A Novel Proton Transfer Self‐Associated Compound from Dipicolinic Acid and Guanidine and Its Cadmium(II) Complex: Synthesis,Characterization, Crystal Structure,and Solution Studies

A novel 1:2 proton transfer self‐associated compound LH₂ , (GH⁺)₂(pydc^2—), was synthesized from the reaction of dipicolinic acid, pydcH₂, (2, 6‐pyridinedicarboxylic acid), and guanidine hydrochloride, (GH⁺)(Cl^—). The characterization was performed using IR, ¹H and ¹³C NMR spectroscopy and single‐crystal X‐ray diffraction. LH₂ · H₂O crystallizes in the space group C2/c of the monoclinic system and contains eight molecules per unit cell. The unit cell dimensions are: a = 26.480(5)Å, b = 8.055(2)Å, c = 14.068(3)Å. The first coordination complex (GH)₂[Cd(pydc)₂] · 2H₂O, was prepared using LH₂ and cadmium(II) iodide, and characterized by ¹H and ¹³C NMR spectroscopy and X‐ray crystallography. The crystal system is triclinic with space group P1¯ with one molecule per unit cell. The unit cell dimensions are: a = 8.5125(7)Å, b = 11.0731(8)Å, c = 13.2404(10)Å. The cadmium(II) atom is six‐coordinated with a distorted octahedral geometry. The two pydc^2— units are almost perpendicular to each other. The protonation constants of the building blocks of the pydc‐guanidine adduct, the equilibrium constants for the reaction of pydc^2— with guanidine and the stoichiometry and stability of the Cd²⁺ complex with LH₂ in aqueous solution were accomplished by potentiometric pH titration. The solution studies strongly support a self‐association between pydc^2— and GH⁺ with a stoichiometry for the Cd^II complex similar to that observed for the isolated crystalline complex. In fact, the [Cd(pydc)₂]^2— complex was found as the most abundant species in solution (> 90 %) at a pH >5.     

Ytterbium triflate-promoted tandem one-pot oxidation-Cannizzaro reaction of aryl methyl ketones

[reaction: see text] Ytterbium triflate was shown to be an effective catalyst in promoting the synthesis of either isopropyl esters or free alpha-hydroxy-arylacetic acids from substituted aromatic glyoxals and aryl methyl ketones, respectively. The reaction to provide acids starting from differently substituted ketones was carried out by an environmentally friendly method using an aqueous medium as a solvent and giving the adducts in 78-99% yield without any further purification after the usual workup.     

Spectrophotometric and derivative spectrophotometric determination of aluminium with Hydroxynaphthol Blue

The reaction of aluminium(III) with Hydroxynaphtol Blue (HNB) in aqueous media at apparent pH 5.5 results in a red complex that is stable for at least 4 hr. Beer's Law is obeyed up to 1.6 microg/ml of aluminium(III) with an apparent molar absorptivity of 1.66 x 10(4) l.mol(-1). cm(-1) at 569 nm. This paper proposes procedures for aluminium(III) determination by ordinary and first-derivative spectrophotometry. The results demonstrated that the linear dynamic range is 0.03-1.60 microg/ml for ordinary spectrophotometry and 11.8-320.0 ng/ml for first derivative spectrophotometry. The HNB is not selectivity for aluminium, but the addition of EDTA allows the aluminium determination in the presence of accepted amounts of Ca(II), Mg(II), Mn(II), Ba(II), Sr(II), Cd(II), Pb(II), La(III), In(III), Bi(III) and Zn(II). The interference of Cu(II) and Hg(II) can be masked by thiosulphate. Ions such as UO(2)(II), Mo(VI), Co(II), Ti(IV) and PO(4)(III) do interfere seriously. This method was applied for aluminium determination in copper-base alloy, zinc-base alloy, magnesium-base alloy, iron ore, manganese ore, cement, dolomite, feldspar and limestone. The results indicated high accuracy and precision.     

Electron transfer in proteins: nonorthogonal projections onto donor-acceptor subspace of the Hilbert space

We develop nonorthogonal projectors, called L?wdin projectors, to construct an effective donor-acceptor system composed of localized donor (D) and acceptor (A) states of a long-distance electron transfer problem. When these states have a nonvanishing overlap with the bridge states these projectors are non-Hermitian and there are various possible effective two-level systems that can be built. We show how these can be constructed directly from the Schr?dinger or Dyson equation projected onto the D-A subspace of the Hilbert space and explore these equations to determine the connection between Hamiltonian and Green function partitioning. We illustrate the use of these effective two-level systems in estimating the electron transfer rate in the context of a simple electron transfer model.     

Identification of an activated catalyst in the iridium-catalyzed allylic amination and etherification. Increased rates, scope, and selectivity

Studies were conducted to determine possible intermediates in the highly enantioselective, iridium-catalyzed amination and etherification of allylic carbonates, and these studies revealed that cyclometalation of the phosphoramidite ligand is likely to generate the active catalyst. The square-planar [Ir(COD)(L1)Cl] (L1 = P(BINOL)(bisphenethylamine)) did not react with cinnamyl carbonate, but did react with amine to generate an Ir(I) trigonal bipyramidal complex coordinated by COD, a cyclometalated kappa2-phosphoramidite, and a kappa1-phosphoramidite. This complex reacted with phosphines to generate products from replacement of the kappa1-phosphoramidite. These cyclometalated complexes were highly active catalysts for allylic amination and etherification and retained the high selectivity of the original catalyst system. In addition, these complexes combined with [Ir(cod)Cl]2 catalyzed reactions of amines with lower loadings, catalyzed reactions of alkylamines and aromatic amines that did not react with the original catalyst system, and catalyzed reactions of phenoxides under milder conditions.     

Volumes of activation for the reactions of Pentacyanocobaltate(III) Complexes in aqueous solution

The volumes of activation in cm³ mol^?1 for the aquation of Co(CN)₅X^3? were determined at 40°C and μ = 1 M (NaClO₄) to be + 7.8 ± 0.5 for X = Cl^?, + 7.6 ± 0.6 for X = Br^?, + 14.0 ± 0.7 for X = I^?, and + 16.8 ± 0.5 for X = N₃^? (0.1 M HClO₄), respectively. The volumes of activation for the aquation of Co(CN)₅Cl^3? at μ = 0.1 M are + 10.0 ± 0.6 cm³ mol^?1 and ± 9.1 ± 0.3 cm³ mol^?1 at 40°C and 25°C, respectively. The corresponding values for the anation of Co(CN)₅OH₂^2? (at 40°C) and μ = 1 M by Br^?, I^?, and NCS^? are +8.4 ± 1.0, +9.4 ± 1.6, and +8.2 ± 0.9 cm³ mol^?1, respectively. These data are discussed in terms of a dissociative (D) mechanism.     

X-ray spectroscopic characterization of Cu2+-phenanthroline complexes intercalated in α-zirconium phosphate

X-ray photoelectron spectroscopy provides evidence that when [Cu(phen)₂]²⁺(phen = 1,10-phenanthroline) is diffused between the layers of -zirconium phosphate, the complex species does not remain intact after intercalation, but some Cu-N bonds are broken, replaced with Cu-O bonds and the released nitrogen atoms can now interact with the PO₃-OH groups of the host. XPS also provides evidence for coordination of the Cu²⁺ ions when they are diffused by ion exchange in the phenanthroline--zirconium phosphate intercalation compound. Although Cu²⁺ and phen are in a 1 : 1 molar ratio in the interlayer region of the host, so that a 1 : 1 coordination could be expected between the two species, the characteristic peaks of the uncoordinated phenanthroline, even though at a low intensity, are still present. The differences between the two Cu(II)-intercalation compounds are discussed.     

Improved catalysts for the palladium-catalyzed synthesis of oxindoles by amide alpha-arylation. Rate acceleration, use of aryl chloride substrates, and a new carbene ligand for asymmetric transformations

Catalysts comprised Pd(OAc)(2) and either PCy(3) or sterically hindered N-heterocyclic carbene ligands provide fast rates for a palladium-catalyzed synthesis of oxindoles by amide alpha-arylation. This catalyst system allowed for room-temperature reactions in some cases and reactions of aryl chlorides at 70 degrees C. Most important, reactions occurred in high yields under mild conditions to form the quaternary carbon in alpha,alpha-disubstituted oxindoles. The combined inter- and intramolecular reaction afforded an efficient synthetic method for formation of alpha-aryloxindole derivatives. Surprisingly, catalysts containing tert-butylphosphine ligands, which have been most reactive for ketone arylations, were less active than those containing PCy(3). Use of new, optically active heterocyclic carbene ligands gave substantial enantioselectivity in formation of an alpha,alpha-disubstituted oxindole. In contrast, a variety of optically active phosphine ligands that were tested gave poor enantioselectivity. Mechanistic studies showed that the reaction involves rate-limiting oxidative addition of aryl halide. Base-induced formation of and reductive elimination from an arylpalladium enolate intermediate were both faster than oxidative addition. Deprotonation of the tethered amide appeared to be faster than reductive elimination of the resulting palladium enolate to form the oxindole product.