Novel Ferrocenyl Polyene Derivatives and Their Binding to Unmodified Cyclodextrins

Two new ferrocene derivatives, 7-ferrocenyl-2,4,6-heptatrienal (1) and 7-ferrocenyl-2,4,6-heptatrienol (2), were synthesized and characterized. These two compounds possess a rigid triene chain conjugated to one of the cyclopentadienyl rings of the ferrocene residue, and as a result, they exhibit very stiff structures. The electronic absorption and electrochemical properties of these compounds were utilized to investigate their host−guest binding interactions with the receptors α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) in aqueous solution. From electronic absorption measurements binding constants in the range 790−12900 M^-1 were obtained; β-CD formed more stable complexes than α-CD with both guests. Electrochemical measurements suggest some degree of site selectivity in the complexation processes, with β-CD binding preferentially to the ferrocene moiety while α-CD interacts with the unsaturated chain.