The interaction of aliphatic amines with transition metal complexes of aromatic dimines. Part 1 Kinetics and thermodinamic of reaction at the tris-85-nitro-1-10 phenantrolyne)Ni(II)

Addition of aliphatic amines to the complex [Ni(nphen)J [C1O4I2 (nphen = 5-nitro-I ,lo-phenanthroiins) in dipolar aprotic solvents gives deep red solutions. A spectrophotometric investigation of these processes leading to the formation of 1 : 2 adducts of complex : amine, most likely ' Meisenheimer ' complexes, has been carried out in dimethylformamide. Both equilibrium and rate constants for adduct formation between [Ni(nphen)J [C1O4I2 and piperidine, n-propylamine, or benzylamine have been calculated by low-temperature stopped-flow techniques. The reactions are exothermic ; the equilibrium data at -50 "C show that co-ordination of the ligand to nickel(ii) largely increases the stability of the adduct between nphen and piperidine. Kinetic data are in agreement with a stepwise mechanism in which nucleophilic attack of the amine at the ligand is followed by proton transfer from the species formed to a second amine molecule. Proton transfer is either fast or rate determining depending on the nature of the amine.