Heterocycle Functionalized [3]Ferrocenophanes: Synthesis, Structural and Properties Study

Abstract

Ferrocenophanes or Ansa ferrocenes are an interesting class of organometallic compounds, where the two Cp rings of a ferrocenyl moiety are joined together with a looped handle type bridge, forming a strained structure. Among them carbon bridged [3]ferrocenophanes involving three bridging carbon centres are also widely studied due to their stability, structural flexibility and functionalization prospects.[1] In spite of extensive synthetic study of carba-[3]ferrocenophanes, heterocyclefunctionalization and tri-functionalization at the bridged carbon atoms have remain largely unexplored. This prompted us to design a solvent free solid supported ring closing reaction strategy to synthesize different heterocycle linked carba-[3]ferrocenophanes. The solid state mediated ring closing reaction between 1,1’-ferrocenedicarboxaldehyde and 2-acetyl pyridine under a facile solid supported condition resulted in the formation of the first known derivative of tri-pyridine functionalized carba-[3]ferrocenophane containing at least two stereogenic centres.[2(a)] Surprisingly, we observed the formation of two diastereomeric tri-pyridinyl carba-[3]ferrocenophane which were structurally confirmed to be a recemate and a meso–type derivatives. Extending the reaction strategy to a thiophene heterocycle led to the formation of an unusual diastereomeric C1, C2, C3 tri-thiophenyl carba-[3]ferrocenophanes with two stereogenic centres. Spectroscopic and structural characterization revealed the diastereomers as one meso type (1S,3R) and a recemate type {(±)1S/R, 3S/R} trithiophenyl [3]ferrocenophanes (Fig. 1).[2(b)]