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

Abstract

Two different synthetic methodologies of silicon dihalide bridged biradicals of the general formula (L(n)•)2SiX2 (n = 1, 2) have been developed. First, the metathesis reaction between NHC:SiX2 and L(n): (L(n): = 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 (L(m) = 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 L(n): when compared with that of NHC:SiCl2. Second, the reaction of L(1):SiCl4 (8) (L(1): =: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 (L(1)•)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 (L(n):)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.

Experimental Charge Density Study of a Silylone

“…[8] Calculations suggest that Kiras silaallene better should be described as a silylone. [12] A second silylone was reported by Driess et al recently. [1] In contrast, further calculations by Kosa 2 Si showed that a silylone with two NHC ligands should experimentally be feasible.…”

“…There are small but significant differences in the bond lengths of Si1 À C1 (1.8454 (2) Figure 5). [23,12] Thus this might be attributed to packing effects. [23] However, compounds with dimethyl groups instead of the cyclohexyl group do not show significant differences in these values, both in the silylone and the germylone.…”

“…[12] A deviation from the planar geometry at the nitrogen atom such as in the free carbene should be observed if the bond between the central atom and the carbene carbon is an electron-sharing bond. [12] A deviation from the planar geometry at the nitrogen atom such as in the free carbene should be observed if the bond between the central atom and the carbene carbon is an electron-sharing bond.…”

Carbene-stabilized main group radicals and radical ions

“…With this knowledge of stability (SiCl 2 > SiBr 2 ), more electronegative substituents on silicon should assist in the stabilization of these types of biradicals. However, attempts to generate the SiF 2 derivative were unsuccessful, 34 although it appears to be a viable synthetic target.…”

Stable Heterocyclopentane‐1,3‐diyls

“…[29] In contrast, housane 2' exhibits a three-membered ring annulated to an almost perpendicular lying four-membered heterocycle with a PÀP banana single bond (P1ÀP2 2.167 ), PÀN single bonds (N1ÀP1 1.757, N2ÀP1 1.797, N1ÀP2 1.792 ) and a localized C=O double bond. [18,19,[31][32][33][34] Also the natural orbital occupation numbers (HOMO: 1.44 and LUMO: 0.56 e) clearly indicate open shell singlet biradical character. NBO occupation of p atomic orbitals perpendicular to the five-membered ring amounts to 5.7 e (C 0.84, N1 1.70, P1 0.66, N2 1.60, P2 0.90).…”