Synthesis and electrochemical properties of a series of ferrocene-containing alcohols

A series of primary ferrocenylalcohols, Fc-(CH2)(m)-OH with m = 1-4 and Fc = ferrocenyl, was synthesised by reduction of the appropriate ferrocenylcarboxylic acids, Fc - (CH2)(n)- COOH (n = 0-3) and the ester methyl 4-ferrocenylbutanoate with LiAIH(4), the reduction of the gamma-ketoacid ferrocylpropanoic acid, Fc-CO-(CH2)(2)-COOH, with AlCl3/LiAlH4, and the reduction of ferrocenylcarboxaldehyde, FcCHO, with NaBH4. The secondary ferrocenyl alcohols CpFe(C5H4-CH(OH)-CH3) and Fe(C5H4-CH(OH)-CH3)(2) were obtained by NaBH4 reduction of acetyl and diacetyl ferrocene. The different reduction methods are compared. The electrochemistry of the alcohols was studied by cyclic voltarnmetry in CH3CN/0.1 M N(BU)(4)PF6 utilising a platinum working electrode. The ferrocenyl group showed reversible electrochemistry with the formal reduction potential (E-o ' versus Fc/Fc(+)) of the ferrocenyl group inversely proportional to side chain length. The influence of the side chain length on E-O ' was more pronounced for the acids because the electron-withdrawing properties of the carbonyl group is stronger than that of the alcohol group. Ion pairing was found to play a major role in the electrochemical behaviour of ferrocenylmethanol, Fc-CH2-OH. (c) 2005 Elsevier Ltd. All rights reserved.