Pyramidanes

Pyramidane
is an elusive but highly desirable target for synthetic
chemists that has attracted a great deal of attention because of its
nonclassical structure and unusual bonding features. Although well
studied on theoretical grounds, neither the parent all-carbon pyramidane
nor its derivatives containing heavier group 14 elements have ever
been isolated and characterized. In this Communication, we report
on the synthesis and structural elucidation of the first stable representatives
of this class of highly strained polyhedral compounds: germa- and
stannapyramidanes Ge[C4(SiMe3)4] and Sn­[C4(SiMe3)4]. The peculiar structural and bonding features of these
compounds are verified by combined experimental and computational
analyses, showing these derivatives to be nonclassical neutral compounds
with a very large contribution of ionic character.