Investigation On The Synthesis And Application Of Aryloxide Cobalt(Ⅱ) Complexes

In this thesis, we focused on the study of the synthesis and reactivity of a series ofcobalt（Ⅱ） complexes supported by the bulky aryloxide ligands. Three anionic cobalt（Ⅱ）aryloxides, a neutral π-oxoaryl cobalt（Ⅱ） complex and an anion radical sodium complexwere synthesized and structurally characterized. The catalytic activity of the anioniccobalt（Ⅱ） aryloxide complexes for the polymerization of cyclic esters were explored aswell. It was found that the catalytic behaviors of these three complexes were greataffected by the structurally minor alteration in aryloxide ligands, as well as the solvent.The detailed results are described as follows:1. Treatment of anhydrous cobalt（Ⅱ） chloride with NaOAr¹（Ar¹=[2,6-（tBu）₂-4-MeC₆H₂]） in1:3molar ratio in THF at room temperature for about24hours afforded the anionic aryloxide complexes （Ar¹O）3CoNa（THF）5.33（1） in high yield.Complex1was characterized by IR and elemental analysis. The definite structure of1was also confirmed by single crystal X-ray diffraction, and which revealed that complex1existed in ion-pair way in the solid state. After complex1was stirred in toluene at80oC overnight, black crystals were obtained. IR spectroscopy indicated different structurefrom complex1. Detailed structure hasn’t been elucidated because of the poor quality ofcrystals.2. Reaction of NaOAr¹（Ar¹=[2,6-（tBu）₂-4-MeC₆H₂]） with anhydrous cobaltchloride in1.5:1molar ratio in THF was performed at room temperature for about24hours, then NaCl was removed by centrifugation, THF was evaporated in vacuo. Theresidue was dissolved in toluene and stirred for another2to3hours at80oC. Aπ-oxoaryl cobalt（Ⅱ） complex2was obtained in low yield. Complex2was characterizedby IR and elemental analysis. Its structure was also confirmed by single crystal X-raydiffraction. Reaction of NaOAr¹（Ar¹=[2,6-（tBu）₂-4-MeC₆H₂]） with anhydrous cobaltchloride in a molar ratio of2:1in toluene at80oC for about24hours gave black crystals.Because of poor quality of crystals, we didn’t get its crystal structure. However, IR characterization implied a very similar structure as the compound obtained fromcomplex1in hot toluene.3. Treatment of NaOAr²（Ar²=[2,6-（tBu）_<sub>2C₆H₃]） with anhydrous cobalt chloride ina molar ratio of3:1in THF at room temperature for about24hours afforded the anionicaryloxide cobalt complexes （Ar²O）3CoNa（THF）6（3） in high yield. Complex3wascharacterized by IR and elemental analysis. Its structure was also confirmed by X-raysingle crystal diffraction. Complex3existed in ion-pair way in the solid state.4. Reaction of NaOAr²（Ar²=[2,6-（tBu）_<sub>2C₆H₃]） with anhydrous cobalt chloride in amolar ratio of2:1in toluene at80oC for about24hours afforded the anion radicalcomplex4. Flame atomic absorption spectrometry disclosed that the only metal existedin4was not cobalt but sodium. Complex4was characterized by IR and elementalanalysis. Its structure was also confirmed by single crystal X-ray diffraction.5. Treatment of NaOAr³（Ar³=[2,4,6-（tBu）3C₆H₂]） with anhydrous cobalt chloridein a molar ratio of3:1in THF at room temperature for about24hours afforded the anionaryloxide coordinated complex （Ar³O）3CoNa（THF）6（5） in high yield. Complex5wascharacterized by IR and elemental analysis. Its structure was also confirmed by singlecrystal X-ray diffraction. Complex5existed in ion-pair way in the solid state.6. Complexes1,3,5could initiate the ring opening polymerization ofε-caprolactone and L-lactide in mild conditions. The property of the substituent group at4-position in aryloxo ligand can affect the polymerization greatly. In the ring openingpolymerization of ε-caprolactone, more sterically hindered aryloxide ligand led tohigher catalytic activity of complex. While in the ring opening polymerization of theL-lactide, complex5showed lower efficiency to produce PLA, however, with narrowPDIs. Complex1exhibited modist activity to generate PLA with broad PDIs. Complex3was demonstrated to be most efficient catalyst in all three cobalt aryloxides.