Synthesis And Characterization Of Organolanthanide Complexes Supported By β-diketiminato And Phenyl-bridged β-ketoimine And Their Catalytic Behavior

Thirty-one organolanthanide complexes supported byβ-diketiminato and phenyl-bridgedβ-ketoimine were synthesized and well characterized. Among them, 22 complexes were further characterized by X-ray diffraction. The catalytic behaviors of these complexes for the polymerization ofε-caprolactone (ε-CL), L-lactide (L-LA) as well as acrylonitrile (AN) were examined. The main results obtained are as follows:1. Reaction of Li(C6H5NC(Me)CHC(Me)NC6H5) (LHLi), Na(p-Cl-C6H4NC(Me)CHC(Me)NC6H4-p-Cl) (LClNa), and Na(p-Me-C6H4NC(Me)CHC(Me)NC6H4-p-Me) (LMeNa), respectively, with LnCl3 in 1:1 molar ratio gave the corresponding complexes LHYbCl2(THF)2 (1), LClPrCl2(THF)2 (2), and LMeNdCl2(THF)2 (3). All complexes were characterized by elemental analysis and IR spectroscopy. The definitive structure of 1 was confirmed by X-ray diffraction.2. Reaction of LMe2LnCl2(THF)2 ( Ln = Yb, Nd; LMe2 = 2,6-Me2-C6H3NC(Me)CHC(Me)NC6H3-2,6-Me2) with LiNPh2 in 1:2 molar ratio gave the correspondingβ-diketiminato diamido complexes LMe2Yb(NPh2)2(THF) (4) and LMe2Nd(NPh2)2(THF) (5), respectively. Complexes 4 and 5 were characterized by elemental analysis, IR spectroscopy and X-ray diffraction. Complexes 4 and 5 were found to be the novel catalysts for ring-opening polymerization ofε-CL with high catalytic activity and for the polymerization of AN with good activity to give atactic polyacrylonitriles.3. Complexes LMe2YbCl(OAr')(THF) (OAr'= 2,6-di-tert-butyl-phenoxide) (6) and LiPr2YbCl(OAr)(THF)2 (7) (OAr = 2,6-di-tert-butyl-4-metyl-phenoxide; LiPr2 = 2,6-i-Pr2-C6H3NC(Me)CHC(Me)NC6H3-2,6-i-Pr2) can be obtained by the reactions of LMe2YbCl2(THF)2 with NaOAr'and NaOAr, respectively, in 1:1 molar ratio. Both complexes were characterized by elemental analysis, IR spectroscopy. Complex 6 was further characterized by X-ray diffraction. These monoaryloxo ytterbium chlorides can act as a single-component initiator for ring-opening polymerization ofε-CL in a controlled manner.4. Reactions of LClLi and LClNa with LnCl3 in 2:1 molar ratio gave (LCl)2YbCl(THF) (8) and (LCl)2PrCl(THF) (9), respectively. Both complexes were characterized by elemental analysis, IR spectroscopy. The molecular structure of complex 8 was identified by single crystal X-ray diffraction.5. Reactions ofβ-diketiminato lithium LxLi with LnCl3 in 3:1 molar ratio afforded the complexes (Lx)3Ln (x = Cl, LCl: Ln = Yb (10), Tb (11), Sm (12), Nd (13), Pr (14), La (15); x = H, LH: Ln = Yb (16), Sm (17), Nd (18); x = Me, LMe: Ln = Yb (19), Sm (20), Nd (21); x = F, LF (p-F-C6H4NC(Me)CHC(Me)NC6H4-p-F): Ln = Yb (22), Nd (23)) in good isolated yields. All complexes were characterized by elemental analysis, IR spectroscopy, and 1H NMR spectroscopy for complex 15. The definitive molecular structures of 10, 12-16, 18 and 20-23 were provided by single crystal X-ray diffraction. These homoleptic tris-β-diketiminato-lanthanide complexes are isostructural. All of them have unsolvated monomeric structure with a six-coordinate lanthanide center ligated by six nitrogen atoms of three chelating bidentateβ-diketiminato ligands.6. It was first found that sterically demanding homoleptic tri-β-diketiminato-lanthanide complexes (except ytterbium one) are efficiently single-component initiators for the polymerization of L-LA andε-CL, demonstrating thatβ-diketiminato ligands serve not only as spectators, but also as an active groups in the polymerization of lactones. The reactivity of complexes depends both onβ-diketiminato group and central metal and the active order is Pr > Nd > Sm > Yb for metal and LCl > LH > LMe forβ-diketiminato ligand.7. Homolepticβ-diketiminato-lanthanide complexes in the presence of 2-propanol can initiate controlled polymerization of L-LA with extremely high activity under mild conditions. The terminal group analysis of an oligomer indicated the active species being in-situ generated Ln-alkoxide. 8. The bimetallic lanthanide complexes supported by a phenyl-bridgedβ-ketoimine (p-OC(Me)CHC(Me)N-C6H4-p-NC(Me)CHC(Me)O)H2 (LPhH2 (24)), LPh[Yb(MeCp)2]2 (25) and LPh[Ln(OAr)2(THF)]2 (Ln = Yb (26), Sm (27), Nd (28), La (29)), can be synthesized in high yields by the reactions of Yb(MeCp)3 and Ln(OAr)3 with LPhH2(24) in 2:1 molar ratio, respectively. Mono-β-ketoimine lanthanum complex [C6H5NC(Me)CHC(Me)O]La(OAr)2·THF (30) was prepared by the same reaction withβ-ketoimine. All complexes were characterized by elemental analysis, IR spectroscopy, and 1H NMR spectroscopy for complexes 29 and 30. The phenyl-bridgedβ-ketoimine 24 and complexes 25-27 and 29 were further characterized by X-ray diffraction.9. Complex LPh[Yb(OAr)Cl(THF)]2 (31) was prepaed by the reaction of Ln(OAr)2Cl with LPhH2 in 2:1 molar ratio. Treatment of 31 with two equiv. of NaCp afforded LPh[Yb(OAr)Cp(THF)]2 (32). Complexes 31 and 32 were characterized by elemental analysis, IR spectroscopy, and single crystal X-ray diffraction for 32.10. Preliminary studies revealed that the bimetallic lanthanide complexes supported by phenyl-bridgedβ-ketoimine can initiate effectively the polymerization ofε-CL and L-LA at room temperature, however, the polymerization was out of control.