Oliver Mogck

Hydrogen bonded homo- and heterodimers of tetra urea derivatives of calix[4]arenes

Abstract Calix[4]arene ethers fixed in the cone conformation and substituted at the upper rim by various urea residues have been synthesized by reaction of the amino calix[4]arenes with isocyanates. Their dimerisation in apolar solvents has been established by the formation of mixed dimers consisting of two different urea derivatives.

Hydrogen-bonded dimers of tetraurea calix[4]arenes: unambiguous proof by single crystal X-ray analysis

Self-assembly of calix[4]arenes substituted by four urea residues at the wider rim leads to hydrogen-bonded dimers; the first single crystal X-ray analysis of such a dimer is reported.

Covalently linked multi-calixarenes

Abstract ipso-Nitration of t-butyl calix[4]arene tetraethers and subsequent hydrogenation provides an easy access to monoamino calix[4]arenes. Reaction with di- and triacid chlorides leads to various double- and triple-calix[4]arenes. With tetraacid chlorides derived from calix[4]arenes in the cone- or 1,3-alternate-conformations penta-calix[4]arenes are available as molecularly uniform species, which may be regarded as the first generation of calix[4]arene based dendrimers. The structure of the mononitro tetraester derivative, which may serve as a general building block has been confirmed by single crystal X-ray analysis.

CALIXARENES AS STOPPERS IN ROTAXANES

The synthesis of the amide-based rotaxane 7a bearing calix[4]arene blocking groups is described for the first time. While rotaxane formation fails if a calix[4]arene is functionalized at the upper rim with only an amino or methylamino group lacking any spacer, the prolonged amine 5a works successfully as stopper unit preventing dethreading of the dimeric wheel 1a by its size. Rotaxane formation of 8b was observed only by MALDI-TOF mass spectrometry of the reaction mixture of the amine 5b, the axle 6 and 1a. With the larger trimeric wheel 1b no stable rotaxane could be obtained. It either does not act as a concave template or its opening is too wide, even for the bulky calixarene stoppers.

Selective ipso-nitration of tert-butylcalix[4]arene 1,3-diethers: X-ray structure of an unexpected side product

1,3-Diether derivatives of tert-butylcalix[4]arene can be selectively nitrated at the para-position of the phenolic units. In this way clix[4]arenes bearing tert-butyl and nitro groups at the upper rim in alternating sequence are easily available in yields up to 75% Ipso-attack may also occur ortho to the phenolic hydroxy group leading in a side reaction to macrocyclic compounds with two 6-nitrocyclohexa-2,4-dienone units. Both types of structures were established by single crystal X-ray analysis.

Synthesis and Extraction Behaviour of Calix(4)arenes Partially Substituted at the Wide Rim by Carbamoylmethylphosphine Oxide (CMPO) Functions

Tetraethers of calix[4]arenes fixed in the cone conformation and substituted at their wide rim by one to three CMPO residues and hydrogen atoms or t-butyl moieties in the remaining position(s) were synthesized. Liquid/liquid extraction studies of selected lanthanides and actinides were undertaken with these calix[4]arenes, including also a linear trimer, in order to obtain a better understanding for the extraction properties of the corresponding calix[4]arene substituted by four CMPO functions. The structure of the 1,3-di-CMPO derivative was confirmed by single crystal X-ray analysis.

Reversible Dimerization of Tetraureas Derived from Calix[4]Arenes

Calix[4]arene derivatives, substituted at the wider rim by four urea functions are easily available in great variety. In apolar solvents like benzene or chloroform they dimerize via NH…O=C hydrogen bonds encapsulating a single solvent molecule as guest. The exclusive formation of dimers has been proved in solution by NMR, while their shape has been characterized by single crystal X-ray analysis. The kinetic stability and the rate of the guest exchange have been studied by NOESY experiments using a derivative with lower symmetry.

Self-Assembled Hydrogen Bonded Dimers of Calix[4]arenes

Self-assembly of suitably functionalized molecules to well defined supramolecular structures has become a topic of current interest. Various molecules have been designed which are able to mimic in part the recognition and self-organisation processes which are found as a general principle in nature.[1]