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Bromination of Unsaturated Dodecahedranes—En Route to C 20 Fullerene
Author(s) -
Sackers Emmerich,
Oßwald Thomas,
Weber Klaus,
Keller Manfred,
Hunkler Dieter,
Wörth Jürgen,
Knothe Lothar,
Prinzbach Horst
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200501609
Subject(s) - halogenation , allylic rearrangement , chemistry , bromine , fullerene , medicinal chemistry , stereochemistry , crystallography , organic chemistry , catalysis
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 CC 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 ‐β‐HBr/ cis ‐β‐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.