Department of Chemistry, University of California , 1 Shields Avenue, Davis, California 95616, United States.
J Am Chem Soc. 2017 May 17;139(19):6586-6595. doi: 10.1021/jacs.7b02269. Epub 2017 Apr 28.
The tin(II) hydride [ArSn(μ-H)](Ar = CH-2,6(CH-2,4,6-Pr)) (1a) reacts with 2 equiv of ethylene or t-butylethylene at ca. 25 °C to yield Sn(Ar)R(R = ethyl or t-butylethyl), which exist either as a symmetric distannene Ar(R)SnSn(R)Ar (2a or 5a) or an unsymmetric stannylstannylene ArSnSnRAr (3a). In contrast, the less crowded Sn(II) hydride [ArSn(μ-H)] (Ar = CH-2,6(CH-2,6-Pr)) (1b) reacts with excess ethylene to give Ar(CHCH)Sn(CHCH)Sn(CHCH)(CHCH)Ar (4) featuring five ethylene equivalents, one of which is dehydrogenated to an vinyl, -CH═CH, group. The Ar isomers of 2a and 3a, i.e., [ArSn(CH)] (2b) and ArSnSn(CH)Ar (3b) are obtained by reaction of [ArSn(μ-Cl)] with EtLi or EtMgBr. The isomeric pairs 2a and 3a are separated by crystallization at different temperatures. Variable-temperature H NMR spectroscopy indicates fast ethyl group exchange between Ar(CH)SnSn(CH)Ar (Ar = Ar (2a) or Ar (2b)) and ArSnSn(CH)Ar (Ar = Ar (3a) or Ar (3b)) with ΔG = 14.2 ± 0.65 kcal mol for 2a/3a and 14.8 ± 0.36 kcal mol for 2b/3b. The bulkier distannenes [ArSn(CHCHBu)] (Ar = Ar (5a) or Ar (5b)), obtained from 1a or 1b and t-butylethylene, dissociate to ArSnCHCHBu monomers in solution. At lower temperature, they interconvert with their stannylstannylene isomers with parameters K = 4.09 ± 0.16 for 5a and 6.38 ± 0.41 for 5b and ΔG = -1.81 ± 0.19 kcal mol for 5a and -1.0 ± 0.03 kcal mol for 5b at 298 K. The 1:1 reaction of 1a or 1b with 5a or 5b yields the unknown monohydrido species SnRHAr which has the structure ArSn-Sn(H)(CHCHBu)Ar (6a) or the monohydrido bridged ArS n(μ-H)S n(CHCHBu)Ar (6b). The latter represents the first structural characterization of a monohydrido bridged isomer of a ditetrelene.
二价锡氢化物[ArSn(μ-H)](Ar = CH-2,6(CH-2,4,6-Pr))(1a)在约 25°C 下与 2 当量的乙烯或叔丁基乙烯反应，生成 Sn(Ar)R(R = 乙基或叔丁基乙基)，其要么以对称的二锡烯 Ar(R)SnSn(R)Ar(2a 或 5a)存在，要么以不对称的锡基锡烯 ArSnSnRAr(3a)存在。相比之下，空间位阻较小的二价锡氢化物[ArSn(μ-H)] (Ar = CH-2,6(CH-2,6-Pr)) (1b)与过量的乙烯反应，生成了具有五个乙烯当量的 Ar(CHCH)Sn(CHCH)Sn(CHCH)(CHCH)Ar(4)，其中一个乙烯被脱氢生成了乙烯基，-CH=CH-基团。通过[ArSn(μ-Cl)]与 EtLi 或 EtMgBr 的反应，可以得到 2a 和 3a 的 Ar 异构体，即[ArSn(CH)] (2b)和 ArSnSn(CH)Ar (3b)。异构体对 2a 和 3a 可以通过在不同温度下结晶来分离。变温 1H NMR 光谱表明，在 Ar(CH)SnSn(CH)Ar(Ar = Ar(2a)或 Ar(2b))和 ArSnSn(CH)Ar(Ar = Ar(3a)或 Ar(3b))之间，乙基基团的交换非常迅速，ΔG = 14.2 ± 0.65 kcal mol 用于 2a/3a，ΔG = 14.8 ± 0.36 kcal mol 用于 2b/3b。从 1a 或 1b 和叔丁基乙烯得到的较大的二锡烯[ArSn(CHCHBu)] (Ar = Ar(5a)或 Ar(5b))在溶液中解离为 ArSnCHCHBu 单体。在较低温度下，它们与它们的锡基锡烯异构体相互转化，参数 K = 4.09 ± 0.16 用于 5a，K = 6.38 ± 0.41 用于 5b，在 298 K 时，ΔG = -1.81 ± 0.19 kcal mol 用于 5a，ΔG = -1.0 ± 0.03 kcal mol 用于 5b。1a 或 1b 与 5a 或 5b 的 1:1 反应生成未知的单氢化物物种 SnRHAr，其结构为 ArSn-Sn(H)(CHCHBu)Ar(6a)或单氢化物桥联的 ArS n(μ-H)S n(CHCHBu)Ar(6b)。后者代表了首例 ditetrelene 单氢化物桥联异构体的结构特征。
