Butadiene zirconocenes in Catalysis

Bochmann et al. have shown that the half-sandwich [(2,3-dimethylbutadiene)(RCp)ZrMe] complex 119 eliminates methane above 

The (Butadiene)zirconocene Route to Active Ziegler-Natta Catalyst Systems 

The solid state structures of the complexes 128 and 130 (and several additional examples) show the presence of an F-[(CrT s)3B Cl I2]-subsuuned distorted 7t-allyl ligand at zirconium. Most characteristic is the pronounced coordination of an ortho-F(Cai-) fluorine atom from one of the C6F5-rings to the strongly electrophilic zirconium center. The resulting Zr-F(CAr) interaction spans ca. 2.4 A (128 2.423(3) A, 130 2.408(2) A) with a Zr F C angle of ca. 140° (128 140.0(3)°, 130 142.6(2)°).135 This Zr-F(CAr) 

A view of the molecular geometry of the parent zirconocene-butadiene-B(C6F5)3 

The Zr-F(CAr) interaction is rather weak (see below). It is easily cleaved by the addition of a suitable two-electron donor such as CO or an isonitrile. The formation of the dipolar [(carbonyl)hafnocene-C4II6 B(C6F5)3] betaine system (131)133 from 128a (M = Hf), or the adduct 132 that was obtained by treatment of 128 (M = Zr) with PMe3, are typical examples.136 The ansa-zirconocene-derived betaine 130 forms similar 

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