Studies on nickel(II) complexes. V.¹ a nuclear resonance study of conformational equilibria

Abstract

Complexes of the general type bis-(R-N.salicylaldimine)-Ni(II) in which R is a see-alkyl group have previously been shown to exist in a planar a tetrahedral equilibrium in solutions of noncoordinating solvents at and above room temperature.³ These complexes have now been thoroughly studied by means of proton magnetic resonance and are found to exhibit isotropic proton hyperfine contact shifts. In this respect they are similar to bis-(N.N-disubstituted aminotroponeimine)-Ni(II) complexes extensively studied by others ^l0 Two sorts of complexes have been examined—those which contain either optically inactive or optically active R groups For the optically inactive species spin densities on the ligand systems have been evaluated from measurement of contact shifts and magnetic moments. For both the optically inactive and active species analysis of the temperature dependence of the contact shifts has yielded values of ΔF. ΔH. and ΔS for the solution equilibria. Complexes containing optically active groups consist of diastereoisomeric mixtures when prepared from racemic amines. Each diastereoisomer is shown to possess a separate set of contact shifts The relation of each such set to a given diastercoisomer is proved and it is shown that the thermodynamic parameters for each isomer can be separately determined. The detection of molecular association in solution is demonstrated from contact shift measurements. Procedures for extensive optical resolution (≥95%) of two see-alkylamines are reported.