Catalytic activation of nucleophile precursors with metal acetates in alcohol media and applications to enantioselective Michael addition reactions

Nickel(II) acetate tetrahydrate works as catalyst to activate nucleophile precursors in Michael addition reactions. Use of alcohol media is essential for the high catalytic activation of nucleophile precursors. Catalytic enantioselective reactions using a chiral nickel(II) acetate tetrahydrate between dimedone and α,β-unsaturated amide acceptors provide a useful synthetic access to enantiomers of enol lactones through the carbon-carbon bond formation.     

Unsymmetric bimetal(II) complexes: Synthesis, structures and catalytic behaviors toward ethylene

A series of unsymmetric bimetal(II) (Fe, Co and Ni) complexes ligated by 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines were synthesized and characterized by IR spectra and elemental analysis, while a representative nickel(II) complex (5a) was determined by single-crystal X-ray crystallography. These iron(II) complexes were found to exhibit good activities for ethylene oligomerization and polymerization in the presence of MMAO and afforded α-olefins in high selectivity, and the composition of oligomers followed the Schluz-Flory distribution. The nickel(II) complexes mainly dimerize ethylene with considerable activity. The influences of coordinative ligands and reaction parameters were fully investigated on the catalytic activity and properties of these complexes.     

New Tetraaza Macrobicyclic Ditopic Receptors for Metal Ions: Synthesis,Redox Response and Kinetics of Phosphate Hydrolysis of Unsymmetrical Macrobicyclic Mono- and Binuclear Nickel(II) Complexes

A new series of macrobicyclic ditopic receptors is derived from the precursor compound 3,4:10,11-dibenzo-1,13[N,N′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}di-aza]-5,9-dioxocyclohexadecane. Using this precursor, mono- and binuclear nickel(II) complexes of type [NiL](ClO₄) and [Ni₂L](ClO₄)₂ have been synthesized to undertake electrochemical and catalytic studies on the basis of macrocyclic ring size. The receptor is a tricompartmental macrocycle consisting of ether oxygen, tertiary nitrogen and imine nitrogen atoms. The redox studies of these systems show that the nickel(II) complexes undergo quasi-reversible one-electron reduction and oxidation. All the nickel(II) complexes have square planar geometry and are EPR silent. Examination of the kinetics of the hydrolysis of 4-nitrophenyl phosphate shows that the catalytic activities of the complexes increase with the macrocyclic ring size of the complexes. As the macrocyclic ring size of the complexes increases, the spectral, electrochemical and catalytic studies of the complexes show considerable variation due to distortion in the geometry around the nickel(II) centre.     

Efficient Synthesis of β‐Hydroxy‐α‐Amino Acid Derivatives via Direct Catalytic Asymmetric Aldol Reaction of α‐Isothiocyanato Imide with Aldehydes

An easily available and efficient chiral N,N′‐dioxide–nickel(II) complex catalyst has been developed for the direct catalytic asymmetric aldol reaction of α‐isothiocyanato imide with aldehydes which produces the products in morderate to high yields (up to 98 %) with excellent diastereo‐ (up to >99:1 d.r.) and enantioselectivities (up to >99 % ee). A variety of aromatic, heteroaromatic, α,β‐unsaturated, and aliphatic aldehydes were found to be suitable substrates in the presence of 2.5 mol % L ‐proline‐derived N,N′‐dioxide L5 –nickel(II) complex. This process was air‐tolerant and easily manipulated with available reagents. Based on experimental investigations, a possible transition state has been proposed to explain the origin of reactivity and asymmetric inductivity.     

Photo-stabilising effect of Ni compounds in photo-oxidative degradation of cis-1,4-poly(butadiene)

The photo-stabilisation effect of two nickel chlorides—bis(tributyl phosphine)nickel-(II)chloride and cyclopentadienyl(triphenyl phosphine)nickel(II)chloride—and three nickel chelates—bis(dithiobenzil)nickel, bis(4-dimethylaminodithiobenzil)nickel and 2,2′-thiobis(4-t-octylphenolato)n-butylamine nickel (Cyasorb® UV 1084)—on the oxidative photo-degradation of cis-1,4-poly(butadiene) has been investigated. Their stabilising effect includes possible mechanisms such as ultraviolet screening, catalytic decomposition of hydroperoxides, radical trapping and singlet oxygen deactivation.     

A nickel-substituted form of nanodiamonds and its catalytic activity in decomposition of hydrogen peroxide

Adsorption of nickel (II) ions with nanodiamonds obtained by the detonation synthesis was studied. A nickel-substituted form of nanodiamonds was obtained. The catalytic activity exhibited by nickel ions (II) in the form of the surface complexes with nanodiamond functional groups in decomposition of hydrogen peroxide was determined.     

An insertion and Cycloaddition reaction of Dimethylketene with di-π-cyclopentadienylnickel

The complex (π-cyclopentadienyl)[σ-α,α-dimethyl-α-{2-3-π-[7,7-dimethyl-6-oxobicyclo[3.2.0]hept-2-en-4-yl]}acetyl]nickel (II) has been identified as the principal product of the reaction of two moles of dimethylketene with di-π-cyclopentadienylnickel. Degradation of II in methanol solution yielded methyl α,α,7,7-tetramethyl-6-oxobicyclo[3.2.0]hept-2-ene-4-acetate (III); and reduction of II gave the 6-hydroxy nickel complex (VI). Complex II is a result of 1,2-cycloaddition of one ketene function to a cyclopentadienyl ring and insertion of a second ketene function into a nickelcarbon bond.     

2-苯并咪唑吡啶镍配合物的合成﹑晶体结构及与DNA相互作用的共振散射光谱研究

合成了2-苯并咪唑吡啶镍配合物[Ni(C12H9N3)3](ClO4)2•H2O, 通过IR, UV-Vis和元素分析对其进行了表征, 并通过X射线单晶衍射确定了其晶体结构. 单晶结构分析表明, 该晶体属于三斜晶系, 空间群为 , a＝1.20076(5) nm, b＝1.22545(5) nm, c＝1.49077(5) nm, α＝88.2430(10)°, β＝71.7970(10)°, γ＝72.544(2)°, Z＝2, 最终偏离因子R1＝0.0608, wR2＝0.1859. 配合物的金属中心与6个配位氮原子形成八面体的几何构型. 用共振瑞利散射(RRS)研究了配合物与DNA的作用, 配合物与DNA相互作用形成复合产物并出现了相应的新的RRS光谱, 且随着配合物浓度的增大引起共振瑞利散射增强, 在低离子强度的环境下与DNA的作用比较明显. 这些实验结果表明了配合物与DNA之间存在较强的相互作用.     

Chiral and Achiral Bis（2-oxazolinylphenolato）nickel（Ⅱ） Complexes-Synthesis, Crystal Structure, and Catalytic Properties

Introduction Oxidation was a very important reaction both in synthetic pathways and in industrial processes. Metal-catalyzed oxidation provided excellent alternatives in synthetic processes. However, molecular oxygen has been applied only in a limited number of metal-catalyzed oxidations, because it was very difficult to activate molecular oxygen and most of transition metal complexes were sensitive to oxygen. It was noted that metal-catalyzed Baeyer-Villiger oxidation was a convenient method…     

Enantioselective α-hydrazination of α-fluoro-β-ketoesters catalyzed by chiral nickel complexes

The catalytic enantioselective electrophilic α-hydrazination promoted by chiral nickel complexes is described. Treatment of α-fluoro-β-ketoesters with azodicarboxylates as electrophilic amination reagents under mild reaction conditions afforded the corresponding α-amino α-fluoro-β-ketoesters with high yields (80-96%) and enantioselectivities (up to 78% ee).     

Silicon hydrides and nickel complexes : II. Mechanism of the hydrosilylation catalyzed by nickel-phosphine complexes

Two ethylene-nickel(0) complexes, viz., [1,2-bis(diphenylphosphino)ethane]-(ethylene)nickel(0) and bis(triphenylphosphine)(ethylene)nickel(0) have been used in a comparison of their catalytic activities in hydrosilylation reactions with those of the corresponding nickel(II) complexes, viz., dichloro [1,2-bis(diphenylphosphino)-ethane]nickel(II) and dichlorobis(triphenylphosphine)nickel(II). The reaction profiles are similar, apart from a significant difference in the induction period; the nickel(II) catalysts requiring a substantially longer time. A mechanism involving a nickel(0) species is proposed for the hydrosilylation.The interchange of hydrogen and chlorine on silicon accompanying the hydrosilylation is related to a high electron density at the nickel atom bearing the phosphine, olefin, and silicon hydride ligands.     

Semi-automatic catalytic titration of metal ion mixtures and its application to metallurgical samples

The semi-automatic catalytic titration of several metal ions and binary mixtures of iron(III) with copper(II), nickel or manganese(II) is described. The 4,4′-dihydroxybenzophenone thiosemicarbazone/hydrogen peroxide system was used in the presence of EDTA or EGTA as inhibitors with copper(II) as catalytic titrant. Two sample aliquots are necessary for the analysis of binary mixtures. In one, both metals are titrated in the presence of EDTA; in the other, only copper, nickel or manganese is titrated with EGTA or EDTA if a masking agent for iron(III) (triethanolamine or fluoride) is added. The iron/metal ratios tolerated range from 1:14 to 13:1 for the 0.2–3.0 μmol range, the relative standard deviation being 1–2%. The method was applied to metallurgical samples with good results.     

Nickel(II) complexes with tetra- and pentadentate aminopyridine ligands: synthesis, structure, electrochemistry, and reduction to nickel(I) species

A series of nickel(II) complexes with polydentate aminopyridine ligands N,N,N'-tris-[2-(2'-pyridyl)ethyl]ethane-1,2-diamine (L1), N,N,N'-tris-[2-(2'-pyridyl)ethyl]-N'-methylethane-1,2-diamine (L2), and N,N'-bis-[2-(2'-pyridyl)ethyl]-N,N'-dimethylethane-1,2-diamine (L3) were synthesized and characterized by elemental analysis and spectroscopic methods. Single-crystal X-ray diffraction studies showed that the Ni(II) ions have five-coordinate square-pyramidal geometry in [NiL2](ClO(4))(2), similar to that previously found in [NiL1](ClO(4))(2) x CH(3)NO(2) (Hoskins, B. F.; Whillans, F. D.J. Chem. Soc., Dalton Trans. 1975, 657), and square-planar geometry in [NiL3](ClO(4))(2). All three nickel(II) complexes are reduced by sodium borohydride or sodium amalgam in organic solvents to nickel(I) species, which were identified by highly anisotropic EPR spectra at 100 K: g(1) = 2.239, g(2) = 2.199, and g(3) = 2.025 for [NiL1](+); g(axially) = 2.324 and g(radially) = 2.079 for [NiL2](+) and [NiL3](+). Cyclic voltammetry of the nickel(II) complexes in acetonitrile exhibited reversible reduction waves at -1.01 V for [NiL1](2+), -0.91 V for [NiL2](2+), and -0.83 V for [NiL3](2+) versus SCE, potentials which are significantly less negative than those of most previously characterized Ni(II) complexes with nitrogen-only donor atoms. Complexes [NiL1](2+) and [NiL2](2+) showed high catalytic activity in the electroreduction of 1,2-trans-dibromocyclohexane to cyclohexene.     

Electrochemical, catalytic and antimicrobial activity of N-functionalized tetraazamacrocyclic binuclear nickel(II) complexes

The five binuclear nickel(II) complexes have been synthesized by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. All the five complexes were characterized by elemental and spectral analysis. The electronic spectra of the complexes show three d-d transition in the range of 550-1055 nm due to 3A2g→3T2g(F), 3A2g→3T1g(F) and 3A2g→3T1g(P). These spin allowed electronic transitions are characteristic of an octahedral Ni2+ center. Electrochemical studies of the complexes show two irreversible one electron reduction waves at cathodic region. The reduction potential of the complexes shifts towards anodically upon increasing the chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves at anodic region. The oxidation potential of the complexes shift towards anodically upon increasing the chain length of the macrocyclic ring. The catalytic activities of the complexes were observed to be increase with increase the macrocyclic ring size. The observed rate constant values for the catalytic hydrolysis of 4-nitrophenyl phosphate are in the range of 5.85×10(-3) to 9.14×10(-3) min(-1). All the complexes were screened for antimicrobial activity.     

Cathodic stripping voltammetric determination of 2-mercaptobenzothiazole using the catalytic cobalt peak

Previously, thiols have been determined indirectly by cathodic stripping voltammetry (CSV) after accumulation as their mercury and copper(I) salts. Following a previous report of the first use of the catalytic nickel peak (for the determination of cysteine), this paper reports the first use of the catalytic cobalt peak in CSV (for the determination of 2-mercaptobenzothiazole (MBT)): only a very ill-defined catalytic cobalt peak had been observed previously with cysteine, and was unreported. MBT is accumulated at pH 4 (Britton-Robinson buffer) as its cobalt(II) complex at -0.1 V, and is then determined indirectly by observing the reduction of the cobalt(II) in the complex at -0.95 V, i.e., with a much lowered overpotential: hydrated cobalt(II) is reduced at -1.2 V. The peak is catalytic because the thiol released on reduction of the complex complexes further cobalt ions and causes their reduction. The detection limit for the determination of MBT was calculated to be 2.5 x 10(-9) M (3sigma) using an accumulation time of 1 min. The sensitivity is about three times that obtained with the corresponding catalytic nickel peak.     

m-Carborane-based chiral NBN pincer-metal complexes: synthesis, structure, and application in asymmetric catalysis

We have succeeded in synthesizing m-carborane-based chiral NBN-pincer ligands, 1,7-bis(oxazolinyl)-1,7-dicarba-closo-dodecaborane (Carbox) (7-9). The combination of bis(hydroxyamides) and 3 equiv of diethylaminosulfur trifluoride (DAST) is a key step for cyclization to form oxazoline rings in excellent yields. X-ray crystal structures of these ligands confirmed three donor sites, one central B and two flanking N atoms in fixed positions. The electrophilic halogenation of the Carbox pincer ligands with iodine and a catalytic amount of Lewis acid led to ring-opening of the oxazolines and afforded bis(haloamides) (13 and 14). The air- and moisture-stable Carbox pincer complexes of rhodium(III), nickel(II), and palladium(II) were synthesized by the oxidative addition of RhCl(3)·3H(2)O, Ni(COD)(2), and Pd(CH(3)CN)(4)[BF(4)](2) to the Carbox pincer ligands (7-9), respectively. The catalytic activity of the rhodium(III) complexes (18-20) was examined for the asymmetric conjugate reduction of α,β-unsaturated esters and reductive aldol reaction. Among these catalysts, [(S,S)-Carbox-iPr]Rh(OAc)(2)·H(2)O (18) showed the highest enantioselective catalytic ability for both asymmetric conjugate reduction and reductive aldol reaction.     

Voltammetric and flow-injection determination of carbohydrates using composite electrodes based on carbon nanotubes and Nickel(II) hexacyanoferrate

The catalytic activities of oxo and hydroxo forms of nickel(II) on the surface of a nickel deposit and an inorganic film of nickel(II) hexacyanoferrate(III) (NiHCF) electrodeposited on a glassy-carbon electrode both unmodified and modified by multi-wall or single-wall (also functionalized) carbon nanotubes in the electrooxidation of glucose, sucrose, and maltose are compared. A more pronounced catalytic effect was obtained in the electrooxidation of these carbohydrates on an electrode modified with functionalized singlewall carbon nanotubes and a NiHCF film. Methods are proposed for the voltammetric and flow-injection determination of carbohydrates on this composite electrode. A linear dependence of the analytical signal on the analyte concentration was observed in the range from 5 × 10^?7 to 5 × 10^?2 M under stationary conditions and from 0.003 to 0.3 μmol under flow conditions.     

Ethylene polymerization by bis(salicylaldiminate)nickel(II)/aluminoxane catalysts

The homopolymerization of ethylene by using different catalytic systems based on dinitro‐substituted bis(salicylaldiminate)nickel(II) precursors such as bis[3,5‐dinitro‐N(2,6‐diisopropylphenyl)]nickel(II) and bis[3,5‐dinitro‐N(phenyl)]nickel(II) in combination with organoaluminum compounds was investigated. In particular, the catalytic performances were studied as a function of the main reaction parameters, such as temperature, pressure, Al/Ni molar ratio, and duration. Methylaluminoxane resulted in the best co‐catalyst. Activities up to 200 kg polyethylene/(mol Ni × h) to give a linear high‐molecular‐weight polymer were achieved. The influence of the bulkiness of the substituents on the N‐aryl group of the aldimine ligand was also checked; it resulted in a determinant for catalytic activity rather than for polymer characteristics. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2534–2542, 2004     

Azetidines as ligands in the Pd(II) complexes series

The preparation of palladium (II) complexes having sterically congested azetidines as ligands is described. Diastereomerically pure α-alkylamino and α-alkylimino azetidines react with Na₂PdCl₄ to afford the corresponding bidendate Pd(II) complexes, whereas 2-cyano azetidines can be used to access bidendate Pd(II) complexes containing an amino-imidate moiety. Preliminary study of the catalytic activity of these new complexes in the Suzuki cross-coupling reaction is presented.     

The role of phosphine and 1,2-diimine complexes of nickel in the oxidation states 0, +1, and +2 in the catalyzed di-, oligo-, and polymerization of ethylene

The turnover frequency and number have been determined for eighteen catalytic systems based on triphenylphosphine and 1,4-diazo-1,3-butadiene complexes of nickel in the formal oxidation states 0, +1, and +2 in the oligoand polymerization of lower alkenes. The main catalytic characteristics are almost independent of the oxidation state of nickel in the precursor and depend on the nature and concentration of the cocatalyst (Lewis acid). The catalytic systems have been studied by ESR. The ESR spectral parameters are presented for nickel(I) 1,4-diazo-1,3-butadiene complexes and radical anions resulting from the reactions of the cocatalyst with nickel α-diimine complexes. Reactions describing the formation, functioning, decomposition, and regeneration of the catalytically active nickel hydride complexes are proposed.