Zirconium pyridines

Other applications of zirconium tetrafluoride are in molten salt reactor experiments as a catalyst for the fluorination of chloroacetone to chlorofluoroacetone (17,18) as a catalyst for olefin polymerization (19) as a catalyst for the conversion of a mixture of formaldehyde, acetaldehyde, and ammonia (in the ratio of 1 1 3 3) to pyridine (20) as an inhibitor for the combustion of NH CIO (21) in rechargeable electrochemical cells (22) and in dental applications (23) (see Dentalmaterials). 

In this process, catalysts, such as boric acid, molybdenum oxide, zirconium, and titanium tetrachloride or ammonium molybdate, are used to accelerate the reaction. The synthesis is either carried out in a solvent (aUphatic hydrocarbon, trichlorobenzene, quinoline, pyridine, glycols, or alcohols) at approximately 200°C or without a solvent at 300°C (51,52). 

The coordination chemistry of ancillary amidinate ligands with a pyridine functionality has been described. Magnesium, aluminum, zirconium, and lanthanum complexes have been prepared in which the amidinate anions act as tridentate, six-electron-donor ligands Amidinate ligands containing quinolyl substituents were constructed in the coordination sphere of lanthanide... 

In the case of the allyl compounds, displacement of the allyl group seems to be required. Thus the reaction of Zr(allyl)4 with pyridine follows a fundamentally different course to the corresponding benzyl compound. In this instance the reaction is irreversible, and an allyl group is displaced to give a trivalent zirconium compound (9) as shown by the equation... 

The structure and nature of acidity of sulphated zirconia has been recently investigated (ref. 8-10). Untreated zirconium hydroxide which is amorphous, crystallises 1n the monoclinic form at 350°C. On the contrary, the sulphate treated zirconium hydroxide crystallises at higher temperature (500ooC) into tetragonal form, which has significantly greater surface area as compared to the monoclinic zirconia. The infra red spectra of absorbed pyridine indicate presence of only coordinatively bonded pyridine and not the protonated pyridine implying that the zirconia is predominantly of Lewis... 

Bis(arene)zirconium complexes, characteristics, 4, 697 Bis(arylamido)pyridines, with Hf(IV), 4, 792 Bis(aryl) bridges, in complexes with chromium(VI), 5, 346... 

The generation of an unsymmetrical titaniumcyclopentadiene from different acetylenes can then be subjected to a [4+2] cycloaddition with a sulfonylnitrile to form an intermediate complex which collapses under acidic conditions to yield substituted pyridines (Scheme 60 Table 2) <2002JA3518>. A similar reaction using zirconium has been reported <2002JA5059>. 

A variety of new ligand designs and ligand combinations were used in attempts to mimic some properties of the ubiquitous bent metallocene environment at the early metal centers consequently, some of these systems were used in the further development of butadiene zirconium chemistry. The pyridine based chelate zirconium dichloride complex 43 cleanly formed the butadiene complex 44 upon treatment with butadiene-magnesium. Its structure shows that the C4H6 is arranged perpendicular to the chelate ligand plane. Complex 44 inserts one equivalent of an alkene or alkyne to form the metallacyclic 7i-allyl system 4545 (Scheme 13). 

Addition of thiocyanate ions to chloride or perchlorate solntions of zirconium and hafnium yields complexes containing from one to eight isothiocyanate groups per metal atom. These systems are of interest because of the importance of thiocyanate complexes in the extraction and separation of the elements. IR spectroscopy indicates that M-N bonds are present in the violet (Zr) and pink (Hf) complexes [NEt4]2[M(NCS)6] analogous complexes have been obtained with alkali metal cations. In the presence of pyridine, the dodecahedral Zr(bipy)2(NCS)4 complex is produced see Ammonia N-donor Ligands). 

Terminal chalcogenido zirconium complexes (23) are conveniently synthesized by the reactions of dicarbonylzir-conocene with either N2O or the elemental chalcogens (S, Se, Te) see Chalcogens) in the presence of pyridine. The Zr=E bond in these complexes is highly reactive and leads to a variety of 1,2-addition and cycloaddition reactions (Scheme 8). ... 

Incompatible with ethanol, ethanol + butadiene, ethanol + phosphorus, ethanol + methanol + HgO, formamide + pyridine + sulfur trioxide, formamide, halogens or interhalogens (e.g., chlorine), mercuric oxide, metals (e.g., aluminum, lithium, magnesium), metal carbides (e.g., lithium carbide, zirconium carbide), oxygen, pyridine, sodium hydride, sulfides. 

The acidity of pillared clays has been characterized by both microcalorimetric measurements of the adsorphon of aromatic molecules and pyridine and the catalytic ethylbenzene test reaction [111]. The aromatic probe molecules used were a reactant and a product of the catalytic reaction ethylbenzene and m-diethylben-zene, respectively. In this way, only the strongest of the accessible acid sites were htrated. The heats of adsorphon of these molecules indicate that a zirconium oxide pillared clay had stronger acidity than an aluminum oxide pillared clay, whereas the pyridine results were equal for both samples. 

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