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

Abstract

A highly modular synthesis of BNB- and BOB-doped phenalenyls is presented. Treatment of the 1,8-naphthalenediyl-bridged boronic acid anhydride <b>1</b> with LiAlH₄/Me₃SiCl afforded the corresponding 1,8-naphthalenediyl-supported diborane(6) <b>2</b>, which served as the starting material for all subsequent transformations. Upon addition of MesMgBr/Me₃SiCl, <b>2</b> was readily converted to the tetraorganyl diborane(6) <b>5</b>. The further heteroatoms were finally introduced through the reaction of <b>2</b> with (Me₃Si)₂NR' or <b>5</b> with H₂NR' or H₂O (R' = H, Me, <i>p</i>-Tol). A helically twisted, fully BNB-embedded PAH <b>11</b> was prepared by combining <b>2</b> with a dibrominated <i>m</i>-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 <b>7</b> (BMes, NMe), the radical-anion salt K[<b>7</b>^•] was generated through chemical reduction with K metal and characterized by EPR spectroscopy. K[<b>7</b>^•] is not long-term stable in a THF/<i>c</i>-hexane solution, but abstracts an H atom with formation of the diamagnetic BNB-doped 1<i>H</i>-phenalene K[<b>7</b>H].