Design Synthesis And Coordination Chemistry Of Aryloxo/alkyl Ligands Containing Diarylmethyl Units

Both aryloxo and alkyl ligands are important type of ligands in coordination chemistry and organometallic chemistry,and their metal complexes have emerged as important homogeneous catalysts or functional materials.In contrast,chelating ligands containing both aryloxo and alkyl donor groups,as well as their metal complexes,are greatly underdeveloped.Hence,The thesis mainly reports the synthesis and characterization of two aryloxo/alkyl ligands containing diarylmethyl substituents,i.e.H₃[COC]and H₃[OCO].The coordination chemistry of these two ligands were also investigated.The lithium complexes were proved to be effective transmetalation reagents for preparaing a series of aryloxo/alkyl metal complexes.The hydroxyl group of 1a ligands can be deprotonated,resulting in an anionic phenolate ligand.The lithium phenolates 2a were reacted with various metal halides in different stoichiometry,to afford four-coordinate transition metal complexes 3a-6a.In contrast,when three equivalent of the aryloxo ligand was treated with anhydrous Fe Cl₂,a three-coordinate ferrous complex 7a can be obtained.Interestingly,using[Mn?CH₂Si Me₃???-CH₂Si Me₃??THF?]₂ as the starting materials?rather than metal halides?,to directly react with the modified 1b and 1c phenols,can avoid the unfavorable inclusion of chloride or lithium ions in the solid-state structure of the products.Hence,two four-coordinate bis?aryloxo?Mn?II?complexes?8b and 8c?were prepared following this synthetic strategy.The metal complexes were characterized by ¹H NMR,X-ray crystallography,Infrared and UV-vis-NIR spectroscopy.Phenols H₃[COC]can undergo triple deprotonation,by reacting with three equivalent of strong base?e.g.ⁿBu Li?,to afford the corresponding trilithium complexes of trianionic bis?trityl?/aryloxo ligands?9a,9b and 9e?.Both crystallographic study and ¹H NMR results clearly show that the protons of the hydroxyl and diarylmethyl groups have been completely removed.metal complexes?10a,11a,12f and 13e?were synthesized by reacting the trianionic ligand with corresponding metal halides.No change of the oxidation states of the metal centers has been observed upon coordination with Mg?II?,Zn?II?or Mn?II?.In contrast,a redox reaction occurred between 9e and Co Cl₂ to give a four-coordinate homoleptic compound 13e.This cobalt complex can be further reduced with KC₈ to generate 14e.All metal complexes were characterized by ¹H NMR,X-ray crystallography,cyclic voltammogram?CV?,IR and UV-vis-NIR spectroscopy.Another series of tridentate[OCO]ligands with two phenolate groups?12a and12b?are also reported.Treatment of 12a with three equivalent of strong base?e.g.ⁿBu Li?can form a lithium compound of a trianionic ligand.Its crystal structure and¹H NMR spectra clearly show that the protons of all hydroxyl and diarylmethyl groups have been deprotonated.In contrast,the crystal structure of 13b indicates that only two phenolic hydroxyl protons are removed.However,the structure contains an unreacted ⁿBu Li unit,which can further deprotonate the diarylmethyl group in situ under certain conditions.Complex 13a reacts with Sn Cl₂ to form a trinuclear complex14a,whose crystal structure contains one Sn?IV?and two Sn?II?centers.Complex13b reacts with anhydrous Fe Cl₂ to form a dimeric compound 15b.Crystallographic study indicates the presence of two Fe centers and a tetradentate phenolate ligand,as a result of an oxidative C-C coupling reaction.In conclusion,we have designed and prepared series of tridentate aryloxo/alkyl ligands.The lithium derivatives of these ligands were proved to be effective transmetallation reagents,for the synthesis of metal complexes with Mg,Zn,Mn,Fe,Co,Sn centers.The molecular structures of these complexes were established by X-ray crystallography.In some of the coordination process,the oxidation state of the metal centers or the ligands have changed.This implies that such aryloxo/alkyl ligands may be redox-active.Furthermore,the reactivity of these metal compounds will be investigated in due course.