There is a large series of Re(I) complexes of the formula fac-ReX(CO)3(L-L) (where X represents a variety of monodentate anionic ligands and L-L represents a large variety of α-diimines such as 2,2’-bipyridine, 1,10-phenthroline or their substituted derivatives). These complexes have been studied for, among other things, their ability to incorporate carbon dioxide from their surroundings as well as for their cytotoxic properties. Both properties are of much current interest. One of the more unusual anionic ligands found in the above series of rhenium(I) complexes is the alkylcarbonate ligand. Alkylcarbonate ligands are not commonly found supporting transition metal complexes and the alkylcarbonate ligands that are found for the above series of Re(I) complexes are prepared in a reaction that combines carbon dioxide from the reaction atmosphere with an alkoxide group from the organic alcohol of the reaction solvent. Our exploration of the reaction conditions for the formation of the alkylcarbonate found that a variety of high boiling alcohols can be combined with carbon dioxide to form the ligand. Our interest in the alkylcarbonate-stabilized complexes was primarily to explore acidolysis reactions of that particular ligand as a synthetic route to deliver other ligands in place of the alkylcarbonate. Two similar acidolysis reactions were successful. Acidolysis, with tetrafluoroboric acid solution as the acid source, of alkylcarbonate-stabilized complexes in a solvent such as acetonitrile leads to the formation of the ionic compound fac-[Re(CO)3(L-L)(NCMe)]BF4. Acidolysis of alkylcarbonate-stabilized complexes in a neat carboxylic acid or a mixed solvent of dichloromethane and carboxylic acid lead to the carboxylate-stabilized complexes such as fac-Re(O2CC5H11)(CO)3(1,10-phenanthroline). All of the complexes were characterized by NMR spectroscopy and some of the complexes were also characterized by cyclic voltammetry and\or optical spectroscopy. One product, fac-Re(O2CC5H11)(CO)3(1,10-phenanthroline), was examined with respect to cytotoxicity versus two human cancer cell lines and one normal human cell line. The complex was found to express selective cytotoxicity towards the cancer cell lines versus the normal cell lines.

Cytotoxicity of a carboxylate-supported complex of rhenium(I) prepared from the acidolysis reaction of a pentylcarbonato ligand

ACS Spring Meeting 2021

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