Silicon-Carbon Bond Cleavage – Methyl/Triflate Exchange Reactions on Trimethylsilyl Groups

Silyl groups, such as the trimethylsilyl (TMS) substituent, are generally considered to be chemically inert. Hence, they are often used to increase the steric demand of bulky anilines to stabilize highly reactive and sensitive... [ view full abstract ]

Silyl groups, such as the trimethylsilyl (TMS) substituent, are generally considered to be chemically inert. Hence, they are often used to increase the steric demand of bulky anilines to stabilize highly reactive and sensitive element-nitrogen compounds.^[1] However, in case of some aminopnictanes of the type RN(SiMe₃)PnCl₂ (R = sterically demanding substituent; Pn = As, Sb) a methyl/(pseudo)halide exchange reaction was observed in the presence of the Lewis acids GaCl₃ or AgOTf (OTf = O₃SCF₃), which led to the substitution of one methyl group at the silicon atom.^[2]

Since this reactivity was already known for arsenic and antimony derivatives, we investigated the behavior of the corresponding bismuth compounds RN(SiMe₃)BiCl₂ towards AgOTf and GaCl₃. Only in case of the Ter derivative (1) the discussed exchange reaction was observed (Scheme 1). In case of the Mes* substituent, an unusual cation (4) could be detected.

Independently of the stoichiometry of silver triflate, only one methyl/triflate exchange at the TMS group was observed (Scheme 1). Using two equivalents, however, both Cl atoms could be substituted by a triflate group (cf. compound 2 vs. 3). The reaction of 1 with GaCl₃ led to decomposition to an amine-GaCl₃ adduct or an ammonium tetrachloridogallate salt.

References:

[1] for example: a) T. J. Hadlington, C. Jones, Chem. Commun. 2014, 50, 2321–2323; b) D. Dange, A. Davey, J. A. B. Abdalla, S. Aldrige, C. Jones, Chem. Commun. 2015, 51, 7128–7131; c) R. J. Wright, J. Steiner, S. beaini, P. P. Power, Inorg. Chim. Acta 2006, 359, 1939–1946; d) V. D. Romanenko, A. V. Ruban, S. V. Iksanova, L. K. Polyachenko, L. N. Markovski, Phosphorus and Sulfur 1985, 22, 365–368; e) C. Hering-Junghans, M. Thomas, A. Villinger, A. Schulz, Chem. Eur. J. 2015, 21, 6713–6717.

[2] a) D. Michalik, A. Schulz, A. Villinger, Inorg. Chem. 2008, 47, 11798–11806; b) C. Hering, M. Lehmann, A. Schulz, A. Villinger, Inorg. Chem. 2012, 51, 8212–8224.