Zirconium complexes structure

The crystal structure of a mono(cyclopentadienyl)zirconium complex containing a novel Me2Si-linked bis(amidinate) ligand was reported (Scheme 203). In this compound the central Zr atom is octahedrally coordinated with the bis(amidi-nate) acting as a tridentate ligand. ... 

Perhaps chemists will be able to mimic nature without duplicating the iron-sulfur-molybdenum structure. For example, a zirconium complex with tetramethyl cyclopentadiene can bind dinitrogen in a manner that breaks the NON bond, as shown below. Treatment with hydrogen gas results in formation of small amounts of ammonia. Although the yields are too low to make this a viable commercial process, researchers hope to make the process more efficient through chemical modifications and changes in conditions. 

Tetraalkoxy zirconium complexes have been employed to improve the quality of rubber, but details of their structures do not seem to be available.20... 

Fig. 17. Molecular structure of the dipolar trimethylphosphine zirconium complex 132.

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. 

Previously, we synthesized and studied various Group 4 complexes with different ligations as alternatives to the cyclopentadienyl ligand. Here we present an overview of the synthesis, structure, and catalytic properties in the polymerization of a-olefins of several zirconium octahedral complexes. We show how the stereoregular polymerization of a-olefins using these octahedral zirconium complexes can be modulated by pressure. These results raise conceptual questions regarding the general applicability of ds-octahedral C2-sym-metry complexes to the stereospecific polymerization of a-olefins. 

Three types of elastomeric polypropylene are known (1) a large molecular weight atactic polymer [125], (2) polymers with alternating isotactic and atactic blocks [108,109,126-129], and (3) polymers formed by the dual-site mechanism [110]. The structure of the obtained elastomeric polypropylene was elucidated by comparison of the 13C-NMR spectra with those of an atactic oily polymer and isotactic polypropylene prepared by the zirconium complex 4. On the basis of the NMR data, for all the samples the statistical lengths of the isotactic blocks between two neighboring epimerization stereodefects were calculated [41]. It was found that for the isotactic polymer 90%), the... 

Figure 7 Molecular structure of bridged 1,2-thloborolyl zirconium complex 116 from X-ray crystallographic data.

Theopold et al. reported the first structural characterization of a phospho-lide. It was obtained through lithium cleavage of a P-chlorophosphole (prepared in turn by transmetallation of a Fagan-Nugent zirconium complex with PC13) and crystallized from TMEDA-ether as [LiTMEDA(PC4Me4)] 4 (Eq. 10) [8] ... 

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