[1.1]Ferrocenophane-1,12-dione as a Precursor of 1,12-Di(cyclopenta-2,4-dienylidene)-[1.1]ferrocenophane, a Doubly Bridged Difulvene

• Published in: Advanced synthesis & catalysis 2009-05, Vol.351 (7-8), p.1139-1147
• Main Authors: Garabatos-Perera, José Ramon, Wartchow, Rudolf, Butenschön, Holger
• Format: Article
• Language: English
• Subjects: conformation; ferrocene; ferrocenophane; fulvenes; variable temperature NMR
• ISSN: 1615-4150; 1615-4169
• DOI: 10.1002/adsc.200800780

An improved synthesis of [1.1]ferrocenophane‐1,12‐dione (2) by oxidation of [1.1]ferrocenophane with 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) is presented. The syn conformer of dione 2 is structurally characterized. The compound undergoes various addition reactions at the bridging carbonyl groups. Attempts to add 1,1′‐dilithioferrocene result, however, in the diadduct 9, not in the symmetric trinuclear diol 8. Reaction of 2 with sodium cyclopentadienide in the presence of aluminium trichloride (AlCl3) gives the respective difulvene 11 in excellent yield. The dynamic behavior of 11 is investigated by variable temperature 1H NMR measurements (VT‐NMR). The cyclovoltammogram of 11 indicates two reversible oxidation steps. Reduction of difulvene 11 with lithium aluminium hydride (LiAlH4) results in the formation of [1.1]ferrocenophane 12 with cyclopentadienyl anion substituents at either one of the two bridges. While attempts to generate a third ferrocene moiety by reaction with iron(II) choride (FeCl2) have failed so far, the formation of 12 is established by protonolysis and methylation reactions.