Benzamidinate zirconium complexes

In general, Group 4 benzamidinates show poor activities as olefin polymerization catalysts.158-162 However, bis(benzamidinate) complex (52) affords isotactic PP (>95% mmmm) at >7 atm propylene pressure 163 at ambient pressure atactic PP is produced.164 An unsymmetrical tris (benzamidinate) zirconium complex has also been shown to afford highly isotactic PP.165... 

Scheme 1 Synthesis route to the bis(benzamidinate) zirconium complexes 1-4 [41]...

Eisen and coworkers reported one such example of these reeently developed octahedral complexes. Benzamidinate zirconium complexes (1 and 2, Figure 6.1) activated by methylaluminoxane... 

Bis(benzamidinate) zirconium catalysts (Figure 9, complexes F9-1 and F9-2) can polymerize propylene monomers into highly isotactic polypropylene (MAO up to 98% [mmmm, T = A9°C) at 25 °G in CH2CI2 under 9.2atm of propylene monomer, as expected from the G2-symmetric octahedral structure of the catalysts. The polymer-... 

Silica-Supported Bis(benzamidinate) Zirconium Dimethyl Complexes. 80... 

Abstract The synthesis and X-ray structure of various octahedral zirconium complexes and their catalytic properties in the polymerization of a-olefins are described. Benzamidinate, amido, allylic, and phosphinoamide moieties comprise the study ligations. For the benzamidinate complexes, a comparison study between homogeneous and heterogeneous complexes is presented. For the phosphinoamide complex, we show that the dynamic symmetry change of the complex from C2 to C2v allows the formation of elastomeric polymers. By controlling the reaction conditions of the polymerization process, highly stereoregular, elastomeric, or atactic polypropylenes can be produced. The formation of the elastomeric polymers was found to be the result of the epimerization of the last inserted monomer to the polymer chain. 

The N,AT-bis(trimethylsilyl)benzarnidinate zirconium dichloride complexes [rj2-4-RC6H4C(NSiMe3)2]2ZrCl2 (R=H (1) or CH3 (2)) were prepared by the reaction of ZrCl4 with two equivalents of bis(trimethylsilyl)benzamidinate lithium-TMEDA (TMEDA=AT,iV,iV/,iV/-tetramethylenediamine) at room temperature in toluene yielding, after removal of the TMEDA and crystallization, 83-89% of pale yellow analytically pure rhombohedral crystals of 1 and 2 (Scheme 1) [31,33]. These complexes were also obtained in a high quality form... 

It is important to point out that the zirconium benzamidinate complexes 1 and 5 have lower catalytic activity in the a-olefin polymerizations than the corresponding metallocene systems (lxlO7 and 6xl06 g polymer-mol Zr -h 1 for ethylene and propylene, respectively [70]). The difference in activity can be rationalized by the structural environment of the metal (Zr) center. In the metallocenes, the cone angle is normally the key feature for unsaturation, whereas in the octahedral complexes the groups at the N-moiety may induce an electronic unsaturation at the metal center. Thus, the lower polymerization activities of the complexes 1 and 5 may be a consequence of the partial saturation at the metal orbitals as compared to the metallocenes [71-73]. 

Salt metathesis was employed to synthesize half-sandwich zirconium and hafnium dichloride complexes 331 incorporating the bidentate, mono-anionic benzamidinate ligand (Equation (26)). The corresponding zirconium dimethyl and dibenzyl complexes have also been prepared using appropriate alkylating reagents.260 The zirconium dichloride complex (R= H), upon activation with MAO, are active for both polymerizations of ethylene... 

Transfer to A1 was reported to be operative with several non-metallocene catalysts. It is the only chain-release mechanism operative with the diamido complexes MCl2 ArN(CH2) NAr catalysts, as well as with the mono-and tris(benzamidinate) catalysts, since no olefinic resonances were observed in the H or 13C NMR spectra of these polymers.275 276 This chain-release reaction is also dominant with bis(phenoxy-imine)zirconium cat-... 

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