BNB-Doped Phenalenyls: Modular Synthesis, Optoelectronic Properties, and One-Electron Reduction

A highly modular
synthesis of BNB- and BOB-doped phenalenyls is
presented. Treatment of the 1,8-naphthalenediyl-bridged boronic acid
anhydride 1 with LiAlH4/Me3SiCl
afforded the corresponding 1,8-naphthalenediyl-supported diborane(6) 2, which served as the starting material for all subsequent
transformations. Upon addition of MesMgBr/Me3SiCl, 2 was readily converted to the tetraorganyl diborane(6) 5. The further heteroatoms were finally introduced through
the reaction of 2 with (Me3Si)2NR′ or 5 with H2NR′ or H2O (R′ = H, Me, p-Tol). A helically
twisted, fully BNB-embedded PAH 11 was prepared by combining 2 with a dibrominated m-terphenylamine, followed
by a Grignard-mediated double ring-closure reaction. All compounds
devoid of B–H bonds show favorable optoelectronic properties,
such as luminescence and reversible reduction behavior. In the case
of the BNB-phenalenyl 7 (BMes, NMe), the radical-anion
salt K­[7•] was generated through chemical
reduction with K metal and characterized by EPR spectroscopy. K­[7•] is not long-term stable in a THF/c-hexane solution, but abstracts an H atom with formation
of the diamagnetic BNB-doped 1H-phenalene K­[7H].

本工作报道了一类高度模块化的BNB掺杂与BOB掺杂菲烯基（phenalenyls）化合物的合成策略。将1,8-萘二基桥连硼酸酐1经氢化铝锂/三甲基氯硅烷（LiAlH4/Me3SiCl）还原处理，制得以1,8-萘二基为支撑骨架的乙硼烷(6)衍生物2，该衍生物为所有后续转化反应的起始原料。向化合物2中加入三甲苯基溴化镁/三甲基氯硅烷（MesMgBr/Me3SiCl），可顺利转化为四有机基取代乙硼烷(6)5。后续杂原子的引入可通过两条路径实现：化合物2与双(三甲基硅基)胺(R'N(SiMe3)₂)反应，或化合物5与伯胺(R'NH₂)或水（H₂O）反应（R' = H、Me、对甲苯基(p-Tol)）。通过将化合物2与二溴代间三联苯胺结合，并经格氏试剂介导的双环合反应，成功制备出一种螺旋扭曲、完全由BNB嵌入的多环芳烃(Polycyclic Aromatic Hydrocarbons, PAH)11。所有不含B-H键的化合物均展现出优异的光电性质，例如发光性能与可逆还原行为。以BNB掺杂菲烯基化合物7（BMes，NMe）为例，通过金属钾化学还原得到其自由基阴离子盐K[7•]，并通过电子顺磁共振波谱(EPR spectroscopy)对其进行表征。K[7•]在四氢呋喃/环己烷（THF/c-hexane）溶液中无法长期稳定存在，会夺取氢原子生成抗磁性的BNB掺杂1H-菲烯钾盐K[7H]。