A
disilyne is a
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
that contains a formal
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
- silicon
triple bondA triple bond in chemistry is a chemical bond between two chemical elements involving six bonding electrons instead of the usual two in a covalent single bond. The most common triple bond, that between two carbon atoms, can be found in alkynes. Other functional groups containing a triple bond are...
and as such is formulated R
2Si
2 (where R is a substituent group) and is the silicon analogue of an
alkyneAlkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC...
. The compound disilyne would be Si
2H
2.
Some chemists use the term silyne to refer to compounds containing a silicon-silicon triple bond whilst others (e.g.) 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.
A
disilyne is a
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
that contains a formal
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
- silicon
triple bondA triple bond in chemistry is a chemical bond between two chemical elements involving six bonding electrons instead of the usual two in a covalent single bond. The most common triple bond, that between two carbon atoms, can be found in alkynes. Other functional groups containing a triple bond are...
and as such is formulated R
2Si
2 (where R is a substituent group) and is the silicon analogue of an
alkyneAlkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC...
. The compound disilyne would be Si
2H
2.
Some chemists use the term silyne to refer to compounds containing a silicon-silicon triple bond whilst others (e.g.) 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 reported disilynes
The first example isolated and characterised by X-Ray crystallography is an emerald green crystalline compound reported in 2004.
This molecule has the structure:
- R'2RSi-Si2-SiRR'2
- where R'= HC(SiMe3)2;R = i-propyl
It was prepared by the reduction of the related tetrabrominated precursor by potassium graphite (KC
8), it is air and moisture sensitive and does not melt or decompose until 128°C.
Considered as a tetrasila-2-yne derivative the four Si atoms in the chain are not collinear and in this respect the compound differs from the related alkyne. The four silicon atoms in the chain are however perfectly coplanar, the first and fourth silicon atoms are trans to one another, and the angle between the triple bond and the adjacent silicon is 137°. The central triple bond is 206 pm (around 4% shorter than Si-Si double bonds (214pm)) and the other 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 substitued 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 2 electron pairs with the other pair in non-bonding orbitals.2. 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:
- R3Si(SiR3)SiMeSi2SiMe(SiR3)SiR3
- where Me = methyl and R = t-butyl
In this the Si-Si triple bond length was calculated as 207 pm.
Comparison to C-C, Ge-Ge, Sn-Sn, Pb-Pb triple bonds
Triple bonded compounds of the heavier members of group 14 have all been prepared,
leadLead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull grayish color when exposed to air...
in 2000
tinTin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead, like the two possible oxidation states +2 and +4...
and
germaniumGermanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. Germanium has five naturally occurring isotopes ranging in atomic mass number from 70 to 76...
in 2002. In all of these the substituents attached to the bonded metal atoms are not collinear as in the alkynes but trans bent.