Cyclic Alkyl(amino) Carbene-Stabilized Monoradicals of Organosilicon(IV) Compounds with Small Substituents

Radicals and biradicals can easily be obtained when silicon­(IV) compounds are reduced and stabilized by the Lewis base cyclic­(alkyl)­(amino)­carbene (cAAC = C­(CH2)­(CMe2)2N-Dipp, Dipp = 2,6-i-Pr2C6H3) featuring strong σ-donor and π-acceptor properties. To obtain the cAAC-stabilized monoradicals with halogen and alkyl substituents at the silicon­(IV) atoms, the Ar substituent (Ar = o-C6H4NMe2) was employed to act as a side-arm nitrogen donor ligand. The resulting monoradicals ArSiCl2(cAAC) (4) and ArSiRCl­(cAAC) (R = Me 5; Et 6) were isolated by the reduction of ArSiCl2 (1) and ArSiRCl2 (R = Me 2; Et 3) with KC8 in the presence of cAAC with a strict ratio of 1:1:1. The three room-temperature stable radicals were kept for at least 3 months in the solid state under dry N2 atmosphere without decomposition. All the compounds were fully characterized by liquid injection field desorption/ionization–mass spectrometry, electron paramagnetic resonance spectroscopy, UV/vis spectroscopy, elemental analysis, and single-crystal X-ray crystallographic studies.