196860-34-1

Upstream product

• 847018-76-2 C-undecylcalix[4]resorcinarene 
• 85686-97-1 1,2-dinitro-4,5-difluorobenzene 

Relevant academic research and scientific papers

Unusually stable molecular capsule formation of a tetraphenyleneurea cavitand

(Chemical equation presented) An unusually stable molecular capsule was formed by heating phenyleneurea-spanned resorcinarene cavitand with 4-methyl-N-p-tolylbenzamide. The molecular capsule behaved as a discrete molecular entity showing a cylindrical D4d structure and showed no guest exchange in toluene-d8 even at 100°C.

Self-folding cavitands

A novel class of resorcinarene-based cavitands 2a-e that fold into a deep (8 x 10 ? dimensions) open-ended cavity by means of intramolecular hydrogen bonds has been synthesized. As follows from the FTIR and 1H NMR spectral data in apolar solvent, a seam of eight intramolecular hydrogen bonds is stitched along the upper rim of the structure 2a-e; the amide C=O···H-N interactions bridge adjacent rings-interannular binding-and are held in place by the seven-membered intraannular hydrogen bonds. The self- folding in 2a-e is reversibly controlled by solvent and temperature. Complexation of self-folding cavitands 2a-e with organic molecules such as (1-substituted) adamantanes, lactams, and cyclohexane derivatives was demonstrated by 1H NMR spectroscopy in CDCl3, benzene-d6 and p-xylene- d10; the binding energy -ΔG°values of 2-4 kcal mol-1 in p-xylene- d10 at 295 K were calculated. The exchange between complexed and free guest species is slow on the NMR time-scale, and it is proposed that hydrogen bonds are responsible for these unique features. Employing the pronounced upfield 1H NMR shifts of the complexed guest molecules, attempts were made to study the structure of the caviplexes 'from inside', and the orientation of the encapsulated adamantanes 12, 13, as well as noncovalent interactions of complexed ε-caprolactam 9b with the host walls were deduced. Even though the guest-exchange process in 2a-e is slow on the NMR time scale (k = 2 ± 1 s- 1), it is still faster than that observed for the completely closed hydrogen-bonded calixarene-based capsules or for covalently sealed hemicarceplexes. This places them in an unusual position in the scale of cavity-containing receptors and opens new perspectives to use 2a-e in catalysis and as 1H NMR supramolecular shift reagents.

Extended cavitands of nanoscale dimensions

New tetrabenzimidazole cavitands with upper rims extended by aromatic groups have been prepared and their X-ray structures were analyzed. The reversible encapsulation of a series of n-alkylammonium guests was studied by NMR spectroscopy and mass spectrometry. These guests showed different binding modes and unique interactions with the hydrophobic cavity. The trimethylammonium guests bearing n-butyl to n-hexyl substituents stabilize the C4v conformation of the cavitand by additional CH...π interactions with the aromatic upper part. The longest n-hexylammonium salt adopts a minimal gauche conformation to fit in the cavity. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Water-stabilized cavitands

Tetrabenzimidazole cavitands 4 were prepared by condensation of ortho esters with octaamino cavitand 3 in 70-80% yield. Molecular modeling predicted that no intramolecular hydrogen bonds are possible between the imidazole fragments in the vase conformation of 4. Instead, this conformation provides four perfect binding sites for hydroxyl-containing molecules through an N-H...O-H...N pattern. Such interactions provide the means for sealing the cavitand's cavity. Accordingly, dry compounds 4 are not soluble in dry CDCl3 but readily dissolve upon addition of small amounts of alcohols or by saturation of the solution with water. 1H NMR spectroscopy revealed that in these solutions molecules 4 adopt a vase conformation while 1D GOESY experiments revealed their monomeric nature. In water-saturated CDCl3, these cavitands 4 form kinetically stable 1:1 inclusion complexes with tetramethylphosphonium bromide and triethylammonium chloride in which the cation is incorporated into the π-basic cavity. Thus, cavitands 4 are a novel class of open-ended molecular containers capable of the formation of highly kinetically stable complexes upon assistance by hydrogen-bonding water molecules. Copyright

Halogen Bonding Molecular Capsules

Molecular capsules based solely on the interaction of halogen bonding (XB) are presented along with their host-guest binding properties in solution. The first example of a well-defined four-point XB supramolecular system is realized by decorating resorcin[4]arene cavitands with polarized halogen atoms for dimerization with tetra(4-pyridyl) resorcin[4]arene cavitands. NMR binding data for the F, Cl, Br, and I cavitands as the XB donor show association constants (Ka) of up to 5370 M-1 (ΔG283 K=-4.85 kcal mol-1, for I), even in XB-competitive solvent, such as deuterated benzene/acetone/methanol (70:30:1) at 283 K, where comparable monodentate model systems show no association. The XB capsular geometry is evidenced by two-dimensional HOESY NMR, and the thermodynamic profile shows that capsule formation is enthalpically driven. Either 1,4-dioxane or 1,4-dithiane are encapsulated within each of the two separate cavities within the XB capsule, with of up to Ka=9.0 108 M-2 (ΔG283 K=-11.6 kcal mol-1).

Synthesis, guest binding, and metal coordination of functionalized self-folding deep cavitands

A simple method to introduce donor functions to the upper rim of self-folding benzimidazole-based deep cavitands is described. The upper rim donors allow controlled noncovalent binding of suitably sized guest species via both self-complementary hydrogen bonding and space-filling interactions, and metal-mediated self-folding is possible if bidentate coordinators are incorporated.

Synthesis and assembly of self-complementary cavitands

Cavitands with self-complementary shapes (3 and 4) were prepared by the covalent attachment of adamantane guest molecules to the upper rim of the host structures. Relatives of the 'self-folding' cavitands 2, these new structures possess a seam of intramolecular hydrogen bonds that stabilize the folded conformation. Their self-complementary shapes result in the formation of noncovalent dimers of considerable kinetic and thermodynamic stability (- ΔAG295 = 4.5 kcal/mol for 3a and 6.5 kcal/mol for 4a in p-xylene-d10). The dimerization of cavitands 3 and 4 is reversible and subject to control by solvent and temperature. The dimerization process is enthalpically favored and entropy opposed and occurs with significant enthalpy-entropy compensation.