Martin Bělohradský

Slippage—an alternative method for assembling [2]rotaxanes

The exploitation of size-complementarity between the macrocyclic component and the stoppers of the dumbbell component of a [2]rotaxane, together with stabilising noncovalent bonding interactions that create a thermodynamic trap, have permitted the development of an alternative method, which can be termed slippage, for the syntheses of [2]rotaxanes in good yields.

The self-assembly of branched [n]rotaxanes—the first step towards dendritic rotaxanes

The self-assembly, by means of a slippage procedure, of three novel rotaxanes incorporating, respectively, one, two and three bisparaphenylene-34-crown-10 macrocyclic components and a single branched component, consisting of three bipyridinium units attached covalently to a 1,3,5-trisubstituted benzene central core and each bearing at its other end a substituted tetraarylmethane blocking group, is described.

The self assembly of [2]- and [3]-rotaxanes by slippage

Both a [2]- and a [3]-rotaxane have been synthesised in good yield by slippage at 55 °C in acetonitrile of bisparaphenylene-34-crown-10 over size-complementary stoppers on a dumbbell-shaped molecule containing two 4,4′-bipyridinium recognition sites.

Crown ether substituted cobalta bis(dicarbollide) ions as selective extraction agents for removal of Cs+ and Sr2+ from nuclear waste

A series of crown ether derivatives of the cobalta bis(dicarbollide) closo-[(1,2-C2B9H11)2-3,3′-Co]− (1) anion was prepared using two synthetic strategies. The first method employs dioxane ring cleavage of the closo-[{8-(C4H8O2)-1,2-C2B9H10}-3,3′-Co-(1′,2′-C2B9H11)]0 zwitterionic species with sodium oxymethyl crowns, producing a series of anions with spacer bonded crown ether moieties varying in crown ether ring size. Three compounds of this group; closo-[{8-(15-crown-5-CH2O)-(CH2CH2O)2-1,2-C2B9H10}-3,3′-Co-(1′,2′-C2B9H11)]− (2), closo-[{8-(18-crown-6-CH2O)-(CH2CH2O)2-1,2-C2B9H10}-3,3′-Co-(1′,2′-C2B9H11)]− (3) and [{8-(21-crown-7-CH2O)-(CH2CH2O)2-1,2-C2B9H10}-3,3′-Co-(1′,2′-C2B9H11)]− (4) were prepared in high yields. The second approach involved reaction of deprotonated closo-[8,8′-(OH-1,2-C2B9H12)2-3,3′-Co]− with p-toluenesulfonyl esters derived from hydroxymethyl crown ethers. Only compounds bearing one crown ether ring resulted in preparative amount from this reaction, the [(8-{(15-crown-5-CH2O)-1,2-C2B9H10}-3,3′-Co-{8′-(HO)-1′,2′-C2B9H10}]− (5) and [{8-(21-crown-7-CH2O)-1,2-C2B9H10}-3,3′-Co-(8′-HO-1′,2′-C2B9H10)]− (6). All compounds were characterized by high field 1H and 11B NMR methods, HPLC and MS, with electrospray ionization, and the molecular structure of the Cs+ complex of species 5 was determined by single crystal X-ray diffraction analysis. These compounds represent the first examples where oxygen crown ethers were successfully bonded to the cage of anion 1. The scope and limitations of the use of these compounds in the liquid–liquid extraction of Cs+ and Sr2+ from nuclear waste were studied, including comparison of extraction efficiency and selectivity of the covalently bonded species under study with synergistic mixtures of hexabrominated anion 1 with crown ethers. As a rule, crown ethers linked to the cobalta bis(dicarbollide) cage display distribution coefficients for Cs+ and Sr2+ comparable to the crown ethers mixed with the hexabromoderivative of 1, however, they were found to exhibit better selectivity with respect to Na+ cation.

The controlled self-assembly of a [3]rotaxane incorporating three constitutionally different components

The self-assembly, by means of a slippage procedure, of a [3]rotaxane comprised of three constitutionally different sub-units—a dumbbell-shaped component, incorporating two 4,4′-bipyridinium units encircled by one bisparaphenylene-34-crown-10 macrocycle and one 1,5-dinaphtho-38-crown-10 macrocycie—is described.

α-Amino acids and dioxopiperazines crowned at the α-carbons with polyether macrorings. Synthesis, complexation and self-assembling properties

Abstract Crowned α-amino acids 7a–c and their dioxopiperazine derivatives 12a–c were prepared from the easily accessible masked tris(hydroxymethyl)aminomethane 1 . X-Ray crystal structures of the free as well as alkali metal ion coordinated compounds were investigated.

Tetrathiafulvalene–Oligo(para‐phenyleneethynylene) Conjugates: Formation of Multiple Mixed‐Valence Complexes upon Electrochemical Oxidation

Short monodisperse oligo- (para-phenyleneethynylene) (pOPE) units bearing laterally attached tetrathio-substituted tetrathiofulvalene (TTF) units have been synthesised from functionalised aromatic building blocks by using the Sonogashira cross-coupling methodology. The unusual redox properties of these TTF-pOPE conjugates were observed by employing electrochemical methods, such as cyclic voltammetry and exhaustive electrolysis. We found that formally one half of the TTF units in the pOPE monomer 1, dimer 2, and trimer 3 (with 2, 4, and 6 TTF units, respectively) are electrochemically silent during the first-step oxidation at 0.49 V. We propose the formation of persistent mixed-valence complexes from the TTF and TTF(+·) units present in an equal ratio. Such mixed-valence dyads (single or multiple in the partially oxidised 1-3) exhibit an unusual stability towards oxidation until the potential of the second oxidation at 0.84 V is achieved. This finding suggests that below this potential the oxidation of the respective mix-valence complexes is extremely slow.

Liquid-Liquid Extractions of Microamounts of 137Cs and 85Sr with Chlorinated Dicarbollide and Crown Ethers into Mixed Dodecanenitrile/n-dodecane Nonpolar Diluent

New methods of extraction of 137Cs and 85Sr into solvent mixture of dodecanenitrile with n-dodecane in the presence of various crown ethers and chlorinated dicarbollide are described. This is the first time when extraction with chlorinated dicarbollide anion was accomplished into a judiciously chosen nonpolar solvent. The theoretical reasoning leading to the choice of such nonpolar solvent is outlined. New crown ethers with laterally branched alkyl chain were synthesized and tested. These, when the same crown moiety is compared, are more effective for Sr2+ extraction than the commonly used DC18C6 (18C6 ring moiety), but less effective for Cs+ extraction compared with DB21C7 (21C7 moiety). The systems may be used both in analytical applications and, hopefully, after further development, as well in a nuclear reprocessing industry.

C-C Coupling reaction of 1,5-dibromo-2,6-dihydroxynaphthalene with alkali 2-naphthoxide. Opposite effects of counterion coordination and hydrogen bonding on stereoselectivity in the formation of cis- and trans-1,1′:5′,1″-ternaphthyls

Abstract The title reaction yields cis- and trans-2,2′,6′,2″-tetrahydroxy-1,1′:5′,1″-ternaphthyls as the main products. In contrast to non-selective distribution of the stereoisomers in the thermodynamic equilibrium, very high selectivity can be attained under conditions of kinetic control. The observed values of cis-/trans- ratios range between the extremes 94:6 and 6:94, depending on the solvent and counterion employed. The coordination of the metal counterion plays a key role in the reaction performed in toluene, supporting formation of the cis-stereoisomer. When the coordination ability of the counterion is supressed by 18-crown-6, intramolecular hydrogen bonding of the departing bromide group prevails in the stereocontrol, providing support for the trans-stereoisomer formation.

A NOVEL ONE-POT CONVERSION OF 2-NAPHTHOLS INTO 1,1'-BINAPHTHALENE-2,2'-DIOLS

Abstract A simple two-step, one-pot procedure based on the treatment of sodium 2-naphthoxide with bromine yields 1,1′-binaphthalene-2,2′-diol in a high yield and an excellent purity. The procedure is applicable also to preparation of the symmetrically disubstituted analogues.