Kinetics of Acid‐Catalyzed Dissociation of Nickel (II) N‐Alkyl‐Substituted Diamino Diamide Complexes

The dissociation kinetics of the nickel (II) complexes of 4‐methyl‐4,7‐diazadecanediamide (4‐Me‐L‐2,2,2), 4,7‐dimethyl‐4,7‐diazadecanediamide (4,7‐N, N′‐Me2‐L‐2,2,2), 4‐ethyl‐4,7‐diazadecanediamide (4‐Et‐ L‐2,2,2), and 4‐methyl‐4,8‐diazaundecanediamide (4‐Me‐L‐2,3,2) have been studied at 25.0 °C and μ = 4.0 M (NaClO₄ + HClO₄) by the stopped‐flow method. These reactions are specific‐acid catalyzed; however, the rate constants of these reactions do not depend on the concentrations of acetic, chloro acetic, and dichloroacetic acids. At pH values be low 1.0, both the proton‐assisted and the direct protonation path ways make contributions to the rates. The ratios of the rate constant of dissociation by the direct protonation path way to the rate constant by the proton‐assisted path way for the complexes in aqueous solution were measured and discussed.     

Kinetics of Acid‐Catalyzed Dissociation of Copper(II) N‐Alkyl‐Substituted Diamino Diamide Complexes

The dissociation kinetics of the copper(II) complexes of 4‐methyl‐4,7‐diazadecanediamide (4‐Me‐L‐2,2,2), 4,7‐dimethyl‐4,7‐diazadecanediamide (4,7‐N,N′‐Me₂‐L‐2,2,2), 4‐ethyl‐4,7‐diazadecanediamide (4‐Et‐L‐2,2,2), and 4‐methyl‐4,8‐diazaundecanediamide (4‐Me‐L‐2,3,2) have been studied at 25.0 °C and μ = 4.0 M (NaClO₄ + HClO₄) by the stopped‐flow method. These reactions are specific‐acid catalyzed; however, the rate constants of these reactions do not depend on the concentrations of acetic, chloroacetic, and dichloroacetic acids. At pH values below 1.4, both the proton‐assisted and the direct protonation pathways make contributions to the rates. The ratios of the rate constant of dissociation by the direct protonation pathway to the rate constant by the proton‐assisted pathway for the complexes in aqueous solution were measured and discussed.     

Solvent Effects in Acid‐Catalyzed Biomass Conversion Reactions

Reaction kinetics were studied to quantify the effects of polar aprotic organic solvents on the acid‐catalyzed conversion of xylose into furfural. A solvent of particular importance is γ‐valerolactone (GVL), which leads to significant increases in reaction rates compared to water in addition to increased product selectivity. GVL has similar effects on the kinetics for the dehydration of 1,2‐propanediol to propanal and for the hydrolysis of cellobiose to glucose. Based on results obtained for homogeneous Brønsted acid catalysts that span a range of pK_a values, we suggest that an aprotic organic solvent affects the reaction kinetics by changing the stabilization of the acidic proton relative to the protonated transition state. This same behavior is displayed by strong solid Brønsted acid catalysts, such as H‐mordenite and H‐beta.     

Synthesis and Characterization of Complexes of Copper(II), Nickel(II) and Cobalt(II) with vic-Dioximes Bearing N''-p-Aminobenzoyl Benzaldehyde Hydrazone

Six different arylhydrazone derivatives of p-aminobenzoic hydrazide of vic-dioximes were synthesized by reaction of chloroglyoxime and dichloroglyoxime with N＇-p-aminobenzoyl benzaldehyde, 4-hydroxybenzaldehyde and 4-methoxybenzaldehyde hydrazones, respectively. Metal-ligand （1 ： 2） complexes of vic-dioxime derivatives with Cu（Ⅱ）, Ni（Ⅱ） and Co（Ⅱ） were prepared from corresponding metal acetates. The ligands and their complexes were characterized on the basis of elemental analyses and spectral data. The complexing abilities of these new vic-dioximes toward transition metals of Co（Ⅱ）, Cu（Ⅱ）, Ni（Ⅱ）, Zn（Ⅱ）, Cd（Ⅱ）, Mn（Ⅱ） and Cr（Ⅲ） were determined by solid-liquid extraction studies.     

Biological Effect,Aquation, and Kinetics of Oxidation of Bis(2‐aminobenzothiazole)dichlorocobalt(II) Complex by Periodate in Aqueous Acidic Medium

The biological effect, aquation, and kinetics of oxidation of bis(2‐aminobenzothiazole)dichlorocobalt(II) complex by periodate in aqueous acidic solutions were studied. The complex exhibited a broad resistance toward the studied pathogens. The average value of the aquation constant was calculated spectrophotometrically as 2.55 × 10^?5 mol² dm^?6. Kinetics of the oxidation reaction showed first‐order dependence on each reactant concentration and increased by increasing pH over the 3.80–4.80 range, 35–50°C, and decreased by increasing the ionic strength over the 0.1–0.5 mol dm^?3 range. The polymerization of acrylonitrile was taken as an evidence for an inner‐sphere mechanism through the formation of free radical intermediates of Co(III) complexes, which were slowly converted to the final Co(III)products.     

Colorimetric Solvent Indicators Based on Nafion Membranes Incorporating Nickel(II)‐Chelate Complexes

To develop solvent‐recognition films, Nafion membranes incorporating cationic nickel‐chelate complexes, that is, [Ni(L¹)(L²)]⁺ (HL¹=acetylacetone, 2,2,6,6‐tetramethyl‐3,5‐heptanedione; L²=N,N‐diethylethylenediamine, N‐butyl‐N,N′,N′‐trimethylethylenediamine), were prepared. Immersion of the films in various solvents effected the color changes varying from red to pale blue green depending on the donor number of the solvents. The color change is based on an equilibrium shift between square‐planar and solvent‐coordinated octahedral geometries of the cations. The degree of the color change depended on the affinity of the incorporated complex to the solvent molecules. The films were robust and exhibited a reversible solvent response. The films exhibited thermochromism when a small amount of appropriate solvents were incorporated and changed from pale blue green at low temperatures to red at high temperatures.     

Mathematical Modeling of Acid‐Catalyzed 1,3‐Propanediol Polymerization

A reaction mechanism for the polymerization of 1,3‐propanediol is proposed for two acid catalysts. Population and mass balance equations are derived for small molecules and for polymeric species of chain distributions distinguishable in terms of protonation state and end group functionality. Since the sulfuric acid catalyzed process has two types of polymer linkages, the derivation of the moment equations is challenging. The reverse reactions are also accounted thus creating a moment closure problem. A mass transfer model is developed to predict reaction mixture water content. The Sanchez‐Lacombe equation of state is used to calculate phase behavior and species partitioning. Optimization of selected parameters is accomplished by comparison to laboratory data resulting in a fully predictive model.

     

Influence of Decreasing Solvent Polarity (1,4‐Dioxane/Water Mixtures) on the Acid–Base and Copper(II)‐Binding Properties of Guanosine 5′‐Diphosphate

The acidity constants of twofold protonated guanosine 5′‐diphosphate, H₂(GDP)^?, and the stability constants of the [Cu(H;GDP)] and [Cu(GDP)]^? complexes were determined in H₂O as well as in 30 or 50% (v/v) 1,4‐dioxane/H₂O by potentiometric pH titrations (25°; I=0.1M , NaNO₃). The results showed that in H₂O one of the two protons of H₂(GDP)^? is located mainly at the N(7) site and the other one at the terminal β‐phosphate group. In contrast, for 50% 1,4‐dioxane/H₂O solutions, a micro acidity‐constant evaluation evidenced that ca. 75% of the H₂(GDP)^? species have both protons phosphate‐bound, because the basicity of pyridine‐type N sites decreases with decreasing solvent polarity whereas the one of phosphate groups increases. In the [Cu(H;GDP)] complex, the proton and the metal ion are in all three solvents overwhelmingly phosphate‐bound, and the release of this proton is inhibited by decreasing polarity of the solvent. Based on previously determined straight‐line plots of log K vs. pK (where R represents a non‐interacting residue in simple diphosphate monoesters ROP(O^?)(?O)? O? P(?O)(O^?)₂, R? DP^3?), which were now extended to mixed solvents (based on analogies), it is concluded that, in all three solvents, the [Cu(GDP)]^? complex is more stable than expected based on the basicity of the diphosphate residue. This increased stability is attributed to macrochelate formation of the phosphate‐coordinated Cu²⁺ with N(7) of the guanine residue. The formation degree of this macrochelate amounts in aqueous solution to ca. 75% (being thus higher than that of the Cu²⁺ complex of adenosine 5′‐diphosphate) and in 50% (v/v) 1,4‐dioxane/H₂O to ca. 60%, i.e., the formation degree of the macrochelate is only relatively little affected by the change in solvent, though it needs to be emphasized that the overall stability of the [Cu(GDP)]^? complex increases with decreasing solvent polarity. By including previously studied systems in the considerations, the biological implications are shortly discussed, and it is concluded that Nature has here a tool to alter the structure of complexes by shifting them on a protein surface from a polar to an apolar region and vice versa.     

Iron(II)‐Catalyzed Hydrophosphination of Isocyanates

The first transition metal catalyzed hydrophosphination of isocyanates is presented. The use of low‐coordinate iron(II) precatalysts leads to an unprecedented catalytic double insertion of isocyanates into the P−H bond of diphenylphosphine to yield phosphinodicarboxamides [Ph₂PC(=O)N(R)C(=O)N(H)R], a new family of derivatized organophosphorus compounds. This remarkable result can be attributed to the low‐coordinate nature of the iron(II) centers whose inherent electron deficiency enables a Lewis‐acid mechanism in which a combination of the steric pocket of the metal center and substrate size determines the reaction products and regioselectivity.     

Synthesis,Spectral, Thermal and Biological Studies of Mn(II), Co(II), Ni(II) and Cu(II) Complexes with 1‐(((5‐Mercapto‐1H‐1,2,4‐triazol‐3‐yl)imino)‐methyl)naphthalene‐2‐ol

Mn(II), Co(II), Ni(II) and Cu(II) complexes of 5‐mercapto‐1,2,4‐triazol‐3‐imine‐2′‐hydroxynaphthaline have been synthesized and characterized by elemental analysis, IR, ¹H NMR, EI‐mass, UV‐Vis, and ESR (electron spin resonance) spectra, molar conductance, magnetic moment measurements, DC conductivity and thermogravimetric analysis. IR spectra confirm that the ligand molecule existed in both thione and thiole forms. The molar conductance values indicate the complexes are nonelectrolyte. The magnetic moment values of the complexes display paramagnetic behavior. All studies confirm the formation of an octahedral geometry for complex 1 and the other complexes have tetrahedral geometrical structures. The structures of the complexes have also been theoretically studied by using the molecular mechanic calculations by the hyperchem. 8.03 molecular modeling program which confirm the proposed structures. The Schiff‐base ligand and its metal complexes have also been screened for their antimicrobial activities.     

NCC Pincer Ni (II) Complexes Catalyzed Hydrophosphination of Nitroalkenes with Diphenylphosphine

An efficient NCC pincer Ni (II)-catalyzed hydrophosphination of nitroalkenes with diphenylphosphine has been developed. Under the optimized conditions, both (hetero)aromatic and aliphatic nitroalkenes were well tolerated, irrespective of electronic effect, to provide the corresponding products in up to 99% yield.     

Host (Nano Cage NaY)/Guest Mn(II), Co(II), Ni(II) and Cu(II) Complexes of N,N‐Bis(3,5‐Di‐Tert‐Butylsalicyidene)‐2,2‐Dimethyle‐1,3‐Diaminopropane: Synthesis and Catalyst Activity

Mn(II), Co(II), Ni(II) and Cu(II) and N,N‐bis(3,5‐di‐tert‐butylsalicyidene)‐2,2‐dimethyle‐1,3‐diaminopropane complexes have been synthesized in Y zeolite cavity by the reaction of ion‐exchanged metal ions with the flexible ligand molecules. The host‐guest materials obtained have been characterized by elemental analysis, XRD, surface area, pore volume, TGA, FT‐IR and UV‐Vis techniques. Analysis of data indicates that formation of complexes in the pores Y zeolite without affecting the zeolite framework structure. Also, we report the oxidation of cyclohexanol catalyzed by host‐guest catalyst with tert‐buthyl hydrogen peroxide as oxygen donor. The activity of benzyl alcohol oxidation decreases in the series‐[Co(L)]/NaY > [Cu(L)]/NaY > [Mn(L)]/NaY > [Ni(L)]/NaY and the percent of product completely depend to catalyst. Zeolite complexes are stable enough to be reused and are suitable to be utilized as partial oxidation catalysts.     

Palladium(II)‐dppe‐arylazoimidazole Complexes: Synthesis and Spectroscopic Charecterization

Reaction of [Pd(dppe)Cl2/Br2] with AgOTf in a dichloromethane medium followed by ligand addition led to [Pd(dppe)(OSO2CF3)2] and then [Pd(dppe)(RaaiR’)](OSO2CF3)2 [RaaiR’＝p-R-C6H4-NN-C3H2-NN-1-R’, (1—3), abbreviated as a N,N’-chelator, where N(imidazole) and N(azo) are represented by N and N’, respectively; R＝H (a), Me (b), Cl (c) and R’＝Me (1), CH2CH3 (2), CH2Ph (3), OSO2CF3 is the triflate anion, dppe＝1,2-bis- (diphenylphosphinoethane)]. 31P NMR confirmed that due to the two phosphorus atom interaction in the azoimine symmetrical environment one sharp peak was formed. The 1H NMR spectral measurements suggest that azo-imine links with lot of phenyl protons in the aromatic region. 13C NMR spectrum, 1H-1H COSY and 1H-13C HMQC spectrum assign the solution structure and stereo-retentive conformation in each complex.     

Rhodium(II)‐Catalyzed Enantioselective Synthesis of Troponoids

We report a rhodium(II)‐catalyzed highly enantioselective 1,3‐dipolar cycloaddition reaction between the carbonyl moiety of tropone and carbonyl ylides to afford troponoids in good to high yields with excellent enantioselectivity. We demonstrate that α‐diazoketone‐derived carbonyl ylides, in contrast to carbonyl ylides derived from diazodiketoesters, undergo [6+3] cycloaddition reactions with tropone to yield the corresponding bridged heterocycles with excellent stereoselectivity.     

The Copper(II)‐Catalyzed Oxidation of Glutathione

The kinetics and mechanisms of the copper(II)‐catalyzed GSH (glutathione) oxidation are examined in the light of its biological importance and in the use of blood and/or saliva samples for GSH monitoring. The rates of the free thiol consumption were measured spectrophotometrically by reaction with DTNB (5,5′‐dithiobis‐(2‐nitrobenzoic acid)), showing that GSH is not auto‐oxidized by oxygen in the absence of a catalyst. In the presence of Cu²⁺, reactions with two timescales were observed. The first step (short timescale) involves the fast formation of a copper–glutathione complex by the cysteine thiol. The second step (longer timescale) is the overall oxidation of GSH to GSSG (glutathione disulfide) catalyzed by copper(II). When the initial concentrations of GSH are at least threefold in excess of Cu²⁺, the rate law is deduced to be ?d[thiol]/dt=k[copper–glutathione complex][O₂]^0.5[H₂O₂]^?0.5. The 0.5^th reaction order with respect to O₂ reveals a pre‐equilibrium prior to the rate‐determining step of the GSSG formation. In contrast to [Cu²⁺] and [O₂], the rate of the reactions decreases with increasing concentrations of GSH. This inverse relationship is proposed to be a result of the competing formation of an inactive form of the copper–glutathione complex (binding to glutamic and/or glycine moieties).