Synthesis, Characterization Of Bridged Bis(aryloxide) Lanthanide Complexes And Their Behavior Of Catalytic Reactivity | | Posted on:2008-12-04 | Degree:Doctor | Type:Dissertation | | Country:China | Candidate:X P Xu | Full Text:PDF | | GTID:1101360278466521 | Subject:Organic Chemistry | | Abstract/Summary: |  PDF Full Text Request | | Lanthanide alkoxides and amides supported by two kinds of bridged bis(phenolato) ligands were synthesized, and their activity for the polymerization of cyclic esters were studied as well. The bridged bis(phenolato) ligands used in this thesis are as follows: carbon-bridged bis(phenolato) ligands: CH2(4-Me-6-tBu-C6H2O)2, abbreviated as MBMP; CH3CH(4,6-di-tBu-C6H2O)2, abbreviated as EDBP. Imidazolidine-bridged bis(phenolato) ligands: C3H6N2[1,4-(2-O-3,5-di-tBu-C6H2CH2)2], abbreviated as [ONNO].1. Reaction of Cp3Ln(THF) with MBMPH2 in a 1:1 molar ratio in THF at room temperature for about an hour, then with 1 equiv. of methanol or benzylic alcohol, gave the neutral bis(phenolate) lanthanide alkoxides [(MBMP)Ln(μ-OMe)(THF)2]2 (Ln = Nd (1), Yb (2)) and [(MBMP)Ln(μ-OPh)(THF)2]2 (Ln = Nd (3), Yb (4)). Half hydrolysis product [(MBMP)Yb(THF)2]2(μ-OPh)(μ-OH) (5) was isolated in low yield during the synthesis of complex 4. Complexes 1-4 were characterized by IR and elemental analysis. The definitive structures of 1 and 5 were confirmed by single crystal X-ray diffraction. Complexes 1 and 2 have dinuclear structure in the solid state.2. Isopropoxide lanthanide complexes supported by EDBP [(EDBP)Ln(μ-OiPr)(THF)2]2 (Ln = Nd (6), Sm(7), Yb (8)) were prepared in the same way as mentioned above. Complexes 6-8 were characterized by IR and elemental analysis. The definitive structures of 6 and 7 were confirmed by single crystal X-ray diffraction. Both complexes have dimeric structures in the solid state. The intermediate species of the reaction (EDBP)LnCp(THF)2 (Ln = Nd (6a), Sm (7a), Yb (8a)) were separated and characterized, the DME adduct (EDBP)YbCp(DME) (8b) was identified by single crystal X-ray diffraction.3. Reaction of Ln[N(TMS)2]3(μ-Cl)Li(THF)3 with 1 equiv. of MBMPH2 in THF afforded the unexpected anionic lanthanide amides [(MBMP)Ln{N(TMS)2}2][Li(THF)4] (Ln = Pr (9), Nd (10), Sm (11), Tb (12), Yb (13)) in relatively high yields. Additionally, Ln[N(TMS)2]3 containing a small amount of NaN(TMS)2 reacted with MBMPH2 to produce the analogous anionic lanthanide amides [(MBMP)Ln{N(TMS)2}2][Na(DME)3] (Ln = Nd (14), Yb (15)). All the complexes were characterized by IR and elemental analysis. Definitive structures of all the complexes except 11 were elucidated by single crystal X-ray diffraction. 4. Reaction of {[N(TMS)2]2Nd(μ-Cl)(THF)}2 with MBMPH2 in a 1:2 molar ratio produced the carbon bridged bis(phenolate) neodymium chloride [(MBMP)Nd(μ-Cl)(THF)2]2 (16). The neutral lanthanide amides (MBMP)LnN(TMS)2(THF)2 (Ln = Nd (17), Yb (18)) can be prepared by the general metathesis reactions of [(MBMP)Ln(μ-Cl)(THF)2]2 with NaN(TMS)2 in a 1:1 molar ratio. The anionic lanthanide amido complexes 14 and 15 can also be synthesized by the same reaction in a 1:2 molar ratio of [(MBMP)Ln(μ-Cl)(THF)2]2 to NaN(TMS)2. Complexes 16-18 were characterized by IR, elemental analysis and single crystal X-ray diffraction (except complex 17).5. The neutral lanthanide amides 17 and 18 reacted with carbodiimide to get the desired lanthanide guanidinate complexes {[(μ-O)MBMP]Nd[(iPrN)2CN(TMS)2]}2 (19) and (MBMP)Yb[(iPrN)2CN(TMS)2] (20). But the ligand redistributed product [(MBMP)2Nd(THF)2][Li(DME)3] (21) can be isolated using complex 10 as the precursor. Complexes 17 and 18 reacted with PhNCO, the unexpected products {(MBMP)Ln[μ-OC(O)NHPh]}2 (Ln = Nd (22), Yb (23)) were isolated, which were postulated to be the products from the reaction of lanthanide hydroxide formed in situ with PhNCO. In order to confirm this postulation, the lanthanide hydroxides formed by the control hydrolysis of (MBMP)LnCp(THF)2 were used to react with PhNCO, after workup, complexes 22 and 23 can be isolated in high yields. All the complexes were characterized by IR, elemental analysis and single crystal X-ray diffraction.6. Reaction of imidazolidine bridged bis(phenol)s [ONNO]H2 with excessive NaH in THF afforded the corresponding sodium salt {[ONNO]Na2(THF)2}2 in almost quantitative yield. The product was characterized by IR, 1H NMR, elemental analysis and single crystal X-ray diffraction. A dimeric structure was observed in the solid state. Reaction of {[ONNO]Na2(THF)2}2, YbCl3 and HMPA in a 1:4:4 molar ratio in THF produced a bimetallic dichloride [ONNO][Yb2Cl2(μ-Cl)2(HMPA)2]2 (24). Complex 24 is a useful precursor for the synthesis of the corresponding lanthanide derivatives by general metathesis reactions. Reaction of 24 with NaOiPr, either in a 1:2 or in a 1:4 molar ratio, gave the corresponding lanthanide alkoxo complex [ONNO][Yb2Cl2(μ-OiPr)2(HMPA)2]2 (25). When more bulky reagent, NaOAr (OAr = 2,6-di-tert-butyl-4-methylphenoxo) was used instead of NaOiPr, ligand redistribution reaction was occurred, (ArO)2YbCl(HMPA)2 (26) and [ONNO]YbCl(HMPA)2 (27) were isolated as final products. Reaction of complex 24 with NaNPh2 in a 1:2 molar ratio also afforded the ligand redistributed products 27 and (Ph2N)2YbCl(HMPA)2 (28). When the molar ratio increased to 1:4, the desired products [ONNO]YbNPh2(HMPA) (29) and (Ph2N)3Yb(HMPA)2 (30) were isolated. Anhydrous YbCl3 reacted with {[ONNO]Na2(THF)2}2 in a 1:2 molar ratio, the anionic ytterbium complex (ONNO)2YbNa(THF)2 (31) could be isolated in about 85% yield. All the complexes were characterized by IR and elemental analysis, the definitive molecular structures of 24-26,29-31 were provided by single crystal X-ray diffraction.7. The silylamido complexes supported by [ONNO] ancillary ligands, [ONNO]LnN(TMS)2(THF) (Ln = Y (32), La (33), Pr (34), Nd (35), Sm (36), Yb (37)), can be synthesized in high yields by the reaction of Ln[N(TMS)2]3(μ-Cl)Li(THF)3 with [ONNO]H2. All the complexes were characterized by IR, and elemental analysis. Complexes 32 and 33 were further confirmed by 1HNMR spectroscopy. Definitive molecular structure of complex 37 was provided by single crystal X-ray diffraction.8. Cyclopentadienyl ytterbium complex based on imidazolidine bridged bis(phenolate) ligands [ONNO]YbCp (38) can be conveniently prepared by the reaction of Cp3Yb(THF) with [ONNO]H2 in a 1:1 molar ratio in THF, which was characterized by IR, elemental analysis and single crystal X-ray diffraction.9. Carbon bridged bis(phenolate) lanthanide alkoxides 1-4, 6-8 can initiate the ring-opening polymerization ofε-caprolactone in controlled manner under mild polymerization conditions, which showed almost the same catalytic activity compared to the isopropoxide analogue. Complexes 6-8 can also initiate the ring-opening polymerization of cyclic carbonate in a higher activity.10. Silylamido lanthanide complexes based on MBMP ancillary ligand can initiate the ring-opening polymerization ofε-caprolactone. Compared with the alkoxide analogues, the neutral amido complexes demonstrated comparable catalytic activity and modest controllability, the anionic amido complexes showed higher activity, and the polymers initiated by complexes 9 and 10 have high molecule weight with narrow molecular weight distribution (MWD). But the MWDs of polymers initiated by complexes 11 and 13 are broad.11. Preliminary studies revealed that the silylamido lanthanide complexes containing [ONNO] ligand are apparently more active initiators for the ring-opening polymerization ofε-caprolactone than the anionic amido complexes supported by carbon bridged bis(phenolate) ligands. Complex 35 can initiate effectively the polymerization of L-lactide even at room temperature.
| | Keywords/Search Tags: | bridged bis(phenolato), lanthanide, synthesis, characterization, cyclic esters, polymerization, reaction | | PDF Full Text Request | Related items |
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