The First Bicyclo[1.1.0]butane Dianion of Heavier Group 14 Elements

Benzodisilacyclobutadienes: 8π-Electron Systems with an Antiaromatic Silicon Ring

Benzodisilacyclobutadienes 2 a-c were isolated as blue to green crystalline solids from the reaction of stable disilyne 1 and 1,2-dibromobenzenes in the presence of potassium graphite. In the solid state, substantial bond alternation was observed within the benzene rings of 2 a-c. In hexane, 2 a-c showed remarkable bathochromic shifts of the π→π* (HOMO→LUMO) absorption bands at 625-670 nm. NMR spectra and theoretical calculations indicated that the diamagnetic ring currents of the benzene rings of 2 a-c are considerably reduced by contributions from the antiaromatic 1,2-disilacyclobutadienes. In their entirety, the obtained results indicate that 2 a-c represent 8π-electron systems that contain an antiaromatic 1,2-disilacyclobutadiene.

Aromaticity of Group 14 Organometallics: Experimental Aspects

The long story of aromatic compounds has extended over almost two centuries, since the discovery by Faraday of "bicarburet of hydrogen", or C(6)H(6), now called benzene. Since then, the chemistry of aromatic compounds has been developed extensively; this is reflected in the synthesis of novel classes of aromatic derivatives including charged species, nonclassical (Möbius, three-dimensional, homo-, metalla-) aromatics, and fullerenes. The theory of aromaticity has also undergone a spectacular evolution since the first definition of aromaticity by Hückel; the classification of aromaticity now requires the consideration of versatile criteria: energetic, structural, magnetic, among others. In this Review, we discuss the current state of affairs in the chemistry of aromatic compounds of the heavier Group 14 elements, the latest experimental achievements, as well as future prospects in the field.