Diphosphametacyclophanes: Structural and Electronic Influences of Substituent Variation within a Family of Bis(diketophosphanyl) Macrocycles

The
condensation of MeP­(SiMe3)2 with a series
of 5-substituted isophthaloyl chlorides (5-R′C6H3-2,6-{C­(O)­Cl}2) affords the diphosphametacyclophanes m-{-C­(O)-C6H3-5-R′-(C­(O)­PMe)}2 (R′ = I, Me, tBu, Ph,
and p-NCC6H4); the analogues m-{-C­(O)-C5H3N-(C­(O)­PMe)}2 and m-{-C­(O)-C6H4-(C­(O)­PPh)}2 are similarly obtained in preference to higher oligomers,
in contrast to precedent reports. The cyclophanes all adopt butterfly-like
conformations in the solid state with the P-organyl substituents adopting
mutually exo arrangements. Structural and computational
data suggest the nature of the 5-R substituent is key in directing
the inter-ring angle and the extent of LUMO stabilization about the
diketophophanyl scaffold. The latter is substantiated by UV/vis spectroscopy
and cyclic voltammetry, which demonstrate these cyclophanes to be
appreciably comparable to the diketophosphanyl systems commonly explored
in the context of organic electronic materials; intriguingly, the
distinct dikeophosphanyl moieties within the macrocycles appear effectively
“insulated” by the macrocycle geometry, rather than
acting as a through-conjugate.

将双(三甲基硅基)甲基膦（MeP(SiMe₃)₂）与一系列5-取代间苯二甲酰氯（5-R′C₆H₃-2,6-{C(O)Cl}₂）进行缩合反应，可得到二磷杂间环芳烷类化合物m-{-C(O)-C₆H₃-5-R′-(C(O)PMe)}₂（其中R′分别为I、Me、tBu、Ph及对氰基苯基(p-NCC₆H₄)）；类似地，可优先合成类似物m-{-C(O)-C₅H₃N-(C(O)PMe)}₂与m-{-C(O)-C₆H₄-(C(O)PPh)}₂，而非高级低聚物，这与既往研究报道的结果相悖。该类环芳烷在固态下均呈现蝶式构象，且磷原子上的有机取代基采取相互外向的排布方式。结构表征与计算数据表明，5位取代基R′的性质是调控环间夹角以及二酮膦基骨架上最低未占据分子轨道（Lowest Unoccupied Molecular Orbital, LUMO）稳定化程度的关键因素。这一结论通过紫外-可见光谱（UV/vis spectroscopy）与循环伏安法得到了证实，结果显示此类环芳烷的性能与有机电子材料领域中常用的二酮膦基体系具有显著可比性；有趣的是，大环内部的两个独立二酮膦基单元似乎被大环的几何结构有效“隔离”，并未表现出贯穿共轭的相互作用。