Hafnium complexes alkyl

Haber process, 116 Hafnium complexes alkyl alkoxy reactions, 358 phthalocyanines, 865 porphyrins, 823 pseudohalides, 228 Hafnium(IV) complexes cupferron, 512 Haloarsine compounds, 1004 Halogen complexes, 675-687 bridge systems, 677-684 asymmetry, 678 theoretical studies, 682 double bridged, 681... 

Bochmann M, Lancaster SJ (1995) Cationic group IV metal alkyl complexes and their role as olefin polymerization catalysts The formation of ethyl-bridged dinuclear and heterodinuclear zirconium and hafnium complex. J Org Chem 494 55-59... 

The supported hafnium complex is quite stable up to 150°C (by FT-IR and GC studies, only traces of neopentane and methane are observed in the gas phase) [43]. Above this temperature, a significant amount of isobutene is also observed. At 250 °C, decomposition is total as no alkyl ligand remains linked to hafnium. 

The first report of catalyzed chain growth on aluminum was presented by Samsel et al., using metallocenes of actinides [13] or hafnium [14, 15], Gibson et al. described a detailed study of chain growth using the bis(imino)pyridyl iron complex 1 in combination with several metal alkyls [16], Other systems reported to... 

Although the surface zirconium complex has a lower thermal stability than the hafnium one, the nature of the gases released during thermolysis is similar, except for isobutene (hardly observed for zirconium) and isopentene (observed only for hafnium). These results suggest that isobutene resulting from ji-alkyl transfer of hafnium (Scheme 11.1) is inserted in the Hf-CHs bond. 

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. 

The pincer like diamino functionalised carbene ligand stabilises the group 4 metal sufficiently to perform a few very interesting insertion reactions with the M-Me bond. The reactions were performed with the hafnium rather than the zirconium complexes [113]. Small molecules used for these insertion reactions include isonitriles (aryl and alkyl) and CO (see Figure 4.36). Reaction of the hafnium carbene dimethyl complex with xylyl-isonitrile results in addition of this excellent donor ligand and subsequent insertion into the Hf-Me... 

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