Isolable Aryl‐Substituted Silyl Radicals: Synthesis, Characterization, and Reactivity

Abstract

Isolable aryl-substituted silyl radicals (tBu2 MeSi)2(Ar)Si(·) (Ar = C6H5, 4-tBuC6H4, 4-PhC6H4, 3,5-tBu2C6H3) were synthesized by the reaction of the corresponding iodosilane with an equimolar amount of potassium graphite (KC8 ) in tetrahydrofuran (THF). The crystal structure of 3,5-tBu2C6H3 derivative, which was determined by X-ray crystallography, showed a planar geometry around the Si atom for the radical center. EPR studies of all four radicals revealed the lack of the delocalization of the unpaired electron over the aromatic ring. Reactivity and spectroscopic studies of the less-hindered phenyl-substituted silyl radical showed that it exists as an equilibrium mixture of the radical and its silene-type dimer in solution.

A Phosphine‐Coordinated Boron‐Centered Gomberg‐Type Radical

“…[22] Comparatively,very little is known about related transformations with main-group radicals.M onomer/dimer interconversions have been observed with p-block radicals (in particular with E = Si, Sn, P, Sb,Bi), [23] but they usually involve EÀEbond formation/ cleavage.I narecent study on aryl-substituted silyl radicals, Sekiguchi et al proposed aS i-C para dimerization process to rationalize the decrease of the EPR signal intensity observed upon cooling. [24] In the case of boron compounds,P h 3 Bw as reported early on to dimerize under reductive conditions (Na). [25] Thei onic nature and instability of the transient triphenylboron anion radical prevented detailed analysis of the dimerization process,b ut aG omberg-type dimeric structure could be proposed based on NMR spectroscopic data.…”

Grand Prix de la Fondation de la Maison de la Chimie: J.‐P. Sauvage / WACKER Silicone Award: A. Sekiguchi / Friedmund Neumann Prize: M. Köhn / Ignaz L. Lieben Award: J. Roithová

“…Sekiguchi’s research is centered on low‐coordinate organosilicon compounds, including doubly and triply bonded organosilicon species, and silicon‐centered radicals, cations, anions, and radical ions. He has reported in Angewandte Chemie on anode materials based on persilyl‐substituted free radicals,2a and in Chemistry—A European Journal on isolable aryl‐substituted silyl radicals 2b …”

Isolation of a Relatively Air‐Stable, Bulky Silyl‐Substituted, Neutral Silicon‐Centered Radical

“…Later, the yield was improved via an alternate synthetic approach by Apeloig and co‐workers . Furthermore, one silyl substituent can be replaced by various aryl groups (compounds III ) …”