Pesticides Curbing Soil Fertility: Effect of Complexation of Free Metal Ions

Researchers have suggested that the reason behind infertility is pernicious effect of broad spectrum pesticides on non target, beneficial microorganism of soil. Here, studying the chelating effect of selective organophosphate and carbamate pesticides with essential metal ions, at all possible combinations of three different pH (4 ± 0.05, 7 ± 0.05 and 9 ± 0.05) and three different temperatures (15 ± 0.5°C, 30 ± 0.5°C and 45 ± 0.5°C), shows very fast rate of reaction which further increases with increase of pH and temperature. Carbonyl oxygen of carbamate and phosphate oxygen of organophosphate were found to be common ligating sites among all the complexes. Formed metal complexes were found to be highly stable and water insoluble on interaction with essential metal ions in solvent medium as well as over silica. Density functional theory (DFT) calculations not only reinforced the experimental observations, but, after a wide computational conformational analysis, unraveled the nature of the high stable undesired species that consist of pesticides complexed by metal ions from the soil. All in all, apart from the direct toxicity of pesticides, the indirect effect by means of complexation of free metal ions impoverishes the soil.

Electrooxidation of alcohols catalyzed by amino alcohol ligated ruthenium complexes

Ruthenium transfer hydrogenation catalysts physisorbed onto edge-plane graphite electrodes are active electrocatalysts for the oxidation of alcohols. Electrooxidation of CH3OH (1.23 M) in a buffered aqueous solution at pH 11.5 with [(η(6)-p-cymene)(η(2)-N,O-(1R,2S)-cis-1-amino-2-indanol)]Ru(II)Cl (2) on edge-plane graphite exhibits an onset current at 560 mV vs NHE. Koutecky-Levich analysis at 750 mV reveals a four-electron oxidation of methanol with a rate of 1.35 M(-1) s(-1). Mechanistic investigations by (1)H NMR, cyclic voltammetry, and desorption electrospray ionization mass spectrometry indicate that the electroxidation of methanol to generate formate is mediated by surface-supported Ru-oxo complexes.

Ruthenium complexes with chiral bis-pinene ligands: an array of subtle structural diversity

A new chiral derivative of the N,N-bis(2-pyridylmethyl)ethylamine (bpea) ligand, Me-pinene[5,6]bpea [(-)-L1], has been prepared from a new aldehyde building block [Me-pinene-aldehyde, (-)-4] arising from the monoterpene chiral pool. The tridentate (-)-L1 ligand has been employed to prepare a new set of Ru-Cl complexes in combination with didentate 2,2'-bipyridine (bpy) with the general formula [RuCl((-)-L1)(bpy)](+). These complexes have been characterized in solution by cyclic voltammetry, UV-vis, and 1D and 2D NMR spectroscopy. Isomeric mixtures of trans,fac-C1a and anti,mer-C1c compounds are formed when (-)-L1 is reacted with a [Ru(bpy)(MeOH)Cl3] precursor. Density functional theory calculations of all of the potential isomers of this reaction have been performed in order to interpret the experimental results in terms of electronic and steric effects and also to unravel the observed isomerization pathway between anti,mer-C1c and trans,fac-C1a.

cis-1,3,5-Triaminocyclohexane as a facially capping ligand for ruthenium(II)

Reaction of cis-[RuCl2(DMSO-S)3(DMSO-O)] with cis-1,3,5-triaminocyclohexane (tach) results in the formation of [RuCl(tach)(DMSO-S)2]Cl, a valuable precursor for a wide range of other tach-containing Ru complexes. Reaction of [RuCl(tach)(DMSO-S)2]Cl with the chelating nitrogen-based ligands (N-N = bipyridine, phenanthroline, and ethylenediamine) affords [Ru(N-N)(DMSO-S)2(tach)][Cl]2. A similar reaction between [RuCl(tach)(DMSO-S)]Cl with the chelating phosphorus-based ligands (P-P = dppm, dppe, dppp, dppb, dppv, and dppben) leads to the formation of [RuCl(P-P)(tach)]Cl. The structures of 10 examples of the tach-containing complexes have been determined by single crystal X-ray diffraction. An examination of the structural metrics obtained from these studies indicates that the tach ligand is a strong sigma donor. In addition, the presence of the NH2 groups in the tach ligand allow for participation in hydrogen bonding further modulating the coordinative properties of the ligand.

New dinuclear ruthenium complexes: structure and oxidative catalysis

The synthesis of new dinuclear complexes of the general formula {[Ru(II)(trpy)]2(μ-pdz-dc)(μ-(L)}(+) [pdz-dc is the pyridazine-3,6-dicarboxylate dianion; trpy is 2,2':6',2″-terpyridine; L = Cl (1(+)) or OH (2(+))] is described. These complexes are characterized by the usual analytical and spectroscopic techniques and by X-ray diffraction analysis. Their redox properties are characterized by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Complex 2(+) is used as the starting material to prepare the corresponding Ru-aqua complex {[Ru(II)(trpy)(H2O)]2(μ-pdz-dc)}(2+) (3(2+)), whose electrochemistry is also investigated by means of CV and DPV. Complex 3(2+) is able to catalytically and electrocatalytically oxidize water to dioxygen with moderate efficiencies. In sharp contrast, 3(2+) is a superb catalyst for the epoxidation of alkenes. For the particular case of cis-β-methylstyrene, the catalyst is capable of carrying out 1320 turnovers with a turnover frequency of 11.0 cycles min(-1), generating cis-β-methylstyrene oxide stereospecifically.

Can the Disproportion of Oxidation State III Be Favored in RuII−OH2/RuIVO Systems?

Three new Ru-aqua complexes containing a mixed carbene and pyridylic ligands with general formulas [Ru(CNC)(bpy)(H2O)](PF6)2 (1) (CNC is 2,6-bis(butylimidazol-2-ylidene)pyridine; bpy is 2,2'-bipyridine) and cis-/trans-[Ru(CNC)(nBu-CN)(H2O)](PF6)2 (cis-2 and trans-2) (nBu-CN is 2-(butylimidazol-2-ylidene)pyridine) have been prepared and structurally characterized both in the solid state (monocrystal X-ray diffraction analysis for 1 and for the related complex trans-[Ru(Br)(CNC)(nBu-CN)](PF6)) and in solution (for all of them) through NMR. The electrochemical properties of these three Ru-aqua complexes have been investigated by cyclic voltammetry, differential pulse voltammetry and Coulombimetric techniques. It is found that, for complex 1 at pH 7, the difference between the IV/III and the III/II redox couples (DeltaE1/2) is 50 mV, which is the smallest ever reported for this type of complex. On the other hand, for complexes cis-2 and trans-2, the oxidation state III is unstable with respect to disproportionation to II and IV. The reactivity of their Ru=O species has been tested toward cis-beta-methylstyrene oxidation, and it has been compared to [Ru(O)(trpy)(bpy)]2+. An inverse correlation between the degree of cis/trans-epoxide isomerization and DeltaE1/2 is found. In particular, for complexes cis-2 and trans-2, which have a DeltaE1/2 < 0, the epoxidation is highly stereoselective, yielding only cis-epoxide.

Atropisomeric Discrimination in New RuII Complexes Containing theC2-Symmetric Didentate Chiral Phenyl-1,2-bisoxazolinic Ligand

A new family of Ru(II) complexes containing the tridentate meridional 2,2':6',2''-terpyridine (trpy) ligand, a C(2)-symmetric didentate chiral oxazolinic ligand 1,2-bis[4'-alkyl-4',5'-dihydro-2'-oxazolyl]benzene (Phbox-R, R = Et or iPr), and a monodentate ligand, of general formula [Ru(Y)(trpy)(Phbox-R)](n+) (Y = Cl, H(2)O, py, MeCN, or 2-OH-py (2-hydroxypyridine)) have been prepared and thoroughly characterized. In the solid state the complexes have been characterized by IR spectroscopy and by X-ray diffraction analysis in two cases. In solution, UV/Vis, cyclic voltammetry (CV), and one-dimensional (1D) and two-dimensional (2D) NMR spectroscopy techniques have been used. We have also performed density functional theory (DFT) calculations with these complexes to interpret and complement experimental results. The oxazolinic ligand Phbox-R exhibits free rotation along the phenyloxazoline axes. Upon coordination this rotation is restricted by an energy barrier of 26.0 kcal mol(-1) for the case of [Ru(trpy)(Phbox-iPr)(MeCN)](2+) thus preventing its potential interconversion. Furthermore due to steric effects the two atropisomers differ in energy by 5.7 kcal mol(-1) and as a consequence only one of them is obtained in the synthesis. Subtle but important structural effects occur upon changing the monodentate ligands that are detected by NMR spectroscopy in solution and interpreted by using their calculated DFT structures.