A Stable Stannaethene

Abstract

The stable stannanediyl 2 and the carbene‐like species 1 react to give stannaefhene 3. The structure of 3 was established by NMR spectroscopy and by X‐ray structure analysis. The very high‐frequency 119Sn‐NMR signal indicates that the C=Sn bond has strongly polar character (ylide form 3A). R1 = Si(CH3)3; R2 = C(CH3)3; R3 = CHR 21.

A Nearly Planar Stannene with a Reactive Tin–Carbon Double Bond

“…This Sn-C separation is even shorter than that of the previous stable stannapentafulvene 2 (d Sn=C = 2.016 Å), [8] which was reported to be the shortest Sn=C bond length among those known (2.025-2.032 Å). [3][4][5] This value of 2.003(5) Å is in agreement with the computed value (1.95-2.06 Å [8,17] depending on the basis set used). The shortening, in relation to the Sn-C single bond (2.14-2.15 Å) [18] is about 7 %.…”

“…[8] Depending on the groups on the tin atom, cryptodiborylcarbene-stannylene adducts display a twist angle (11.9°) comparable to that of 3 Ϫ with a trans bending structure and a bent angle of 13.2 (Sn) and 9.7°(C) [6] Ϫ or even greater twist angle ranging from 36 to 61°. [3][4][5] Thus, stannene 3 exhibits the geometric parameters (planarity, amount of bond shortening) that are the closest to those of the ideal double bond in alkenes and predicted by theoretical calculations.…”

“…[9] Thus, it seems that the introduction of two tertbutyl groups increases dramatically the thermal stabilization of the stannene, but has practically no influence on the tin chemical shift. The great difference in chemical shifts observed with stannenes derived from the electrophilic cryptodiborylcarbene (647-835 ppm [3,4] ) is rationalized by the more positive tin nuclei due to noticeable contribution of the resonance structure B (Scheme 1). The introduction of aryl groups on tin in such adducts shifts the 119 Sn signal to lower frequency (δ = 374 ppm [5] ).…”

“…By contrast, relatively few stable Sn=C compounds have been prepared [3][4][5][6][7][8][9] (Scheme 1). The main synthetic methods consist in stannylene-carbene coupling [3][4][5][6] or in dehydrohalogenation of halostannanes [7][8][9] with lithium compounds as bases. Noteworthy is the accurate description of the reaction outcomes of nucleophilic carbenes (imidazol-2-ylidenes, cyclopropylidenes) with stannylenes as the ylidic resonance structure A.…”

“…[3][4][5][6] The chemistry of the Sn=C bond has been sparsely explored. Only punctual studies of the reactions of long-lived stannenes with protic reagents, [3,7,8] benzophenone, [14] 2,3-dimethylbutadiene, [8] methyl iodide, [7b] reduction by LiAlH 4 [7b] along with their head-to-tail dimerization have been reported. [7] Investigation of the chemical behaviour of the transient stannene Me 2 Sn=C(SiMe 3 ) 2 [15] has been limited to its reaction with alkenes, dienes, azides and phenyllithium.…”