Substituent effects on axle binding in amide pseudorotaxanes: comparison of NMR titration and ITC data with DFT calculations.

The binding behaviour of differently substituted diamide axle molecules to Hunter/Vögtle tetralactam macrocycles was studied with a combination of NMR titration, isothermal titration calorimetry (ITC) experiments and calculations employing density functional theory (DFT), along with dispersion-corrected exchange-correlation functionals. Guests with alkyl or alkenyl chains attached to the diamide carbonyl groups have a significantly higher binding affinity to the macrocycle than guests with benzoyl amides and their substituted analogues. While the binding of the benzoyl and alkenyl substituted axles is enthalpically driven, the alkyl-substituted guest binds mainly because of a positive binding entropy.

Synthesis of multivalent host and guest molecules for the construction of multithreaded diamide pseudorotaxanes.

A series of di-, tri- and tetravalent axles and wheels for the synthesis of pseudorotaxanes bearing the tetralactam macrocycle/diamide axle binding motif was prepared. Starting from iodinated monovalent precursors, Sonogashira cross-coupling reactions were utilized to couple the binding sites to appropriate spacer groups. Through this "Lego" or "toolbox" approach, the convergent synthesis of host and guests with a well-defined number of the binding sites is possible.

Effects of subtle differences in ligand constitution and conformation in metallo-supramolecular self-assembled polygons.

3,3'-Bis(pyridin-[n]-ylethynyl)biphenyl (n = 3, 4) and the corresponding 2,2'-bipyridines assemble with (dppp)Pt(II) triflate into metallo-supramolecular polygons. Depending on the position of the terminal pyridine N atoms, the assembly reaction leads to different equilibrium products. With the slow ligand exchange on Pt(II) complexes, the equilibrium is reached on a many-hour time-scale.

Synthesis of 5-acetyloxazoles and 1,2-diketones from β-alkoxy-β-ketoenamides and their subsequent transformations.

Lithiated alkoxyallenes, nitriles, and carboxylic acids have been employed as precursors in a three-component reaction leading to highly substituted β-alkoxy-β-ketoenamides. Upon treatment with trifluoroacetic acid, these enamides could be easily cyclized to 5-acetyloxazole derivatives. The synthesis is very flexible with respect to the substitution pattern at C-2 and C-4 of the oxazole core.

Thermodynamically controlled self-sorting of hetero-bimetallic metallo-supramolecular macrocycles: what a difference a methylene group makes!

(31)P NMR and tandem MS experiments provide clear evidence for the thermodynamically controlled self-assembly of hetero-bimetallic metallo-supramolecular macrocycles through self-sorting caused by different ancillary ligands.

A double intramolecular cage contraction within a self-assembled metallo-supramolecular bowl.

When isolated in the high vacuum of an ESI-FTICR mass spectrometer, bowl-shaped metallo-supramolecular M(6)L(4) assemblies undergo a surprising and mechanistically interesting intramolecular double cage contraction to yield smaller M(3)L(2) cages.

A modular "toolbox" approach to flexible branched multimacrocyclic hosts as precursors for multiply interlocked architectures.

Tetralactam macrocycles can be functionalized by a variety of cross-coupling reactions. A modular "toolbox" strategy is presented that allows 1) several tetralactam macrocycles to be covalently connected with each other or with a central spacer, 2) the macrocycles to be substituted with or connected to different chromophores, and 3) metal-coordination sites to be attached to the macrocycles. With this approach a series of different oligo-macrocyclic hosts was obtained with great structural diversity and enormous potential for further functionalization.