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 CoII 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)2C=O, propylene oxide) containing CoII in a trigonal bipyramidal environment was prepared. A new angular structural parameter related to t is defined, where t¢ may be used to compare complexes with trigonal monopyramidal structures. In contrast, ligands containing a pendant pyridyl donor afford dimeric species including {Co(m-CH3OH)[O2NN¢]AmAmPy}2. In the absence of base and in the presence of excess cobaltous acetate, trimetallic complexes were isolated containing a central CoII in an octahedral environment coordinated to four CH3OH and two bridging acetate ligands between two Co[O2NN¢] fragments with CoII in a trigonal bipyramidal setting. The paramagnetic CoII complexes reported were also characterized by UV-vis spectroscopy, mass spectrometry, cyclic voltammetry and magnetic measurements.