Catalytic hydrogenation of aromatic nitriles and dinitriles with nickel compounds

Nickel(0) catalysts of the type, [(dippe)Ni(η2–NC–R)] (R = –Ph, –PhCN) prepared in situ from the nickel(I) dimmer, [(dippe)Ni(μ-H)]2 (1) in the presence of benzonitrile or the benzodinitriles (1,2-, 1,3- or 1,4-dicyanobenzenes) were used to hydrogenate these substrates. In the case of benzonitrile, 100% conversion was achieved after 72 h at 140 °C while pressurizing a reactor vessel with 60 psi of H2. N-Benzyl-benzylimine was obtained in 97% yield, accompanied by a small amount of dibenzylamine (2%). Hydrogenation of dicyanobenzenes was found to require more forceful conditions. In the case of 1,4-dicyanobenzene a 62% conversion of the substrate was achieved at 180 °C and 60 psi of H2 after 72 h. Hydrogenation of 1,3-dicyanobenzene yielded only a 38% conversion, which could only be achieved at 180 °C while pressurizing at 120 psi. The major products from these reactions, 4-{[(4-cyanobenzyl)imino]methyl}benzonitrile and 3-{[(3-cyanobenzyl)imino]methyl}benzonitrile, were obtained in 97 and 98% yield respectively. The 1,2-dicyanobenzene did not show any reactivity under the conditions used for the other two substrates.

Graphical abstractThe catalytic hydrogenation of benzonitrile and benzodinitriles was achieved under relatively mild conditions to mainly produce the corresponding Schiff base. In the case of terephthalonitrile, the use of an increased loading of catalyst permitted the isolation of a double Schiff base. The hydrogenation of the 1,2-benzodinitrile, phthalonitrile, did not yield any product either derived from hydrogenation or condensation.Figure optionsDownload full-size imageDownload as PowerPoint slide