Novel dioxolene nickel complexes with sterically hindered diazabutadienes. Coupling of aza-ligands coordinated to nickel

Abstract

A square-planar bis-o-semiquinonato nickel complex interacts with N,N′-disubstituted 1,4-diazabutadienes-1,3 forming six-coordinate compounds. The X-ray structural study indicates complex geometry to be close to the octahedral. Magnetic properties are determined by metal–ligand ferromagnetic exchange interactions which are promoted by complex geometry. In polar solvents (THF, CH₂Cl₂, and CHCl₃) complexes are partly dissociated into corresponding diazabutadiene-nickel catecholate and free o-quinone. In the case of the most sterically hindered 1,4-bis-(2,6-di-iso-propylphenyl)-2,3-dimethyl-1,4-diazabutadiene-1,3 in n-hexane or toluene the above-mentioned reaction is accompanied by the coupling through the back-bonded methyl groups of diazabutadiene. The organic product of the coupling was eliminated from the complex, isolated and structurally characterized. Taking into account the quantitative yield the coupling reaction is the actual procedure for the synthesis of new potential nitrogen ligands.