Zirconium neopentyl complex

The /3-methyl elimination reactions are rare by comparison, examples being the decomposition of zirconium neopentyl complexes 109... 

Zirconium—ally complexes also have catalytic properties. Tetraally zirconium [12090-34-5] on a siUca substrate catalyzes ethylene polymerization (265). Supported on sihca, ZrR (R = allyl or neopentyl) catalyzes olefin isomerization (266). 

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-... 

Cavell also reported alkyl derivatives. Tetrabenzyl zirconium was found to react separately with one molar equivalent of two parent methanes to afford complexes 135 and 136 in excellent yields.66 The 13C NMR chemical shifts of the methandiide centres in 135 (Ad = adamantyl) and 136 of 82.8 and 84.4 ppm are clearly different from the dichloride congeners and reflect the substitution of the chlorides by alkyls. The corresponding hafnium dialkyl 137 was also prepared from 133 and neopentyl lithium and the methanide resonance for this complex appeared at 71.6 ppm in its 13C NMR spectrum.63 Noteably, these alkyls displayed far greater stability than their homoleptic tetraalkyl cousins. 

Zirconium tris-neopentyl surface complex 1 was synthesized by the sublimation of tetra-neopentylzirconium complex onto the surface of partially dehydroxylated silica at 500°C [26, 27] and fully characterized by IR, NMR, EXAFS, elemental analysis, and gas quantification methods as well as chemical methods [3, 28, 29]. Furthermore, in order to confirm its surface structure, the grafting experiment was carried out with deuterated silica and tetra-neopentylzirconium. Evolution of 1 mol of deuterated neopentane per mole of grafted zirconium proved that there is a single bond between zirconium and oxygen. This monopodal surface structure was further confirmed by EXAFS experiment with 1. 

In order to assess the relative effectiveness (Section 3.1) of the two synergetic factors, i.e. inductive effect and steric bulk of the alkyl groups, a detailed study was carried out in 1952 on the molecular complexities of all the 8 isomeric tertiary amyloxides of titanium and zirconium (Table 2.5). Amongst these, the neopentyloxides are of special significance as the neopentyl alcohol, in spite of being a primary alcohol, had been known to cause steric effects comparable to those of secondary alcohols. The closer resemblance of the neopentoxides of both the metals to their secondary rather than primary amyloxides tended to indicate the greater influence of steric factors in determining the molecular complexity and volatility of these derivatives. 

A similar type of C-C bond cleavage was also observed for zirconium cation compounds [9]. The complex, as shown in Eq. 7 with a neopentyl group, showed the elimination of isobutene and the formation of the methylzirconocene complex. 

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