Zirconium tetrabenzyl

Analysis of the products of the photolysis of Zr (benzyl) 4 in toluene at 30°C in the region 300-450-nm with mass spectrometry shows that the predominant peak is due to p-benzyl toluene with small amounts of dibenzyl, and 4,4 -dimethyl diphenyl. Rate measurements (Fig. 5a) suggest that in this region of the spectrum the polymerization proceeds through radical intermediates (29). This concept is supported by the fact that the spectrum of zirconium tetrabenzyl has a maximum at 317 nm and is identical with that found for the benzyl radical using flash photolysis techniques (30). Also zirconium tetrabenzyl on irradiation in toluene solution produces... 

Titanium and zirconium tetrabenzyl and the mixed metal—benzyl halides are soluble in hydrocarbon solvents and will polymerize ethylene and a-olefins, the latter to stereo-specific polymers [64], The structures of the true initiators are not known but they are unlikely to be the simple organo-metal compounds. Catalysts of higher activity are obtained when they are used in combination with aluminium alkyls. It is of interest to note that titanium tetra(dimethyl amide) reacts with acrylonitrile to form an active species, which then forms high molecular weight polymer by coordination polymerization [65]. 

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. 

Monoanionic boratabenzene ligands are isoelectronic to cyclopentadienide anion and can be nsed to synthesize Zr equivalent metallocenes (eqnation 29). A more congested complex of 9-phenyl-9-borata-anthracene (C 1-synunetry) was obtained by a similar way. Mono and bis boratabenzene complexes can also be prepared by reaction of a nentral boratabenzene-PMes adduct with tetrabenzyl zirconium or hafnium. Boratabenzene ansa metallocenes with CH2-CH2 or Si(CH3)2 bridges as well as Cp-boratabenzene mixed complexes or CG complexes were synthesized. 

Syndiotactic polystyrene prepared with tetrabenzyltitanium or tetrabenzyl-zirconium and methylalumoxane was analysed by I3C NMR in regard to end-groups.155 A boiling butanone-soluble low molecular weight fraction shows signals due to both chain ends as shown below ... 

Zirconium chloride - catalyzed condensation of 2,3 4->6-tetra-0-acetyl-1-thio- C-D-glucopyranose with 1,3,4 6-tetrabenzyl- -D-fructo... 

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