Zirconium dichloride complexes

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). 

The N,AT-bis(trimethylsilyl)benzarnidinate zirconium dichloride complexes [rj2-4-RC6H4C(NSiMe3)2]2ZrCl2 (R=H (1) or CH3 (2)) were prepared by the reaction of ZrCl4 with two equivalents of bis(trimethylsilyl)benzamidinate lithium-TMEDA (TMEDA=AT,iV,iV/,iV/-tetramethylenediamine) at room temperature in toluene yielding, after removal of the TMEDA and crystallization, 83-89% of pale yellow analytically pure rhombohedral crystals of 1 and 2 (Scheme 1) [31,33]. These complexes were also obtained in a high quality form... 

A few stable metal-metal bonded complexes (70) have been described. They are synthesized by reaction of a zirconium dichloride complex with an organometallate of iron or ruthenium (see following section). CO2 and CS2 insertion into the polar metal metal bond affords hetero dinuclear complexes of the second family (71) (Scheme 18). The /U.-OXO complexes are representative complexes of the (71) group. They are readily prepared by the smooth hydrolysis of most metallocenes. Arrangement (71) is also present in the methyl-bridged homo dinuclear species (77) formed by reaction of methylzirconocene cation with Cp2ZrMc2. 

The analogous zirconium dichloride complex bearing a phosphoranimino-carbene ligand 188 was obtained from the salt metathesis reaction between the dilithiated salt of the ligand and ZrCl4(THF)2161 (Scheme 37). The Zr=C... 

Salt metathesis was employed to synthesize half-sandwich zirconium and hafnium dichloride complexes 331 incorporating the bidentate, mono-anionic benzamidinate ligand (Equation (26)). The corresponding zirconium dimethyl and dibenzyl complexes have also been prepared using appropriate alkylating reagents.260 The zirconium dichloride complex (R= H), upon activation with MAO, are active for both polymerizations of ethylene... 

Another example of the nucleophilic chloro ligand substitution involves the reaction of the zirconium dichloride complex 468 with lithium ester enolates (Scheme 112). Its reaction with 2 equiv. of stable lithium ester enolates such as lithium tert-butyl isobutyrate in TF1F produces the bis(ester enolate) complex 499 as a crystalline solid.344 The same reaction but with the unstable lithium methyl isobutyrate leads to the isolation of the decomposition product, the bis(methoxide) complex 500, which exists as a dimer in the solid state. Treatment of the bis(ester enolate)... 

Double deprotonation of the bifunctional mono-CpH/alcohol racemic ligand linked by the 2,6-pyridyl unit followed by salt metathesis with ZrGL yielded the ansa-Cp/oxo zirconium dichloride complex 555, but with the concomitant formation of the undesired complex 556 incorporating the mono-anionic form of the ligand and the simple adduct of the neutral ligand and Z1CI4 0 (Scheme 126). The latter two undesired species have been structurally characterized however, complex 555 obtained forms an insoluble oligomeric species after the loss of THF upon purification. 

Bridged ansa-bis(fluorenylidene) zirconium dichloride complexes with fused ring systems ° ° have... 

The influence of methyl substituents at the fluorenyl ligand in au5a-bis(fluorenylidene)zirconium dichloride complexes on the catalytic performance has been of further interest. The fluorenyl positions 4 and 5 are directly located at the active center and therefore have an important effect on the catalyst activity but are supposed to have less effect on the molecular weight of the formed polymer due to their nonbulky nature (Figure 15). Indeed, methyl substituents at position 4 or 5 at the fluorenyl fragment dramatically increase the catalytic activity of these metallocene complexes. As already discussed in the previous section, these substituents obviously pro-... 

Based on a series of molecular mechanic calculations and polymerization experiments performed with a number of ania-bis-(fluorenyl)zirconium dichloride complexes, Alt et al. [109-112] demonstrated that the size of the bridging unit plays an important role in the final catalytic activity of these complexes towards ethylene polymerization. A bigger bite angle, i.e., bigger opening around the active site, is supposed to increase the catalytic activity because of a less-hindered monomer... 

Epoxide ring opening by thiophene was catalysed by 10 mol% of bis(cyclo-pentadienyl)zirconium dichloride complex. The reaction was performed in acetonitrile and, rather surprisingly, the 3-alkylated thiophene 17 was isolated in 71% yield (Scheme 25) [46]. 

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