ヤヌス型シロキサン開発物語

抄録

Janus molecules, named after the ancient Roman god of beginnings and doors, generally possess a spatial architecture with dissimilar functional groups on two opposing faces. The existence of structural asymmetry and varied properties in a single molecular unit makes Janus molecules attractive building blocks in materials science. This review centers around the development of Janus structured organic-inorganic hybrid silicon compounds which show great potential in hybrid materials like silane coupling agents, coatings, semiconductors. However, the acquisition of pure Janus silicon molecules is still quite challenging. In this review, we started with the discovery circumstance of the 1st generation of Janus cubes, 3D cubic silsesquioxanes T₈. These primary Janus cubes without reactive substituents were firstly observed but not isolated from the transformation of symmetric T₈. Later, all-cis cyclic silanols, main precursors for the preparation of well-defined cage-/ladder-type silsesquioxanes, were proved to be efficient starting materials to access Janus silicon compounds. The synthesis of the first isolated Janus cube determined by X-ray structure analysis as well as the 2nd generation of Janus cubes bearing reactive groups (H, OH, vinyl) using cyclic silanols were summarized. Besides, other cage-type Janus siloxanes (Janus prism T₆ and Janus lantern cage) obtained from cyclic silanols were briefly described as well. In the last part, we summed up the preparation of various functional groups substituted Janus rings (planar Janus-type cyclotetrasiloxanes) obtained by extension of all-cis cyclic silanols/silanolates, and exhibited the obtention of Janus structured ladder- and bat-siloxanes derived from Janus rings.