Main group metallocenes with substituted cyclopentadienyl ligands: From bonding problems to discotic phases

Abstract

Metallocenes of main group 1,2, 3 and 4 elements containing pentamethyl-, pentaphenyl- or pentaben-zylcyclopentadienyl ligands demonstrate different behaviours in solution and in the solid state. Single crystal X-ray analyses show monomeric, oligomeric, or polymeric structures, depending on the electronic situation around the different metals and the steric arrangement of the organic groups bond to the cyclopentadienyl anions. From the comparison with some new transition metal and f-element metallocenes containing the same ligandsconclusions have been drawn to the bonding situation in the monomeric and polymeric metallocenes. Pentaphenylcyclopentadiene reacts with acyl chlorides to form cyclopentadienes containing five para-substituted phenyl groups. They can be transferred to penta(para-benzoic acid ester)cyclopentadiene derivatives, which are metallated to yield overcrowded metallocenes containing a discotic cyclopentadienyl anion like in some thallium complexes. © 1991 IUPAC