Synthesis Of Heterometallic Rare Earth Metal-Zinc/Magnesium Complexes Stabilized By Diethylene Glycolamine-Bridged Bis?Phenolato? Ligand And Their Applications In Catalyzing Reactions Of CO₂ And Epoxides

As a common C1 resource,carbon dioxide(CO2)catches more and more attention.Converting carbon dioxide into value-added compounds through chemical fixation not only relieves fossil material crisis,but also has a positive effect on the ecological environment.In this thesis,a series of homo-and heteronuclear rare earth containing complexes supported by diethylene glycolamine-bridged bis(phenolato)ligand were synthesized,including 1)homonuclear rare earth complexes,abbreviated as L2RE2(THF)n,2)heterometallic rare earth metal-zinc complexes,abbreviated as L2RE2Zn(OCH2Ph)2(THF)2,3)heterometallic rare earth metal-magnesium complexes,abbreviated as L2RE2Mg(OCH2Ph)2(THF)2.The catalytic property of these complexes for the reactions of CO2 and epoxides was explored.The diethylene glycolamine-bridged bis(phenolate)ligand used is N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-2-(2-aminoethoxy)ethanol,abbreviated as H3L.RE refers to rare earth metal and only yttrium(Y),yttrium(Yb),yttrium(Nd)and lanthanum(La)are considered.1.Synthesis of rare earth metal-zinc complexes supported by diethylene glycolamine-bridged bis(phenolato)ligand and their applications in catalyzing reactions of CO2 and epoxides(1)Homonuclear rare earth complexes L2RE2(THF)n[RE=Y(1),Yb(2),Nd(3),La(4)]were prepared through protonolysis of Cp3RE(THF)n with ligand precursor H3L.H3L and Cp3RE(THF)were dissolved in tetrahydrofuran at a molar ratio of 1:1,and 0.5 equivalent of Zn(OAc)2 was added after reacting at room temperature for 12 hours.The zinc complex LZnH(5)was obtained instead of acetate bridged rare earth-zinc heteronuclear complexes.Substituting Zn(OAc)2 for Zn(OCH2Ph)2,the desired heteronuclear complexes L2RE2Zn(OCH2Ph)2(THF)n[RE=Y(6),Yb(7),Nd(8),La(9)]were obtained in good isolated yields of 77-87%.1H DOSY was employed to reveal the solution structure of these dinuclear complex,which revealed that the dinuclear structure is maintained in solution.(2)With these homonuclear rare earth metal and hetero-rare earth metal-zinc complexes in hand,the catalytic properties in coupling reaction of CO2 with epoxides to produce cyclic carbonates were evaluated using 1,2-epoxyhexane as a template reaction.Through the optimization of reaction conditions,the optimum reaction conditions were 0.5 mol%of complex 9 as catalyst,2 mol%of TBAB as cocatalyst,and 25? under 1 atm pressure CO2 for 24 hours.Most monosubstituted terminal epoxides were commendably converted to the corresponding cyclic carbonates in 88-96%yields under the optimal conditions.Furthermore,those bulky and/or internal epoxides with larger steric hindrance and lower reactivity were also tested,and all of them can be transferred to cyclic carbonates at elevated temperature or after prolonged reaction time.The study on reaction mechanism showed that synergy effect between polymetallic centers is promising for CO2 conversion.(3)The catalytic property of complexes 6-9 for the copolymerization of CO2 with cyclohexene oxide was explored.It was found that the metal center,reaction temperature,solvent,loadings of catalyst had obvious influence on the catalytic activity and the content of polycarbonate link of polymers obtained.It was found that adding quaternary ammonia is advantageous to increase the conversion of epoxide.The produced copolymer was further analyzed by MALDI-TOF-MS spectroscopy,indicating that the initiating groups in this system were both the alkoxo group and anions in quaternary ammonium salts.1.Synthesis of rare earth metal-magnesium complexes supported by diethylene glycolamine-bridged bis(phenolato)ligand and their applications in catalyzing reactions of CO2 and epoxides(1)Reaction of benzyl alcohol with Mg(n-Bu)2 gave magnesium alkoxide complex(Mg(OCH2Ph)2).The tetrahydrofuranm solution of Cp3RE(THF)and H3L was added to the magnesium alkoxide prepared above.After workup,the desired heterobimetallic rare earth metal-magnesium complexes L2RE2Mg(OCH2Ph)2(THF)n[RE=Y(10),Yb(11),Nd(12),La(13)]were obtained in good isolated yields of 79-96%.(2)The coupling reaction of CO2 with epoxides to produce cyclic carbonates catalyzed by heterometallic rare earth metal/magnesium complexes in the presence of quaternary ammonium salt was also explored.The reaction conditions were optimized using 1,2-epoxyhexane as a template reaction under atmospheric condition and the the optimum reaction conditions selected were 0.5 mol%of complex 13 as catalyst,1 mol%of TBAB as cocatalyst for 24 hours.Under the optimal reaction conditions,most monosubstituted epoxides were transformed into the corresponding cyclic carbonates in excellent yield of 92-98%.Moreover,those disubstituted epoxides with larger steric hindrance were fully converted to the corresponding cyclic carbonates at elevated temperature and CO2 pressure.In addition,we determined the reaction order of epoxyoxide,complex 13 and TBAB by kinetics study.