Magic Blue‐Promoted Synthesis of a Highly Planar Tetraphenylbenzidine: Evaluation of Its Fundamental Properties and Unraveling the Intriguing Mechanism for Its Formation

Abstract Magic blue [ MB , ( p ‐BrC 6 H 4 ) 3 N •+ SbCl 6 − ]‐promoted oxidation of the tetracyclodecane derivative mm‐ 1 containing two triphenylamine ( TPA ) moieties and subsequent reduction using triethylamine results in formation of the uncharged pentacyclic product 4 that possesses a novel, cage‐framework‐constrained tetraphenylbenzidine ( TPB ) moiety. This process follows an electron‐transfer mechanism involving formation of the intermediate radical cation 4 •+ through intramolecular aryl coupling of a di(radical cation) mm‐ 1 2(•+) . The TPB biphenyl type conjugated moiety in 4 is highly planar. Moreover, 4 has a higher energy HOMO and greater electrochemical stability than does the parent TPB . Notably, because it undergoes a fully reversible two‐step–two‐electron oxidation–reduction reaction, 4 is an ideal electron donor for use in electronic devices. Finally, conversion of 4 •+ to the corresponding dication 4 2+ by SbCl 6 – ‐promoted “auto”oxidation is described.