Structural influences on the electrochemistry of 1,1′-di(hydroxyalkyl)ferrocenes. Structure of [Fe{η5-C5H4–CH(OH)–(CH2)3OH}2]

• Oxidation potentials reach an asymptotic minimum at n = 4 in dialcohols Fc{(CH2)nOH}2.
• The crystal structure of the new compound Fc{(CHOH)(CH2)3OH}2 was solved.
• The 1H NMR Cp signal positions of the ferrocenyl has an asymptotic minimum at n = 4.
• Functional group IR bands of all intermediates towards Fc{(CH2)nOH}2 are compared.

A series of 1,1′-di(hydroxyalkyl)ferrocenes, [Fc′{(CH2)nOH}2], with n = 1 (1), 2 (2), 3 (3) and 4 (4) and Fc′ = Fe(η5-C5H4)2, was synthesized. The electrochemistry of the di(hydroxyalkyl)ferrocenes was studied by cyclic voltammetry in CH2Cl2/0.1 M [NnBu4][PF6] utilizing a glassy carbon working electrode. The ferrocenyl group showed reversible electrochemistry with the formal reduction potential, Eo′Eo′, inversely proportional to alkyl chain length and approximately 59 mV smaller than those of the corresponding mono(hydroxyalkyl)ferrocenes derivatives [Fc(CH2)mOH] with m = 1 (1m), 2 (2m), 3 (3m), and 4 (4m) and Fc = Fe(η5-C5H5)(η5-C5H4−). The tetraalcohol [Fc′{CH(OH)(CH2)3OH}2], 5, possessing four OH functionalities, two in the terminal positions and two more, one on each of the two α-C relative to the ferrocenyl (Fc′ for dialcohols or Fc for monosubstituted derivatives) group, was isolated as a side product during the synthesis of 4. The formal reduction potential of 5 was Eo′=−24mVvs. FcH/FcH+ and closely approached Eo′Eo′ of [FcCH(OH)CH3] (Eo′=−11mV), [Fc′{CH(OH)CH3}2] (−21 mV) and 1 (0.00 mV vs. FcH/FcH+). The single crystal X-ray structure of the tetraalcohol 5 (Z = 8, orthorhombic, space group Pbca) was also solved.

The ferrocene-containing dialcohols Fc{(CH2)nOH}2, n = 1–4 was synthesised and “n” was related to ferrocenyl oxidation potential and 1H NMR Cp resonance positions. The structure of [Fc{CH(OH)(CH2)3OH}2] was solved.Figure optionsDownload as PowerPoint slide