Syntheses And Catalytic Activities Of New Rare-Earth Metal Alkyl Complexes

Rare-earth metal alkyl complexes have received a great attention as they provide highly reactive Ln-C (σ) bonds, which can undergo various transformations. However, these complexes are difficult to synthesize due to their instability. This dissertation mainly focused on the syntheses, structures and catalytic activities of rare-earth metal alkyl complexes supported by indenyl and tridentate nitrogen ligands.1. Reactions of 1,3-bis(trimethylsilyl)indene with Ln(CH2SiMe3)3(THF)2 gave half-sandwich rare-earth metal complexes (1,3-(SiMe3)2C9H5)Ln(CH2SiMe3)2(THF) (Ln= Sc, Y, Lu, Dy). These complexes were characterized by single crystal X-ray diffraction, which showed theη5 hapticity of indenyl ligands in all of the complexes. The catalytic behaviors of the complexes for intramolecular hydroamination of aminoalkenes were investigated. The catalytic activity increased with increasing of the metal ion size, and the Y and Dy complexes showed excellent activities to a variety of aminoalkenes.2. By using a series of indene with silyl substitutes as ligand precursors, eight mono(indenyl) Sc dialkyl complexes were prepared via the alkane elimination reactions. Upon activation with [Ph3C][B(C6F5)4], these complexes showed good activities for the styrene polymerization. However, the study on mono(indenyl) Sc dialkyl/[Ph3C][B(C6F5)4] systems disclosed that [Ph3C][B(C6F5)4] abstract aπ-bonded indenyl ligand rather than aσalkyl ligand. The abstraction pathway is influenced by the substituents on the indenyl ligands, and can be controlled by employing different indenyl ligands. For the styrene polymerization, two abstraction pathways, alkyl abstraction and indenyl abstraction, result in syndiospecific and aspecific styrene polymerization, respectively. The addition of AIR3 to (1,3-(SiMe3)2C9H5)Sc(CH2SiMe3)2(THF)/[Ph3C][B(C6F5)4] system can greatly promote the activities for ethylene polymerization and copolymerization of ethylene with various a olefins.3. Three new tridentate NNN ligands were synthesized and subsequent metalations with in situ generated Ln(CH2SiMe3)3(THF)n (Ln= Nd, Sm, Y and Lu) provided six solvent-free dialkyl rare-earth metal complexes. Five of the rare-earth metal complexes were characterized by single crystal X-ray diffraction, which showed that the pendant arm bonds to the metal ion in the solid states. The NMR spectrum of these complexes in C6D6 showed such coordination interaction is retained in the solution. These dialkyl rare-earth complexes show high activities for the ring-opening polymerization of s-caprolactone, in which narrow polydispersity polymers were produced. The size of the pendant arm has a significant effect on the molecular weight of the polymer obtained.4. A newβ-diketimine bearing the pendant pyridyl group was synthesized. The reaction of it with one equivalent of Sc(CH2SiMe3)3(THF)2 at room temperature gave a singly deprotonated product. Y(CH2SiMe3)3(THF)2 under the same conditions led to the unexpected dimer, in which the ligand precursor was triply deprotonated. The reaction of it with Y(CH2SiMe3)3(THF)2 at-35℃provided a mixture of singly deprotonated product and doubly deprotonated product. The reactions of this newβ-diketimine with Ln[N(SiMe3)2]3 (Ln=Y, La) at room temperature gave only singly deprotonated products. Five of the complexes have been characterized by single crystal X-ray diffraction.5. A series of magnesium, zinc, and calcium monoalkyl or monoamide complexes containing tridentate nitrogen ligands have been synthesized, and six of which were characterized by single crystal X-ray diffraction. The X-ray diffraction results show that the metal complexes are all solvent-free monomers and the pendant arm bonds to the metal ion. These metal complexes are highly active for the ring-opening polymerization of rac-lactide and give preference for heterotactic polylactide.