A trimethylsilyl group (abbreviated TMS) is a
functional group in
organic chemistry. This group consists of three
methyl groups bonded to a
silicon atom [−Si(CH3)3], which is in turn bonded to the rest of a molecule. This structural group is characterized by
chemical inertness and a large
molecular volume, which makes it useful in a number of applications.
A trimethylsilyl group bonded to a methyl group forms
tetramethylsilane, which is abbreviated as TMS as well.
Compounds with trimethylsilyl groups are not normally found in nature. Chemists sometimes use a trimethylsilylating
reagent to derivatize rather non-volatile compounds such as certain
alcohols,
phenols, or
carboxylic acids by substituting a trimethylsilyl group for a hydrogen in the
hydroxyl groups on the compounds. This way
trimethylsiloxy groups [−O-Si(CH3)3] are formed on the molecule. A couple of examples of trimethylsilylating agents include
trimethylsilyl chloride and
bis(trimethylsilyl)acetamide. Trimethylsilyl groups on a molecule have a tendency to make it more volatile, often making the compounds more amenable to analysis by
gas chromatography or
mass spectrometry. An example of such trimethylsilylation is mentioned in the
Brassicasterol article. Such derivatizations are often done on a small scale in special
vials.
In an
NMR spectrum, signals from atoms in trimethylsilyl groups in compounds will commonly have chemical shifts close to the
tetramethylsilane reference peak at 0 ppm. Also compounds, such as high temperature silicone "
stopcock"
grease, which have
polysiloxanes (often called silicones) in them will commonly show peaks from their methyl groups (attached to the silicon atoms) having NMR chemical shifts close to the tetramethylsilane standard peak, such as at 0.07 ppm in CDCl3.[1]
Otherwise very reactive molecules can be isolated when enveloped by bulky trimethylsilyl groups. This effect can be observed in
tetrahedranes.
Super silyl groups
Related to trimethylsilyl groups are "super" silyl groups of which there exist two varieties: A silicon group connected to three trimethylsilyl groups makes a tri(trimethylsilyl)silyl group (TTMSS or TMS3Si) and a silicon group connected to three
tert-butyl groups. The TTMSS group was proposed in 1993 by
Hans Bock. With a
van der Waals volume of up to 7 cubic
angstrom it surpasses the related
TIPS group (around 2)[2][3] and one potential application is its use as a temporary substituent promoting
asymmetric induction for example in this
diastereoselectiveone-pot reaction involving two sequential
Mukaiyama aldol reactions:[4]
^Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities.
J. Org. Chem. 1997, 62(21), pp 7512-7515.
doi:
10.1021/jo971176v
^ "Super Silyl" Group for Diastereoselective Sequential Reactions: Access to Complex Chiral Architecture in One Pot Matthew B. Boxer and Hisashi Yamamoto
J. Am. Chem. Soc.; 2007; 129(10) pp 2762 - 2763; (Communication)
doi:
10.1021/ja0693542
^Tris(trimethylsilyl)silyl-Governed Aldehyde Cross-Aldol Cascade Reaction Boxer, M. B.; Yamamoto, H. J. Am. Chem. Soc.; (Communication); 2006; 128(1); 48-49.
doi:
10.1021/ja054725k
^Chatgilialoglu, Chryssostomos; Ferreri, Carla; Landais, Yannick; Timokhin, Vitaliy I. (25 June 2018). "Thirty Years of (TMS)3SiH: A Milestone in Radical-Based Synthetic Chemistry". Chemical Reviews. 118 (14): 6516–6572.
doi:
10.1021/acs.chemrev.8b00109.
PMID29938502.
S2CID49413857.
^Brook, Michael A. (2000). Silicon in Organic, Organometallic, and Polymer Chemistry. New York: John Wiley & Sons, Inc. pp. 172–173.
^Nicolaou, K. C.; Yang, Z.; Liu, J. J.; Ueno, H.; Nantermet, P. G.; Guy, R. K.; Claiborne, C. F.; Renaud, J.; Couladouros, E. A. (1994-02-17). "Total synthesis of taxol". Nature. 367 (6464): 630–634.
Bibcode:
1994Natur.367..630N.
doi:
10.1038/367630a0.
PMID7906395.
S2CID4371975.
^Nicolaou, K. C.; Claiborne, Christopher F.; Nantermet, Philippe G.; Couladouros, Elias A.; Sorensen, Erik J. (1994-02-01). "Synthesis of Novel Taxoids". Journal of the American Chemical Society. 116 (4): 1591–1592.
doi:
10.1021/ja00083a063.
ISSN0002-7863.
^W. J. Middleton, E. M. Bingham "Diethylaminosulfur Trifluoride" Organic Syntheses, Coll. Vol. 6, p.440; Vol. 57, p.50.
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