Incomplete Electrocyclization of a Sterically Hindered 1,4‐Diphosphabutadiene
Incomplete Electrocyclization of a Sterically Hindered 1,4‐Diphosphabutadiene
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位阻 1,4-二磷酸丁二烯的不完全电环化
DOI：
10.1002/cplu.201900632
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发表时间：
2019
期刊：
影响因子：
3.4
通讯作者：
Ito Shigekazu
中科院分区：
文献类型：
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作者：
Shinozaki Tomokazu;Rosas‐Sanchez Alfredo;Hashizume Daisuke;Ito Shigekazu
丁烯是最简单的中性无环闭壳π共轭体系，通常足够稳定，足以避免电环化为环丁烯。相比之下，大多数含有较重元素的丁二烯同系物很容易转化为相应的4元环丁烯体系。在这里，我们证明了在空间位阻的2，3-二磷酸丁腈（P= C-C =P）骨架中的左1，4-二磷酸丁腈（P= C-C =P）骨架，（亚膦基）-1，4-二硅烷可以由于“不完全电环化”而显著扰动，其中P= C-C =P部分形成相应的1，2-二氢二磷酸酯（三、4-二磷杂环丁烯）通过[2+2]在溶液中获得的31 P NMR数据表明，闭环的共存大大降低了电环化的开环特征。P= C-C =P部分。然而，2，3-bis（phosphanylidene）-1，4-disilinane的31 P CP-MAS光谱表明，P= C-C =P结构在固态下占主导地位。单晶X射线分析表明，降低温度促进了少量不完全的结晶态1，2-二氢二磷酸体系的生成。此外，1，2-二氢二磷酸酯单元在加热单晶时消失，并且这种独特的固态电环化反应是可逆的。
Butadiene is the simplest neutral acyclic closed‐shell π‐conjugated system and is typically sufficiently stable enough to avoid electrocyclization to cyclobutene. In contrast, most congeners of butadiene containing heavier elements are easily converted into the corresponding 4‐membered cyclobutene system. Herein, we demonstrate that the gauche 1,4‐diphosphabutadiene (P=C−C=P) skeleton in a sterically encumbered 2,3‐bis(phosphanylidene)‐1,4‐disilinane can be remarkably perturbed due to “incomplete electrocyclization” where P=C−C=P partially form the corresponding 1,2‐dihydrodiphosphete (3,4‐diphosphacyclobutene) by [2+2] electrocyclization.31P NMR data obtained in solution indicated that the coexistence of a closed ring substantially reduces the open‐ring characteristics of the P=C−C=P moiety. However, the31P CP‐MAS spectrum of 2,3‐bis(phosphanylidene)‐1,4‐disilinane showed that the P=C−C=P structure is predominant in the solid‐state. Single‐crystal X‐ray analysis revealed that decreasing the temperature promoted the generation of small amounts of incomplete 1,2‐dihydrodiphosphete system in the crystalline state. Furthermore, the 1,2‐dihydrodiphosphete units disappeared upon warming the single crystal, and this unique solid‐state electrocyclization reaction was reversible.