Silylation is the introduction of one or more (usually) substituted silyl groups (R3Si) to a molecule. Silylations are core methods for production of organosilicon chemistry. Silanization involves similar methods but usually refers to attachment of silyl groups to solids.[1]

Of organic compounds

Bis(trimethylsilyl)acetamide, a popular reagent for silylation

Alcohols, carboxylic acids, amines, thiols, and phosphates can be silylated. The process involves the replacement of a proton or an anion with a trialkylsilyl group, typically trimethylsilyl (-SiMe3), as illustrated by the synthesis of a trimethylsilyl ethers from alcohols and trimethylsilyl chloride (Me = CH3):

ROH + Me3SiCl → ROSiMe3 + HCl

Generally a base is employed to absorb the HCl coproduct.

Bis(trimethylsilyl)acetamide ("BSA", Me3SiNC(OSiMe3)Me is an efficient silylation agent. The reaction of BSA with alcohols gives the corresponding trimethylsilyl ether, together with acetamide as a byproduct (Me = CH3):[2]

2 ROH + MeC(OSiMe3)NSiMe3 → MeC(O)NH2 + 2 ROSiMe3

Use of silylation

Silylation has two main uses: manipulation of functional groups and preparation of samples for analysis.

Manipulation of functional groups

Often silylation is employed to protect OH and NH groups. The derivatives, silyl ethers and silyl amides, are resilient toward many reagents that would attack their precursors. The other main role of silylation is to trap silyl enol ethers, which represent a reactive tautomer of many carbonyl compounds.

Silylation for analysis

The introduction of a silyl group(s) gives derivatives of enhanced volatility, making the derivatives suitable for analysis by gas chromatography and electron-impact mass spectrometry (EI-MS). For EI-MS, the silyl derivatives give more favorable diagnostic fragmentation patterns of use in structure investigations, or characteristic ions of use in trace analyses employing selected ion monitoring and related techniques.[3][4]

Desilylation

Desilylation is the reverse of silylation: the silyl group is exchanged for a proton. Various fluoride salts (e.g. sodium, potassium, tetra-n-butylammonium fluorides) are popular for this purpose.[5][6]

ROSiMe3 + F− + H2O → ROH + FSiMe3 + OH−

Of metals

CpFe(CO)2Si(CH3)3, a trimethylsilyl complex.

Coordination complexes with silyl ligands are well known. An early example is CpFe(CO)2Si(CH3)3, prepared by silylation of CpFe(CO)2Na with trimethylsilyl chloride. Typical routes include oxidative addition of Si-H bonds to low-valent metals. Metal silyl complexes are intermediates in hydrosilation, a process used to make organosilicon compounds on both laboratory and commercial scales.[7][8]

See also

References

  1. ↑ Pape, Peter G. (2017). "Silylating Agents". Kirk-Othmer Encyclopedia of Chemical Technology. pp. 1–15. doi:10.1002/0471238961.1909122516011605.a01.pub3. ISBN 9780471238966.
  2. ↑ Young, Steven D.; Buse, Charles T.; Heathcock, Clayton H. (1985). "2-Methyl-2-(Trimethylsiloxy)pentan-3-one". Organic Syntheses. 63: 79. doi:10.15227/orgsyn.063.0079.
  3. ↑ Luis-Alberto Martin; Ingrid Hayenga. "Silylation of Non-Steroidal Anti-Inflammatory Drugs". sigmaaldrich.com. Retrieved 24 September 2023.
  4. ↑ Blau, Karl; J. M. Halket (1993). Handbook of Derivatives for Chromatography (2nd ed.). John Wiley & Sons. ISBN 0-471-92699-X.
  5. ↑ Mercedes Amat, Sabine Hadida, Swargam Sathyanarayana, and Joan Bosch "Regioselective Synthesis of 3-Substituted Indoles: 3-Ethylindole" Organic Syntheses 1997, volume 74, page 248. doi:10.15227/orgsyn.074.0248
  6. ↑ Nina Gommermann and Paul Knochel "N,N-Dibenzyl-n-[1-cyclohexyl-3-(trimethylsilyl)-2-propynyl]-amine from Cyclohexanecarbaldehyde, Trimethylsilylacetylene and Dibenzylamine" Organic Syntheses 2007, vol. 84, page 1. doi:10.15227/orgsyn.084.0001
  7. ↑ Moris S. Eisen "Transition-metal silyl complexes" in The Chemistry of Organic Silicon Compounds. Volume 2 Edited by Zvi Rappoport and Yitzhak Apeloig, 1998, John Wiley & Sons
  8. ↑ Corey, Joyce Y.; Braddock-Wilking, Janet (1999). "Reactions of Hydrosilanes with Transition-Metal Complexes: Formation of Stable Transition-Metal Silyl Compounds". Chemical Reviews. 99 (1): 175–292. doi:10.1021/CR9701086. PMID 11848982.
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