An Isolable NHC-Stabilized
Silylene Radical Cation:
Synthesis and Structural Characterization
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Abstract
The silyl-substituted silylene–NHC complex bis(tri-<i>tert</i>-butylsilyl)silylene–(1,3,4,5-tetramethylimidazol-2-ylidene)
[(<sup><i>t</i></sup>Bu<sub>3</sub>Si)<sub>2</sub>Si:←NHC<sup>Me</sup>, <b>2</b>] was synthesized and isolated as air- and
moisture-sensitive orange crystals by reductive debromination of the
dibromosilane (<sup><i>t</i></sup>Bu<sub>3</sub>Si)<sub>2</sub>SiBr<sub>2</sub> (<b>1</b>) with 2.0 equiv of KC<sub>8</sub> in the presence of NHC<sup>Me</sup>. In addition, the silylene–NHC
complex <b>2</b> cleanly underwent one-electron oxidation with
1.0 equiv of Ph<sub>3</sub>C<sup>+</sup>·Ar<sub>4</sub>B<sup>–</sup> (Ar<sub>4</sub>B<sup>–</sup> = tetrakis[4-(<i>tert</i>-butyldimethylsilyl)-2,3,5,6-tetrafluorophenyl]borate)
in benzene to afford the NHC-stabilized silylene radical cation [(<sup><i>t</i></sup>Bu<sub>3</sub>Si)<sub>2</sub>Si←NHC<sup>Me</sup>]<sup>•+</sup>·Ar<sub>4</sub>B<sup>–</sup> (<b>3</b>). The radical cation <b>3</b> was isolated
as air- and moisture-sensitive yellow crystals and structurally characterized
by X-ray crystallography and electron paramagnetic resonance spectroscopy,
which showed that <b>3</b> has a planar structure with a π-radical
nature
