Search results for "Cyclophane"
showing 10 items of 93 documents
Protonation, coordination chemistry, cyanometallate "supercomplex" formation and fluorescence chemosensing properties of a bis(2,2'-bipyridino)cyclop…
2013
A new polyazamacrocycle (L) containing two 2,2'-bipyridino (bpy) units, where the heteroaromatic nitrogen atoms point outwards from the macrocyclic cavity, was synthesized and characterized by elemental analysis, ESI-MS, (1)H and (13)C NMR, FTIR and TGA. Five protonation constants involving aliphatic nitrogens with log K in the range 9.39-3.07 were determined by potentiometry and NMR and a sixth protonation (log K = 2.2) involving a bipyridine moiety could be detected by UV-Vis and NMR titrations. The interaction of L with the cyanometallate anions [Pt(CN)4](2-) and [Co(CN)6](3-) was studied by potentiometry yielding respectively log K values in the ranges 4.0-6.4 and 5.2-10.5, covering pro…
Coamplexation of mercury(II) compounds by crown ethers in organic media
1991
Complexes between crown ethers having ring sizes of 15–24 atoms and 5 to 8 oxygens with HgX2 species (X = Cl, I, CN, SCN) have been prepared and studied. Interactions of the substituents X bound to mercury with groups or fragments in the crown compound are essential in determining the characteristics and stability of the complexes formed. Complexes with crowns of 18C6 ring sizes are the most favourable except for HgX2 compounds for which the size of X is larger than the macrocycle ring, as is the case for X = CF3.
A Hybrid Cavitand Made by Capping Permethylated α-Cyclodextrin with Cyclotriveratrylene
2012
A hybrid C 3 -symmetric cavitand 1, in which permethylated α-cyclodextrin (PM α-CDX) is capped with cyclotriveratrylene (CTV), has been prepared in 8 % yield by intramolecular cyclization of a vanillyl alcohol derivative attached to the primary rim of the CDX platform. The reaction proceeds diastereoselectively (dr ≈ 6:1), the chirality of the α-glucopyranosyl units controlling the chirality of the CTV component. Interestingly, in polar solvents, 1 shows self-complexation properties as the primary methoxy groups of the CDX component are directed towards the CTV cavity.
Neue extrem deformierte (Biphenylen‐)Kohlenwasserstoff‐Gerüste
1992
New Extremely Deformed (Biphenylene)Hydrocarbon Skeletons The tetracyclic carbon skeleton 2-oxo[3](1,8)biphenylenophane (4) was synthesized by cyclization of a mixture of the bis(bromomethyl) compounds 7a, b with p-tolylsulfonylmethyl isocyanide. 2-Hydroxy[3](1,8)biphenylenophane (5) and the [3](1,8)biphenylenophane hydrocarbon 6 were obtained by reduction of 4 with LiAlH4 and NaBH4, respectively. X-ray analyses of 4 and 6 illustrate the dramatic deformation of bond lengths and angles in these molecules.
Small hydrocarbon cyclophanes: Synthesis, X-ray analysis and molecular modelling
2002
Small hydrocarbon cyclophanes, such as [2.2.0]m,m,m-cyclophane (20) and [2.2.0]p,m,m-cyclophane (21), are strained analogues of the well-known π-prismand [2.2.2]p,p,p-cyclophane (1). The synthetic route to these molecules is based on well-established cyclophane methodology which offers a general access to a whole family of hydrocarbon cyclophanes. Single crystal X-ray analysis and molecular modelling showed that the reduction of the ring size from 18-membered (1) to 14-membered (21) or 13-membered (20) has a substantial effect on the size and the shape of the cyclophane’s cavity, thus blocking its ability to complex Ag+ ions. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
Photoinduced electron transfer in molecular organizates at the gas-water interface
1994
Abstract The influence of the molecular geometry is of fundamental importance for a better understanding of the photoinduced electron transfer mechanism. Because of their typical molecular structures, cyclophane rings have proved to be suitable for this purpose as electron acceptor molecules adsorbed under an amphiphile monolayer. We used a pyrene-labelled phospholipid derivative both as molecular anchor for the cyclophane ring and electron donor molecule. The co-spreading technique was used to prepare the complex monolayers. Surface pressure and surface potential measurements have indicated similar monolayer behaviour as with dimyristoylphosphatidic acid as anchor molecule, leading to the …
Tri- and tetraurea piperazine cyclophanes: synthesis and complexation studies of preorganized and folded receptor molecules.
2010
A series of symmetrical tri- and tetrameric N-ethyl- and N-phenylurea-functionalized cyclophanes have been prepared in nearly quantitative yields (86-99 %) from the corresponding tri- and tetraamino-functionalized piperazine cyclophanes and ethyl or phenyl isocyanates. Their conformational and complexation properties have been studied by single-crystal X-ray diffraction, variable-temperature NMR spectroscopy, and ESI-MS analysis. The rigid 27-membered trimeric cyclophane skeleton assisted by a seam of intramolecular hydrogen bonds results in a preorganized ditopic recognition site with an all-syn conformation of the urea moieties that, complemented by a lipophilic cavity of the cyclophane, …
Asymmetrically substituted calix[4]arenes; A two-dimensional 1H NMR study of a tetraester derivative in the cone-conformation
1991
Abstract Several new chiral calix[4]arenes with three or four different substituents in the p-position have been prepared by fragment condensation. Standard derivatization procedures always led to the formation of mixtures of various conformational isomers from which the derivative in the cone-conformation could be isolated only by preparative HPLC. For a tetraester derivative it was shown by two-dimensional 1H NMR spectroscopy, that due to the different substituents the cone-conformation is strongly distorted. The sodium complex of this tetraester, however, assumes a regular cone-conformation again.
Regioselective synthesis of calixcrowns derived from p-tert-butylcalix[5]arene
1993
Abstract Alkylation of p-tert-butylcalix[5]arene with oligoethylene glycol-ditosylates in the presence of CsF affords the 1,3-bridged calix[5]crowns 1a–c in 51 to 72% yield. In the case of hexaethylene glycol the isomeric 1,2-bridged calix[5]crown-7 2c was obtained additionally. The calixcrowns were further modified by alkylation of the remaining hydroxyl groups.
Diastereoselective Functionalization of a Spherand‐Type Calixarene
1994
Condensation of 5,5'-di-tert-butyl-2,2'-dihydroxybiphenyl (1) with formaldehyde yields a cyclic trimer 2 (and tetramer 3) having three (four) methylene groups less than a calix[6]arene (calix[8]arene). Alkylation of the (flexible) trimer with ethyl bromoacetate gives exclusively the stereoisomer 4 with C 2 symmetry, while the isomer with D 3 symmetry is not observed. Two isomers 6a and 6b (C 2 and C 1 symmetry) are obtained by treatment with tert-butyl bromoacetate which both are converted by transesterification with methanol into the same hexamethyl ester 5 having C 2 symmetry. These results are rationalized by restricted rotation around Ar-Ar bonds for larger O-alkyl groups also around Ar…