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 alpha-cyclodextrin (alpha-CD) and beta-cyclodextrin (beta-CD) in aqueous solution. From electronic absorption measurements binding constants in the range 790-12900 M(-)(1) were obtained; beta-CD formed more stable complexes than alpha-CD with both guests. Electrochemical measurements suggest some degree of site selectivity in the complexation processes, with beta-CD binding preferentially to the ferrocene moiety while alpha-CD interacts with the unsaturated chain.