Hafnocene complexes reactivity

In a rare example which demonstrates the possibilities of the approach Biirgi and Dubler-Steudler (1988a) have recently combined structure and reactivity data in a detailed study of the ring-inversion reaction of a homogeneous set of organometallic compounds. The reaction is the auto-merization of zircocene and hafnocene complexes [73 M = Zr or Hf, X = C or O], known from temperature-dependent NMR measurements to undergo the equilibration [73]—s.[73 ]. Principal-component analysis of... 

Thermolysis of a toluene solution of 30 at 90 °C in the presence of excess butadiene results in the liberation of 1 equivalent of ethene and the formation of the reactive Cp2Hf(r 2-CH2 = CH2) intermediate, which subsequently reacts with butadiene to form a 2-vinylmetallacyclopentane complex 31, which is however unstable under the reaction conditions and was isolated as the corresponding isomeric (r 3-allyl)hafnocene complex 32 35... 

The chemistry of group 4 silyl compounds is closely associated with the dehydrogenating coupling of hydrosilanes. This reaction was discovered by Harrod and coworkers who converted PhSiHa with a catalytic amount of Cp2TiMe2 to H(PhSiH) H [370]. Later Tilley and coworkers showed that if zirconocene and hafnocene complexes are used in the reaction a catalytic cycle is involved which consists of o-bond metathesis steps [371]. To enhance o-bond metathesis reactivity with Si-H and C-H bonds Cp2Hf(Me)Si(SiMe3)3 and related compounds were treated with B(C6F5)3 to obtain cationic Hf complexes [372]. 

While Cp2Hf (CO)(PPh3) (62) was found to be more reactive toward acetylenes than Cp2Hf(CO)2 (3), no monocarbonyl-rj2-acetylene complexes of hafnocene were observed, in contrast to the reaction of acetylenes with Cp2Ti(CO)(PPh3) (42) (50). Instead, the reaction of 62 with RfeCR (R = Et, Ph) led to the respective hafnacyclopentadienes (55). 

Mono-diene complexes of zirconocene and hafnocene have been prepared by two methods [129-131 ], viz the photochemical reaction of diphenylzirconocene in the presence of diene and the reaction of metallocene dichlorides with diene magnesium adduct. The structures and reactivity of s-cis-dicm complexes indicate that the metal-lacyclopentene (B) is the preferred canonical form. Complexes of the type Cp2Zr(j-/ra/25-1,3-diene), have been prepared they were the first examples of this mode of coordination (C). Insertion of unsaturated compounds into a diene coordinated to zirconocene results in regioselective C—C bond formation [132-136]. 

---