Second Molecular Hyperpolarizability of Mixed Transition Metal, Non-Metal Clusters

The real and imaginary parts of third order nonlinear optical susceptibilities ( ⁽³⁾) of 10^–4M solutions of [{Fe₂(CO)₆}( ₃-Y₃P){CpCr(CO)₂}] (Y=S (1) or Se (2)) and the well known precursor clusters [Fe₃(CO)₉( ₃-Y)₂] (Y=S (3) or Se (4)) in toluene were measured using Z-scan and ARINS techniques respectively. Compounds 1 and 2 possess nearly three times the _R values of their corresponding precursor compounds, 3 and 4. The results suggest a rich potential of mixed-metal, mixed-nonmetal class of clusters as materials exhibiting large nonlinearity.     

(Z)-alpha-haloacrylates: an exceptionally stereoselective preparation via Cr(II)-mediated olefination of aldehydes with trihaloacetates

(Z)-alpha-Fluoro-, (Z)-alpha-chloro-, and (Z)-alpha-bromoacrylates were obtained with unprecedented yield and stereocontrol (>99%) via addition of the corresponding commercial trihaloacetates to aldehydes at room temperature using stoichiometric Cr(II) salts or catalytic Cr(II) with a regeneration system. The intermediate 2,2-dihalo-3-hydroxy adducts could be isolated in good yields under conditions of limited reagent at 0 degrees C.     

Transfer free energies of some ions from water to dimethylsulfoxide-water and urea-water mixtures

The standard free energies of transfer (G _t ^o ) of some electrolytes from water to aqueous mixtures of dimethylsulfoxide (DMSO) and of urea have been split into the contribution from individual ions by use of the reference electrolyte Ph ₄ AsBPh ₄ (RE), where Ph=phenyl. For each of the solvents, G _t ^o (Ph ₄ AsBPh ₄ ) was determined from the solubility products of the salts KBPh ₄ , Ph ₄ AsPi, and KPi, where Pi=picrate ion. The observed G _t ^o (i) values for the individual ions are strikingly different from the corresponding values obtained by the simultaneous extrapolation (SE) procedure reported earlier.     

TiCl(4)-promoted Baylis-Hillman reactions of substituted 5-isoxazolecarboxaldehydes with cycloalkenones)

The Baylis-Hillman (BH) reaction of substituted 5-isoxazolecarboxaldehydes with cyclohexenone in the presence of TiCl(4) invariably lead to the formation of hemiacetals beside the BH adducts. A similar reaction in the presence of DABCO, DBU, or 3-HQN yielded minor quantities of phenols in addition to the usual BH adducts. Similar to 5-isoxazolecarboxaldehydes, the TiCl(4)-mediated BH reaction of cyclohexenone with various benzaldehydes also furnishes hemiacetals in considerable yields. The reaction mechanism involving the formation of alpha-chloromethyl enone as an intermediate has been proposed. The synthesis of hemiacetals 5 and 14 from compound 4 in the presence of cyclohexenone and cyclopentenone, respectively, under acidic conditions indicates that enolization and aromatization of the cyclohexene ring are the key steps in the reaction mechanism.     

Effect of metal ions on monolayer collapses

A Langmuir monolayer of stearic acid on pure water and in the presence of certain divalent metal ions such as Cd and Pb at pH approximately 6.5 of the subphase water collapses at constant area, while for other divalent ions such as Mg, Co, Zn, and Mn at the same subphase pH the monolayer collapses nearly at constant pressure. Films of stearic acid with Cd, Pb, Mn, and Co in the subphase (at pH approximately 6.5) have been transferred onto hydrophilic Si(001) using a horizontal deposition technique, just after and long after collapse. Electron density profiles obtained from X-ray reflectivity analysis show that a three-molecular-layer structure starts to form just after constant area collapse, where in the lowest molecular layer, in contact with the substrate, molecules are in asymmetric configuration, i.e., both hydrocarbon tails are on the same side of the metal-bearing headgroup that touches the substrate, while the molecules above the first layer are in symmetric conformation of the tails with respect to the headgroups. Further along collapse, when the surface pressure starts to rise again with a decrease in area, more layers with molecules in the symmetric configuration are added, but the coverage is poor. On the other hand, only bimolecular layers form after constant pressure collapse, with the lower and upper layers having molecules in asymmetric and symmetric configurations, respectively, and the upper molecular layer density increases with compression of the monolayer after collapse. A "Ries mechanism" for constant area collapse and a "folding and sliding mechanism" for constant pressure collapse have been proposed.     

Complexometric titration of the sum of calcium and magnesium using aluminon as metal indicator

Summary Calcium and magnesium were estimated separately and in a mixture with EDTA (Titriplex III) using aluminon as metal indicator. Methylene blue is used for screening the yellow colour at the end point. The estimation should be carried out in theph range 8.5–9.9. Ammonia-ammonium chloride buffer was required for the estimation. Total hardness for a number of water samples was also determined.

---

Zusammenfassung Calcium und Magnesium werden allein oder in Mischung (als Summe) mit Hilfe von ÄDTA-Lösung titriert, wobei Aluminon zusammen mit Methylenblau als Indicator dient. Die Bestimmung soll imph-Bereich 8,5–9,9 (NH₄OH-NH₄Cl-Puffer) durchgeführt werden. Sie eignet sich auch zur Gesamthärte-Bestimmung in Wasserproben.

     

In situ cyclopropanation: a rapid one-pot method for the synthesis of resin bound cyclopropyl phenyl methanones as combinatorial scaffolds

An efficient, high yielding one-pot synthesis of 4-substituted cyclopropyl phenyl methanones bound to RAM and WANG resins has been developed. The resin bound cyclopropyl phenyl methanone served as a combinatorial scaffold for the generation of structurally diverse alicyclic compounds.     

Synthesis,spectral characterisation and electrochemical studies of dichloro-{1-benzyl-2-(arylazo)imidazole}platinum(II) complexes and their dioxolene derivatives

1-Benzyl-2-(arylazo)imidazoles, p-RC₆H₄N=NC₃H₂-N₂1-CH₂Ph [RaaiBz (2); R=H(a), Me(b), Cl(c)], react with K₂PtCl₄ in boiling MeCN–H₂O (1:1 v/v) to give brownish-red Pt(RaaiBz)Cl₂ (3) complexes. Addition of dioxolene in the presence of Et₃N to a CHCl₃–MeOH solution of Pt(RaaiBz)Cl₂ yields green mixed complexes of composition [Pt(RaaiBz)(O,O)] [O,O = catecholate (cat) (4); 4-tert-butylcatecholate (tbcat), (5); 3,5-di-tert-butylcatecholate (dtbcat), (6); tetracholorocatecholate (tccat), (7)] which were characterised by elemental analyses, i.r., u.v.–vis.–near i.r. and ¹H-n.m.r. spectral data. The solution electronic spectra exhibit ligand-to-ligand charge-transfer (l.l.c.t) transitions in the red to near i.r. region; the position and symmetry of the band depend upon the substituent on the dioxolene and arylazoimidazole. This effect is qualitatively assigned as HOMO(dioxolene) LUMO(RaaiBz). A cyclic voltammogram of the dioxolene complex reveals two consecutive oxidative couples corresponding to catechols to semiquinones and semiquinone to quinone, respectively and the reductive couples represent azo reductions.     

Atom-efficient cross-coupling reactions of triarylbismuths with acyl chlorides under Pd(0) catalysis

The atom-efficient cross-coupling reaction of triarylbismuths with a variety of aliphatic, aromatic, and hetero-aromatic acyl chlorides was demonstrated to afford high yields of cross-coupled ketones under palladium catalysis. The corresponding cross-coupling reaction with diacid chlorides also furnished bis-coupled ketones in good yields.     

Nucleophilic ligand displacement in dichloro[2-(arylazo)heterocycle]palladium(II) complexes by benzimidazole – a kinetic and mechanistic study

The reactions of benzimidazole (Bimz) with dichloro{2-(arylazo)pyridine}palladium(II), [Pd(aap)Cl₂ (3), aap = RC₆H₄N= N-2-C₅H₄N; R = H(a), o-Me(b), m-Me(c), p-Me(d), p-Cl(e)] and dichloro{2-(arylazo)pyrimidine}palladium(II), [Pd(aapm)Cl₂ (4), aapm = RC₆H₄N=N-2-C₆H₃N₂; R = H(a), o-Me(b), m-Me(c), p-Me(d), p-Cl(e)] were followed separately. The kinetics were examined under pseudo-first order conditions with reference to Bimz in MeCN at 385 and 390 nm, respectively and at 298 K using a u.v.–vis. spectrophotometer. The product was isolated and characterised as trans-Pd(Bimz)₂Cl₂. The reaction between Pd(aap)Cl₂ and Bimz follows the rate law, rate = K[Bimz]²[Pd(aap)Cl₂], a single step process, whereas biphasic behaviour is observed for the reaction between Pd(aapm)Cl₂ and Bimz; each step is first order with respect to the concentration of complex and to Bimz. The rate data support a nucleophilic association path and the rate decreases upon addition of Cl^–(LiCl). The aryl ring substituent of the arylazoheterocycle influences the substitution rate as follows: k(e) > k(a) > k(d) > k(c) > k(b). The k-values are linearly correlated with Hammett constants with usual deviations for the m-Me and o-Me substituents because of their steric crowding. The rate follows the order: k(aap) > k(aapm). This is unusual with reference to the -acidity order of the heterocycles, pyridine < pyrimidine, as the increased -acidity will enhance the nucleophilic association. The charge density calculation by MNDO method shows that in the pyrimidine ring of arylazopyrimidine, the peripheral m-N(uncoordinated) carries a high negative charge which may retard the nucleophilic association rate. This effect is absent in the pyridine ring of arylazopyridine and may be the reason for the faster single step nucleophilic substitution in Pd(aap)Cl₂.