Synthesis And Characterization Of Titanium And Zirconium Complexes With Novel β-Diketiminato Derivative Dianionic Ligands

Since Ziegler-Natta catalyst was developed in 1950s, many academic and industrial research laboratories have engaged in the design and synthesis of organometallic olefin polymerization catalysts with the aim to obtain high-performance polyolefins. During the 1980s and 1990s, metallocene olefin polymerization catalysts have been extensively and thoroughly investigated. In recent years, there was a tendency to explore non-metallocene catalysts, among the "non-Cp" type ligands,β-diketiminato ligands are one of the most promising ligand families. The precursors for these ligands can be readily prepared by condensation ofβ-diketones with amines. The steric and electronic properties of these ligands can be easily tuned by an appropriate choice ofβ-diketone and amine. On considering both steric and electronic properties of theβ-diketiminato ligands, we have designed and synthesized a series of tridentate dianionic NNN ligands and a series of bidentate monoanionic NN ligands, and have prepared the corresponding titanium and zirconium metal complexes, which will be applied for the olefin polymerization.In the first part, we described three main stages of the development of the transition metal polyolefin catalyst, especially that of non-metallocene titanium and zirconium olefin polymerization catalysts, and illustrated our design in the ligands and metal complexes.In the second part, six new tridentate nitrogen ligand precursors H₂L1～6 (compounds 9～12 and 15～16) was synthesized, subsequent metallation of ligand precursors 10,11 and 12 with 2 equivs of n-BuLi afforded dilithium derivatives LLi₂(THF)_n (compounds 10a～12a). The dilithium salts reacted with TiCl₄·2THF (or TiCl₄) or ZrCl₄·2THF to afford six corresponding titanium or zirconium metal complexes (10b, 10c, 11b, 11c, 12b and 12d). Zirconium metal complexes 10c and 11c, which both containing a coordinated THF, were converted into the corresponding THF-free complexes 10d and 11d by removal of the THF in vacuo. These eight complexes were characterized by NMR spectrum and elemental analysis. Single crystals of the complexes (10c, 10d and 12b) were obtained from their toluene solution and characterized by single crystal X-ray diffraction. The results revealed that the ligands serve as tridentate dianionic donors, and double chlorine ions also coordinate to the metal center. In addition, a class of bidentate nitrogen ligand precursors HL1～4(25～28) were synthesized.