An Extremely Simple Dibenzopentalene Synthesis from 2-Bromo-1-ethynylbenzenes Using Nickel(0) Complexes: Construction of Its Derivatives with Various Functionalities

An extremely simple dibenzopentalene synthesis from readily available 2-bromo-1-ethynylbenzenes using a nickel(0) complex is described. Although the yields are moderate, the formation of three C-C bonds in a single process and the high availability of the starting materials are important advantages of this reaction. The corresponding aryl-nickel(II) complex as ail important intermediate was isolated as relatively stable crystals, and the structure was confirmed b X-ray crystallographic analysis. The high stability of. this complex should play a key role in this reaction. The reaction is applicable to the preparation of dibenzopentalenes bearing various functional groups. Their electronic properties are consistent with theoretical calculations. The cyclic voltammograms of these compounds reveal highly amphoteric redox properties. In particular, the electron-donating property of a tetramethoxy derivative is greater than that of oligothiophenes and dibenzodithiophenes and almost comparable to that of pentacene.