Substitution and Redox Properties of Some Organoisocyanide Cobalt(II) Complexes

The reactions of four tetrakis(arylisocyanide)cobalt(II) complexes, [Co(CNR)4(ClO4)2] {R = 2,6-Me2C6H3 (A), 2,4,6-Me3C6H2 (B), 2,6-Et2C6H3 (C), and 2,6-iPr2C6H3 (D)}, with two pyridines, 4-CNpy and 4-Mepy, have been kinetically studied in trifluoroethanol medium. Each of the reactions, which was monitored over a temperature range of 293 to 318 K, exhibited two distinct processes proposed to be an initial fast substitution process followed by a slow reduction process. For each pyridine, steric hindrance was observed to play a significant role in the rates of the reactions, which decrease with increasing size of the arylisocyanide ligand in the order k(A) > k(B) > k(C) > k(D). Addition of each of three triarylphosphines, PR3 (R = Ph, C6H4Me-p, C6H4OMe-p), to solutions of pentakis(t-octylisocyanide)cobalt(II), [Co(CNC8H17-t)5](ClO4)2, resulted in a shift in the λmax of the electronic spectrum accompanied by a change in color of the solutions. The shift is attributed to ligand substitution. The reactions of the cobalt(II) complex [Co(CNC8H17-t)5]2+ with the triarylphosphines are proposed to proceed via a combination of substitution, reduction, and disproportionation mechanisms with final formation of disubstituted Co(I) complexes. The order of reactivity of the complex with the triarylphosphines was found to be P(C6H4OMe-p)3 > P(C6H4Me-p)3 > PPh3. This order is explained in terms of the electron donating/π-acceptor properties of the phosphines

Understanding the interactions between triolein and cosolvent binary mixtures using molecular dynamics simulations

Biodiesel is one of the emerging renewable sources of energy to replace fossil-fuel-based resources. It is produced by a transesterification reaction in which a triglyceride reacts with methanol in the presence of a catalyst. The reaction is slow because of the low solubility of methanol in triglycerides, which results in low concentrations of methanol available to react with triglyceride. To speed up the reaction, cosolvents are added to create a single phase which helps to improve the concentration of methanol in the triglyceride phase. In this study, molecular dynamics simulations are used to help understand the role of cosolvents in the solvation of triglyceride (triolein). Six binary mixtures of triolein/cosolvent were used to study the solvation of triolein at 298.15 K. Results of 100 ns simulations at constant temperature and pressure to simulate mixing experiments show that in the first 10 ns all the binary mixtures remain largely unmixed. However, for the cosolvents that are fully miscible with triolein, the partial densities across the simulation boxes show that the systems are fully mixed in the final 10 ns. Some solvents were found to interact strongly with the polar part of triolein, while others interacted with the aliphatic part. The radial distribution functions and clustering of the solvents around triolein were also used as indicators for solvation. The presence of cosolvents also influenced the conformation of triolein molecules. In the presence of solvents that solubilize it, triolein preferred a propeller conformation but took up a trident conformation when there is less or no solubilization. The results show that tetrahydrofuran is the best solvent at solubilizing triolein, followed by cyclopentyl methyl ether, diethyl ether, and hexane. With 1,4-dioxane, the solubility improves with an increase in temperature. The miscibility of a solvent in triolein is aided by its ability to interact with both the polar and nonpolar parts of triolein

Oxidation of cysteinato complexes of dimeric molybdenum(V) by hexachloroiridate(IV) in aqueous perchlorate solution

1855-1859The kinetics and mechanism of the oxidations of [Mo2(O)2(μ-O)2 (cys)2]2- abbreviated (Mo2O4) , [Mo2(O)2(μ-O) (cys)2]2- (Mo2O3S), and [Mo2(O)2(μ-O)2 (cys)2]2- (Mo2O2S2) by [IrCl6]2- have been studied in aqueous perchlorate solution at ionic strength , I = 1.0 mol dm-3 (LiClO4) and [H+]= 0.2 mol dm-3  (HClO4) . The effects of the replacement of the ethylenediaminetetraacetate (EDTA) ligand with the cysteinato (cys) ligand, as well as the progressive substitution of the bridging oxygen atoms with sulphur atoms, are discussed. At 25.0°C, the values (in dm3 mol-1 s-1) of k1, the electron transfer rate constants, are 8.90±0.07, 8.09±0.18, and 7.54±0.06 for Mo2O4, Mo2O3S, and Mo2O2S2, respectively. Similarly, k-1/k2, a measure of the stability of the intermediates formed in the reactions, have values of (1.02±0.03)×103, (1.63±0.09)×103 and ( 1.81±0.04) ×103, (dm3 mol-1) , for Mo2O4, Mo2O3S, and Mo2O2S2, respectively. Activation parameters, ΔH≠ and ΔS≠, are 6.64±0.72 kJ  mol-1 and -204±21 J K-1 mol-1 for oxidation of Mo2O4, 9.86±0.28 kJ  mol-1 and -194± 18 J K-1 mol-1 for Mo2O3S, and 10.75±0.15 kJ mol-1 and -192± 17 J K-1 mol-1 for Mo2O2S2. All reactions occur via outer- sphere electron transfer

<b>Non-bridging ligand effects on the kinetics of reduction of chloro- and azido-pentaamminecobalt(III) by some polypyridyl complexes of ruthenium(II)</b>

Pentaamminecobalt(III) complexes, [Co(NH3)5X]2+ (X = Cl-, N3-), are reduced by [Ru(bipy)3]2+ and [Ru(terpy)(bipy)Cl] + in aqueous media at a constant ionic strength of 0.5 M (HCl/LiCl). At 308 K, the second order rate constants (M-1 s-1) are as follows: 17.9 for the reduction of the azidocobalt(III) complex by [Ru(bipy)3]2+, and 1.41 and 2.63 for the [Ru(terpy)(bipy)Cl]+ reduction of the azido- and chlorocobalt(III) complexes, respectively. Activation enthalpies (&Delta;H&#135;) and entropies (&Delta;S&#135;) were determined from temperature dependence measurements with the following results: &Delta;H&#135;= 72.1 kJ mol-1 and &Delta;S&#135; = 13.3 J mol-1 K-1 for the [Ru(bipy)3]2+ reduction of the azidocobalt(III) complex, while for the reduction of the cobalt(III) complexes by [Ru(terpy)(bipy)Cl] +, &Delta;H&#135; (N3-) = 20.3 kJ mol-1, &Delta;H&#135; (Cl-) = 40.6 kJ mol-1, &Delta;S&#135;(N3-) = -177 J mol-1 K-1, and &Delta;S&#135; (Cl-) = -106 J mol-1 K-1. The relative rates of electron transfer in the different reactions and the influence of &pi;-acceptor ligands on the ruthenium(II) reduction of the cobalt(III) complexes are discussed

ReaxFF study of the decarboxylation of methyl palmitate over binary metallic nickel-molybdenum catalysts

Biodiesel has emerged as a possible replacement for fossil-based fuels, particularly in the transportation industry. Because of its high oxygen content, it has several limitations including high viscosity, pour point and cloud point. Converting biodiesel to hydrocarbons is one method of improving the poor flow properties. In this study, Reactive Force Field (ReaxFF) molecular dynamics was used to study the decarboxylation of methyl palmitate on α-NiMoO4, β-NiMoO4 and Ni3Mo catalysts. The results show that the reactions are faster in the presence of α-NiMoO4 and β-NiMoO4, and the number of stable products, carbon dioxide and ethene was higher than they were without the catalyst. With Ni3Mo catalyst, there is rapid initial formation of CO2 and C2H4 until a maximum is reached followed by a decrease in their quantity. The C2H4 was found to decompose to C2H2 and H2 while CO2 was reduced to CO. All reactions were found to follow first-order kinetics, from which the activation energies (Ea) were determined. The Ea drops from 36.89 kcal/mol for uncatalyzed reaction to 25.66, 19.34 and 11.69 kcal/mol for the α-NiMoO4, β-NiMoO4 and Ni3Mo catalysed reactions, respectively. The Ni3Mo catalysed system’s Ea was also closest to the experimentally reported value of 10.11 kcal/mol [1].</p

The transfer hydrogenation of cinnamaldehyde using homogeneous Cobalt(II) and Nickel(II) (E)-1-(Pyridin-2-yl)-N-(3-(triethoxysilyl)propyl)methanimine and the complexes anchored on Fe 3 O 4 support as pre-catalysts: an experimental and in silico approach

The imino pyridine Schiff base cobalt(II) and nickel(II) complexes (C1 and C2) and their functionalised γ-Fe3O4 counterparts (Fe3O4@C1 and Fe3O4@C2) were synthesised and characterised using IR, elemental analysis, and ESI-MS for C1 and C2, and single crystal X-ray diffraction for C1, while the functionalised materials Fe3O4@C1 and Fe3O4@C2 were characterized using IR, XRD, SEM, TEM, EDS, ICP-OES, XPS and TGA. Complexes C1, C2 and the functionalised materials Fe3O4@C1 and Fe3O4@C2 were tested as catalysts for the selective transfer hydrogenation of cinnamaldehyde and all four pre-catalysts showed excellent catalytic activity. Complexes C1 and C2 acted as homogeneous catalysts with high selectivity towards the formation of hydrocinnamaldehyde (88.7% and 92.6%, respectively) while Fe3O4@C1 and Fe3O4@C2 acted as heterogeneous catalysts with high selectivity towards cinnamyl alcohol (89.7% and 87.7%, respectively). Through in silico studies of the adsorption energies, we were able to account for the different products formed using the homogeneous and the heterogeneous catalysts which we attribute to the preferred interaction of the C=C moiety in the substrate with the Ni centre in C2 (−0.79 eV) rather than the C=O (−0.58 eV)

The Transfer Hydrogenation of Cinnamaldehyde Using Homogeneous Cobalt(II) and Nickel(II) (E)-1-(Pyridin-2-yl)-N-(3-(triethoxysilyl)propyl)methanimine and the Complexes Anchored on Fe₃O₄ Support as Pre-Catalysts: An Experimental and In Silico Approach

The imino pyridine Schiff base cobalt(II) and nickel(II) complexes (C1 and C2) and their functionalised γ-Fe3O4 counterparts (Fe3O4@C1 and Fe3O4@C2) were synthesised and characterised using IR, elemental analysis, and ESI-MS for C1 and C2, and single crystal X-ray diffraction for C1, while the functionalised materials Fe3O4@C1 and Fe3O4@C2 were characterized using IR, XRD, SEM, TEM, EDS, ICP-OES, XPS and TGA. Complexes C1, C2 and the functionalised materials Fe3O4@C1 and Fe3O4@C2 were tested as catalysts for the selective transfer hydrogenation of cinnamaldehyde and all four pre-catalysts showed excellent catalytic activity. Complexes C1 and C2 acted as homogeneous catalysts with high selectivity towards the formation of hydrocinnamaldehyde (88.7% and 92.6%, respectively) while Fe3O4@C1 and Fe3O4@C2 acted as heterogeneous catalysts with high selectivity towards cinnamyl alcohol (89.7% and 87.7%, respectively). Through in silico studies of the adsorption energies, we were able to account for the different products formed using the homogeneous and the heterogeneous catalysts which we attribute to the preferred interaction of the C=C moiety in the substrate with the Ni centre in C2 (−0.79 eV) rather than the C=O (−0.58 eV)