Synthesis and investigation of square planar bis(ferrocenyl) dithiolene complexes of nickel, palladium, and platinum: Control of near-infrared absorption and other properties by ligand modification

Date of Completion

January 2002


Chemistry, Inorganic|Chemistry, Organic




Fifteen ferrocenyl-substituted d8 transition-metal dithiolenes were synthesized to investigate the chemical and physical properties of this class of square-planar complexes. The synthetic methods developed afforded precise control over the near-infrared maximum absorption wavelength, solubility, and other properties of these dyes. ^ The nickel, palladium, and platinum bis(ferrocenyl) dithiolenes displayed a range of maximum absorption wavelength from 1007 nm to 1737 nm with very low absorbance in the visible region of the spectrum. Three dyes were found to absorb at longer wavelengths than any other dithiolene complex. With respect to the near-infrared absorption mechanism associated with these materials, the 1737 nm value represents the lowest-energy electronic transition known for any complex. These dyes were found to be air-stable and did not suffer oxidative decomposition associated with other low-energy absorbers. ^ It was shown that absorption frequency maxima varied with the degree of rotational freedom and donor strength of the ferrocenyl substituents, although peak intensities were not greatly affected. The absorption frequency of a secondary electronic transition, common to this class of ferrocenyl dithiolenes and located at the edge of the visible region, was found to be predominantly influenced by inductive effects rather than coplanarity or extension of a delocalized π-system. ^ Dyes were functionalized so that their absorption behavior could be studied in both polar and nonpolar solvents, ranging from dimethylformamide and water (pH 3 to 9) to methylene chloride and hexane. Such functionalization has expanded the potential for use of these dithiolenes. One dye has been combined with an immunoconjugate molecule to form a prototypical photodynamic therapeutic agent. The demonstrated antitumor activity of this new material results in large part from the response to near-infrared radiation of the bis(ferrocenyl) dithiolene complex. ^