparation in air, a new synthetic procedure using VOCl(3) has been applied towards dinuclear vanadium(v) complexes (R(a),S,S)- and (R(a),S,S)-. To the best of our knowledge, (R(a),S,S)-, and show considerably higher catalytic activity than previously reported vanadium complexes for the oxidative coupling of 2-naphthols.     

Crystal structure,thermal decomposition mechanism and catalytic performance of hexaaquaaluminum methanesulfonate

Hexaaquaaluminum methanesulfonate crystals, [Al(H₂O)₆][CH₃SO₃]₃ were synthesized by a hydrothermal reaction of Al(OH)₃ with methanesulfonic acid. Single-crystal diffraction determination revealed that Al³⁺ was coordinated by six water molecules in octahedral geometry, while the CH₃SO₃^– anion connected with Al³⁺ through coordinated water molecules by hydrogen bonds. The six-coordinate environment of Al was also determined by ²⁷Al MAS NMR measurement. Thermogravimetric analysis and Fourier transform infrared spectroscopy showed that the decomposition intermediate at 265–365 °C was Al₂(μ-OH)(CH₃SO₃)₅ and the final product was amorphous Al₂O₃ residue with about 0.8 wt% SO₃ at 520–800 °C. A pure phase of [Al(H₂O)₆][CH₃SO₃]₃ was confirmed by powder X-ray diffraction analysis. Esterification of n-butyric acid with n-butanol and ketalization of cyclohexanone with glycol catalyzed by [Al(H₂O)₆][CH₃SO₃]₃ and Al₂(μ-OH)(CH₃SO₃)₅, respectively, proceeded in 100% yield by continuously removing the produced water. In the case of tetrahydropyranylation of n-butanol at room temperature in dichloromethane, the catalytic activity of [Al(H₂O)₆][CH₃SO₃]₃ was much lower than that of Al₂(μ-OH)(CH₃SO₃)₅. Furthermore, both [Al(H₂O)₆][CH₃SO₃]₃ precursor and Al₂(μ-OH)(CH₃SO₃)₅ catalysts could be recycled.     

Nickel complexes incorporating an amido phosphine chelate with a pendant amine arm: synthesis, structure, and catalytic Kumada coupling

A series of organonickel(II) complexes incorporating an amido phosphine ligand tethered with an amino pendant have been prepared and characterized. Deprotonation of N-(dimethylaminoethyl)-2-diphenylphosphinoaniline (H[PNN]) with one equivalent of n-BuLi in ethereal or hydrocarbon solutions at -35 °C generates cleanly dimeric {Li[PNN]}(2) as yellow crystals. The reaction of NiCl(2)(DME) with {Li[PNN]}(2) in THF at -35 °C affords green crystalline [PNN]NiCl. Treating [PNN]NiCl with NaX in acetone solutions gives [PNN]NiX (X = Br, I). Alkylation or arylation of [PNN]NiCl with appropriate Grignard reagents in THF at -35 °C produces red crystalline [PNN]NiR (R = Me, Et, i-Bu, n-hexyl, CH(2)Ph, Ph). The chloride complex [PNN]NiCl was found to be an active catalyst precursor for Kumada coupling reactions of PhX (X = I, Br, Cl) with aryl or alkyl Grignard reagents, including those containing β-hydrogen atoms. The X-ray structures of {Li[PNN]}(2) and [PNN]NiX (X = Cl, Br, Me, Et, n-hexyl) are reported.     

手性双提蓝钴卟啉配合物催化二氧化碳对环氧的不对称环加成（英文）

绿色化学是当今化学科学研究的前沿领域.仿生催化是绿色合成技术和方法学研究的一个重要方面.生物质和酶分子在酶催化转化过程中的"构-效"关系可以通过仿生催化进行模拟研究.CO_2作为温室气体的主要成分是造成全球气候变暖的主要因素,但它同时也是C1化学的重要原料.利用CO_2与有机环氧化合物通过偶联反应制备有机环碳酸酯或聚碳酸酯则是CO_2化学研究的热点之一,并已经取得了长足的进步.但是运用手性催化剂对此反应进行不对称环加成得到手性环碳酸酯的研究不多.本文首次设计并合成了具有双提篮结构的手性钴卟啉螯合物.其中的提篮部分由手性联萘酚(S或R)和L-苯丙氨酸组成,从卟啉骨架的meso位引入,首先制备了两种手性结构的自由卟啉配体(6a,7a);然后与醋酸钴反应得到两种二价钴卟啉手性配合物(6b,7b),加入醋酸后,通过空气氧化得到三价钴卟啉手性催化剂(6c,7c).采用紫外、红外光谱、质谱和核磁共振(包括二维NMR)等技术对得到的卟啉中间化合物、配合物和催化剂进行了详细的表征,确定了化合物的结构.将得到的三价钴卟啉配合物作为手性催化剂用于CO_2和环氧化合物的不对称环加成反应.结果表明,提篮的手性基团对小分子的环氧化合物环氧丙烷具有手性选择性,在低温-20°C下,可以得到大于50%的ee值.同时由于提篮与卟啉平面空间的有限性,导致分子体积较大的环氧化合物与CO_2的反应很慢,也没有发现其对环碳酸酯的对映选择性.我们相信本工作对于合成手性卟啉分子及其在不对称催化中的应用具有一定的意义.     

Ruthenium-catalyzed asymmetric epoxidation of olefins using H2O2, part II: catalytic activities and mechanism

Asymmetric epoxidation of olefins with 30 % H2O2 in the presence of [Ru(pybox)(pydic)] 1 and [Ru(pyboxazine)(pydic)] 2 has been studied in detail (pybox = pyridine-2,6-bisoxazoline, pyboxazine = pyridine-2,6-bisoxazine, pydic = 2,6-pyridinedicarboxylate). 35 Ruthenium complexes with sterically and electronically different substituents have been tested in environmentally benign epoxidation reactions. Mono-, 1,1-di-, cis- and trans-1,2-di-, tri-, and tetra-substituted aromatic olefins with versatile functional groups can be epoxidized with this type of catalyst in good to excellent yields (up to 100 %) with moderate to good enantioselectivies (up to 84 % ee). Additive and solvent effects as well as the relative rate of reaction with different catalysts have been established. It is shown that the presence of weak organic acids or an electron-withdrawing group on the catalyst increases the reactivity. New insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed epoxidation are proposed on the basis of density functional theory calculation and experiments.     

Highly regioselective, catalytic asymmetric reductive coupling of 1,3-enynes and ketones

[reaction: see text] Highly regioselective, catalytic asymmetric reductive coupling reactions of 1,3-enynes and ketones have been achieved using catalytic amounts of Ni(cod)(2) and a P-chiral, monodentate ferrocenyl phosphine ligand. These couplings represent the first examples of catalytic, intermolecular reductive coupling of alkynes and ketones, enantioselective or otherwise, and afford synthetically useful 1,3-dienes possessing a quaternary carbinol stereogenic center in up to 70% ee.     

Dinuclear vanadium complexes with rigid phenylpolycarboxylate ligands: synthesis,structure, and catalytic bromination reaction with potential detection of hydrogen peroxide

Vanadium complexes (VO)₂(2,2′-bipy)₂(bta)(H₂O)₂ (1) and (VO)₂(1,10-phen)₂(bta)(H₂O)₂ (2) (H₄bta?=?1,2,4,5-benzenetetracarboxylic acid, 2,2′-bipy?=?2,2-bipyridine and 1,10-phen?=?1,10-phenanthroline) have been synthesized by the reaction of V₂(SO₄)₃, H₄bta, 2,2′-bipy (for 1) and 1,10-phen (for 2) by hydrothermal methods. The complexes were characterized by elemental analysis, IR, UV–vis, thermogravimetric analyses, and single-crystal X-ray diffraction. Structural analyses indicate that 1 and 2 are both VO-bta-N-heterocycle system complexes. The central vanadium is coordinated by N₂O₄ donors to form a distorted octahedral geometry. The complexes exhibit catalytic bromination activity in a single-pot reaction with conversion of phenol red to bromophenol blue in a mixed solution of H₂O-DMF at 30?±?0.5?°C with pH 5.8, indicating that they can be considered as a functional model of vanadium-dependent haloperoxidases. The practical application of H₂O₂ detection has also been studied.     

Synthesis and catalytic performance of a soluble asymmetric zinc phthalocyanine

The soluble asymmetric phthalocyanine (Pc) (ZnPc-OH) was synthesized and used as a photosensitizer to degrade water pollutants. The catalytic ability of zinc Pc was proved by degrading Rhodamine B. In addition, ZnPc-OH, which has good solubility, can be used in photodynamic therapy.     

Effects of promoters on catalytic performance of Fe-Co/SiO2 catalyst for Fischer-Tropsch synthesis

2%Fe-10%Co/SiO₂ catalysts with different potassium or zirconium loadings were prepared by aqueous incipient wetness impregnation and tested for Fischer-Tropsch synthesis in a flow reactor, using H₂/CO = 1.6 (molar ratio) in the feed, under the condition of an overall pressure of 1 MPa, GHSV of 600 h⁻¹ and temperature of 503 K. The zirconium and potassium promoters remarkably influenced hydrocarbon distribution of the products. CO conversion increased on the catalysts with the increase of zirconium loadings, which indicated that zirconium enhanced the activity of iron-cobalt catalysts. Low potassium loadings also enhanced the activity of the catalysts. However, high potassium loading made CO conversion on the catalysts decrease and weakened the secondary hydrogenations. The catalyst was characterized by BET, XRD and TPR. The catalyst characterization revealed that the Co₃O₄ phase was presented on the fresh catalyst, whereas the spinel phase of Fe-Co alloy and CoO existed on the used catalyst.     

Acidity, surface structure, and catalytic performance of WO(x) supported on monoclinic zirconia

The relationship between the acidity, catalytic activity, and surface structure for tungsten oxide supported on zirconia was investigated for a series of solids prepared by equilibrium adsorption on monoclinic zirconia. The catalysts were active for propanol dehydration only above a threshold in W loading. The acidity was studied by infrared spectroscopy of adsorbed probe molecules (2,6-dimethylpyridine and CO), and the onset of activity was correlated with that of the formation of relatively strong Br?nsted acid sites. The variation in the abundance of these sites correlated with the catalytic activity. Lewis sites were present but could not be directly associated with the activity. Raman, IR, and UV spectroscopy results indicated that the active sites were related to polymeric W surface species.