HOST-GUEST COMPLEXION .67. A HIGHLY ADAPTIVE AND STRONGLY BINDING HEMICARCERAND

• Published in: Journal of the American Chemical Society Vol. 116; no. 1; pp. 111 - 122
• Main Authors: ROBBINS, TA, KNOBLER, CB, BELLEW, DR, CRAM, DJ
• Format: Journal Article
• Language: English
• Published: WASHINGTON Amer Chemical Soc 12.01.1994
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology
• ISSN: 0002-7863
• DOI: 10.1021/ja00080a014

Two new hemicarcerands (1 and 2) are reported, the former of which was induced to form 30 capsular complexes stable enough at 25-degrees-C in CDCl3 to be isolated and characterized. The compounds are globe-shaped and composed by attaching two tetraaryl bowls to one another at their rims through four O(CH2)4O groups. To impart desired solubility properties to the final host, four C6H5CH2CH2 groups are attached to each bowl at their bases in 1, and four CH3(CH2)4 groups to each in 2. The shell closure, 2 Ar(OH)4 + 4 TsO(CH2)4OTs --> Ar[O(CH2)40]4Ar, conducted in (CH3)2NCOCH3-Cs2CO3 at 70-degrees-C, gave 1.(CH3)2NCOCH3 (30-40%), and the same type of reaction in (CH3)2SO-Cs2CO3 gave 2.(CH3)2SO (15-20%), a molecule of solvent being incarcerated in each case. Empty 1 was obtained by heating 1.(CH3)2NCOCH3 in (C6H5)2O (molecules too large to be incarcerated) at 195-degrees-C for 5 days (94%). Neat CH2Cl2 went in and out of the interior of 1 fast enough at 25-degrees-C to be useful as solvent in chromatography of 1 and its complexes. By heating empty 1 at 70-170-degrees-C for several hours up to 6 days in solutions of potential guests as solvent, or with 100 equiv of guest in (C6H5)2O as solvent, 30 hemicarceplexes were formed, isolated, purified, and characterized. In the crystal structure of 1.6H2O.4o-(CH3)2C6H4, the northern and southern hemispheres were twisted relative to one another around their polar axis by approximately 13-degrees. The crystal structures Of 1.p-I2C6H4.2C6H5NO2, 1.p-(CH3)2C6H4.2NO2C6H5, 1.O2NC6H5.2C6H5NO2 , 1.o-BrC6H4OH.2C6H5NO2, and 1.(CH3)2NCOCH3.2C6H5NO2 were untwisted and belonged to the same space group. The lengths along the polar axes decreased in the order listed through conformational changes in the O(CH2)40 bridges. The E(a) for decomplexation of 1.(CH3)2NCOCH3 in C6D5NO2 at 140-170-degrees-C (four temperatures) was 23.5 kcal mol-1. The rotations relative to their shells of large incarcerated guests, such as 2,4-Cl2C6H3CH3, 3,4-Cl2C6H3CH3, and 4-CH3C6H4OCH3, were slow enough on the H-1 NMR time scale at 25-degrees-C to produce different chemical shifts for the same host protons located in the northern and southern hemispheres of the complex. The smallest guest incorporated in 1 was Xe, but 1.Xe as a solid gave up its guest over days at ambient temperature.