152507-88-5Relevant articles and documents
Hemicarcerands that encapsulate hydrocarbons with molecular weights greater than two hundred
Cram, Donald J.,Jaeger, Ralf,Deshayes, Kurt
, p. 10111 - 10116 (2007/10/02)
Syntheses are reported for the globe-shaped hemicarcerands 1 and 2 composed of two rigid bowl-like units (polar caps) attached to one another at their rims through four OCH2C≡CC≡CCH2O units (equatorial spacers). Eight pendant CH3(CH2)4 groups in 1 and C6H5CH2CH2 groups in 2 attached in assemblies of four to each polar cap render the hosts soluble in organic solvents. The important shell-closing reactions 2Ar(OCH2C≡CH)4 + [O] → Ar(OCH2C≡CC≡CCH2O)4Ar went in 5-8% yields in pyridine-O2-Cu(OAc)2 to give a hemicarcerand free of pyridine. The higher solubility of 1 (compared to that of 2) in organic solvents led to an examination of its binding properties. By heating 1 dissolved either in potential guests or in 1,3,5-[(CH3)3C]3C6H3 (too large to enter 1) containing dissolved potential guests at 80-140 °C for 2-7 days, 1:1 hemicarceplexes mixed with the empty host were isolated in those cases when the potential guests were just small enough to enter the host's portals at high temperatures but large enough not to depart during isolation as stable solids. Thus, constrictive bonding played a large role in kinetic stabilization of the hemicarceplexes. The 1H NMR spectra of both the host and the guest were markedly modified upon complexation. The half-lives in hours of representative complexes dissolved in CDCl3 at 25 °C were as follows: 1·1,3,5-[(CH3)2CH]3C6H 3, 1628; 1·1,3,5-Et3C6H3, 960; 1·4-Et[2.2]paracyclophane, 24; 1·1,3-dimethyladamantane, 13.5; 1-[3.3]paracyclophane, 13; 1·tetradehydro[2.2]paracyclophane, 11; 1·[2.2]paracyclophane, 5; 1·4,12-dihydroxy[2.2]paracyclophane, 4; and 1·[2.3]paracyclphane, 0.5. Complexes of smaller guests such as CHCl3, ferrocene, adamantane, and 1,3,5-trimethylbenzene were unstable to room-temperature isolation conditions. Larger guests such as [3.4]paracyclophane and 4,12-dinitro[2.2]paracyclophane did not enter the portals of 1 at temperatures under which host 1 was stable, whereas smaller guests such as CH2Cl2 and pyridine entered and departed the host at 25 °C rapidly on the NMR time scale. Catalytic reduction (H2, PdC) of the eight acetylenic bonds of 1 produced an empty host of much more flexible structure, 3, whose binding properties have not yet been examined.
