From dihydropentafulvalenes to asymmetric biferrocene and terferrocene

In order to realize a step-by-step synthesis of terferrocenes tetramethyldihydropentafulvalene has been mono-deprotonated and further converted to ferrocene and pentamethylferrocene which are both substituted by tetramethylcyclopentadiene (4 and 9, respectively). In these syntheses the intermediate half-sandwich (C5Me5)Fe(hfa)(MeCN) (hfa=hexafluoroacetylacetonate) proved to be a useful reagent. Compounds 4 and 9 could be deprotonated to corresponding ferrocenes which are substituted by tetramethylcyclopentadienyl anions (5 and 10, respectively). Anions 5 and 10 are building blocks for termetallocenes which has been demonstrated by the synthesis of octamethylated terferrocene from 5 and FeCl2. Tetradecamethylbiferrocene has been obtained by reaction of tetramethylpentafulvalene dianion with FeCl2. NMR features and redox properties of the new compounds have been analyzed.