In:
Science, American Association for the Advancement of Science (AAAS), Vol. 331, No. 6022 ( 2011-03-11), p. 1306-1309
Abstract:
The cyclobutadiene (CBD) molecule C 4 H 4 deviates from a high-symmetry square geometry to compensate for its antiaromatic electronic structure. Here, we report a CBD silicon analog, Si 4 (EMind) 4 ( 1 ), stabilized by the bulky 1,1,7,7-tetraethyl-3,3,5,5-tetramethyl- s -hydrindacen-4-yl (EMind) groups, obtained as air- and moisture-sensitive orange crystals by the reduction of (EMind)SiBr 3 with three equivalents of lithium naphthalenide. X-ray crystallography reveals a planar and rhombic structure of the Si 4 four-membered ring, with alternating pyramidal and planar configurations at the silicon atoms. The large 29 Si chemical shift differences (Δδ 〉 350 parts per million) in the solid-state nuclear magnetic resonance spectra suggest a contribution of an alternately charge-separated structure. The rhombic-shaped charge-separated singlet state of compound 1 thus stabilizes its cyclic 4π-electron antiaromaticity in a manner that contrasts sharply with the bond-length alternation, characterizing the rectangular distortion of carbon-based CBD.
Type of Medium:
Online Resource
ISSN:
0036-8075
,
1095-9203
DOI:
10.1126/science.1199906
Language:
English
Publisher:
American Association for the Advancement of Science (AAAS)
Publication Date:
2011
detail.hit.zdb_id:
128410-1
detail.hit.zdb_id:
2066996-3
detail.hit.zdb_id:
2060783-0
SSG:
11
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