Synthesis, characterization and electrochemical studies of osmocenyl alcohols with biomedical applications

English: A series of osmocene-containing carboxylic acids, Oc(CH2)mCOOH where m = 1, 2 and 3, and osmocene-containing alcohols, Oc(CH2)nOH where n = 1, 2, 3 and 4, were obtained in multiple synthetic steps and characterised with the aid of infrared spectroscopy, 1H nuclear magnetic resonance spectroscopy, elemental analysis and melting point measurements. New methods were developed for the synthesis of these osmocene-containing carboxylic acids and alcohols. The structures of 2-osmocenylacetonitrile (monoclinic, P21/c, Z = 4, R = 0.057) and 2-osmocenylethanol (trigonal, P-3, Z = 18, R = 0.092) were determined by single crystal X-ray crystallography. The alcohol, 2-osmocenylethanol, showed an extensive hydrogen bonding network involving the OH functionalities of six neighbouring molecules, arranged in a hexagonal pattern. Electrochemical studies, utilising cyclic voltammetry, were performed on all compounds synthesised, including precursor compounds. Electrochemical experiments were conducted in DCM and 0.1 M [NBu4][B(C6F5)4] as supporting electrolyte. A trend was observed between the number of –CH2– spacers and the formal reduction potentials (E°´) for both the carboxylic acids and alcohols. The formal reduction potentials for both the carboxylic acids and the alcohols were found to decrease as the number of –CH2– spacers increased. Dimerisation of the osmocenyl moiety, similar to the known dimerisation of ruthenocene, was observed. It was found that the degree of dimerisation diminishes as the number of –CH2– groups increases for both the osmocenecontaining carboxylic acids and alcohols. The formal reduction potentials for 2-osmocenylethanoic acid, 3-osmocenylpropanoic acid and 4-osmocenylbutanoic acid are 418 mV, 357 mV and 317 mV, respectively. The formal reduction potentials for osmocenylmethanol, 2-osmocenylethanol, 3-osmocenylpropanol, and 4-osmocenylbutanol, are 410 mV, 340 mV, 313 mV and 321 mV, respectively. Dimerisation was observed electrochemically for 2-osmocenylethanoic acid, 3-osmocenylpropanoic acid, 2-osmocenylethanol and 3-osmocenylpropanol. No dimerisation was observed electrochemically for 4-osmocenylbutanoic acid and 4-osmocenylbutanol.