Synthesis And Catalytic Properties Of Novel Rare Earth Phenolate Compounds

Exploring the chemistry of lanthanide phenolate compounds has become one of the most valuable and exciting areas of lanthanide chemistry because of their useful application in catalysis and easily preparation. A series of lanthanide phenolate compounds with novel structures have been synthesized and characterized. Their catalytic characters on the ring-opening polymerization (ROP) of cyclic esters have been investigated. Studies of the kinetics of ROP and polymer end group analysis have been undertaken to understand polymerization mechanism. The alkyl yttrium complex supported by carbon bridged bisphenolate ligand has been synthesized and employed to catalyze the polymerization of conjugated dienes.A series of yttrium trisalicylaldimine complexes in situ formed by the reaction of trialkyl complex [Y(CH2SiMe3)3(THF)2] with3equivalent salicylaldimine were used as initiators for ring-opening polymerization (ROP) of ε-caprolactone (CL). Electronic and steric effects of the salicylaldimine ligand played important roles on the catalytic properties of the yttrium complexes. The yttrium trisalicylaldimine complex Y(L)3(L=(S)-2,4-di-tert-butyl-6-((1-phenylethylimino) methyl) phenol) most effectively initiated controlled ROP of CL to prepare PCLs with high molecular weights and moderate molecular weight distributions.The synthesis and structures of lanthanide complexes supported by benzoxazine-functionalized amine bridged bis(phenolate) ligand6,6'-(2-(8-tert-butyl-6-methyl-2H-benzo[e][1.3]oxazin-3(4H)-yl)ethylazanediyl)bis(m ethylene)bis(2-tert-butyl-4-methylphenolato)(L1)2-are described. Salt metathesis reaction between lanthanide trichloride and2eq of LNa2in THF at room temperature afforded the corresponding "ate" complexes [L12LnNa(THF)2](Ln=Y (1), Nd (2), Er (3), Yb (4)). Further treatment of the product with18-crown-6afforded discrete ion-pair complexes [L12Ln][(18-crown-6)Na(THF)2](Ln=Y (5), Yb (6)). The single-crystal structural analyses of1and3-6revealed that the lanthanide cation and the sodium cation were bridged by two phenolate oxygen atoms in complexes1.3and4, while in complexes5and6, the anion comprises a lanthanide cation coordinated by two L2-and the cation is comprised of a sodium cation surrounded by an18-crown-6and two THF molecules. These complexes are employed to catalyze the controlled ROP of CL and L-lactide (L-LA). and the experimental results showed that the contact "ate" complexes are more active than their discrete ion-pair counterpart in ROP of CL.A novel carbon-bridged bis(phenolate) yttrium alkyl complex [(EDBP)Y(CH2SiMe3)(THF)2](7) was synthesized by reaction of2,2'-ethylidene-bis(4,6-di-tert-butyl-phenol)(EDBPH2) and [Y(CH2SiMe3)3(THF)2]. The structure of complex7was determined by X-ray crystallography. Upon activation with the combination of triisobutylaluminum (TIB A) and methylaluminoxane (MAO). compound7catalyzed the controlled homo-, copolymerization of isoprene and1.3-butadiene. The effects of TIBA/MAO molar ratio and the total Al/Y ratio on the activity and selectivity of isoprene polymerization, the kinetics and "living" character of the polymerization system have been investigated.Three carbon-bridged bis(phenolate) neodymium complexes,[(MBMP)2Nd(μ3-Cl)Li(THF)2Li(THF)](8),[(MBBP)2Nd(μ3-Cl)Li(THF)2Li(THF)](9) and [(THF)2Nd(EDBP)2Li(THF)](10) have been synthesized by one-pot reaction of NdCl3and LiCH2SiMe3with6,6'-methylenebis(2-tert-butyl-4-methylphenol)(MBMP-H2),6,6'-methylenebis(2,4-di-tert-butylphenol)(MBBP-H2) and6,6'-(ethane-1,1-diyl)bis(2,4-di-tert-butylphenol)(EDBP-H2), respectively, in a molar ratio of1:4:2. The definitive structures of complexes9and10were determined by X-ray diffraction studies. Experimental results show that8-10efficiently initiate the ROP of ε-caprolactone and ROP of L-lactide.