Synthesis,Crystal Structures And Properties Of Manganese And Cobalt Complexes With Bulky BIAN Ligands

Most N-containing?-diimine ligands are redox-active and can coordinate to transition metals to generate a variety of organometallic complexes with stable structures and interesting reactivities.Therefore,such ligands and the corresponding complexes have attracted great attentions of chemists.As an important type of redox-active ligands,bis?arylimino?anthracene?BIAN?ligands are derivatives of?-diimine ligands,have low-energy?*orbitals and can adopt multiple successive oxidation states.Metal complexes supported with BIAN ligands have found great applications in homogeneous catalysis.In this paper,a series of bulky asymmetric BIAN ligands with benzhydryl substituents and the corresponding manganese and cobalt complexes were designed and synthesized.The structures of these sterically encumbered BIAN ligands have been characterized by nuclear magnetic resonance?NMR?and infrared spectroscopy?IR?methods.A total of 20 metal complexes were prepared and characterized by NMR,IR,UV-vis spectroscopy and X-ray crystallography.In Chapter 2,we report the preparation of a series of Co complexes with tunable electronic properties,through the direct reaction of BIAN ligands and anhydrous CoCl₂.Single crystal X-ray diffraction study of these complexes found that the cobalt centers are four-coordinate with a tetrahedral coordination geometry.The NMR spectra of the cobalt complex exhibited significant broadening and shift of the resonance peaks,indicating the paramagnetic nature of these compounds.In the third chapter of this paper,ten manganese complexes with various electronic structures were obtained by reacting the asymmetric BIAN ligands with anhydrous MnCl₂.The solid state structures of these complexes were characterized by X-ray crystallography.The results revealed that the synthesized manganese complexes show mononuclear,dinuclear or trinuclear molecular structures,depending on the ligands and solvents used for the preparation/crystallization.The five-coordinate mononuclear manganese complexes,show trigonal bipyramidal coordination geometry,with the manganese center coordinating with two BIAN nitrogen atoms,two chlorine atoms,and one oxygen atom from THF solvent.In contrast,most prepared Mn complexes show chlorine-bridged dinuclear structures,with each manganese center adopting a five-coordinate distorted tetragonal pyramidal geometry.The three Mn atoms in the trinuclear manganese complexes are not equivalent.The central Mn atom is six-coordinate,with four chlorine atoms and two THF oxygen atoms,showing an octahedral coordination geometry.In contrast,the other symmetry-related Mn centers are five-coordinate,in a tetragonal pyramidal coordination environment.The cyclic voltammetric study of the cobalt and manganese complexes confirmed the presence of two consecutive ligand-based single electron transfer processes.Furthermore,it is demonstrated that the redox potentials of these compounds can be finetuned to some extent,by variation of the para-substituent on the central aryl ring of the N-aryl group in the BIAN ligands.Such investigation shed lights on further development of first-row transition metal complexes supported by BIAN ligands with various oxidation states.