An Isolable Tetrasilicon Analogue of a Planar Bicyclo[1.1.0]butane with π‑Type Single-Bonding Character

Isolable
compounds that contain π bonding without an underlying
σ-bond framework (π-type single bonding) remain scarce.
Herein we report the synthesis and properties of 1,3-diiodotetrasilabicyclo[1.1.0]­butane 2 via 1,2-diiodination of the corresponding bridgehead disilene 1. Single-crystal X-ray diffraction analysis of 2 revealed a planar
bicyclic silicon ring with a planar geometry around the bridgehead
silicon atoms and a long bridgehead Si–Si distance. DFT calculations
suggested a π-type single bond between the bridgehead Si atoms
in 2 and indicated that the high planarity of 2 should most likely be attributed to the bulky substituents at the
bridge positions.