Disilyne

Disilyne, Si2H2, is a metalloid hydride composed of silicon and hydrogen. Disilyne is not well-characterised, and it is kinetically unstable with respect to isomerisation. The most stable isomer is a dibridged singlet, named di-μH-disilyne, followed by a monobridged μH-disilyne. A third, unbridged singlet ismomer is predicted to exist before disilyne - disilenylidene. Disilyne, Si2H2, is a metalloid hydride composed of silicon and hydrogen. Disilyne is not well-characterised, and it is kinetically unstable with respect to isomerisation. The most stable isomer is a dibridged singlet, named di-μH-disilyne, followed by a monobridged μH-disilyne. A third, unbridged singlet ismomer is predicted to exist before disilyne - disilenylidene. Substituted disilynes contain a formal silicon–silicon triple bond and as such are sometimes written R2Si2 (where R is a substituent group). They are the silicon analogues of alkynes. The term silyne has two different meanings. Some chemists use it to refer to compounds containing a silicon–silicon triple bond, whereas others use the term to refer to compounds containing a silicon–carbon triple bond by analogy to silene, which often refers to compounds containing silicon–carbon double bonds. The term polysilyne can refer to the layer polymer (SiH)n or substituted derivatives. The first example isolated and characterised by X-ray crystallography is an emerald green crystalline compound reported in 2004.This molecule has the structure: where R ′ {displaystyle {ce {R'}}} = HC(SiMe3)2 and R ″ {displaystyle {ce {R''}}} = HCMe2 It was prepared by the reduction of the related tetrabrominated precursor by potassium graphite (KC8). It is air and moisture sensitive but is a stable solid up until 128 °C. The geometry of the central four-silicon chain is unlike that of analogous carbon structures. Whereas substituted alkynes are linear, having a 180° bond angle at each end of the carbon–carbon triple bond, the silicon chain is bent to 137° at each end. The four silicon atoms in the chain are however perfectly coplanar, with the first and fourth silicon atoms trans to one another. The central triple bond length is 206 pm, which is around 4% shorter than the typical bond-length of Si–Si double bonds (214 pm)) and the Si–Si single bonds are 237 pm. The colour is believed to be due to a weak π–π* transition. 29Si-NMR shows upfield shift 89.9 ppm relative to silyl substituted disilenes. Calculations show a bond order of 2.6. An alternative calculation of the bond order by a different group describes the bonding as essentially due to only two electron pairs, with the third pair in a non-bonding orbital. Reaction of this compound with phenylacetylene produced a 1,2 disilabenzene.Other workers have also reported another related compound which contains a hexasila-3-yne chain: