Róbert Kurdi

Natural Abundance Isotopic Chirality in the Reagents of the Soai Reaction

Isotopic chirality influences sensitively the enantiomeric outcome of the Soai asymmetric autocatalysis. Therefore magnitude and eventual effects of isotopic chirality caused by natural abundance isotopic substitution (H, C, O, Zn) in the reagents of the Soai reaction were analyzed by combinatorics and probability calculations. Expectable enantiomeric excesses were calculated by the Pars–Mills equation. It has been found that the chiral isotopic species formed by substitution in the otherwise achiral reagents provide enantiomeric excess (e.e.) levels that are higher than the sensitivity threshold of the Soai autocatalysis towards chiral induction. Consequently, possible chiral induction exerted by these e.e. values should be taken into account in considerations regarding the molecular events and the mechanism of the chiral induction in the Soai reaction.

Preparation and characterization of kaolinite nanostructures: reaction pathways, morphology and structural order

Abstract Clay-based nanostructures were prepared from kaolinites of varying structural order by two different methods. In the first method the kaolinite-urea precursor, obtained by dry grinding, was intercalated further with triethanolamine and the tetraalkylammonium salt was synthesized in the interlamellar space. Exfoliation was achieved by the use of sodium polyacrylate (PAS). In the second method, the kaolinite-potassium acetate (kaolinite-KAc) precursor, obtained via two different methods, was intercalated further with ethylene glycol (EG) and then n-hexylamine (HA). Intercalation with EG was also achieved by heating either directly or with microwaves. The morphology that results depends on the method of precursor preparation, the method of heat treatment and the degree of structural order of the original clay. Higher structural order facilitates the formation of a tubular morphology, while mechanical treatment and microwave agitation may result in broken tubes. Molecular mechanical (MM) calculations showed that organo-complexes may be exfoliated to a d value of 10-11 Å.

Intermediates of cobalt-catalysed PTC carbonylation of benzyl halides

AbstractIntermediates of the cobalt carbonyl-catalysed carbonylation ofortho-substituted benzyl halides were identified by IR, 1 H- and 13 C-NMR spectra. The molecular structures of the acyl-type derivatives 2-MeC 6 H 4 CH 2 C(O)Co(CO) 3 PPh 3 and2-PhC 6 H 4 CH 2 C(O)Co(CO) 3 PPh 3 were determined by X-ray crystallography. Structural features of these complexes arediscussed.© 2003 Elsevier Science B.V. All rights reserved. Keywords: Phase transfer catalysis; Hydroxycarbonylation; Carbonylation; Acylcobalt carbonyls; Alkylcobalt carbonyls; 3 -benzylcobaltcarbonyls 1. IntroductionPhase transfer catalysis (PTC) became a well-estab-lished, environmentally friendly (green) method inpreparative organic chemistry [1]. The combinationof PTC with transition metal molecular catalysts(TM) is one of the most promising potentialities oftransition metal chemistry. TM–PTC is characterisedby dramatic increase in reaction rates, consequentlyenables mild conditions, favourable operational costsand high selectivities [2–8].

Autosolvation: Architecture and Selection of Chiral Conformers in Alkylcobalt Carbonyl Molecular Clocks

Autosolvation is an important factor in stabilizing the architecture of medium complicated molecules. It is a kind of “supramolecular force” acting in intramolecular manner, consisting of orbital-orbital interactions between polar groups, separated by more than one covalent bonds within the same molecule. This effect facilitates also the development of chiral conformations. Two typical alkylcobalt carbonyl type molecules are discussed here as examples of autosolvating intramolecular interactions, leading to dramatic selection of chiral conformers and indicating also to the limits of the effect. The conformers stabilized by autosolvation and their interconversion are excellent examples of a “molecular clockwork”. Operation mode of these molecular clockworks gives some insight into the intramolecular transfer of chiral information.

ADSORPTION AND INTERCALATION OF SMALL MOLECULES ON KAOLINITE FROM MOLECULAR MODELLING STUDIES

Kaolinite is an abundant natural material with considerable industrial potential. Despite its simple composition (Al2Si2O5(OH)4 and layered structure being a phyllosilicate), it is notable that only little known about the interaction of kaolinite sheets with small organic reagents at the molecular level. These assumed to govern intercalation, delamination, and then the complete exfoliation processes. A common methodology to model the molecular structure of kaolinite is the employment of periodic boundary conditions. The application of molecular cluster models gained importance nowadays by capitalizing on the availability of wide range of theoretical tools for describing structural features and reaction mechanisms. In this study, we present our results using theoretical methodologies and modelling strategies from literature that are applied for adsorption and intercalation of urea, ethylene glycol, and potassium acetate.

Two-Way Intramolecular Transfer of Chirality in Organocobalt Complexes

ROC(O)CH2Co(CO)3PR3 complexes (R = S-EtOC(O)CH(CH3), R = Ph a; R = (1S,2R,5S)-2-isopropyl-5-methylcyclohexyl, R = Ph, b; R = (1R,2S,5R)-2isopropyl-5-methylcyclohexyl, R = Ph, c; R = isopropyl, R3 = Ph2{(1S,2S,5R)-2isopropyl-5-methylcyclohexyl}, d) were prepared and characterised by analyses including IR, H NMR, C{H} NMR spectra, as well as by x-ray diffraction structure determination. Principles of self-organisation of chiral conformations were deduced from the structural data.

Molecular-Level Machines: The Clockwork Model

Crystalline phases and solutions of the flexible complexes ROC(O)CH2Co(CO)3PPh3 contain enantiomeric pairs of chiral conformers characterized by two forms of the PPh3 ligand of opposed helical chirality, each of which is accompanied by only one conformation of the ester fragment. The interconversion amongst enantiomers is very fast and the stereoselectivity is high. No diastereomers have been detected so far. A member of this family, [(etoxycarbonyl)methyl]cobalt tricarbonyl triphenylphosphine (I) was chosen as a model to study the mechanism of the highly specific selection of the si,M and re,P enantiomers found in the crystalline phase.

Isotope chirality in long-armed multifunctional organosilicon (“Cephalopod”) molecules

Long-armed multifunctional organosilicon molecules display self-replicating and self-perfecting behavior in asymmetric autocatalysis (Soai reaction). Two representatives of this class were studied by statistical methods aiming at determination of probabilities of natural abundance chiral isotopomers. The results, reported here, show an astonishing richness of possibilities of the formation of chiral isotopically substituted derivatives. This feature could serve as a model for the evolution of biological chirality in prebiotic and early biotic stereochemistry.