Publication Date:
2011-03-12
Description:
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 (Deltadelta 〉 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 4pi-electron antiaromaticity in a manner that contrasts sharply with the bond-length alternation, characterizing the rectangular distortion of carbon-based CBD.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Suzuki, Katsunori -- Matsuo, Tsukasa -- Hashizume, Daisuke -- Fueno, Hiroyuki -- Tanaka, Kazuyoshi -- Tamao, Kohei -- New York, N.Y. -- Science. 2011 Mar 11;331(6022):1306-9. doi: 10.1126/science.1199906.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Functional Elemento-Organic Chemistry Unit, RIKEN Advanced Science Institute, Wako, Saitama, Japan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21393541" target="_blank"〉PubMed〈/a〉
Print ISSN:
0036-8075
Electronic ISSN:
1095-9203
Topics:
Biology
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Chemistry and Pharmacology
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Computer Science
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Medicine
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Natural Sciences in General
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Physics
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