Hydrolysis zirconium complexes

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. 

All of the members of the final review team contributed, if not text, then comments to all of the chapters of the book. Their primary responsibilities for the different sections/chapters were divided as follows. Paul Brown prepared the introduction, and the sections on elemental zirconium, the zirconyl ion, the gaseous zirconium oxides, zirconium hydride, the halogen compounds and complexes, the chalcogen compounds and complexes, the Group 15 compounds and complexes, zirconium carbides and silicates. He was assisted by Christian Ekberg in the interpretation of aqueous zirconium complexes in these sections. Some initial work was done by Ken Jackson on the zirconium sulphate, nitrate and phosphate compounds and complexes. Bernd Grambow was responsible for the drafting of the sections on zirconium hydrolysis, the ion and the section on crystalline and amorphous zirconium oxides. Enzo Curti drafted the section on the zirconium carbonates. 

The extremely complicated aqueous solution chemistry of and HP has been reviewed by Larsen, Solovkin and Tsvetkova,and Clearfield. Zirconium(IV) and hafnium(IV) ions undergo extensive hydrolysis, and the predominant solution species are polynuclear, even in dilute (>10 -10 M) solutions of high acidity (1-2 M). Spectrophotometric, " ultracentrifugation, " and light scattering studies point to trinuclear and tetranuclear hydrolysis products complexes such as [M3(OH)4] and [M4(OH)8] have been suggested. ITie mononuclear ions are predominant solution species only at trace metal ion... 

Berkessel, A. Herault, D.A. Discovery of peptide-zirconium complexes that mediate phosphate hydrolysis by batch screening of a combinatorial undecapeptide library. Angew. Chem., Int. Ed. Engl. 1999, 38 (1/2), 102-105. 

Hydrolysis of complexes of the type MFe is catalysed not only by acid but also by a series of metal ions. Kinetic data have been obtained for catalysis of hydrolysis of PFe, AsFg", AsFgCOH)- and also of BF4-, by beryllium(ii), aluminium(iii), zirconium(iv), and thorium(rv). Again this may be seen as an extension of studies on cation catalysis of hydrolysis of transition-metal complexes, e.g. the numerous studies of mercury(ii)-catalysed aquations of cobalt(iii)-ammine-halide complexes, or the recent study of metal ion catalysis of chloro(ethylenediaminetriacetato)-cobaltate(m). ... 

Zirconium complexes of dienes react with carbon dioxide to give metallacycles, which also undergo reaction with another equivalent of carbon dioxide to give dicarboxylic acids after hydrolysis" . Oxidative coupling of dienes with carbon dioxide is also observed using nickel (o) catalysts" . 

Zirconium [7440-67-7] is classified ia subgroup IVB of the periodic table with its sister metallic elements titanium and hafnium. Zirconium forms a very stable oxide. The principal valence state of zirconium is +4, its only stable valence in aqueous solutions. The naturally occurring isotopes are given in Table 1. Zirconium compounds commonly exhibit coordinations of 6, 7, and 8. The aqueous chemistry of zirconium is characterized by the high degree of hydrolysis, the formation of polymeric species, and the multitude of complex ions that can be formed. 

Zirconium hydrides undergo 1,2-addition with 1,3-dienes to give y,5-unsaturated complexes in 80—90% yield. Treatment of these complexes with CO at 20°C and 345 kPa (50 psi) followed by hydrolysis gives y,5-unsaturated aldehydes (235). 

In related studies, Cp2ZrCl2 has been found to catalyze at room temperature an aluminum hydride (i-Bu2AlH) reduction of CO to linear Ci-C5 alcohols (430). The system involves reaction of complex 55 with CO, which precipitates the starting zirconium(IV) complex and leaves a yellow solution, that on hydrolysis yields the alcohols. Toluene solutions of Cp2Ti(CO)2 complex under H2/CO effect Eq.(69), i.e., a homogeneous stoichiometric hydrogenation of carbon monoxide to methane (426). 

Sequences 246 and 249 were tested for their ability to catalyze hydrolysis while in solution rather than while attached to a support. The Zr4 complex of sequence 246 was found to catalyze the hydrolysis of phosphate ester 243b five times faster than the complex of peptide 249. Since the control complex 249 does not catalyze hydrolysis it appears that the small amount of catalysis that was observed was due to free zirconium metal (Scheme 29). 

Reaction of tris(neopentyl) complexes of titanium, zirconium and hafnium with molecular oxygen furnishes the corresponding tris(neopentoxy) complexes [42, 43, 51]. A peroxo complex is an intermediate in this reaction, being relatively stable in the case of titanium [42]. The alkoxide species can also be formed upon reaction with alcohols under mild conditions [42, 52]. The alcoholysis reaction is fast, with a low dependence on the steric hindrance of the alkyl chain [42]. Hydrolysis leads to ](=SiO)M(OH)3] or ](=SiO)2M(OH)2], depending on the precursor species. Deu-... 

Because K2HfF6 is —1.7 times more soluble in water than K2ZrF6,528 zirconium and hafnium can be separated by fractional crystallization of the hexafluorometallates. This approach is used on an industrial scale in the USSR.286 Conductance measurements on aqueous solutions of M2MF6 (M = K, Rb, or Cs) indicate very little hydrolysis of the [MF6]2- ions.529 Alkaline hydrolysis of potassium and ammonium fluorozirconates yields crystalline M ZrF3(0H)2-H20 complexes, which are easily dehydrated to M ZrF3(OH)2. 

The complications which result from the hydrolysis of alkali metal cyanides in aqueous media may be avoided by the use of non-aqueous solvents. The one most often employed is liquid ammonia, in which derivatives of some of the lanthanides and of titanium(III) may be obtained from the metal halides and cyanide.13 By addition of potassium as reductant, complexes of cobalt(O), nickel(O), titanium(II) and titanium(III) may be prepared and a complex of zirconium(0) has been obtained in a remarkable disproportion of zirconium(III) into zirconium(IV) and zirconium(0).14 Other solvents which have been shown to be suitable for halide-cyanide exchange reactions include ethanol, methanol, tetrahydrofuran, dimethyl sulfoxide and dimethylformamide. With their aid, species of different stoichiometry from those isolated from aqueous media can sometimes be made [Hg(CN)3], for example, is obtained as its cesium salt form CsF, KCN and Hg(CN)2 in ethanol.15... 

As was observed in the case of the extraction of zirconium and hafnium from nitrate media, it is probable that the different tendencies of the metals towards hydrolysis has some effect on the selectivity observed,298 313 expecially in view of the proved extraction of hydroxo complexes. The extraction of both metals decreases markedly in the presence of sulfate ions in the aqueous phase (a feature that is utilized in the stripping of the loaded hafnium with sulfuric acid), although the selectivity for hafnium over zirconium is simultaneously increased on account of the higher stability constants of the inextractable sulfato complexes of zirconium.298... 

No formation of bimetallic complexes is observed on MoO(OPr )4 dissolution in the alcohol solutions of zirconium isopropoxide, due presumably to the high stability of the structure of the latter. A very unusual complex of Zr3Mo,024(OPri)12( PrOH)4 composition precipitates slowly from solutions of isopropoxides in hexane subjected in advance to evacuation to dryness and redissolution repeated three times. The structure of the complex obtained is very close to that of the zirconium methoxide hydrolysis product, Zr O OMe) (Fig. 5.1 c) [901]. The formation of a complex very rich in oxoligands is presumably due to the trend of ZrCOPhV PrOH to form oxocomplexes on desolvation (see Section 12.12). 

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