Cyanophenylation of Aromatic Nitriles by Terephthalonitrile Dianion: Is the Charge‐Transfer Complex a Key Intermediate?

Abstract

AbstractThe interaction of terephthalonitrile (1) dianion (12–) with benzonitrile (2) or m‐tolunitrile (3) provides 4,4'‐dicyanobiphenyl (4) or 4,4'‐dicyano‐2‐methylbiphenyl (5), respectively. This result shows that dianion 12– serves as a reagent for p‐cyanophenylation of aromatic nitriles. Based on experimental data, such as the chemical trapping of the 4,4'‐dicyanobiphenyl precursor 4‐cyano‐1‐(p‐cyanophenyl)cyclohexa‐2,5‐dienyl anion (7) and the failure to obtain biphenyl 4 through the interaction of independently generated radical anions (RAs) 1·– and 2·–, as well as on the results of quantum‐chemical calculations, a mechanism is suggested that includes a charge‐transfer complex (CTC) between 12– and the aromatic nitrile as the key intermediate. The formation of this CTC is followed either by an intracomplex electron transfer (ET) and recombination of terephthalonitrile and aromatic nitrile RAs within an unequilibrated RA pair, or by synchronous ET and bonding of the ipso‐carbon atom of terephthalonitrile with the p‐carbon atom of the aromatic nitrile. The synthetic significance of p‐cyanophenylation of arenecarbonitriles by dianion 12– is illustrated by the high yield of biphenyl product 4 (approx. 90 %) as well as by the possibility of a one‐pot synthesis of 4‐butyl‐4'‐cyanobiphenyl and 4‐butyl‐4'‐cyano‐2‐methylbiphenyl by successive treatment of dianion 12– with nitrile 2 or 3 and butyl bromide. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)