Hafnocene complex

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 Remarkable Features of (rj -Conjugated Diene)zirconocene and -hafnocene Complexes... 

Two major factors are likely to be responsible for the relative stability of (5-rrani-i7 -diene)zirconocene and -hafnocene complexes. It seems that the characteristic bonding features of the bent metallocene unit thermodynamically favor coordination of the 5-trans over the i-cis conjugated-diene... 

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 ... 

Automerization Activation Barriers of Selected (s-cu-Diene)zirconocene And -HAFNOCENE Complexes (5)... 

NMR spectroscopy is a convenient and rather reliable method for identifying dienezirconocene and -hafnocene complexes belonging to the s-cis or s-trans series (25, 55, 45, 48). For most conjugated diene ligands used, isomers 3 and 5 show several characteristically different NMR... 

Selected NMR Data for (s-trans- and (j-m-DiENE)ziRCONocENE and -hafnocene complexes" ... 

The rapid 3 4 equilibrium makes the coordinatively unsaturated mono(olefin)zirconocene (-hafnocene) complex 4 an easily accessible organometallic synthon even at extremely low temperatures, a fact that certainly will make its readily available precursor 3 a good starting material for the preparation of many novel organometallic compounds in the future. 

Recent Developments in Theoretical Organometallic Chemistry. 15, I Redistribution Equilibria of Organometallic Compounds, 6, 171 Redistribution Reactions of Transition Metal Organometallic Complexes, 23, 9S Redistribution Reactions on Silicon Catalyzed by Transition Metal Complexes, 19, 213 Remarkable Features of (7] -Conjugated Diene) zirconocene and -hafnocene Complexes, 24, I Selectivity Control in Nickel-Catalyzed Olefln Oligomerization, 17, lOS Silyl. Germyl, and Stannyl Derivatives of Azenes. N H Part I. Derivatives of Diazene, N,H2, 23, 131... 

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