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.