Catalytic hydrogenation of aromatic nitriles and dinitriles with nickel compounds Original Research Article

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.