Hafnium complex oxide

In contrast, exposure of 14-VE (diene)MCp Cl complexes (M = Zr, Hf) to CO (1 atm) results in the formation of cyclopentadienes70. The mechanism proposed for this transformation was elucidated with a carbon labeled CO ( CO) as requiring an initial coordination of CO to generate a (diene)MCp (CO)Cl complex 153 (Scheme 37). For the hafnium complex, the intermediate 153 (M = Hf) was observed by infrared spectroscopy. Insertion of CO into the a2, jt diene generates a metallacyclohexenone, which undergoes reductive elimination to generate the dimeric metallaoxirane species 154. -Hydride elimination from 154 (M = Zr, Hf) followed by 1,2-elimination produces substituted cyclopentadienes and the polymeric metal-oxide 155. Treatment of (diene)TiCp Cl with CO leads to isolation of the metallaoxirane complex 154 (M = Ti). 

For tri-n-octylphosphine oxide, for example, the shift in the P=0 stretching frequency from its value for the free extractant is greater for the hafnium complex (85 cm-1) than for the zirconium complex (70 cm-1).297... 

The first 1,3,5-triphosphinine 133 with only two-coordinate phosphorus atoms is produced by the hafnium-mediated cyclotrimerization of f-BuC=P in toluene at -78°C and the subsequent release of 133 from 132 by oxidization with hexachloroethane in toluene in the range -78 to 20°C (Scheme 36).67 Low temperatures are crucial for the generation of hafnium complexes with ligated cyclotrimers of the phosphaalkyne. At 140°C, cyclodimerization to give (cot)(i74-l,3-diphosphete)hafnium is observed, whereas... 

A 1,3,5-triphosphinine was liberated from the coordination compound 25 by oxidation with hexachloroethane in toluene. If, however, the chlorination of complex 25 was conducted in pentane complex 26 was obtained in 44% yield. The hafnium complex 26 was hydrolyzed by an excess of water to the bicyclic diphosphirane 27 in 53% yield together with 10% of the 1,3,5-triphosphinine. Under milder and more controlled conditions, for example, the treatment of 26 with silica gel containing 2% H2O or with Na2SO4 10H2O, the addition of the second equivalent of water was suppressed and the two heterocycles 28 and 29 were formed in equal amounts (Scheme 10) <1999EJI763>. 

Low temperature protonation of the zerovalent anion [> -CpTi(CO)3(PPh3)]" by acetic acid can be considered an oxidative addition The resultant hydride complex, > -CpTi(CO)3(PPh3)(H), is thermally unstable. Zerovalent (f -toluene)2M(PMe3) (M = Zr, Hf) undergoes an oxidative addition reaction with Me3SnSnMe3 to form M(/7 -toluene)2(SnMe3)2 the hafnium complex has been structurally characterized . 

Zirconium/Hafnium Complexes in Oxidation States +i and Below 697... 

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