Unravelling Structural Mysteries of Simple Organozinc Alkoxides

Simple RZnOR’ alkoxides are among the first known organozinc compounds, and widespread interest in their multifaced chemistry has been driven by their fundamental significance and potential applications including various catalytic reactions. Nevertheless, their chemistry in solution and in the solid state remains both relatively poorly understood and a subject of constant debate. Herein, the synthesis and structural characterization of long-sought structural forms, a roof-like trimer [(tBuZn)₃(μ-OC(H)Ph₂)₂(μ₃-OC(H)Ph₂)] and a ladder-type tetramer [(PhZn)₄(μ-OC(H)Ph₂)₂(μ₃-OC(H)Ph₂)₂], incorporating diphenylmethanolate as a model alkoxide ligand, are reported. Both novel aggregates are robust in the solid state and resistant towards mechanical force. By using ¹H NMR and diffusion-order spectroscopy, it is demonstrated that new RZnOR’ alkoxides are kinetically labile in solution and readily undergo ligand scrambling, such as in the case of Schlenk equilibrium. The elucidated key structural issues, which have remained undiscovered for decades, significantly advance the chemistry of RZnOR’ alkoxides and should support the rational design of zinc alkoxide-based applications.     

Bonding in Barium Boryloxides,Siloxides, Phenoxides and Silazides: A Comparison with the Lighter Alkaline Earths

Barium complexes ligated by bulky boryloxides [OBR₂]⁻ (where R=CH(SiMe₃)₂, 2,4,6-ⁱPr₃-C₆H₂ or 2,4,6-(CF₃)₃-C₆H₂), siloxide [OSi(SiMe₃)₃]⁻, and/or phenoxide [O-2,6-Ph₂-C₆H₃]⁻, have been prepared. A diversity of coordination patterns is observed in the solid state for both homoleptic and heteroleptic complexes, with coordination numbers ranging between 2 and 4. The identity of the bridging ligand in heteroleptic dimers [Ba(μ₂-X₁)(X₂)]₂ depends largely on the given pair of ligands X₁ and X₂. Experimentally, the propensity to fill the bridging position increases according to [OB{CH(SiMe₃)₂}₂)]⁻<[N(SiMe₃)₂]⁻<[OSi(SiMe₃)₃]⁻<[O(2,6-Ph₂-C₆H₃)]⁻<[OB(2,4,6-ⁱPr₃-C₆H₂)₂]⁻. This trend is the overall expression of 3 properties: steric constraints, electronic density and σ- and π-donating capability of the negatively charged atom, and ability to generate Ba ⋅ ⋅ ⋅ F, Ba ⋅ ⋅ ⋅ C(π) or Ba ⋅ ⋅ ⋅ H−C secondary interactions. The comparison of the structural motifs in the complexes [Ae{μ₂-N(SiMe₃)₂}(OB{CH(SiMe₃)₂}₂)]₂ (Ae = Mg, Ca, Sr and Ba) suggest that these observations may be extended to all alkaline earths. DFT calculations highlight the largely prevailing ionic character of ligand-Ae bonding in all compounds. The ionic character of the Ae-ligand bond encourages bridging coordination, whereas the number of bridging ligands is controlled by steric factors. DFT computations also indicate that in [Ba(μ₂-X₁)(X₂)]₂ heteroleptic dimers, ligand predilection for bridging vs. terminal positions is dictated by the ability to establish secondary interactions between the metals and the ligands.     

Novel Method for HPLC Analysis of Triterpenic Acids Using 9-Anthryldiazomethane Derivatization and Fluorescence Detection

Triterpenic acids are a group of secondary plant metabolites which are part of the cuticular waxes covering fruits, leaves, and flowers. To date, quantitative analysis of these compounds has often been conducted using high-performance liquid chromatography coupled with spectrophotometric detection or mass spectrometry; however, these methods have some major drawbacks. This paper reports a new method of analysis implementing derivatization with 9-anthryldiazomethane and fluorescence detection. The method consists of the extraction of analytes from a matrix, purification with anion exchanging SPE columns, and an optional step of the alkaline hydrolysis of triterpenic acid esters. The paper also describes a fast and easy method for the synthesis of the derivatization agent. The detection limits of the method presented are approximately 100-fold lower than in a similar method using ultraviolet spectrophotometry as the mode of detection. The recovery and repeatability of the method are at satisfactory levels.     

Formation of Chiral β-Silyl-Vinyl Ethers

Chiral formates derived from propane-1,2-diol, 1,2- O -isopropylidene- f - D -xylo- and f - D -gluco-furanoses were subjected to treatment with cyclopentadienyl [tris(trimethylsilylmethyl)] titanium (IV). A mixture of the corresponding ( E )- and ( Z )- g -silylvinyl ethers were obtained with predominance of the former. It was found that in contrast to ( Z )-vinyl ethers, which give g -lactams with chlorosulfonyl isocyanate, the ( E )-vinyl ethers gave unstable cycloadducts which undergo rapid elimination reaction leading to ( E )- f , g -unsaturated amides.     

New Procedure of Kinetic Resolution of t-Butylphenylphosphine Oxide

Abstract

The title compound optically active t-butylphenylphosphine oxide 1 is widely used as a key substrat for the synthesis of other optically active derivatives such as α-hydroxyphosphine oxides, vinylphosphine oxides Till now, it has been obtained by a few rather laborious procedures¹     

The Mechanism of Reaction between Poly(vinyl Alcohol) and Phosphorous Acid

The reaction mechanism of phosphorous acid and poly(vinyl alcohol) is presented. It has been found that there during this reaction mono- and diesters are formed in which most of the acid radicals are in the phosphonic form. To confirm the presence of this form in the product obtained, reactions with diethyleneamine and chloral have been carried out as characteristic tests for phosphonic groups. The occurrence of C—P bonds resistant to hydrolysis has been also found in the reaction product.     

Thermal behavior of the highly luminescent poly(3-hydroxybutyrate):Eu(tta)3(H2O)2 red-emissive complex

The aim of this study has been to gain a fundamental understanding of the mechanisms governing thermal degradation of luminescent poly(3-hydroxybutyrate) (PHB). PHB was doped with diaquatris(thenoyltrifluoroacetonate) europium(III) complex, [Eu(tta)₃(H₂O)₂], and different luminescent systems were obtained. The thermal-stability of the luminescent films was discussed and the products of decomposition were analyzed. Thermal degradation of PHB:Eu(tta)₃ x % systems (x = 0, 1, 5, 10, and 15 %) was elucidated by means of thermogravimetric analysis (TG), the thermal-stability decreases with the increase of europium complex concentration. The PHB polymer decomposed with evolution of carbon dioxide and 2-butenoic acid molecules. The TG–FTIR results, of the gaseous degradation products of PHB in nitrogen atmosphere, indicated that the polymer is stable at temperatures up to 200 °C. Polymer matrix at concentrations above 5 % decomposed with evolution of water molecules among the other gaseous products, which implied the presence of a hydrated complex in the system. The luminescent films showed more flexibility due to a loss in crystallinity, which suggested a potential usefulness in technical applications.