Disilyne

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Disilyne
Structural formula of disilyne
Names
IUPAC name
Disilyne
Other names
Disilyn
Identifiers
3D model (JSmol)
ChemSpider
Properties
H2Si2
Molar mass 58.19 g·mol−1
Related compounds
Related silyls
Alkyne
Silylene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Disilyne, Si
2
H
2
, 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.[clarification needed]

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 refer to compounds containing a silicon–silicon triple bond,[1] whereas others use the term to refer to compounds containing a silicon–carbon triple bond[2] by analogy to silene, which often refers to compounds containing silicon–carbon double bonds.[3] The term polysilyne can refer to the layer polymer (SiH)n or substituted derivatives.[1]

The first reported disilynes[edit]

The structure of the first disilyne characterised

The first example isolated and characterised by X-ray crystallography is an emerald green crystalline compound reported in 2004.[4] This molecule has the structure:

where = HC(SiMe3)2 and = 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.[relevant? ] 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.[5][6][7] Reaction of this compound with phenylacetylene produced a 1,2 disilabenzene.[8] Other workers[9] 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 compound, the Si–Si triple bond length was calculated as 207 pm.

Heavier group 14 analogues[edit]

Triple bonded compounds of the heavier members of group 14 have also been prepared; lead in 2000, [10] and tin[11] and germanium[12] in 2002. The general geometries of these other Group 14 cases are the same as for silicon: the substituents bent with trans orientation rather than linear as for carbon-based alkynes.

See also[edit]

References[edit]

  1. ^ a b Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5
  2. ^ Miriam Karni; Yitzhak Apeloig (January 2002). "The quest for a stable silyne, RSi ≡ CR′. The effect of bulky substituents [1]". Silicon Chemistry. 1 (1): 59–65. doi:10.1023/A:1016091614005. 
  3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9. 
  4. ^ Akira Sekiguchi; Rei Kinjo; Masaaki Ichinohe (September 2004). "A Stable Compound Containing a Silicon-Silicon Triple Bond". Science. 305 (5691): 1755–1757. Bibcode:2004Sci...305.1755S. PMID 15375262. doi:10.1126/science.1102209. [1][permanent dead link]
  5. ^ Carlo A. Pignedoli,; Alessandro Curioni,; Wanda Andreoni, (2005). "Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics Calculations". ChemPhysChem. 6 (9): 1795–1799. PMID 16144004. doi:10.1002/cphc.200500064. 
  6. ^ Gernot Frenking, Prof.; Andreas Krapp, Dipl.-Chem.; Shigeru Nagase, Prof.; Nozomi Takagi,; Akira Sekiguchi, Prof. (2006). "Comment on Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics Calculations". ChemPhysChem. 7 (4): 799–800. PMID 16596606. doi:10.1002/cphc.200500689. 
  7. ^ Carlo A. Pignedoli,; Alessandro Curioni,; Wanda Andreoni, (2006). "Reply to Comment on Disproving a Silicon Analog of an Alkyne with the Aid of Topological Analyses of the Electronic Structure and Ab Initio Molecular Dynamics Calculations". ChemPhysChem. 7 (4): 801–802. doi:10.1002/cphc.200600025. 
  8. ^ Rei Kinjo; Masaaki Ichinohe; Akira Sekiguchi; Nozomi Takagi; Michinori Sumimoto; Shigeru Nagase (2007). "Reactivity of a Disilyne RSiSiR (R = SiiPr[CH(SiMe3)2]2) toward π-Bonds: Stereospecific Addition and a New Route to an Isolable 1,2-Disilabenzene". J. Am. Chem. Soc. 129 (25): 7766–7767,. doi:10.1021/ja072759h+S0002-7863(07)02759-X. 
  9. ^ Nils Wiberg, Prof., Sham Kumar Vasisht, Gerd Fischer, Peter Mayer (2004). "Disilynes. III [1] A Relatively Stable Disilyne RSiSiR (R = SiMe(SitBu3)2)". Zeitschrift für anorganische und allgemeine Chemie. 630 (12): 1823–1828. doi:10.1002/zaac.200400177. 
  10. ^ Pu, L.; Twamley, B.; Power, P. P. (2000). "Synthesis and Characterization of 2,6-Trip2H3C6PbPbC6H3-2,6-Trip2 (Trip = C6H2-2,4,6-i-Pr3): A Stable Heavier Group 14 Element Analogue of an Alkyne". J.Am. Chem. Soc(Communication);. 122 (14): 3524–3525. doi:10.1021/ja993346m. 
  11. ^ Phillips, A. D.; Wright, R. J.; Olmstead, . M.; Power, P. P. (2002). "Synthesis and Characterization of 2,6-Dipp2-H3C6SnSnC6H3-2,6-Dipp2 (Dipp = C6H3-2,6-Pri2): A Tin Analogue of an Alkyne". J. Am. Chem. Soc.(Communication). 124 (21): 5930–5931. doi:10.1021/ja0257164.  [2][permanent dead link]
  12. ^ Matthias Stender; Andrew D. Phillips; Robert J. Wright; Philip P. Power (2002). "Synthesis and Characterization of a Digermanium Analogue of an Alkyne". Angew Chem Int Ed. 41 (10): 1785. doi:10.1002/1521-3757(20020517)114:10<1863::AID-ANGE1863>3.0.CO;2-I. [3][permanent dead link]