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

Abstract

Nice and easy: A very simple synthesis for dibenzopentalenes, which starts from 1-bromo-2-ethynylbenzenes, has been developed. It uses Ni(0) complexes (see scheme), from which a relatively stable Ni(II) complex as an important intermediate has been isolated. Dibenzopentalenes with various functional groups can be prepared by the procedure, and their electronic properties are consistent with theoretical calculations.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 an important intermediate was isolated as relatively stable crystals, and the structure was confirmed by 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.

Theoretical study of aromatic-antiaromatic pairs as material in organic solar cells of double light harvesting

“…This fact is relevant in semiconductor design with application in OSCs, owing to the UV-Vis absorption of the solar spectrum [31]. Regarding to pentalene (1) and s-indacene (2), they have been synthesized with small substituents in order to minimize the dimerization process [10,11]. These antiaromatic compounds have been characterized by UV-Vis absorption spectroscopy, where is noted that the HOMO-LUMO transition is not allowed, showing transitions with a very low oscillator strength.…”

“…Therefore, in order to have two semiconductors that absorb in different intervals of the solar spectrum, we propose the strategy: using organic semiconductors with the same or similar HOMO-LUMO gap, but dephased, where one of them, donor or acceptor, corresponds to an antiaromatic system with an inversion center. This implies that their frontier molecular orbitals will have the same parity [9][10][11]. By means of group theory, parity implies a forbidden HOMO-LUMO transition by symmetry, according to the Laporte's rules [12].…”

Synthesis and Reactions of Dibenzo[a,e]pentalenes

“…The yield of 1uu was improved to 46% in the presence of Ni(cod) 2 , PPh 3 and Zn at 110 ºC. This method enabled the synthesis of a variety of dibenzopentalenes (1324% yields) (Scheme 24 and 25) [43]. It is noted that the electronic nature of substituents on the aromatic rings did not affect the formation of dibenzopentalenes.…”

“…Being inspired by this catalytic system, an extremely simple synthesis of dibenzopentalenes from 2-bromoethynylbenzenes was reported. Treatment of 2-bromoethynylbenzene 25d with an equivalent of Ni(PPh 3 ) 2 Cl 2 and 1.5 equivalents of Zn at 80 ºC produced dibenzopentalene 1uu in 41% yield (Scheme 23) [43]. Reaction of 25d with Ni(cod) 2 and PPh 3 at 50 °C afforded Ni complex 36, which was transformed into 1uu at 80 ºC.…”

Pentalene – von hochreaktiven Antiaromaten zu Ausgangsmaterialien für die Materialwissenschaften

“…[7] Ein Beispiel ist das ortho-Bromphenylacetylen 14, das unter den in Schema 4 gezeigten Bedingungen in 46 % Ausbeute das 5,10-disilylierte Dibenzopentalen 15 liefert. Wie Kawase, Kubo und Mitarbeiter fanden, gehen verschiedene 2-Brom-1-ethinylbenzole in einer Nickel-vermittelten Dimerisierung in einem Schritt in mittleren Ausbeuten in symmetrisch substituierte Dibenzopentalene über.…”