SYNTHESIS SOLUTION STEREOCHEMISTRY AND ELECTRON DELOCALIZATION PROPERTIES OF BIS(BETA-IMINOAMINO)NICKEL(2)COMPLEXES

Reaction of β-ketoamines with primary amine hydrochlorides yields a series of β-iminoamines RαC(NR)=CHC(NHR)Rα (Rα = H, CH3; R = benzyl, aryl). These compounds react with nickel(II) salts under nonaqueous conditions to form bischelate complexes of the general type Ni[RαC(NR)CHC(NR)Rα]2. Magnetic, spectral, and proton resonance properties of these complexes indicate that they adopt a pseudo-tetrahedral structure with a spin-triplet ground state in chloroform solution and that no diamagnetic planar stereoisomer is present in any case. All complexes manifest large isotropic proton contact shifts in solution which have been interpreted in terms of an effective π-delocalization mechanism involving ligand →metal antiparallel spin transfer. The mode of spin transfer is considered in some detail, and experimental spin densities at several ligand positions evaluated from contact shift measurements are shown to be consistent with ~1/13 unit of free spin in the highest filled π MO of the ligand anion. Two or more of the four possible diastereoisomers of the Rα = CH3, R = o-tolyl complex have been detected by proton resonance. Proton resonance spectra of the free ligands indicate that, at least on the time scale of the measurements, they exist as symmetrical hydrogen-bonded species or undergo rapid intramolecular proton transfer between the two nitrogens. © 1968, American Chemical Society. All rights reserved.