Zirconium complex formation

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. 

There are a few values in the literature relating to the cations Zr " " and Ge. In the zirconium case log Ki and log K2 values are reported for formation of quercetin complexes, but as these were obtained in 0.5 M HCl these values may well apply to ternary chloride-containing species (225). Equilibrium constants have been determined for reaction of two or of three maltol ligands with Ge(0H)4 (149), but these values are not comparable with values in the Tables elsewhere in this section, since these all refer to complex formation from aqua-cations or oxoaqua-cations. 

Figure 18.5 Formation of an isotactic-atactic polypropylene copolymer from a bis(phenylindenyl)zirconium complex.

The use of titanium and zirconium complexes as electron shuttles to transfer electrons from excess aluminum present in the reaction solution to the fluorinated substrate has been described,210 e.g. formation of perfluoronaphthalene from perfluorodecahydronaphthalene. 

In systems completely free of chloride, complex formation between the titanium or zirconium compound and the trialkylaluminum was not detected by either NMR or UV spectroscopy 191), or by cryoscopy (189). Such systems were thus assumed to be inactive for polymerization. However, NMR-spectroscopic studies in the presence of ethylene revealed a weak but lasting insertion of ethylene, with formation of polyethylene. 

C to form the dinuclear (butadienyl)zirconium system 120. Treatment with B(C6F5)3 leads to the formation of a mono-addition product (121), even in the presence of excess borane. Complex 121 (Scheme 40) shows only a marginal ethene polymerization activity. This led to the notion that such formation of dimeric zirconium complexes might represent desactivation pathways in homogeneous Ziegler-Natta catalyst chemistry.125... 

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. 

Using deuterium in place of hydre en, CD4 is produced. Tliis liydrc cnaiion has features in common with the stoichiometric work by Bercaw using zirconium complexes (17)- The driving force for these deoxygenation reactions may be the formation of metal oxides. 

A zirconium complex of the wigra-octaethylporphyrinogen ligand reacts with KH to yield a polynuclear hydride. When the reaction is performed in a 1 1 KH Zr ratio, a dinuclear complex is observed. Using a 2 1 KH Zr ratio under rigoronsly controlled reaction conditions leads to the formation of a polynuclear species. In the dinuclear complex, each Zr atom is... 

Recently one of the solutions to overcome this problem has been proposed.This does concern surface modification of the pyrochlore-based oxide.s. It is known that cerium and zirconium chlorides provide vapor phase complexes with aluminum chloride at elevated temperatures.The new surface modification technique utilizes the formation of these vapor complexes to remove and modify the top surface of the pyrochlore ceria-zirconia solid solution. This method is named "chemical filing". Application of the above complexes formation has already been demonstrated for the vapor phase extraction and mutual separation of rare earths based on the so-called chemical vapor transport (CVT). ... 

C-N chelation has also been observed for the titanium and zirconium complexes (68), (69), and (70). These compounds belong to the class of the sterically hindered phosphoraniminato complexes, and exhibit modest catalytic activity in ethene polymerization. The complex formation is reflected by the elongation of the NP bond length, 163.1(3) pm in (70) versus 156.2(1) pm in the free ligand... 

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