Access to a Stable Si₂N₂ Four-Membered Ring with Non-Kekulé Singlet Biradical Character from a Disilyne

Abstract

The reactions of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with an equivalent amount of trans- and cis-3,3',5,5'-tetramethylazobenzenes produced a Si(2)N(2) four-membered ring biradicaloid [RSi(μ-NAr)(2)SiR] 2 (R = Si(i)Pr[CH(SiMe(3))(2)](2), Ar = 3,5-Me(2)C(6)H(3)), which was isolated as air- and moisture-sensitive dark purple crystals. Compound 2 displays no EPR signal, and the molecular structure of 2 was characterized by NMR spectroscopy and X-ray crystallography, revealing that 2 has a planar centrosymmetric Si(2)N(2) four-membered ring. The Si1-Si1' distance is 2.63380(9) Å, and there is no bond interaction between the Si1 and Si1' atoms of 2. The reactions of 2 with methanol and carbon tetrachloride show that 2 has both closed-shell and radical-type reactivity.

Metalloid Sn clusters: properties and the novel synthesis via a disproportionation reaction of a monohalide

“…The bonding situation is thus comparable to other biradicaloid systems (Breher 2007, Nied et al 2009, Wang et al 2009, Takeuchi et al 2011, and the biradicaloid character increases with an increasing angle α. (B) In region (B), a classical 2c2e Sn-Sn single bond is present, where the arrangement at the tin atoms becomes pyramidal with an increase in angle α.…”

Conversion of a Singlet Silylene to a stable Biradical

“…Singlet biradicals of main group elements have been reported by Niecke, [2] Power, [3] Lappert, [4] Bertrand, [5] and Sekiguchi. [6] In most cases, these localized singlet biradicals have noncarbon skeletons that are based on four-membered ring motifs. In contrast, stable triplet biradicals of main group elements are rare.…”

Recent Developments in the Reactivity of Stable Disilynes

“…Disilyne 20 reacts with 3,3¤,5,5¤-tetramethylazobenzene, 41 but as intimated, the isolated product is not the [2 + 2] addition product or even the hydrazine-bridged bis(silylene), which might be expected from the analogous reaction of azobenzene with a digermyne. 42 In this case purple crystals of the fourmembered ring species 51 were isolated from the reaction mixture in reasonable yield (58%) (Scheme 19).…”