The generation of hexamethyl-1,4-disilabenzene and its novel thermal chemistry

On-surface synthesis of disilabenzene-bridged covalent organic frameworks

Substituting carbon with silicon in organic molecules and materials has long been an attractive way to modify their electronic structure and properties. Silicon-doped graphene-based materials are known to exhibit exotic properties, yet conjugated organic materials with atomically precise Si substitution have remained difficult to prepare. Here we present the on-surface synthesis of one- and two-dimensional covalent organic frameworks whose backbones contain 1,4-disilabenzene (C₄Si₂) linkers. Silicon atoms were first deposited on a Au(111) surface, forming a AuSi_x film on annealing. The subsequent deposition and annealing of a bromo-substituted polyaromatic hydrocarbon precursor (triphenylene or pyrene) on this surface led to the formation of the C₄Si₂-bridged networks, which were characterized by a combination of high-resolution scanning tunnelling microscopy and photoelectron spectroscopy supported by density functional theory calculations. Each Si in a hexagonal C₄Si₂ ring was found to be covalently linked to one terminal Br atom. For the linear structure obtained with the pyrene-based precursor, the C₄Si₂ rings were converted into C₄Si pentagonal siloles by further annealing.

Disila- and digermabenzenes

Reactions of isolable disilynes and digermynes with alkynes can result in the formation of the corresponding disila- (DSBs) and digermabenzenes (DGBs), wherein two carbon atoms of the benzene ring are replaced by silicon or germanium atoms. Detailed structural and spectroscopic analyses of these DSBs and DGBs have revealed that they exhibit considerable aromaticity, comparable to that of benzene. However, in contrast to the all-carbon system benzene, these DSBs and DGBs are highly reactive toward small molecules such as oxygen, hydrogen, 1,3-dienes, and water. During the investigation of their reactivity, we discovered that a 1,2-DGB works as a catalyst for the cyclotrimerization of arylalkynes, which provides access to the corresponding 1,2,4-triarylbenzenes. In this perspective article, our recent progress in the area of DSB and DGB chemistry is summarized.

The formation of a 1,4-disilabenzene and its isomerization into a disilabenzvalene derivative

A stable 1,4-disilabenzene was generated from the reaction of a stable disilyne with 3-hexyne.