Hafnocene complexes structures

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... 

The activation barrier of this characteristic automerization process of (5-c -conjugated diene)zirconocene and -hafnocene complexes has proved to be very dependent on structure and substituents of the diene ligand (22, 45). The highest known activation energy was observed for compound 51, the zirconocene complex of Hoogeveen s diene ... 

A series of zirconocene bis(thiolate) complexes (912, Equation (56)) has been synthesized by the reaction of Cp 2ZrCl2 with NaER and shown to exhibit rich luminescence behavior.694 The crystal structure of Cp 2Zr(SBun)2 has been determined by X-ray diffraction. Unlike the zirconocene analogs, the reaction of Cp 2Hfd2 with NaER did not lead to the desired Cp 2Hf(ER)2 complexes, but only to the monosubstituted derivatives Cp 2Hf(ER)Cl. On the other hand, the use of LiSR in DME produces the hafnocene bis(thiolate) complexes shown in Equation (56).695 The structures of these hafnocene complexes have been determined these compounds also exhibit rich luminescence behavior. 

Using the parent zirconocene-butadiene complex as a representative example, a typical bonding situation in these types of molecules is presented in Scheme 48. For 297, equilibration between the s-trans and the s-cis isomers occurs with a barrier of 23 kcal mol 1 at 283 K. The 72-olefin complex is believed to be a high-energy intermediate on the interconversion reaction surface. Significantly, structural data indicates that the s-cis complexes are best described as Zr(iv) compounds with a er2, ir ligand.158,175 The dynamic NMR measurements have also been extended to ansa-zirconocene and hafnocene butadiene complexes.176 Moreover, photoelectron spectroscopy has been used to determine the relative energetics of the two isomers for // -metallocenes.177... 

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]. 

With ansa(chiral) titanocenes, zirconocenes, and hafnocenes in combination with methylalumoxane (MAO) it is possible to obtain highly isotactic polypropene [366-374]. When changing the symmetry of the complex, different structures of the polypropene are yielded. The activity of these hydrocarbon soluble catalysts are extremely high. 

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