Electrophilic Formylation of Arenes by Silylium Ion Mediated Activation of Carbon Monoxide

Abstract

Arene-stabilized silylium ions react with carbon monoxide rather than carbon monoxide adducts of silylium ions reacting with arenes. This mechanism is supported by quantum-chemical calculations. Even sterically hindered mesitylene and electronically deactivated chlorobenzene engage in this electrophilic aromatic substitution. The silylium ion mediated formylation corresponds to Gattermann-Koch reactions promoted by strong Brønsted acids. The resulting silylcarboxonium ion of the arenecarbaldehyde was crystallographically characterized, for the first time revealing the molecular structure of this synthetically important intermediate.

Chiral Chalcogenyl‐Substituted Naphthyl‐ and Acenaphthyl‐Silanes and Their Cations

“…The last 25 years have witnessed the successful development of silyl cations from laboratory curiosities to valuable catalysts in organic transformations [1–8] . By virtue of their high Lewis acidity, silyl cations have proven to be excellent catalysts in Diels–Alder reactions, [9–12] hydrodefluorination [13–21] and CO‐activation reactions [22, 23] . In these applications, it is mandatory that the high Lewis acidity of the tricoordinate silylium ion is pacified by an intramolecular or intermolecular donor to control the reactivity of the silyl Lewis acid.…”

Activation of CS2 and CO2 by Silylium Cations

“…In 2010 we published the insertion reaction of sulfur dioxide into a hydride‐bridged silylium cation to give [ i Pr 3 SiOS(H)OSi i Pr 3 ] + [10] . Recently, the silylium ion mediated activation of carbon monoxide has been reported by Oestreich et al [11] . Silylium‐catalyzed C−F bond activation followed by trapping of carbon disulfide resulted in the formation of an S ‐heterocyclic carbene [12] …”

Silicon–Halogen Bond Activation in Mixed Si/Al Compounds and an Approach to Intramolecular Stabilized Silylium Ions

“…Intramolecular stabilization of silyl cations was achieved by polar π (p‐π) interactions or in bridged systems such as Si ··· H ··· Si ,. [6b], Recently the application of solvent coordinated silylium ions has been reported which ranges from silylium ion catalyzed C‐F bond activation in hydro‐defluorination, intramolecular Friedel‐Crafts arylation, Lewis acid type reactivity in Diels‐Alder reactions, imine reductions, electrophilic formylations and olefin polymerization to CO 2 and H 2 activation by a silylium/phosphane based FLP . Silyl cations have three‐coordinate Si atoms in a planar coordination sphere [∑(C‐Si‐C) = 360°] and only weak van der Waals contacts to substituents in axial positions above and below the molecular plane.…”