In less than one minute dianion 1 can be oxidized with 1,2-dibromoethane to give pure tetrakis(trimethylsilyl)cyclobutadiene (2, see scheme). The bridged cyclobutadiene derivative 6 was also similarly synthesized and characterized by X-ray crystallography; it exhibits a planar rectangular structure with localized C=C bonds.
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Sekiguchi et al. (2001) studied this question.
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