Study of the nature of counterion of α-diimine radical-anion complexes found in Brookhart-type catalytic systems

• The radical-anions of two diimines generated by reduction with alkali metals are studied.
• Spin exchange coupling effect is found for sodium complexes.
• Theoretical model for description of the observed spectra is developed.
• It is shown that in catalytic systems radical-anion of ligand is bound with aluminum center.

The purpose of this work is to reveal the nature of counterion that stabilizes radical-anions found in Brookhart-type catalytic systems. Radical-anions of two typical α-diimine ligands for Brookhart-type catalytic systems bis(2,6-diisopropylphenyl)diazabutadiene and bis-(2,6-diisopropylphenyl)-bis(imino)acenaphthene generated by reduction of a ligand with alkali metals has been investigated. It has been found that the reduction results in different products. In case of sodium complexes, it is shown that the formation of structured associates takes place in which the effect of spin exchange coupling appears. It is noticeable that this is a first example of spin exchange coupling described for diimine compounds. It has been shown that the interaction of diimine radical-anion complexes of both ligands with alkali metals with methylaluminoxane yields in formation of aluminum radical-anion complexes. Their ESR spectra are the same to ones registered in the catalytic systems.

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