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ABSTRACT: As part of a study to achieve selective oligo(poly)bromination-ultimately perbromination-of the dodecahedral C(20) skeleton, the extent and direction of the ionic bromination of dodecahedrene and 1,16-dodecahedradiene were explored. Along sequences of Br(+) additions/deprotonations and allylic rearrangements, up to ten hydrogen atoms were substituted (traces of C(20)H(x)Br(10)). Tetrabromododecahedrenes obtained under defined conditions in up to 50 % total yield with three and four allylic bromine substituents protecting the extremely bent C==C bonds, proved highly unreactive even towards oxygen but reacted rapidly with CH(2)N(2). Upon electron impact ionization (MS) of the newly secured oligo(poly)bromododecahedra(e)nes, sequential loss of the substituents ended generally in polyunsaturated dodecahedranes (in the extreme C(20)H(4), "tetrahydro-C(20) fullerenes"). Only subsequently did skeletal fragmentations occur. From X-ray crystal-structure analyses, more information was obtained on the structural response of the dodecahedral skeleton to the strain induced by the voluminous substituents. As Appendix, the forcing radical bromination of 1,6-dibromododecahedrane and exploratory cis-beta-HBr/cis-beta-Br(2) eliminations in bromododecahedranes with [Fe(2)(CO)(9)], P(2)F/[FeCp(2)] and [Fe(tmeda)Cp*Cl] (in situ protection) are presented.
Chemistry 09/2006; 12(24):6242-54. · 5.93 Impact Factor
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Fabian Wahl,
Andreas Weiler,
Peter Landenberger, Emmerich Sackers,
Torsten Voss,
Alois Haas,
Max Lieb,
Dieter Hunkler,
Jürgen Wörth,
Lothar Knothe,
Horst Prinzbach
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ABSTRACT: "One-pot" substitution of the twenty hydrogen atoms in pentagonal dodecahedrane (C(20)H(20)) by OH, F, Cl, and Br atoms is explored. Electrophilic insertion of oxygen atoms with DMDO and TFMDO as oxidizing reagents ended, far off the desired C(20)(OH)(20), in complex polyol mixtures (up to C(20)H(10)(OH)(10) decols, a trace of C(20)H(OH)(19)?). Perfluorination was successful in a NaF matrix but (nearly pure) C(20)F(20) could be secured only in very low yield. "Brute-force" photochlorination (heat, light, pressure, time) provided a mixture of hydrogen-free, barely soluble C(20)Cl(16) dienes in high yield and C(20)Cl(20) as a trace component. Upon electron-impact ionization of the C(20)Cl(16) material sequential loss of the chlorine atoms was the major fragmentation pathway furnishing, however, only minor amounts of chlorine-free C(20) (+) ions. "Brute-force" photobrominations delivered an extremely complex mixture of polybromides with C(20)HBr(13) trienes as the highest masses. The MS spectra exhibited exclusive loss of the Br substituents ending in rather intense singly, doubly, and triply charged C(20)H(4-0) (+(2+)(3+)) ions. The insoluble approximately C(20)HBr(13) fraction (C(20)Br(14) trienes as highest masses) obtained along a modified bromination protocol, ultimately allowed the neat mass selection of C(20) (-) ions. The C(20)Cl(16) dienes and C(20)H(0-3)Br(14-12) tri-/tetraenes, in spite of their very high olefinic pyramidalization, proved resistant to oxygen and dimerization (polymerization) but added CH(2)N(2) smoothly. Dehalogenation of the respective cycloaddition products through electron-impact ionization resulted in C(22-24)H(4-8) (+(2+)) ions possibly constituting bis-/tris-/tetrakis-methano-C(20) fullerenes or partly hydrogenated C(22), C(23), and C(24) cages.
Chemistry 09/2006; 12(24):6255-67. · 5.93 Impact Factor
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Jens Reinbold, Emmerich Sackers,
Thomas Osswald,
Klaus Weber,
Andreas Weiler,
Torsten Voss,
Dieter Hunkler,
Jürgen Wörth,
Lothar Knothe,
Frank Sommer,
Nina Morgner,
Issendorff Bernd von,
Horst Prinzbach
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ABSTRACT: The highly pyramidal, highly strained 1,4,16-dodecahedratriene (4) and C20H12 1,4,10(14),16-dodecahedratetraene (5) are cage olefins with an intriguing "inner life". For 5 DFT calculations give information about the energetic and geometrical consequences of one-/two-electron oxidation and reduction. Attempts to prepare 4 and 5 through thermal retro[2+2]/[4+2]cycloaddition strategies proved unsuccessful. Still, the C20H14/C20H12 cage cations and anions are liberated upon electron impact or gas-discharge ionization of their thermally extremely stable tris-/tetrakisanthraceno-anellated derivatives. Mass-selection (photoelectron (PE) characterization) of the anions failed, however, due to the very small anion intensity, the preferential formation of hydrogen-poor ions, and minor cage disruption.
Chemistry 02/2002; 8(2):509-24. · 5.93 Impact Factor
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ABSTRACT: Methodological alternatives for the preparation of highly strained, highly pyramidalized dodecahedrene 2 (Estr=87.3 kcal mol−1; ϕ=43.5°, MM2) and 1,16-dodecahedradiene 3 (Estr=105.3 kcal mol−1; ϕ=42.9°, MM2) have been explored, protection/deprotection strategies have been tested—with the eye on their utilization
for the generation of higher unsaturated dodecahedranes (e.g. 1,4, 16-triene 4, 1,4,10 (14),16-tetraene 5). For the acquisition
of preparative quantities of monoene 2 the “P2F” catalyzed cis-β-elimination in bromododecahedrane, of diene 3 the FVP fragmentation of a “twofold protected” precursor (bis-furan adduct)
have become the protocols of choice, which both profit from the recent synthetic advances along the pagodane → dodecahedrane
scheme. Because of unusually effective steric protection the highly tilted C=C double bonds of 2 (λmax (CH3CN) = 254 nm, ν
C=C = 1658 cm−1, δC=C = 164.4) and 3 (δC=C = 170.5) enter into thermal stabilization pathways (dimerization, oligomerization) only at higher temperatures (for 2 ca.
50% consumption after 5 h at 100°C in a 3·10−3 molar toluene solution); extreme sensitivity to oxygen is primarily attributed to kinetically and thermodynamically promoted
allylic hydrogen abstraction.
Research on Chemical Intermediates 04/1996; 22(7):667-702. · 0.70 Impact Factor
