Numerous cationic metallocene complexes of the rare-earth metals have been reported within the last 20 years (Table A.1.2), supported by a variety of cyclopentadienyl derivatives (Chart A.1.1).1-15 The synthetic methods (I–V) for their preparation are illustrated in Table A.1.1. The unsolvated tetraphenylborato complexes in particular have a wide applicability as starting materials for the synthesis of neutral bis- and tris(cyclopentadienyl) derivatives, since tetraphenylborate can be replaced by a variety of ligands such as cyclopentadienyl and alkyl (Scheme A.1.1). In the presence of THF, ring-opened products are reported to be potentially produced instead.
