Self-Folding Cavitands of Nanoscale Dimensions

Abstract

New types of resorcinarene-based nanoscale container molecules 2 and 3 are described. They feature reversibly folding unimolecular cavities of nanoscale dimensions and ∼800 Å 3 internal volume; they are among the largest synthetic unimolecular hosts prepared to date. Two seams of intramolecular hydrogen bonds, provided by 12 secondary amides, control the guest uptake and release. The hydrogen bonds resist the unfolding of the host and increase the energetic barrier to guest exchange. Exchange is slow on the NMR time scale (room temperature), and kinetically stable complexes result. The direct observation of bound species and the stoichiometry of the complexes are reported. A series of adamantyl and cyclohexyl guests 11-19 of various shapes and lengths were prepared and used to estimate the hosts' capacities. Compound 2 exists in an S-shaped conformation and its two cavities act independently; each half of host 2 formed kinetically stable complexes with either two identical or different guest molecules. The C-shaped host 3 accommodates rigid and long guests with association constants (K a ) between 500 ( 50 M -1 (-∆G 295 ) 3.6 ( 0.1 kcal mol -1 ) and 270 ( 100 M -1 (-∆G 295 ) 3.2 ( 0.2 kcal mol -1 ) for adamantyl derivatives. With the more flexible and/or shorter guests, fast exchange between the free and complexed guest species was observed at room and higher temperatures (in toluene-d 8 ). Guest exchange rates of the new hosts are considerably faster than rates seen with typical hemicarceplexes but slower than those of other open-ended cavitands.

A Phthalocyanine Clathrate of Cubic Symmetry Containing Interconnected Solvent‐Filled Voids of Nanometer Dimensions

“…Relative to reported hydrogenbonded clathrate structures, the proportion of included solvent within the crystal structure of 1 is unremarkable; however, its distribution into such large well-defined cavities is unprecedented. Molecular enclosure on the subnanoscale may be achieved within the voids of discrete molecular cages, [21] crystalline clathrates, [4] and network coordination polymers; [22] however, only a few examples approach, [23] and fewer exceed, [24] an enclosed volume of 1 nm 3 . Of interest, is the potential for the exploitation of the functionalities present in the phthalocyanine unit to provide catalytic sites that would be embedded in the wall of the cavities and accessible only through the narrow size-selective channels.…”

Functional cavitands: Chemical reactivity in structured environments

“…The addition of the fourth wall and reduction to the diamine gave the common precursor to the monofunctionalized cavitands. These include the self-complementary structure 11, (25) the introverted acid 12 (26), the dipyrrole 13 (27), the porphyrin 14 (28,29), the biscavitand 15 (30), the phenanthroline 16 (20), salen 17 (31), and the pyridone 18 ( Fig. 5) (32).…”

Resorcarenes: Hollow Building Blocks for the Host-Guest Chemistry

“…In compound 61a (Chart 31) two deepened cavities were shown to act independently, by simultaneously complexing two different (adamantyl and cyclohexanyl) guests, one per each cavity [113] On the other hand, the similar compound 61b formed stable 1:1 inclusion complexes with diaryl substituted adamantanes 62a,b [113]. Finally, a porphyrin derivative linker was used to attach two cavitands and to prepare one of the hugest synthetic hosts [114].…”