Self-assembly of tetraurea calix(4)arenes [Elektronische Ressource] : hyrogen bonded capsules with supramolecular chirality / Anca Elena Bogdan

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Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2005
• Nombre de lectures: 41
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Self-assembly of Tetraurea Calix[4]arenes:
Hydrogen Bonded Capsules with
Supramolecular Chirality


Dissertation
zur Erlangung des Grades
“Doktor der Naturwissenschaften”

am Fachbereich Chemie und Pharmazie
der Johannes Gutenberg-Universität
in Mainz


Anca Elena Bogdan
geboren in Cluj-Napoca, Rumänien

Mainz 2004 1. Introduction
1. INTRODUCTION ....................................................................................................................................... 1
1.1 CALIXARENES .......................................................................................................................................... 1
1.1.1 Definition, Synthesis and Conformations ........................................................................................ 1
1.1.2 Chemical modification of calix[4]arene.......................................................................................... 2
1.2 SELF-ASSEMBLY WITH THE HELP OF HYDROGEN BONDS........................................................................... 4
1.2.1 Glycoluril derivatives...................................................................................................................... 4
1.2.2 Calix[4]arenes fixed in cone conformation..................................................................................... 6
1.2.3 Rosettes ........................................................................................................................................... 8
1.2.4 Capsules of resorcarene derivatives ............................................................................................. 12
2. TETRAUREA DERIVATIVES OF CALIX[4]ARENE......................................................................... 17
2.1 EVIDENCE OF DIMERIZATION.................................................................................................................. 17
2.2 SYMMETRY AND CHIRALITY IN HOMO- AND HETERODIMERS OF TETRAUREA ......................................... 21
2.3 GUEST ENCAPSULATION......................................................................................................................... 23
2.4 STEREOCHEMICAL ANALYSIS OF HOMODIMERS OF MIXED TETRAUREAS ................................................ 23
2.4.1 ABBB- and AABB-Types ............................................................................................................... 24
2.4.2 ABAB-Type.................................................................................................................................... 28
3. SYNTHESES.............................................................................................................................................. 31
3.1 PARTIAL PROTECTION ............................................................................................................................ 31
3.2 REACTION WITH ISOCYANATES .............................................................................................................. 31
3.3 MULTISTEP SYNTHESIS........................................................................................................................... 34
3.4 SYNTHESIS OF LOOP DERIVATIVES ......................................................................................................... 40
3.4.1 Synthesis of mono-loop derivatives ............................................................................................... 40
3.4.2 Synthesis of di-loop derivatives..................................................................................................... 43
3.5 SYNTHESIS OF BIS-[2]CATENANES.......................................................................................................... 46
4. RESULTS ................................................................................................................................................... 49
4.1 HOMODIMERS OF ABAB-TYPE TETRAUREAS 49
4.2 REGIOSELECTIVE DIMERIZATION OF ABBB-TYPE TETRAUREAS ............................................................ 55
4.3 REGIOSELECTIVE DIMERIZATION OF AABB-TRAUREAS 59
4.3.1 Mono-loop derivatives................................................................................................................... 59
4.3.2 Di-loop derivatives........................................................................................................................ 69
4.4 HETERODIMERIZATION EXPERIMENTS 72
4.4.1 Programmed self-assembly ........................................................................................................... 72
4.4.2 Size selectivity ............................................................................................................................... 75
4.5 CATENANES ........................................................................................................................................... 78
5. SUMMARY................................................................................................................................................ 82
6. EXPERIMENTAL PART......................................................................................................................... 85
7. BIBLIOGRAPHY.................................................................................................................................... 126







21. Introduction
1. Introduction
1.1 Calixarenes
1.1.1 Definition, Synthesis and Conformations
In 1978 D. Gutsche introduced the name “calixarenes” to describe cyclic oligomers
produced by condensation of p-substituted phenols with formaldehyde under alkaline
conditions. In our days under this name different derivatives of [1 ]metacyclophanes n
(aromatic units connected via a -CHR-, -CH -, -S-, or -CH OCH - bridges) are presented. 2 2 2
Started with the original p-tert-butylcalixarenes and calixresorcarenes derivatives like
calixnaphthalene, calixpyrroles, calixfuranes, calixthiophenes, calixindoles,
calixbenzofurans or thiacalixarenes are cited here just to illustrate the variety of
1compounds , each of them having specific features subject of research all over the world.
The number of aromatic units in one molecule is other factor of increasing diversity.
Calixarenes having from 4 to 8 aromatic units are commonly used but derivatives like p-
tert-butylcalix[9-20]arenes were also obtained.
In the very beginning the synthesis of calixarenes was not so easy. Clear reaction
conditions were established for the synthesis of p-tert-butylcalix [4,6 and 8]arenes. They
are reproducible and offer the compounds in relatively good yields and purity. The
synthesis started with p-tert-butylphenol, HCHO and NaOH/KOH as base, followed by
dissolution in an appropriate solvent (diphenyl ether or xylene) and reflux for several
hours. These conditions work much less well for any other p-substituted phenol, but many
specific conditions were found which cannot be summarized in here. No direct method
could be found for the synthesis of calixarenes from 4-nitro-, 4-cyano- and 4-phenoxy-
phenol, as well as from 4-hydroxybenzoic acid, and 4-hydroxyacetophenone. All these
compounds have electronically deactivating groups in para-position to OH which disturb
the course of reaction.
For a long time the chemists handling calixarenes could not understand why from
simple alkylation reactions complicated mixture were obtained. Later was establish that
calixarenes are flexible molecules and can adopt different conformations. Four main
conformations were found and they are named cone, partial cone, 1,2-alternate and 1,3-
alternate (figure 1). Using modern techniques to characterize chemical compounds, many
examples were found possessing different conformations and symmetry in solution and/or
11. Introduction
in solid state. In the cone conformations often two aryl ring are found almost parallel while
the other two splays outward. This conformation was named “pinched cone“ or “flattened
cone” and we met it in our work.

tBu tButBu tBu But
HO HO HO HO HO HO HOOH OH OH OH
OH HO OHOH OH
tBu tBu tBu tBu tBu tBu tBu tButBu tBu tBu
cone partial cone 1,2-alternate 1,3-alternate
Figure 1: Representation of the four main conformations of p-tert-butylcalix[4]arene.
Two aspects should be mentioned:
• as long as in the molecule free OH, methoxy or ethoxy groups exist those phenolic
units are able to pass the annulus and the conformation of the molecule is changed;
propyl residues are large/long enough to prevent such an inversion and to “fix” a
certain conformation.
• for a flexible compound the conformation in solution could be (totally) different
2from the one found in the solid state.
Increasing the number of aromatic units has a direct influence in flexibility of the
molecule. The conformational representation becomes more difficult and less precise.
1.1.2 Chemical modification of calix[4]arene
There are mainly two places to functionalize a calixarene: the phenolic OH groups
(esterification, etherification) and the phenyl ring (most often the para-position).
Conditions to get mono-, di- (1,2 and 1,3), tri- and tetraalkyl ether or, esters were found.
Much research focused the elaboration of condition for the selective or exclusive formation
of one isomer from all possible regioisom