The New Type Of Bridging Imidazole Cyclopentadienyl Ligand And Ivb Family Synthesis And Characterization Of A Single Metallocene Complexes

In recent decades, the development of metallocene-type catalysts had an enormous bearing upon the industrial and theoretical chemistry of polymers. The Group 4 transition metal complexes that are the target compounds of this current investigation relate to the so-called Constrained-Geometry-Catalysts (CGCs) family. CGCs, a comparatively new class of catalysts for homogeneous polymerization and co-polymerization of olefins, exhibit the unique catalytic activity in co-polymerizations of ethylene withα-olefins due to their specific structural and electronic features. Thus, even on the background of somewhat "cooling" of the attention paid to the "classical" metallocene catalysts, academic and commercial interest towards CGCs still remains high, if not enormous.CGCs that have received much commercial attention are the ansa-monocyclopentadienyl-amido (CpA) Group 4 catalysts developed concurrently by Dow and Exxon. Although the imidazole-containing complexes exhibited a set of unique structural features and properties in organic synthesis and polymerization reactions, few literature sources refer to the Group 4 cyclopentadienyl complexes with imidazole-type moieties as the second ligand. Therefore, synthetic approach to three novel Cp-(C₂-link)-(2-imidazolyl) ligands, their dilithium salts and corresponding Group 4 transition metal complexes were developed in this investigation. All compounds within this research work were adequately characterized by ¹H NMR, ¹³C NMR, GC-MS, elemental and X-ray diffraction analyses (the last three methods were applied where appropriate).The tactics of the general procedure was based on the novel key compound, (1-diethoxymethyl)-2-methylimidazole (1). Compounds 4a-c were generated by a reaction of lithiated 1 with corresponding fulvene followed by acidic hydrolysis under mild conditions. In their protic forms, all of them present mixtures of isomers on the relative positions of the hydrocarbyl subsituent and the system of the double bonds in the Cp-ring (¹H NMR and ¹³C NMR spectral data).Subsequent metallation of compounds 4a-c with 2 equivs of n-BuLi afforded dilithium derivatives 5a-c as extremely air and moisture sensitive colorless to pale yellow crystalline solids. For performance of the subsequent reactions with TiCl₄, dilithium salts 5a and 5c were intermediately converted into the bis(trimethylsilyl) derivatives 6a and 6c.On the basis of the "organic" part of this study, Ti(IV) monocyclopentadienyl amido-dichloro complexes 7a and 7c were prepared. Application of silylated derivatives 6 advantageously simplified the isolation procedure. Preparation of Zr(IV) analogues (dichlorides) met more problems. Thus, purification of them from LiCl was difficult (if possible at all) due to their extremely low solubility even in THF. To destroy coordination polymer of 8, treatment with 3 or 2 equivs. of MeLi in ether was applied, that resulted in formation of monomeric tri- and dimethyl complexes 9a and 9b (respectively). Their structures were established by means on ¹H and ¹⁴C NMR spectroscopy.