‘Starburst’-type nona- and dodecadiazo compounds were designed and synthesized by using the cyclotrimerization of ethynyl ketones as a key step. Construction of the larger dodecadiazo compounds was facilitated by using a trimethylsilyl protecting group for an acetylenic moiety. The diazo compounds were photolyzed in MTHF solid solution at cryogenic temperatures and analyzed by means of Faraday magnetometry and ESR spectroscopy. From the field dependence of the magnetization, the nonacarbene, the photoproduct of nonadiazo compound, was evidenced to have a nonadecet (S = 9) ground state. This spin multiplicity is the highest value ever reported for purely organic materials. On the other hand, the spin multiplicity was low and antiferromagnetic interaction operated in the photoproduct of the dodecadiazo compound. This result was interpreted not in terms of the intermolecular antiferromagnetic interaction but of the intramolecular cross-linking between the carbene centers. In the ‘Starburst’-type polycarbenes with extended branching, the reactive carbene centers can become mutually too close to each other in space and so appear to recombine readily. This study showed one of the limitations of the extension of the carbene network by way of flexible ‘Starburst’-type structures.
以
乙炔酮的环三聚化为关键步骤,设计并合成了 "星爆 "型壬二氮和
十二烷二氮化合物。通过使用三甲基
硅烷保护基团来保护
乙炔基,有助于合成较大的十二重氮化合物。重氮化合物在
MTHF 固溶体中低温光解,并通过法拉第磁力仪和 ESR 光谱进行分析。从磁化的磁场依赖性来看,壬二氮化合物的光致产物壬二碳烯被证明具有非十进制(S = 9)基态。这一自旋多重性是迄今为止纯有机材料所报道的最高值。另一方面,
十二烷偶氮化合物的光反应产物中自旋倍率较低,存在反
铁磁相互作用。对这一结果的解释不是分子间的反
铁磁作用,而是碳烯中心之间的分子内交联。在具有扩展分支的 "星爆 "型聚
碳酸酯中,活性碳烯中心在空间上会相互过于靠近,因此很容易发生
重组。这项研究显示了通过灵活的 "星爆型 "结构扩展碳烯网络的局限性之一。