The interactions between Ni-II cations and bidentate Schiff base ligands, N-alkyl-5-X-salicylaldimine HL (X = H; R = Et, nPr, tBu; X = Cl, OMe, NO2; R = nPr), and bis(N-n-alkyl-5-X-salicylaldiminato)nickel(II) complexes [NiL2] (X = H; R = Et, nPr, nBu; X = Cl, OMe, Me; R = nPr) were investigated by UV/Vis spectrophotometry in acetonitrile. The kinetics for the formation of Ni-II/HL 1:1 adducts was studied by stopped-flow techniques, which showed that the process followed a two-consecutive mechanism, Experimental evidence and theoretical calculations indicated the formation of an unidentate intermediate in the first step, according to a dissociative interchange mechanism. Ring-closure occurs in the second step and its rate is slower for electron-withdrawing-substituted Schiff bases. Nickel(II) cations interact with [NiL2] affording [NiL](+) and [Ni2L3](+) species; the associated equilibrium constants were found to be related to the electronic effects of the 5-X ligand substituents.
Kinetics and Equilibria of Nickel(II)-Schiff Base Adducts Formation
CACELLI, IVO;CARBONARO, LAURA;
2002-01-01
Abstract
The interactions between Ni-II cations and bidentate Schiff base ligands, N-alkyl-5-X-salicylaldimine HL (X = H; R = Et, nPr, tBu; X = Cl, OMe, NO2; R = nPr), and bis(N-n-alkyl-5-X-salicylaldiminato)nickel(II) complexes [NiL2] (X = H; R = Et, nPr, nBu; X = Cl, OMe, Me; R = nPr) were investigated by UV/Vis spectrophotometry in acetonitrile. The kinetics for the formation of Ni-II/HL 1:1 adducts was studied by stopped-flow techniques, which showed that the process followed a two-consecutive mechanism, Experimental evidence and theoretical calculations indicated the formation of an unidentate intermediate in the first step, according to a dissociative interchange mechanism. Ring-closure occurs in the second step and its rate is slower for electron-withdrawing-substituted Schiff bases. Nickel(II) cations interact with [NiL2] affording [NiL](+) and [Ni2L3](+) species; the associated equilibrium constants were found to be related to the electronic effects of the 5-X ligand substituents.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
