Bridged-sandwich complexes

Theoretical studies of polymetallocenylene-related polymers have been carried by Burdett and Canadell [67]. There are two different electron counts associated with a bandgap corresponding to iron and chromium polymers in the band structure of a naphthalene-bridged sandwich complex polymer, 16 [67], whereas one bandgap is found in the band structure of polyferroce-nylene [60]. This is due to a three-orbital interaction between the and d y of metal and the LUMO of naphthalene, causing three bands in the band structure. 

The electronic properties of C2B3-bridged tetradecker (and larger) sandwich complexes have been examined via electrochemical, ESR, and other methods. In general, it was found that in paramagnetic species the unpaired electron(s) are largely delocalized over the three metal centers. 

The cyclo-P3 unit can also behave as a three electron bridging ligand (45) to give a variety of homo and heterometallic triple-decker sandwich complexes which are treated in a recent review (100). 

A typical structure of these so called triple-decker sandwich complexes is that of the complex [(p3)Ni -(j)3-P3) Ni(p3)](BPh4)2-2.5Me2CO (73). In each complex the trihapto P3 (or trihapto As3) groups form a bridge between the two Ni(p3) residues.292 Each nickel atom is thus six-coordinated by three phosphorus atoms from the ligand p3 and by three phosphorus atoms from the cyclo-P3 (or arsenic atoms from the cyclo-As ), which acts as a three-electron-donor ligand. 

Recent work of Boisson et al. focuses on silylene-bridged Nd complexes of the type depicted in Scheme 10. The respective bis fluorenyl complex [Me2Si(Ci3H8)2]NdCl [307] and the mixed Cp/fluorenyl complex [Me2Si(C5H4) - (Ci3H8)]NdCl [308,309] have been described. The work on silylene-bridged Nd sandwich complexes performed by Boisson et al. is reviewed in [310]. 

Unbridged, bridged, substituted, and half-sandwich complexes have been used as metallocenes for ethylene polymerization (Figs. 1 and 2). To compare the activities and molecular masses, the polymerizations are carried out under the same conditions (30°C, 2 bar ethylene pressure, with toluene as a solvent) (105). Table IV shows the polymerization behavior of various met-allocene/alumoxane catalysts. Generally, zirconium-containing catalysts are... 

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