A silicon analogue of a fused bicyclic borirene derivative

The replacement of all carbon atoms in aromatic rings with main-group elements to afford inorganic ring systems is highly desirable due to their distinct aromatic character. However, fused polycyclic main-group element rings are rare and the feasibility of aromaticity in such compounds has yet to be explored. To explore aromaticity in fused polycyclic main-group element rings, a stable di-silicon analogue of fused bicyclic borirene, namely bicyclo[1.1.0]-2,4-diborylenyldisil-1(3)-ene 5 was synthesized from an N-phosphinoamidinato chlorosilylene 3. Compound 5 consists of a bridgehead Si[double bond, length as m-dash]Si double bond bonded with two bridging borons resulting in an unsaturated fused bicyclic skeleton. The bridgehead Si[double bond, length as m-dash]Si σ- and π-electrons and bridging Si-B σ-electrons are stabilized by both σ- and π-aromatic delocalization on the Si₂B₂ fused bicyclic ring.