Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology , 2-12-1 Ookayama, Meguro, Tokyo 152-8552, Japan.
J Am Chem Soc. 2013 Nov 20;135(46):17610-6. doi: 10.1021/ja409625x. Epub 2013 Nov 1.
We have developed methods for installing aryl substituents directly on the phosphino groups of the 1,3-diphosphacyclobutane-2,4-diyl system. The aryl substituents tuned the electronic and structural characteristics of the biradical unit both in solution and in the solid state. 1-tert-butyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobuten-4-yl anion, prepared from phosphaalkyne (MesC≡P; Mes = 2,4,6-tBu3C6H2) and t-butyllithium, was allowed to react with an electron-deficient N-heterocyclic reagent. The corresponding N-heteroaryl-substituted P-heterocyclic biradicals were produced via SNAr reactions. Biradicals bearing perfluorinated pyridyl substituents exhibited photoabsorption properties comparable to those of previously reported derivatives because the highest occupied and lowest unoccupied molecular orbit levels were reduced by a similar amount. In contrast, the triazine substituent reduced the band gap of the biradical unit, and the large red shift in the visible absorption and high oxidation potential were further tuned via subsequent SNAr and Negishi coupling reactions. The amino-substituted triazine structure provided a strongly electron-donating biradical chromophore, which produced unique p-type semiconducting behavior even though there was no obvious π-overlap in the crystalline state. The single-electron transfer reaction involving Mes*C≡P, phenyllithium, and iodine afforded 1,3-diphenyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl via the intermediate P-heterocyclic monoradical. The tetraaryl-substituted symmetric biradical product was used to determine the electron density distribution from the X-ray diffraction data. The data show highly localized radicalic electrons around the skeletal carbon atoms, moderately polarized skeletal P-C bonds in the four-membered ring, and no covalent transannular interaction.
我们已经开发出了在 1,3-二磷杂环丁烷-2,4-二基系统的膦基上直接安装芳基取代基的方法。芳基取代基在溶液中和固态中都调节了自由基单元的电子和结构特性。由磷炔(MesC≡P;Mes=2,4,6-三特丁基苯)和叔丁基锂制备的 1-叔丁基-2,4-双(2,4,6-三特丁基苯基)-1,3-二磷杂环丁烯-4-基阴离子与缺电子的 N-杂环试剂反应。通过 SNAr 反应生成相应的 N-杂芳基取代的 P-杂环双自由基。具有全氟吡啶基取代基的双自由基表现出与先前报道的衍生物相当的光吸收特性,因为最高占据和最低未占据分子轨道水平降低了相似的量。相比之下,三嗪取代基降低了双自由基单元的能带隙,并且通过随后的 SNAr 和 Negishi 偶联反应进一步调谐了可见吸收的大红移和高氧化电势。氨基取代的三嗪结构提供了一个强供电子双自由基发色团,即使在晶体状态下没有明显的π重叠,它也产生了独特的 p 型半导体行为。涉及 Mes*C≡P、苯锂和碘的单电子转移反应通过中间的 P-杂环单自由基生成 1,3-二苯基-2,4-双(2,4,6-三特丁基苯基)-1,3-二磷杂环丁烷-2,4-二基。四芳基取代的对称双自由基产物用于从 X 射线衍射数据确定电子密度分布。数据显示骨架碳原子周围的自由基电子高度局域化,四元环中骨架 P-C 键适度极化,并且没有共价的跨环相互作用。