Silyl protecting groups

In organic chemistry, various triorganosilyl compounds are used as protecting groups. The simplest is the trimethylsilyl group, but others are known.

Methylsilyl groups

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]

Super silyl groups

the tri(trimethylsilyl)silyl group Tris(trimethylsilyl)silane: R=H

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 diastereoselective one-pot reaction involving two sequential Mukaiyama aldol reactions:^[4]

TTMSS can also stand for tris(trimethylsilyl)silane,^[5][6] which is comparable as a chemical reagent to tributyltin hydride without the associated toxicity concern of organotin and tributyltin compounds.^[7][8] The reagent is employed in radical reductions, hydrosilylation and consecutive radical reactions.^[9]