Synthesis Of Binuclear Rare Earth Complexes And Their Catalytic Behavior For The Ring-opening Polymerization Of Lactones

Homoleptic dinuclear rare-earth-metal complexes and dinuclear aryloxo/alkoxorare-earth-metal complexes stabilized by salen-type ligandN,N-bis（3,5-di-tert-butyl-salicylidene）-1,3-diaminobenzene （H₂L） were synthesized andcharacterized. The catalytic behavior of these complexes for the ring-openingpolymerization of ε-caprolactone （ε-CL） and L-lactide was also studied. The mainresults are as followings:1. Reaction of [（TMS）₂N]₃Ln （THF）₂（Ln=La, Nd,Sm,Y; TMS=SiMe₃） with H₂Lin a2:3molar ratio at room temperature afforded the homoleptic dinuclearrare-earth-metal complexes [Ln₂（μ-L）₃]（Ln=La （1）, Nd （2）, Sm （3）, Y（4））. Complexes14were characterized by single crystal X-ray diffraction, FT-IR and element analysis.2. Complexes13are efficient catalysts for the polymerization of ε-caprolactone.The catalytic activity depends on the metal center. The activity trend is1>2>3.3. The kinetic study of ε-CL polymerization initiated by complex2showed showeda pseudo-first order kinetics. The average number molecular weights （Mn） of theresulting polymers increased proportionally with the monomer conversion, while themolecular weight distributions （M_w/M-n） kept almost unchanged. These resultsdemonstrated that the polymerization proceeded in a controlled manner.4. Reaction of Yb[N（TMS）₂]₂Cl（THF）₂with H₂L in a1:1molar ratio at roomtemperature afforded the dinuclear ytterbium chloride [（thf）YbCl]₂（μ-L）₂（5）, which wascharacterized single crystal X-ray diffraction, FT-IR and element analysis.5. Reaction of [（thf）YbCl]₂（μ-L）₂（5） with NaOAr （Ar=2,6-^tBu₂-4-Me-C₆H₂） in1:1molar ratio in THF gave the dinuclear ytterbium aryloxide complex （YbOAr）₂（μ-L）₂（6）. Complex6was characterized by single crystal X-ray diffraction, FT-IR and elementanalysis. 6. Salt metathesis reaction of [（thf）LnCl]₂（μ-L）₂（formed in situ by the reaction ofLnCl₃with1equiv of Na₂L） with t-C₄H₉OK in THF at room temperature afforded thedinuclear alkoxo rare-earth-metal complexes [（thf）₂Na（μ-OBut）₂La]₂（μ-L）₂（7）,[（thf）₃K（μ-OBu^t）NdOBu^t]₂（μ-L）₂（8）,[（thf）₃K（μ-OBu^t）SmOBu^t]₂（μ-L）₂（9）,[（thf）YbOBu^t]₂（μ-L）₂（10）. Complexes7-10were characterized by single crystal X-raydiffraction, FT-IR and element analysis.7. The dinuclear aryloxo/alkoxo rare-earth-metal complexes6-10could initiate thepolymerization of ε-caprolactone and L-lactide with high activity.8. The kinetics study of L-LA polymerization initiated by complex9showed apseudo-first order kinetics. The average number molecular weights （Mn） of the resultingpolymers increased proportionally with the monomer conversion, while the molecularweight distributions （M_w/M_n） kept almost unchanged. These results demonstrated thatthe polymerization proceeded in a controlled manner.