Synthesis And Characterization Of Lanthanocene Amide Complexes And Their Catalytic Behavior

Three neutral lanthanocene amides and three anionic lanthanocene amides supported by two methylcyclopentadienyl groups were synthesized. The catalytic activity of these complexes for addition of amines to nitriles, guanylation of amines with carbodiimides, amidation of aldehydes with amines, polymerization of methyl methacrylate and polymerization ofε-caprolactone and lactide were tested. The catalytic activity of neutral lanthanocene amides was compared with that of the ytterbium amide complex supported by a bridged bis(amidinate) ligand. Moreover, The catalytic activity of anionic lanthanocene amides for the above mentioned reactions was examined to compare with those of the corresponding neutral lanthanocene amides.1. Reactions of (CH₃C₅H₄)₂LnCl with NaNH(2,6-Me₂C₆H₃) or NaNH(2,6-iPr₂C₆H₃) in 1 : 1 molar ratio in THF respectively afforded the amide complexes (CH₃C₅H₄)₂LnNHAr(THF) [(Ar = 2,6-Me₂C₆H₃, Ln = Yb (1), Y (3); Ar = 2,6-iPr₂C₆H₃, Ln = Yb (2)]. These complexes were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. X-ray crystal structure determination revealed that complexes 1-3 are isostructural. The central metal in each complex coordinated to two methylcyclopentadienyl groups, one amide group and one oxygen atom from THF to form a distorted tetrahedron. The coordination number of central metal for each complex is eight.2. Reaction of (CH₃C₅H₄)₂LnCl with NaNH(2,6-Me₂C₆H₃) in 1 : 2 molar ratio in THF afforded the anionic amide complexes [(MeC₅H₄)₂Ln(NH(2,6-Me₂C₆H₃))₂][Na(DME)₃] {Ln = Pr (4), Yb (5), Y (6)}. X-ray crystal structure determination revealed that these compounds were made up of cationic portion and anionic portion. The central metal in each complex coordinated to two methylcyclopentadienyl groups and two amide groups to form a distorted tetrahedron in anionic portion. The Na atom coordinated to three DME solvent molecule in cationic portion.3. Complexes 1-3 were found to be efficient catalysts for addition of amines to nitriles to give the monosubstituted N-arylamidines, the systems have the advantage of tolerance to various substrates. Reactions of aromatic nitriles, except o-methoxybenzonitrile and 4-cyanopyridine, with primary aromatic amines proceed smoothly. The catalytic activity of complex 2 was compared with those of Yb[N(SiMe₃)₂]₃(μ-Cl)Li(THF)₃ and ytterbium amide supported by a bridged bis(amidinate) ligand. The influence of central metals and amide groups on the activity of amide complexes was observed. In view of the selectivity, the lanthanocene amide and ytterbium amide supported by a bridged bis(amidinate) ligand are better than Yb[N(SiMe₃)₂]₃(μ-Cl)Li(THF)₃. In view of the activity, the active order is complex with a bridged bis(amidinate) ligand > complex 2 > Yb[N(SiMe₃)₂]₃(μ-Cl)Li(THF)₃.4. The lanthanocene amides could catalyze the guanylation of amines with carbodiimides. However, their activity is lower than that of amide complex with a bridged bis(amidinate) ligand.5. The lanthanocene amides exhibit highly catalytic activity in the polymerization of methyl methacrylate. The reactions can be carried out over a quite broad range of polymerization temperatures from -45℃to 60℃. The catalytic activity of these complexes decreases with an increase of ionic radii of the metal elements. The complex with less amide group exhibits higher activity. 1H NMR spectra of PMMA revealed that tacticity of PMMA is mainly syndiotactic. The lanthanocene amides show much higher activity than the amide complex with a bridged bis(amidinate) ligand.6. The lanthanocene amides could catalyze the polymerization ofε-caprolactone or lactide,but their catalytic activity is low. The amide complex with a bridged bis(amidinate) ligand shows much higher activity than the lanthanocene amides in the polymerization ofε-caprolactone or lactide, respectively.7. The anionic lanthanocene amides exhibit extremely high catalytic activity in the polymerization of methyl methacrylate. The reaction can be carried out in a wide range of polymerization temperatures from 0℃to 40℃. Effects of polymerization time, polymerization temperature, solvent on the polymerization were examined. It was found that the polymerizations initiated by the anionic lanthanocene amide proceeded in a living fashion. ¹H NMR spectra of PMMA revealed that the resulting PMMA is syndiotactic rich polymer. The anionic lanthanocene amides show higher activity than the neutral lanthanocene amides.8. The anionic lanthanocene amides exhibit almost the same activity as the neutral lanthanocene amides in amidation of aldehydes with amines.