Half-open metallocenes

Complexes containing an open chain are also metallocenes analogs. For instance, pentadienyl anions see Pentadienyl Ligand) form open metallocenes with transition metals as efficiently as do cyclopentadienyls. Half-open metallocenes can be obtained in a similar way starting from CpZrCl2Br (Scheme 17). ... 

Nickel - The disilyl-bridged cyclopentadienyl nickelocene derivative 91 has been prepared in the reaction of NiBr2(THF)i.3 with the cyclopentadienyl anion and deprotonated tetrahydro-4,4,8,8-tetramethyl-4,8-disila-s-indacene. " The triple decker cation [CpNi( -Cp)NiCp] BF4 reacts with the half open metallocene 92 to give the unusual complex 93. ... 

C. Half-Open Metallocenes with Halide and Related Ligands. 158... 

The half-open metallocenes of titanium and zirconium have proven of great value in allowing for direct comparisons of the metal-ligand bonding involving pentadienyl and cyclopentadienyl ligands, and they have also exhibited very rich reaction chemistry (Section V). 

Complex 5.71, an analogue of 2.65, is an example of a lanthanide-based constrained geometry catalyst (see Section 6.5.1). Note that it is a half-metallocene complex that has a rather open structure for coordination. 

Half-metallocene complexes are included because they play an important role, particularly in the synthesis of syndiotactic polystyrene. Much interest in non-metallocene complexes of group 4 metals, Ni, Pd, Fe, and Co for polymerization catalysts has recently been shown. They will be described with regard to stereoregular polymerization. Ring-opening polymerization of lactones, lactams, and lactides is excluded in this chapter. Ring-opening metathesis polymerization (ROMP) has received much interest recently however, it is not discussed here because few metallocene complexes are used for ROMP. 

---