An Isolable NHC-Stabilized Silylene Radical Cation: Synthesis and Structural Characterization

The silyl-substituted silylene-NHC complex bis(tri-tert-butylsilyl)silylene-(1,3,4,5-tetramethylimidazol-2-ylidene) [((Bu3Si)-Bu-t)(2)Si:<--NHCMe, 2] was synthesized and isolated as air- and moisture-sensitive orange crystals by reductive debromination of the dibromosilane ((Bu3Si)-Bu-t)(2)SiBr2 (1) with 2.0 equiv of KC8 in the presence of NHCMe. In addition, the silylene-NHC complex 2 cleanly underwent one-electron oxidation with 1.0 equiv of Ph3C+center dot Ar4B- (Ar4B- = tetrakis[4-(tert-butyldimethylsilyl)-2,3,5,6-tetrafluorophenyl]borate) in benzene to afford the NHC-stabilized silylene radical cation [((Bu3Si)-Bu-t)(2)Si<--NHCMe](center dot+)center dot Ar4B- (3). The radical cation 3 was isolated as air- and moisture-sensitive yellow crystals and structurally characterized by X-ray crystallography and electron paramagnetic resonance spectroscopy, which showed that 3 has a planar structure with a pi-radical nature.