Silylation
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
[edit]
Bis(trimethylsilyl)acetamide, a popular reagent for silylation
acetamide.svg)
Alcohols, carboxylic acids, amines, thiols, and phosphates can be silylated. This is done through an SN2 reaction as the formerly mentioned functional groups attack the silicon atom of a substituted silyl group causing it's leaving group to go into solution.[2] The mechanism 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):[3]
- 2 ROH + MeC(OSiMe3)NSiMe3 → MeC(O)NH2 + 2 ROSiMe3
Use of silylation
[edit]Silylation has two main uses: manipulation of functional groups and preparation of samples for analysis.
Manipulation of functional groups
[edit]Silylation is often employed as a protecting group for alcohols and amines. The products after silylation, namely silyl ethers and silyl amines, are resilient toward basic conditions.[4] The other main role of silylation is to trap silyl enol ethers, which represent a reactive tautomer of many carbonyl compounds.[5]
Silylation for analysis
[edit]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.[6][7]
Desilylation
[edit]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.[8][9]
- ROSiMe3 + F− + H2O → ROH + FSiMe3 + OH−
Of metals
[edit]
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.[10][11]
See also
[edit]References
[edit]- ^ Pape, Peter G. (2017). "Silylating Agents". Kirk-Othmer Encyclopedia of Chemical Technology. pp. 1–15. doi:10.1002/0471238961.1909122516011605.a01.pub3. ISBN 9780471238966.
- ^ Pagliano, Enea; Campanella, Beatrice; D'Ulivo, Alessandro; Mester, Zoltán (September 2018). "Derivatization chemistries for the determination of inorganic anions and structurally related compounds by gas chromatography - A review". Analytica Chimica Acta. 1025: 12–40. doi:10.1016/j.aca.2018.03.043.
- ^ 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.
- ^ Clayden, Jonathan; Greeves, Nick; Warren, Stuart (2012). Organic chemistry (2nd ed.). Oxford: Oxford university press. pp. 549–550. ISBN 978-0-19-927029-3.
- ^ Clayden, Jonathan; Greeves, Nick; Warren, Stuart (2012). Organic chemistry (2nd ed.). Oxford: Oxford university press. pp. 466–467. ISBN 978-0-19-927029-3.
- ^ Luis-Alberto Martin; Ingrid Hayenga. "Silylation of Non-Steroidal Anti-Inflammatory Drugs". sigmaaldrich.com. Retrieved 24 September 2023.
- ^ Blau, Karl; J. M. Halket (1993). Handbook of Derivatives for Chromatography (2nd ed.). John Wiley & Sons. ISBN 0-471-92699-X.
- ^ 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
- ^ 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
- ^ 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
- ^ 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.