Synthesis and structure of mono-, bi- and trimetallic amine-bis(phenolate) cobalt(ii) complexes

Abstract

A series of cobalt(II) amine-bis(phenolate) complexes 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, diethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H₂[O₂NN′]^AmAmNEt2 and 2-pyridylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H₂[O₂NN′]^AmAmPy; were reacted with cobaltous acetate tetrahydrate under varying conditions to afford a range of monometallic, bimetallic and trimetallic species. An unusual four coordinate complex Co[O₂NN′]^AmAmNEt2 containing Co^II in a trigonal monopyramidal environment was structurally characterized, whereas using a less sterically demanding ligand a series of five coordinate complexes Co[O₂NN′]^BuBuNMe2(L) (L = H₂O, CH₃OH, (CH₃)₂CO, propylene oxide) containing Co^II in a trigonal bipyramidal environment was prepared. A new angular structural parameter related to τ is defined, where τ′ may be used to compare complexes with trigonal monopyramidal structures. In contrast, ligands containing a pendant pyridyl donor afford dimeric species including {Co(μ-CH₃OH)[O₂NN′]^AmAmPy}₂. In the absence of base and in the presence of excess cobaltous acetate, trimetallic complexes were isolated containing a central Co^II in an octahedral environment coordinated to four CH₃OH and two bridging acetate ligands between two Co[O₂NN′] fragments with Co^II in a trigonal bipyramidal setting. The paramagnetic Co^II complexes reported were also characterized by UV-vis spectroscopy, mass spectrometry, cyclic voltammetry and magnetic measurements.