Redistribution reactions of some transition-metal chelates. Part I. Thermodynamics of bidentate ligand exchange between nickel(II) chelates

Abstract

The redistribution reaction between chelates NiL¹₂ and NiL²₂ to give NiL¹L² where L¹ and L² are bidentate salicylaldimine or β-keto-imine residues has been monitored by use of contact shifts in the ¹H or ¹⁹F n.m.r. spectra of the chelates. Equilibrium constants, enthalpies, and entropies for the redistribution are presented for several systems. The mixed compound is in general formed in less than statistical amount, enthalpies of redistribution then usually being positive. This unusual result is discussed in relation to previous work. In a number of systems no reaction was observed. The redistribution between NiL₂¹ and ML₂²(where M is Cu, Zn, or Co) has also been examined. These reactions have shed light on the reason for non-reactivity of the bis-(N-n-propylsalicyaldiminato)nickel(II)-bis-(N-t-butylsalicylaldiminato)nickel(II) system.