Easy Access to Silicon(0) and Silicon(II) Compounds

Two different synthetic methodologies of silicon dihalide bridged biradicals of the general formula (Ln•)2SiX2 (n = 1, 2) have been developed. First, the metathesis reaction between NHC:SiX2 and Ln: (Ln: = cyclic akyl­(amino) carbene in a 1:3 molar ratio leads to the products 2 (n = 1, X = Cl), 4 (n = 2, X = Cl), 6 (n = 1, X = Br), and 7 (n = 2, X = Br). These reactions also produce coupled NHCs (3, 5) under C–C bond formation. The formation of the coupled NHCs (Lm = cyclic alkyl­(amino) carbene substituted N-heterocyclic carbene; m = 3, n = 1 (3) and m = 4, n =2 (5)) is faster during the metathesis reaction between NHC:SiBr2 and Ln: when compared with that of NHC:SiCl2. Second, the reaction of L1:SiCl4 (8) (L1: =:C­(CH2)­(CMe2)2N-2,6-iPr2C6H3) with a non-nucleophilic base LiN­(iPr)2 in a 1:1 molar ratio shows an unprecedented methodology for the synthesis of the biradical (L1•)2SiCl2 (2). The blue blocks of silicon dichloride bridged biradicals (2, 4) are stable for more than six months under an inert atmosphere and in air for one week. Compounds 2 and 4 melt in the temperature range of 185 to 195 °C. The dibromide (6, 7) analogue is more prone to decomposition in the solution but comparatively more stable in the solid state than in the solution. Decomposition of the products has been observed in the UV–vis spectra. Moreover, compounds 2 and 4 were further converted to stable singlet biradicaloid dicarbene-coordinated (Ln:)2Si­(0) (n = 1 (9), 2 (10)) under KC8 reduction. Compounds 2 and 4 were also reduced to dehalogenated products 9 and 10, respectively when treated with RLi (R = Ph, Me, tBu). Cyclic voltametry measurements show that 10 can irreversibly undergo both one electron oxidation and reduction.