Misplaced Pages

Organosilicon chemistry is the study of organometallic compounds containing carbon–silicon bonds, to which they are called organosilicon compounds. Most organosilicon compounds are similar to the ordinary organic compounds, being colourless, flammable, hydrophobic, and stable to air. Silicon carbide is an inorganic compound.

History

In 1863 Charles Friedel and James Crafts made the first organochlorosilane compound. The same year they also described a «polysilicic acid ether» in the preparation of ethyl- and methyl-o-silicic acid. Extensive research in the field of organosilicon compounds was pioneered in the beginning of 20th century by Frederic S. Kipping. He also had coined the term "silicone" (resembling ketones, this is erroneous though) in relation to these materials in 1904. In recognition of Kipping's achievements the Dow Chemical Company had established an award in 1960s that is given for significant contributions into the silicon chemistry. In his works Kipping was noted for using Grignard reagents to make alkylsilanes and arylsilanes and the preparation of silicone oligomers and polymers for the first time.

In 1945 Eugene G. Rochow also made a significant contribution into the organosilicon chemistry by first describing Müller-Rochow process.

Occurrence and applications

Organosilicon compounds are widely encountered in commercial products. Most common are antifoamers, caulks (sealant), adhesives, and coatings made from silicones. Other important uses include agricultural and plant control adjuvants commonly used in conjunction with herbicides and fungicides.

Biology and medicine

Carbon–silicon bonds are absent in biology, however enzymes have been used to artificially create carbon-silicon bonds in living microbes. Silicates, on the other hand, have known existence in diatoms. Silafluofen is an organosilicon compound that functions as a pyrethroid insecticide. Several organosilicon compounds have been investigated as pharmaceuticals.

Bonding

In the great majority of organosilicon compounds, Si is tetravalent with tetrahedral molecular geometry. Compared to carbon–carbon bonds, carbon–silicon bonds are longer and weaker.

The C–Si bond is somewhat polarised towards carbon due to carbon's greater electronegativity (C 2.55 vs Si 1.90), and single bonds from Si to electronegative elements are very strong. Silicon is thus susceptible to nucleophilic attack by O, Cl, or F; the energy of an Si–O bond in particular is strikingly high. This feature is exploited in many reactions such as the Sakurai reaction, the Brook rearrangement, the Fleming–Tamao oxidation, and the Peterson olefination.

The Si–C bond (1.89 Å) is significantly longer than a typical C–C bond (1.54 Å), suggesting that silyl substitutents have less steric demand than their organyl analogues. When geometry allows, silicon exhibits negative hyperconjugation, reversing the usual polarization on neighboring atoms.

Preparation

The first organosilicon compound, tetraethylsilane, was prepared by Charles Friedel and James Crafts in 1863 by reaction of tetrachlorosilane with diethylzinc.

The bulk of organosilicon compounds derive from organosilicon chlorides (CH
₃)
_4-xSiCl
_x. These chlorides are produced by the "Direct process", which entails the reaction of methyl chloride with a silicon-copper alloy. The main and most sought-after product is dimethyldichlorosilane:

2 CH
₃Cl + Si → (CH
₃)
₂SiCl
₂

A variety of other products are obtained, including trimethylsilyl chloride and methyltrichlorosilane. About 1 million tons of organosilicon compounds are prepared annually by this route. The method can also be used for phenyl chlorosilanes.

Hydrosilylation

Another major method for the formation of Si-C bonds is hydrosilylation (also called hydrosilation). In this process, compounds with Si-H bonds (hydrosilanes) add to unsaturated substrates. Commercially, the main substrates are alkenes. Other unsaturated functional groups — alkynes, imines, ketones, and aldehydes — also participate, but these reactions are of little economic value.

Hydrosilylation requires metal catalysts, especially those based on platinum group metals.

In the related silylmetalation, a metal replaces the hydrogen atom.

Cleavage of Si-Si bonds

Hexamethyldisilane reacts with methyl lithium to give trimethylsilyl lithium:

(CH₃)₆Si₂ + CH₃Li → (CH₃)₃SiLi + (CH₃)₄Si

Similarly, tris(trimethylsilyl)silyl lithium is derived from tetrakis(trimethylsilyl)silane:

((CH₃)₃Si)₄Si + CH₃Li → ((CH₃)₃Si)₃SiLi + (CH₃)₄Si

Functional groups

Silicon is a component of many functional groups. Most of these are analogous to organic compounds. The overarching exception is the rarity of multiple bonds to silicon, as reflected in the double bond rule.

Silanols, siloxides, and siloxanes

Silanols are analogues of alcohols. They are generally prepared by hydrolysis of silyl chlorides:

R
₃SiCl + H₂O → R
₃SiOH + HCl

Less frequently silanols are prepared by oxidation of silyl hydrides, a reaction that uses a metal catalyst:

2 R
₃SiH + O
₂ → 2 R
₃SiOH

Many silanols have been isolated including (CH
₃)
₃SiOH and (C
₆H
₅)
₃SiOH. They are about 500x more acidic than the corresponding alcohols. Siloxides are the deprotonated derivatives of silanols:

R
₃SiOH + NaOH → R
₃SiONa + H₂O

Silanols tend to dehydrate to give siloxanes:

2 R
₃SiOH → R
₃Si-O-SiR
₃ + H₂O

Polymers with repeating siloxane linkages are called silicones. Compounds with an Si=O double bond called silanones are extremely unstable.

Silyl ethers

Silyl ethers have the connectivity Si-O-C. They are typically prepared by the reaction of alcohols with silyl chlorides:

(CH
₃)
₃SiCl + ROH → (CH
₃)
₃Si-O-R + HCl

Silyl ethers are extensively used as protective groups for alcohols.

Exploiting the strength of the Si-F bond, fluoride sources such as tetra-n-butylammonium fluoride (TBAF) are used in deprotection of silyl ethers:

(CH
₃)
₃Si-O-R + F
+ H₂O → (CH
₃)
₃Si-F + H-O-R + OH

Silyl chlorides

Organosilyl chlorides are important commodity chemicals. They are mainly used to produce silicone polymers as described above. Especially important silyl chlorides are dimethyldichlorosilane (Me
₂SiCl
₂), methyltrichlorosilane (MeSiCl
₃), and trimethylsilyl chloride (Me
₃SiCl) are all produced by direct process. More specialized derivatives that find commercial applications include dichloromethylphenylsilane, trichloro(chloromethyl)silane, trichloro(dichlorophenyl)silane, trichloroethylsilane, and phenyltrichlorosilane.

Although proportionately a minor outlet, organosilicon compounds are widely used in organic synthesis. Notably trimethylsilyl chloride Me
₃SiCl is the main silylating agent. One classic method called the Flood reaction for the synthesis of this compound class is by heating hexaalkyldisiloxanes R
₃SiOSiR
₃ with concentrated sulfuric acid and a sodium halide.

Silyl hydrides

The silicon to hydrogen bond is longer than the C–H bond (148 compared to 105 pm) and weaker (299 compared to 338 kJ/mol). Hydrogen is more electronegative than silicon hence the naming convention of silyl hydrides. Commonly the presence of the hydride is not mentioned in the name of the compound. Triethylsilane has the formula Et
₃SiH. Phenylsilane is PhSiH
₃. The parent compound SiH
₄ is called silane.

Silenes

Organosilicon compounds, unlike their carbon counterparts, do not have a rich double bond chemistry. Compounds with silene Si=C bonds (also known as alkylidenesilanes) are laboratory curiosities such as the silicon benzene analogue silabenzene. In 1967, Gusel'nikov and Flowers provided the first evidence for silenes from pyrolysis of dimethylsilacyclobutane. The first stable (kinetically shielded) silene was reported in 1981 by Brook.

Disilenes have Si=Si double bonds and disilynes are silicon analogues of an alkyne. The first Silyne (with a silicon to carbon triple bond) was reported in 2010.

Siloles

Siloles, also called silacyclopentadienes, are members of a larger class of compounds called metalloles. They are the silicon analogs of cyclopentadienes and are of current academic interest due to their electroluminescence and other electronic properties. Siloles are efficient in electron transport. They owe their low lying LUMO to a favorable interaction between the antibonding sigma silicon orbital with an antibonding pi orbital of the butadiene fragment.

Pentacoordinated silicon

Unlike carbon, silicon compounds can be coordinated to five atoms as well in a group of compounds ranging from so-called silatranes, such as phenylsilatrane, to a uniquely stable pentaorganosilicate:

The stability of hypervalent silicon is the basis of the Hiyama coupling, a coupling reaction used in certain specialized organic synthetic applications. The reaction begins with the activation of Si-C bond by fluoride:

R-SiR'
₃ + R"-X + F
→ R-R" + R'
₃SiF + X

Various reactions

In general, almost any silicon-heteroatom bond is water-sensitive, and will spontaneously hydrolyze. Unstrained silicon-carbon bonds, however, are very strong, and cleave only in a small number of extreme conditions. Strong acids will protodesilate arylsilanes and, in the presence of a Lewis acid catalyst, alkylsilanes. Most nucleophiles are too weak to displace carbon from silicon: the exceptions are fluoride ions and alkoxides, although the latter often deprotonate the organosilane to a silicon ylide instead.

As a covalent hydride source, hydrosilanes are good reductants.

Certain allyl silanes can be prepared from allylic esters such as 1 and monosilylcopper compounds, which are formed in situ by the reaction of the disilylzinc compound 2, with Copper Iodide, in:

In this reaction type, silicon polarity is reversed in a chemical bond with zinc and a formal allylic substitution on the benzoyloxy group takes place.

Unsaturated silanes like the above are susceptible to electrophilic substitution.

Environmental effects

Organosilicon compounds affect bee (and other insect) immune expression, making them more susceptible to viral infection.

See also

• Compounds of carbon with period 3 elements: organoaluminum compounds, organophosphorus compounds, organosulfur compounds
• Compounds of carbon with other group 14 elements: organogermanium compounds, organotin compounds, organolead compounds
• Silylenes, the carbene counterparts
• Silylenoids, the carbenoid counterparts
• Decamethylsilicocene

References

1. ^ Muller, Richard (January 1965). "One hundred years of organosilicon chemistry". Journal of Chemical Education. 42 (1): 41. doi:10.1021/ed042p41. ISSN 0021-9584.
2. ^ Thomas, Neil R. (October 2010). "Frederic Stanley Kipping—Pioneer in Silicon Chemistry: His Life & Legacy". Silicon. 2 (4): 187–193. doi:10.1007/s12633-010-9051-x. ISSN 1876-990X.
3. Kipping, Frederic Stanley (1912-01-01). "CCXXII.—Organic derivatives of silicon. Part XV. The nomenclature of organic silicon compounds". Journal of the Chemical Society, Transactions. 101: 2106–2107. doi:10.1039/CT9120102106. ISSN 0368-1645.
4. Handbook of detergents. Part F, Production. Uri Tsoler, Paul Sosis. Boca Raton, FL: CRC Press. 2009. ISBN 978-1-4200-1465-5. OCLC 319710487.{{cite book}}: CS1 maint: others (link)
5. "Frederic Stanley Kipping Award in Silicon Chemistry". American Chemical Society. Retrieved 2022-12-22.
6. Rochow, Eugene G. (June 1945). "The Direct Synthesis of Organosilicon Compounds". Journal of the American Chemical Society. 67 (6): 963–965. doi:10.1021/ja01222a026. ISSN 0002-7863.
7. ^ Janeta, Mateusz; Szafert, Sławomir (2017). "Synthesis, characterization and thermal properties of T8 type amido-POSS with p-halophenyl end-group". Journal of Organometallic Chemistry. 847: 173–183. doi:10.1016/j.jorganchem.2017.05.044.
8. Choi, Charles. "Possibility Of Silicon Based Life Grows". Astrobiology Magazine. Archived from the original on 2017-08-21. Retrieved 28 October 2019.{{cite web}}: CS1 maint: unfit URL (link)
9. Frampton, Mark B.; Zelisko, Paul M. (2009). "Organosilicon Biotechnology". Silicon. 1 (3): 147–163. doi:10.1007/s12633-009-9021-3. S2CID 195219283.
10. Pawlenko, S. (2011) . Organosilicon Chemistry. de Gruyter. p. 7. ISBN 978-3-11-086238-6.
11. Kinrade, Stephen D.; Gillson, Ashley-M. E.; Knight, Christopher T. G. (2002). "Silicon-29 NMR evidence of a transient hexavalent silicon complex in the diatom Navicula pelliculosa". J. Chem. Soc., Dalton Trans. (3): 307–9. doi:10.1039/b105379p.
12. Bains, W.; Tacke, R. (2003). "Silicon chemistry as a novel source of chemical diversity in drug design". Curr. Opin. Drug Discov. Dev. 6 (4): 526–543. PMID 12951816.
13. ^ "Common crop chemical leaves bees susceptible to deadly viruses". Phys.org. 2017.
14. ^ "Properties of atoms, radicals, and bonds" (PDF). Zakarian lab, UCSB. Retrieved 28 Nov 2022.
15. Handbook of Chemistry and Physics (81st ed.). CRC Press. June 2000. ISBN 0-8493-0481-4. Parameter error in {{ISBN}}: Missing ISBN.
16. Colvin, E. (2014) . Silicon in Organic Synthesis. Butterworth. ISBN 978-1-4831-4223-4.
17. Röshe, L.; John, P.; Reitmeier, R. (2003). "Organic Silicon Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Wiley. doi:10.1002/14356007.a24_021.
18. Marciniec, B., ed. (2009). "Hydrosilylation". Advances in Silicon Science. Vol. 1. Springer. pp. 3–51. doi:10.1007/978-1-4020-8172-9_1. ISBN 978-1-4020-8172-9.
19. Ramírez-Oliva, E.; Hernández, A.; Martínez-Rosales, J.M.; Aguilar-Elguezabal, A.; Herrera-Pérez, G.; Cervantes, J. (2006). "Effect of the synthetic method of Pt/MgO in the hydrosilylation of phenylacetylene" (PDF). Arkivoc. 126: 136.
20. Linderman, Russell J.; Stiasni, Nikola; Hiersemann, Martin (2009). "Trimethylsilyllithium". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rt312.pub2. ISBN 978-0471936237.
21. Dickhaut, Joachim; Giese, Bernd (1992). "Tris(trimethylsilyl)silane". Org. Synth. 70: 164. doi:10.15227/orgsyn.070.0164.
22. ^ Lickiss, Paul D. (1995). "The Synthesis and Structure of Organosilanols". Advances in Inorganic Chemistry. 42: 147–262. doi:10.1016/S0898-8838(08)60053-7. ISBN 9780120236428.
23. Flood, E.A. (1933). "Preparation of Triethylsilicon Halides". J. Am. Chem. Soc. 55 (4): 1735–6. doi:10.1021/ja01331a504.
24. Chatgilialoglu, Chryssostomos; Ferreri, Carla; Landais, Yannick; Timokhin, Vitaliy I. (2018). "Thirty Years of (TMS)₃SiH: A Milestone in Radical-Based Synthetic Chemistry". Chemical Reviews. 118 (14): 6516–72. doi:10.1021/acs.chemrev.8b00109. PMID 29938502. S2CID 49413857.
25. Ottosson, Henrik; Steel, Patrick G. (2006). "Silylenes, Silenes, and Disilenes: Novel Silicon-Based Reagents for Organic Synthesis?". Chem. Eur. J. 12 (6): 1576–85. doi:10.1002/chem.200500429. PMID 16138382.
26. Gusel'Nikov, L.E.; Flowers, M.C. (1967). "The thermal decomposition of 1,1-dimethyl-1-silacyclobutane and some reactions of an unstable intermediate containing a silicon–carbon double bond". Chem. Commun. (London) (17): 864–5. doi:10.1039/C19670000864.
27. Brook, Adrian G.; Abdesaken, Fereydon; Gutekunst, Brigitte; Gutekunst, Gerhard; Kallury, R. Krishna (1981). "A solid silaethene: isolation and characterization". J. Chem. Soc., Chem. Commun. (4): 191–2. doi:10.1039/C39810000191.
28. Baines, Kim M. (2013). "Brook silenes: inspiration for a generation". Chem. Commun. 49 (57): 6366–9. doi:10.1039/C3CC42595A. PMID 23752786.
29. Gau, D.; Kato, T.; Saffon-Merceron, N.; De Cózar, A.; Cossío, F.; Baceiredo, A. (2010). "Synthesis and Structure of a Base-Stabilized C-Phosphino-Si-Amino Silyne". Angewandte Chemie International Edition. 49 (37): 6585–8. doi:10.1002/anie.201003616. PMID 20677192.
30. "Direct synthesis of 2,5-dihalosiloles" (PDF). Organic Syntheses. 85: 53–63. 2008. doi:10.15227/orgsyn.085.0053.
31. Aubouy, Laurent; Gerbier, Philippe; Huby, Nolwenn; Wantz, Guillaume; Vignau, Laurence; Hirsch, Lionel; Jano, Jean-Marc (2004). "Synthesis of new dipyridylphenylaminosiloles for highly emissive organic electroluminescent devices". New J. Chem. 28: 1086–90. doi:10.1039/b405238b.
32. Deerenberg, Sirik; Schakel, Marius; de Keijzer, Adrianus H. J. F.; Kranenburg, Mirko; Lutz, Martin; Spek, Anthony L.; Lammertsma, Koop (2002). "Tetraalkylammonium pentaorganosilicates: the first highly stable silicates with five hydrocarbon ligands". Chem. Commun. 4 (4): 348–9. doi:10.1039/b109816k. hdl:1874/14327. PMID 12120068. S2CID 20937906.
33. Pawlenko 2011, p. 3.
34. Elschenbroich, Christoph (2006) . Organometallics. Translated by Oliveira, José; Elschenbroich, Christoph (3rd ed.). Wiley. pp. 240–244. ISBN 978-3-527-29390-2.
35. Schmidtmann, Eric S.; Oestreich, Martin (2006). "Mechanistic insight into copper-catalysed allylic substitutions with bis(triorganosilyl) zincs. Enantiospecific preparation of -chiral silanes". Chem. Commun. (34): 3643–5. doi:10.1039/b606589a. PMID 17047792.
36. By isotopic desymmetrisation on the substrate (replacing hydrogen by deuterium) it can be demonstrated that the reaction proceeds not through the symmetrical π-allyl intermediate 5 which would give an equal mixture of 3a and 3b but through the Π-δ intermediate 4 resulting in 3a only, through an oxidative addition or reductive elimination step
37. Fine, Julia D.; Cox-Foster, Diana L.; Mullin, Christopher A. (2017-01-16). "An Inert Pesticide Adjuvant Synergizes Viral Pathogenicity and Mortality in Honey Bee Larvae". Scientific Reports. 7: 40499. Bibcode:2017NatSR...740499F. doi:10.1038/srep40499. PMC 5238421. PMID 28091574.

External links

• Magnus Walter's Selected Aspects of Organosilicon Chemistry
• Silicon in organic synthesis
• S. Marsden (Editor): Contemporary organosilicon chemistry. Thematic Series in the Open Access Beilstein Journal of Organic Chemistry.

v t e Compounds of carbon with other elements in the periodic table
CH He CLi CBe CB CC CN CO CF Ne CNa CMg CAl CSi CP CS CCl CAr CK CCa CSc CTi CV CCr CMn CFe CCo CNi CCu CZn CGa CGe CAs CSe CBr CKr CRb CSr CY CZr CNb CMo CTc CRu CRh CPd CAg CCd CIn CSn CSb CTe CI CXe CCs CBa CLu CHf CTa CW CRe COs CIr CPt CAu CHg CTl CPb CBi CPo CAt Rn Fr CRa Lr Rf Db CSg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og   CLa CCe CPr CNd CPm CSm CEu CGd CTb CDy CHo CEr CTm CYb Ac CTh CPa CU CNp CPu CAm CCm CBk CCf CEs Fm Md No
Legend	Chemical bonds to carbon Core organic chemistry Many uses in chemistry Academic research, no widespread use Bond unknown

• Organosilicon compounds