Host-Guest Complexation. 44. Cavitands and Caviplexes Composed of Eight Anisyl Groups

Donald J. Cram, Richard A. Carmack, Mark P. Degrandare, George M. Lein, Israel Goldberg, Carolyn B. Knobler, Emily F. Maverick, Kenneth N. Trueblood

Research output: Contribution to journalArticlepeer-review

Abstract

The syntheses, crystal structures, and binding properties of cavitands 1 and 2 are reported. Macrocycle 1 is composed of eight anisyl units bonded to one another in their 2,6-positions ((C6H3OCH3)g) and was prepared in 1.4% yield by Fe(acac)3oxidation of the dilithium organometallic formed by treatment of 3,3'-dibromo-2,2'-dimethoxy-l, 1 '-biphenyl (4) with H-BuLi. Macrocycle 2 is composed of eight 4-methylanisyl units bonded to one another in their 2,6-positions ((CH3C6H2OCH3)8). It was prepared by Fe(acac)3oxidation of the dilithium organometallic formed by treatment of 3,3'-dibromo-2,2',2,2'-tetramethoxy-5,5',5,5'-tetramethylquaterphenyl (9) with sec-butyllithium. The yield was maximal at 4.7% when the ring closure was carried out in the presence of CsBr. The crystal structures of 1, 2, and 2-C2H5OH reveal that each of the eight oxygens is anti to its two neighboring oxygens to provide an (up-down)4conformational arrangement. In 1, four of the methyls attached to the oxygens are turned inward (those on rings A, B, E, and F), and four are turned outward (those on rings C, D, G, and H). The resulting cavity is small and egg-shaped, with one half lined with methyls and the other half with oxygen's unshared electron pairs. In 2, two of the methyls attached to oxygens are turned inward (those on rings A and E), and six are turned outward (those on rings B, C, D, F, G, and H). Additionally, a para methyl carbon of an adjacent host is located 3.3-3.5 A from the oxygens of rings B, D, F, and H. The cavity of 2 is larger than that of 1 and is shaped like a tangerine, with one quarter lined with methyls and three quarters lined with oxygen's unshared electron pairs. In 2'C2H5OH, three of the methyls attached to oxygens are turned inward (those on rings A, E, and H) and the other five are turned outward. The C2H5OH molecule is external to the cavity and overlies ring E, and its hydroxyl hydrogen bonds the oxygen of ring E. The crystal structure of 2•CsC104shows the Cs+guest to be ligated by the eight oxygens located at the apices of a square antiprism. The squares are 2 A apart and have sides ranging from 4.3 to 4,7 A. An oxygen from C104” completes the coordination about Cs+. The free energies were determined at 25 °C in CDCl3saturated with D20 for 1 and 2 binding the picrate salts of Li+, Na+, K+, Rb+, Cs+, NH4+, CH3NH3+, and ?-BuNH3+. The -AG° values are maximal for 1 and 2 complexing Cs+(11.8 and 13.9 kcal mol”1, respectively) and minimal for 1 and 2 complexing /-BuNH3+(3.2 and 4.0 kcal mol”1, respectively). The relationships between structure and binding are discussed in terms of the principle of preorganization.

Original languageEnglish
Pages (from-to)7068-7073
Number of pages6
JournalJournal of the American Chemical Society
Volume109
Issue number23
DOIs
StatePublished - 1 Nov 1987
Externally publishedYes

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