Mono- and trimetallic cobalt (II) and monometallic cobalth (III) amine-bis(phenolate) complexes: synthesis and structural properties

Abstract

This thesis describes the syntheses and structures of a series of monometallic and two trimetallic cobalt(II) amine-bis(phenolate) complexes. The protonated tripodal tetradentate ligand precursors dimethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H₂[O₂NN']BuBuNMe2 and diethylaminoethylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H₂[O₂NN']AmAmNEt2 were reacted with cobaltous acetate tetrahydrate under varying conditions to afford both mono- and trimetallic species. X-ray crystallographic data of monometallic complexes [LCo[O₂NN']BuBuNMe2] (L = H₂O, CH₃OH, CH₃COCH₃, propylene oxide) showed that the Coᴵᴵ ion adopts a distorted trigonal bipyramidal coordination environment. 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 mono- and trimetallic Coᴵᴵ complexes reported were also characterized by UV-vis spectroscopy, mass spectrometry, cyclic voltammetry and magnetic measurements. The Coᴵᴵ ions in these complexes are all high-spin and the trimetallic species show very weak antiferromagnetic behaviour when modeled as a linear isotropic trimer. Electrochemical studies reveal that the redox processes are most likely ligand based but a metal centered redox process is also possible. These works have recently been published: U. K. Das, J. Bobak, C. Fowler, S. E. Hann, C. F. Petten, L. N. Dawe, A. Decken, F. M. Kerton* and C. M. Kozak*, Dalton Trans., 2010, 39, 5462. -- This thesis also describes several oxidation attempts and a successful synthesis of a monometallic Coᴵᴵᴵ amine-bis(phenolate) complex. The oxidation reactions were carried out using a variety of oxidizing agents under both aerobic and anaerobic conditions. However, only silver nitrate gave promising results in yielding a monometallic COᴵᴵᴵ amine-bis(phenolate) complex under aerobic conditions. The monometallic species was characterized by ¹H NMR spectroscopy, mass spectrometry, and elemental analysis.