Zirconium complexes applications

The use of a zirconium complex (dibutylzirconocene, — 78 °C to rt, 2 h) to induce intramolecular co-cyclization of A-methyl-5-azanona-l,8-diene to an intermediate zirconacycle was a key step in a new azepane synthetic route hydrolysis (MeOH, aq. NaHC03) of this intermediate then realized the trans- 1,4,5-trimethylazepane in 75% yield the active reagent for the initial cyclization was zirconocene (1-butene). The overall transformation represents a type d ring construction process <2006SL3439>. This synthetically versatile process is also applicable to aza eneyne and aza diyne precursors as well as benz-fused analogues. 

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. 

Stoichiometric hydroesterification can be carried out using the zirconium complex [(CsHs)2Zr(H)Cl], as described in Section 4.1.S in the context of carboxylic acid synthesis, and, apart from the use of alcoholic rather than aqueous bromine in the rinal cleavage reaction, the same procedure is applicable (equation 33). ... 

Zirconium-aryne complexes have found applications in organic synthesis. For example, treating diallylamine 22 with BuLi and zirconocene(methyl) chloride forms an aryne-zirconium complex that undergoes intramolecular olefin insertion to yield metallacycle 23, and trapping this metallacycle with iodine gives 24, further manipulation of which allows rapid construction of 25, an analogue of the pharmacophore of the antitumour agent CC-1065 [21] (Scheme 4). 

Despite all this work, until the end of the 1990s the only aryne-metal complexes for which synthetic applications had been developed were a few zirconium complexes. The principal drawback of this chemistry was the use of stoichiometric amounts of metal complexes and, as a consequence, its poor atom economy (in both ligands and metals) and high cost. 

The route shown in Fig. 9.12 is one which has been operated commercially in the U.K. on a fairly small scale, quite successfully. As in the case of niobium, it is convenient to use the crude ferro alloy as feed to the chlorination stage. The chloride purification stages lead to pure vanadium trichloride, which is reduced with magnesium in a manner similar to that employed for titanium, zirconium or hafnium. Some of the complexities, applicable in the latter processes owing to the volatile nature of the chlorides, are absent with vanadium. The vanadium metal sponge has some properties in common with the other metal sponges. 

But Alves and co-workers prepared a completely different kind of zirconium alkoxide bulky complexes, 25, which were moderately active in LA ROP (Table 7.2, entry 58-59) [26]. Their investigations showed that di-alkoxide zirconium complex were more active than mono-alkoxide chloro derivative. This difference was attributed to the presence of chlorine atom that withdraws electron from zirconium and lowers the nucleophilicity of Zr-OTr moiety which proved by DFT calculation. As a result, the ROP reaction retarded in which became inactive at room temperature and was needed higher temperature to initiate polymerization. Another versatility of this research was incorporation of Bn Cyclam instead of OPh or SPh to the end of PLA which made biodegradable PLA as an interesting candidate utilizes various biomedical and sensing applications. 

Zirconium. The long half life (78.4 h) of Zr, a positron emitter, is of particular interest to immuno-PET since it can enable the longer reaction times required for radioimmunodiagnostic applications and has been explored for its potential to act as a theranostic pair with and Lu. In 2005 van Dongen et al. chelated Zr to cetuximab via succinylated desferrioxamine B (A-sucDf) with p-benzyl isothiocyanate-l,4,7,10-tetra-azacyclododecane-l,4,7,10-tetraacetic acid (p-SCN-Bz-DOTA) and p-iso-thiocyanatobenzyl diethylenetriaminepentaacetic acid (p-SCN-Bz-DTPA) for comparisons with Lu and (was used in the place of Y). The data showed that the zirconium complexes could accurately predict the lutetium and yttrium biodistribution. Subsequently, van Dongen et al. 

A NEW FAMILY OF ZIRCONIUM COMPLEXES ANCHORED BY DIANIONIC CYCLAM-BASED LIGANDS SYNTHESES, STRUCTURES, AND CATALYTIC APPLICATIONS... 

The extraction of metals by liquid amines has been widely investigated and depends on the formation of anionic complexes of the metals in aqueous solution. Such applications are illustrated by the use of Amberlite LA.l for extraction of zirconium and hafnium from hydrochloric acid solutions, and the use of liquid amines for extraction of uranium from sulphuric acid solutions.42,43... 

In situ densitometry has been the most preferred method for quantitative analysis of substances. The important applications of densitometry in inorganic PLC include the determination of boron in water and soil samples [38], N03 and FefCNfg in molasses [56], Se in food and biological samples [28,30], rare earths in lanthanum, glass, and monazite sand [22], Mg in aluminum alloys [57], metallic complexes in ground water and electroplating waste water [58], and the bromate ion in bread [59]. TLC in combination with in situ fluorometry has been used for the isolation and determination of zirconium in bauxite and almnimun alloys [34]. The chromatographic system was silica gel as the stationary phase and butanol + methanol + HCl -H water -n HF (30 15 30 10 7) as the mobile phase. 

For application in organic synthesis, the regiochemistry of insertion of carbenoids into un-symmetrical zirconacydes needs to be predictable. In the case of insertion into mono- and bicydic zirconacydopentenes where there is an wide variety of metal carbenoids insert selectively into the zirconium—alkyl bond [48,59,86], For more complex systems, the regiocon-trol has only been studied for the insertion of lithium chloroallylides (as in Section 3.3.2) [60]. Representative examples of regiocontrol relating to the insertion of lithium chloroal-lylide are shown in Fig. 3.2. 

Inter- and intramolecular (cyclometallation) reactions of this type have been ob-.served, for instance, with titanium [408,505,683-685], hafnium [411], tantalum [426,686,687], tungsten [418,542], and ruthenium complexes [688], Not only carbene complexes but also imido complexes L M=NR of, e.g., zirconium [689,690], vanadium [691], tantalum [692], or tungsten [693] undergo C-H insertion with unactivated alkanes and arenes. Some illustrative examples are sketched in Figure 3.37. No applications in organic synthesis have yet been found for these mechanistically interesting processes. 

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