Synthesis And Characterization Of Earth-abundant Metal Complexes Supported By Sterically Encumbered Phenolate Ligands

Sterically bulky phenolate ligands are of great importance in coordination chemistry,and are commonly employed to stabilize low-coordinate metal centers.This paper will discuss two types of bulky phenolate ligands,both of which contain benzhydryl substituents.They are sterically encumbered salicylaldiminate ligands and unsymmetric monodentate phenolate ligands.The synthesis,characterization and coordination chemistry of these ligands will be covered.In Chapter 2,complexes of sterically bulky salicylaldiminate ligands,[OC₆H₂^tBu₂C?H?=NAr*]?Ar*=-C₆H₂-2,6-?CHPh₂?₂-4-X,X=F or OCH₃?,with Al?III?,Mn?II?,Fe?II?or Co?II?were synthesized through salt metathesis reactionsin good to excellent yields.The composition,structures and properties of these complexes were determined by ¹H NMR,IR,UV-vis spectroscopy and X-ray crystallography.Furthermore,the spin state of the transition metal compounds were determined by the Evans method.The molecular structures of the aluminum complexes show that the ligands are bidentate and can bind in either 1:1 or 1:2 ratio,with a tetrahedral or trigonal bipyramidal coordination geometry,respectively.In contrast,all the prepared transition metal derivatives contain two bidentate ligands permetal center,with most compounds featuring a tetrahedral coordination environment.The only exception is complex 3a,the metal center of which also interacts with an oxygen atom of a solvent THF molecule,thus rendering the manganese center five-coordinate.Most of the synthesized four-coordinate show tetrahedral configuration.Only the ferrous complexes 4a adopts a rare four-coordinate seesaw geometry,possibly because of the strong intramolecular steric repulsion between the two salicylaldiminate ligands.Detailed structural parameters???NN-OO??of a series of cobalt bis?salicylaldiminate?complexes were compared,which revealed that the benzhydryl-containing Ar*group imposes less steric bulk when compared to the commonly used 2,6-diisopropylphenyl group.In Chapter 3,the preparation of some benzhydryl-substituted unsymmetric bulky phenols are reported,the compostion and purity of which are confirmed by ¹H NMR methods.Furthermore,a series of lithium complexes are synthesized through the direct reaction of such phenols with ⁿBuLi.The composition and structures of these lithium derivatives are investigated by single crystal X-ray diffraction.The results revealed that,both the phenolic proton and the benzylic proton from CHPh₂ group are acidic enough to react with ⁿBuLi,resulting in the formation of lithium complexes with a dianion.By controlling the stoichiometry of base used,the 1:1 lithium phenolate complex could also be isolated.