Bis-cyclopentadienyl Derivatives

The organometalhc chemistry of the rare earths deals mainly with bis(cyclopentadienyl) derivatives due to the easy available bis(cyclopentadienyl) rare earth chlorides and other halides via reaction of the rare earth trichlorides with two equivalents of a cyclopentadienyl alkali salt. Bis(cyclopentadienyl)lanthanide chlorides are formed as chloride-bridged dimers (Figure 28a), as monomers stabihzed by a donor molecule like THF (Figure 28b) or as ate complexes with alkali hahdes (Figure 28c). 

A number of facile procedures were developed for the synthesis of mono and bis cyclopentadienyl derivatives of titanium, e.g., the (tt-CsH )-trialkoxytitanium derivatives, (77-C5H5)-titanium trihalides (406, 407-409), (77-C5H5)-titanium internal complexes (409), triaroxytitanium cyclopentadienyls (410), compounds containing different groups (alkoxy, aryloxy. 

The structures of two bis-cyclopentadienyl derivatives of group-IV metals, ( 5— 5115)2811 and (A5—C5H5)2Pb, have been determined by gas-phase electron diffraction ) (see Fig. 

Ricci, G Panagia, A. R Porri, L. Polymerization of 1,3-dienes with catalysts based on mono- and bis-cyclopentadienyl derivatives of vanadium. Polymer 1996, 37, 363-365. 

Several mono- and bis-cyclopentadienyl derivatives of neodymium and ytterbium with o-aldehydophenolato and fiirfuralcoholato chelate ligands have been obtained from the direct reaction of the corresponding alcohol with CpjLn [83]. The products have been characterized by element analysis, IR spectroscopy and mass-spectrometry. Mass-spectroscopy allowed to establish the existence of the equilibrium Cp2LnX CpLnX2 on heating of the complexes. 

The diethylamido ligands in the bis(cyclopentadienyl) derivative can then be replaced by a variety of protonic or electrophilic reagents ... 

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