Structural variations in the coordination chemistry of amine-bis(phenolate) cobalt(II/III) complexes

Abstract

A series of cobalt(II), cobalt(III) and mixed valence cobalt(II/III) compounds has been prepared and characterized. The protonated tripodal tetradentate ligand precursors (dimethylaminoethylamino-N,N-bis(2-methylene-4-tert-butyl-6-methylphenol), H2[O2NN′]BuMeNMe2, dimethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H2[O2NN′]BuBuNMe2, and 2-pyridylamino-N,N-bis(2-methylene-4-tert-butyl-6-methylphenol), H2[O2NN′]BuMePy were reacted with cobaltous acetate tetrahydrate under varying conditions to afford a range of monometallic, bimetallic and trimetallic species. Monometallic compounds, 1 and 2, were obtained with pendant amine-containing ligands [O2NN′]BuMeNMe2 and [O2NN′]BuBuNMe2, respectively. Compound 1 is a trigonal bipyramidal CoII acetone adduct, CoII(OCMe2)[O2NN′]BuMeNMe2, and 2 is a distorted octahedral CoIII acetate complex, CoII(OAc)[O2NN′]BuBuNMe2. A dimethoxo-bridged dicobalt(III) complex, 3, was obtained using the pyridyl group-containing ligand, [O2NN′]BuMePy, after oxidation in air of a methanol solution of {Co[O2NN′]BuMePy}2. Two side-products, 4 and 5 were also obtained from this reaction. Complex 4 contains two octahedrally coordinated cobalt(III) atoms, each bonded to a tetradentate amine-bis(phenolate) ligand and bridged by one syn,syn η1:η1:μ2 acetate ligand, and one hydroxide ligand. Complex 5 is a heterotrimetallic compound and consists of two Co[O2NN′]BuMePy fragments, each bridged by a syn,anti η1:η1:μ2 acetate ligand to a central CaII(HOMe)4 fragment. Mixed valence CoIII–CoII–CoIII trimetallic complexes, 6 and 7, were obtained by reaction of H2[O2NN′]BuMePy or H2[O2NN′]BuBuPy ligands, respectively, with Co(OAc)2·4H2O in 2:3 molar ratios in methanol under nitrogen followed by aerobic oxidation. Diethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H2[O2NN′]AmAmNEt2 was reacted with cobaltous chloride hexahydrate under acidic conditions to give the ionic compound {H3[O2NN′]AmAmNEt2}+2[CoCl4]2−, 8.