Synthesis, Characterization And Catalytic Property Of Nitrogen Bridged Tri(phenolate) Rare Earth Metal Complexes

A series of rare earth metal complexes supported by nitrogen-bridged tri(phenolato) ligands were synthesized and their catalytic property for the reaction of heterocumulenes with epoxides was explored. The ligands used include 2,2’,2’’-[nitrilotris(methylene)]tris[4,6-dimethylphenol], abbreviated as L1H3, 2,2’,2’’-[nitrilotris(methylene)]tris[4,6-dichlorophenol], abbreviated as L2H3 and 2,2’,2’’-[Nitrilotris(methylene)]tris[6-tert-butyl-4-methylphenol], abbreviated as L3H3.1. Synthesis of rare earth metal complexes supported by nitrogen-bridged tri(phenolato) ligands(1) Reactions of L1H3 with RECp3(THF) [RE = Y, Sm, Nd, La] in a 1:1 molar ratio in THF gave the corresponding rare earth metal complexes L1RE(THF)3 [RE = Y(1), Sm(2), Nd(3), La(4)] in good isolated yields. All of these complexes were characterized by IR, elemental analysis, and 1H NMR、13C NMR spectroscopy in the cases of complex 1 and 4. The definitive molecular structure of complexes 2-4 were determined by single-crystal X-ray structure analysis.(2) Reactions of Nd Cp3(THF) with L2H3 and L3H3 in a 1:1 molar ratio in THF gave the corresponding rare earth metal complexes L2Nd(THF)3(5) and L3Nd(THF)3(6) in good isolated yields, respectively. Complexes 5 and 6 were characterized by X-ray structure determination, IR spectrum and elemental analysis.2. Addition reaction of isocyanates with epoxides to produce oxazolidinones catalyzed by rare earth metal complexes 1-4The addition reaction of isocyanates with epoxides to produce oxazolidinones catalyzed by complexes 1-4 in the presence of quaternary ammonium salt was explored. Through the optimization of reaction tempareture, time, solvent, solvent volume, catalysts, molar ratio of catalyst to substrate, quaternary ammonium salts, as well as the loading of quaternaryammonium salts, the optimized reaction conditions were 0.5 mol% of 3, 1.0 mol% of NBu4 I, 80 °C, 12 h and toluene as the solvent. A series of epoxides bearing a varity of substituents as well as non-terminal epoxides and isocyanates bearing an alkyl, ether, halogen substituents were commendably converted to the corresponding oxazolidinones in good to excellent yields(57 to 95%) under mild conditions.3. Additioon reaction of CO2 with epoxides to produce cyclic carbonates catalyzed by rare earth metal complexes 1-6The coupling reaction of CO2 with epoxides to produce cyclic carbonates catalyzed by complexes 1-6 in the presence of quaternary ammonium salt was explored. Through the optimization of the reaction conditions, the optimized reaction conditions were 0.067 mol% of complex 5, 0.4 mol% of NBu4 Br, and 95 ?C. A series of monosubstituted terminal epoxides bearing an alkyl, aryl, ester, morpholine, ether, halogen, hydroxyl or alkene substituent were commendably converted to the corresponding cyclic carbonates in good to excellent yields(58 to 96%) under atmospheric pressure of CO2. Furthermore, the bulky or internal epoxides, which were generally considered as substrates of low reactivity were also tested, and all of them were transformed into the corresponding cyclic carbonates in good to excellent yields(83 to 91%) at elevated pressure(10 bar CO2) or after prolonged reaction time.4. Reaction of CO2, epoxides and amine to produce oxazolidinones catalyzed by rare earth metal complexes 1-5The coupling reaction of CO2, epoxides and amines to produce oxazolidinones catalyzed by complexes 1-5 in the presence of quaternary ammonium salt was explored. Through the optimization of the reaction conditions, the optimized reaction conditions were 0.25 mol% of complex 5, 0.25 mol% of NBu4 Br, 95 ?C and 10 bar. A series of amine were commendably converted to the corresponding oxazolidinones in good to excellent yields(57 to 95%) under mild conditions.