A free boratriptycene-type Lewis superacid

Bicyclic pyrazabole-bridged ferrocenes with BH groups at their bridgehead positions were prepared from [Li(thf)]₂[1,1′-fc(BH₃)₂] and pyrazole or 3,5-dimethylpyrazole in the presence of Me₃SiCl (1 or 1Me, respectively; 1,1′-fc = 1,1′-ferrocenylene); Me₃SiH and H₂ are released as byproducts. Treatment of 1 or 1Me with 1 eq. of the hydride scavenger [Ph₃C][B(C₆F₅)₄] afforded the borenium salts [2][B(C₆F₅)₄] (72%) and [2Me][B(C₆F₅)₄] (77%). According to X-ray crystallography, [2Me]⁺ contains one trigonal-planar borenium cation, the cyclopentadienyl (Cp) rings of the 1,1′-fc fragment remain parallel to each other, but the Cp–B bond vector is bent out of the Cp plane by an unprecedentedly large dip angle α* of 40.6°. The Fe⋯B(sp²) distance is very short (2.365(4) Å) and the ¹¹B NMR signal of the cationic B(sp²) center is remarkably upfield shifted (23.4 ppm), suggesting a direct Fe(3d) → B(2p) donor–acceptor interaction. Although this interpretation is confirmed by quantum-chemical calculations, the coupling between the associated orbitals corresponds to an energy of only 12 kJ mol⁻¹. Accordingly, both the experimental (e.g., Gutmann–Beckett acceptor number AN = 111) and theoretical assessment (e.g., Et₃PO and F⁻-ion affinities) of the Lewis acidity proves that [2]⁺ is among the strongest boron-based Lewis acids available to date.

An exceptionally strong ferrocene-containing, cationic boratriptycene-type Lewis acid is stabilized by a weak Fe⋯B through-space interaction.     

Cooperative motion in amorphous polymers; application to the study of free-radical migration in solids

A Monte Carlo method has been used for studying the effect of the motion of some submolecular structures on the migration of radical centres and on the free-radical decay and its dependence on density. Motions of crank, crankshaft, kink, and double kink type are considered. A cooperative type of motions is also taken into account. The results show that cooperative motions support diffusion of radical centres and thus also the free-radical decay but, at higher densities, the cooperation of motions is restricted. The density of the system, where the decay of radicals is followed, affects the rate of the decay, its increase causes radical decay retardation. This is in line with the high pressure effect, which also retards the radical decay rate.     

New materials with high π conjugation by reaction of 2-oxazoline containing phenols with polyamidines and inorganic base

The non-covalent interactions between 2-oxazoline containing phenols and an aliphatic polyamidines as well as an inorganic base were studied. The reaction of a weak acid with a strong base results in the formation of the deprotonated species and subsequently in the formation of a new electronic structure. A bathochromic shift of the wavelength of the absorption maxima of the chromophores bounded to polyamidine was observed. Depending on the structure of the chromophore, the shift of the absorption maxima is 40-100 nm. The changes in photochemical behavior can be explained by the higher portion of quinoid structures in the conjugated π-system. The degree of deprotonation is dependent on the molar ratio of the chromophore and the polymeric base. Analogous results were obtained with an inorganic base.     

Correlation between glass transition temperature and chain structure for randomly crosslinked high polymers

The empirical form for the dependence, T_g(n) ≅ T_g(∞)·(1 + α/n), of the glass transition temperature T_g on the average number n of repeat units between crosslinks, is generalized for randomly crosslinked high polymers. The new form, T_g(n) ≅ T_g(∞) · [1 + c/(n·N_rot)], is based on a correlation study of data for 77 samples of 10 different sets of resins. The fitting parameter α is resolved into composition-dependent N_rot and composition-independent c terms. N_rot summarizes the average number of rotational degrees of freedom per repeat unit, and is estimated in a straightforward manner from the structure and mol fraction of each repeat unit. The value of c is found from data analysis to be 5 ± 2. The results of this work are consistent with expectations based on the entropy theory of glasses, and provide improved understanding and predictive ability for the properties of crosslinked polymers. © 1996 John Wiley & Sons, Inc.     

Determination of organic acids in tobacco by capillary isotachophoresis

Nine organic acids and phosphate have been separated and quantified in tobacco by capillary isotachophoresis. Two operating systems for the separation were found: hydrochloric acid (10 mmol l(-1)) adjusted with beta-alanine to pH 2.9 plus 0.1% poly(vinylpyrrolidone) was used as the leading electrolyte and 10 mmol l(-1) nicotinic acid as the terminating electrolyte and hydrochloric acid (10 mmol l(-1)) including 5.5 mmol l(-1) 1,3-bis[tris(hydroxymethyl)methylamino]propane plus 0.1% poly(vinylpyrrolidone) was used as the leading electrolyte and 5 mmol l(-1) 2-morpholinoethanesulfonic acid as the terminating electrolyte. Linearity was observed from 0.008 to 0.100 mmol l(-1) with a coefficient of determination (r2) of 0.999. The separation of anions was achieved in less than 16 min. The minimal sample pretreatment and relatively low running cost make isotachophoresis a good alternative to existing methods.     

Calculation of rotational barriers in amorphous polymers

The Monte Carlo method was used for generation of amorphous polyethylene configurations on a diamond lattice. Chain building was performed on the tetrahedral lattice of edges 36, 62 and 43 Å with periodic boundary conditions imposed.32 chains were generated, each with a length of 100 CH₂-groups (resulting density = 0.81 g·cm⁻³). Small spherical volumes with a radius of 10 Å were chosen at random from the total volume for the calculation of rotational barriers. The rotating bond was chosen to be close to the center of this sphere. We employed the method of molecular mechanics in order to calculate the rotational barriers. The calculation was made for 578 rotating bonds and the obtained distribution of rotational barriers is approximated by the corresponding Γ-distribution.     

Gas-Free Amino- and Alkoxycarbonylation of Aryl Iodides in a Bioinspired Deep Eutectic Solvent with Mo(CO)6 as a Safe CO Source

The Pd-catalyzed amino- and alkoxycarbonylation of aryl iodides has been exploited, for the first time, in a bioinspired Deep Eutectic Solvent and under gas-free conditions, by using Mo(CO)₆ as the CO source. The method allows for the preparation of carboxylic amides and esters in high yields (up to 99 %), short reaction time (2 h) and under mild reaction conditions (80 °C), with a low catalyst loading (2.5 mol %). Noteworthy, in the case of N-hexylbenzamide, it has been demonstrated that both the catalyst and DES can be used for four consecutive runs, with a moderate decrease of catalytic efficiency. The methodology has been also applied to the preparation of an Active Pharmaceutical Ingredient used for the treatment of human scabies and lice.     

Azo‐group labelled polyesters by end‐capping with 2‐oxazoline derivatives – preparation

Two azobenzene containing 2‐oxazolines were used for labelling of polyesters with carboxylic end groups by the end‐capping method. The reaction proceeded under the conditions of reactive processing, and in a solution. High conversions in melt were achieved in several minutes. The coupling of the modifiers was proved by NMR spectroscopy.     

Functional derivatives of sterically hindered amines. 1. Glycidyl compounds

Four polymerizable glycidyl derivatives of sterically hindered amines were prepared from derivatives of 2, 2, 6, 6-tetramethyl-4-hydroxypiperidine and 14, 16-dioxo-7, 15-diazadispiro [5, 1, 5, 3] hexadecane. One of them is a stable nitroxyl derivative.