Zirconium complexes isolated, preparation

Codimers with alkynes can also be obtained from 1,2-diphenylcyclopropene when the trimethylphosphane-stabilized metallocene complexes 20 (M = Ti, Zr) of this cyclopropene derivative are used as substrates. The titanocene complex is prepared from bis(>/ -cyclopen-tadienyl)bis(trimethylphosphane)titanium (18), while the zirconocene complex is most conveniently formed from (f7 -but-l-ene)bis(f7 -cyclopentadienyl)(trimethylphosphane)zirconium (19) via a substitution reaction of the butene ligand. When 20 (M = Ti) is reacted with but-2-yne, the titanacycle 21 can be isolated as blue crystals in 71% yield. The zirconacycle 21 (M = Zr) is obtained in 78% yield as an orange powder. ... 

Chmura et al. also prepared air and moisture resistant chiral imino phenoxide complexes of zirconium and titanium, 14 [16]. They envisioned to study the effect of supporting ligand chirality on the stereoselectivity of LA ROP reaction. But at the end, they did not gain acceptable evidence enable to support any relationship. They showed that all isolated polymers had similar and moderate heterotactic microstructure which implied simple chain end control mechanism and resulted to the selective racemic enchainment during the propagation process. First, they investigate polymerization in toluene at 80°C and ambient temperature in which titanium complexes were absolutely inactive and zirconium coxmterparts showed moderate activity after 2 and 24 hours, respectively. Then they checked out solvent free conditions at 130°C and received almost complete conversion after 30 minutes for both titanium and zirconium alkoxide complexes (Table 7.2, entry 33-36). In this condition, titanium coxmterpart, in contrast to zirconium, resulted to full atactic polymer. Their investigation also showed that zirconium complex retained its activity in moisture or with lactic acid impurity in crude monomer which is deleterious for most metal alkoxide catalysts. 

Manriquez JM, Bercow JE (1974) Preparation of a dinitrogen complex of bis(pentamethyl-cyclopentadienyl)zirconium(II). Isolation and protonation leading to stoichiometric reduction of dinitrogen to hydrazine. J Am Chem Soc %(19) 6229-6230... 

Like zirconium, the first fully characterized carbonyl complex of hafnium was reported in 1976 by Thomas and Brown (6). This complex, bis(i7-cyclopentadienyl)dicarbonylhafnium (3) was prepared via the reductive carbonylation of Cp2HfCl2 using sodium amalgam. While the reaction proceeded to give a moderate yield of 3 (30%), this corresponded to only 60 mg of isolated product. 

No zirconium(III) complexes with oxygen donor ligands have been isolated. However, the electronic absorption spectra of aqueous solutions of Zrl3 have been interpreted in terms of the formation of aqua complexes (equation 4).29 The spectrum of a freshly prepared solution of Zrl3 exhibits a band at 24 400 cm-1, which decays over a period of 40 minutes, and a shoulder at 22000 cm-1, which decays more rapidly. The 24400 cm-1 band has been assigned to [Zr(H20)6]3+, and the 22000 cm-1 shoulder has been attributed to an unstable intermediate iodo-aqua complex. If it is assumed that the absorption band of [Zr(H20)6]3+ is due to the 2T 2Ee ligand-field transition, the value of A is 24 400 cm. This corresponds to a A value of 20 300 cm-1 for [Ti(H20)6]3+ 30 and 17 400 cm-1 for the octahedral ZrCl6 chromophore in zirconium(III) chloride.25... 

A variety of peroxo and hydroperoxo complexes of zirconium(IV) and hafnium(IV) have been isolated from aqueous or aqueous methanolic hydrogen peroxide solutions that contain additional ligands such as sulfate, oxalate or fluoride. Examples of recently reported complexes are listed in Table 8 along with characteristic vibrational frequencies and the pH employed in the aqueous preparations. Earlier work on peroxo compounds has been reviewed by Connor and Ebsworth180 and by Larsen.5... 

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... 

The yellow crystalline half-sandwich 38 was prepared in 81% yield from the tricyclic zirconium species 37 upon treatment with the dioxane complex of germanium dichloride in tetrahydrofuran (THF) at 70 °C for 48 h. lodination of 38 in toluene at —30 °C led to the immediate disappearence of the purple color. After stirring for 18 h at 25 °C the tricyclic cage compound 39 was formed quantitatively according to nuclear magnetic resonance (NMR) spectra. Due to its excellent solubility the isolated yield dropped to only 21% (Scheme 14) <20030M2891>. 

In general, isolable zirconium and hafnium alkene complexes are rare, as they typically undergo carbon-carbon coupling reactions with additional olefin to yield metallacyclopentanes. Addition of an exogenous donor ligand is a common strategy for stabilizing alkene complexes. Several classes of these compounds have been prepared those... 

Mechanistic studies of the formation of the zirconium alkylidene complexes of type 462 have been carried out.326 Neither the independently prepared monobenzyl complex nor the tribenzyl derivative is thermally sensitive or reacts with light as a separate species, but the equimolar mixture is thermolyzed to give the benzylidene species. The reaction of the trichloride 461 with 2 equiv. of KCH2Ph generates an equilibrium mixture of benzyl complexes consisting of monobenzyl 464, tribenzyl 463, and the bis(benzyl) derivative. The dibenzyl complex is spectroscopically detectable, but not isolable and co-exists with the mono- and tribenzyl species however, it is the bis(benzyl) species that is photochemically and thermally labile for a facile cr-hydrogen abstraction process, leading... 

---