Synthesis and Characterization of fac-[M(CO)3(P)(OO)] and cis-trans-[M(CO)2(P)2(OO)] Complexes (M = Re, 99mTc) with Acetylacetone and Curcumin as OO Donor Bidentate Ligands

The synthesis and characterization of neutral mixed ligand complexes fac-[M(CO)(3)(P)(00)] and cis-trans-[M(CO)(2)(P)2(OO)] (M = Re, Tc-99m), with deprotonated acetylacetone or curcumin as the OO donor bidentate ligands and a phosphine (triphenylphosphine or methyldiphenylphosphine) as the monodentate P ligand, is described. The complexes were synthesized through the corresponding fac-[M(CO)(3)(H2O)(OO)] (M = Re, Tc-99m) intermediate aqua complex. In the presence of phosphine, replacement of the H2O molecule of the intermediate complex at room temperature generates the neutral tricarbonyl monophosphine fac-[Re(CO)(3)(P)-(OO)] complex, while under reflux conditions further replacement of the trans to the phosphine carbonyl generates the new stable dicarbonyl bisphosphine complex cis-trans-[Re(CO)(2)(P)(2)(OO)]. The Re complexes were fully characterized by elemental analysis, spectroscopic methods, and X-ray crystallography showing a distorted octahedral geometry around Re. Both the monophosphine and the bisphosphine complexes of curcumin show selective binding to beta-amyloid plaques of Alzheimer's disease. At the Tc-99m tracer level, the same type of complexes, fac-[Tc-99m(CO)(3)(P)(OO)] and cis-trans-[Tc-99m(CO)(2)(P)(2)(OO)], are formed introducing new donor combinations for Tc-99m(I). Overall, beta-diketonate and phosphine constitute a versatile ligand combination for Re(I) and Tc-99m(I), and the successful employment of the multipotent curcumin as beta-diketone provides a solid example of the pharmacological potential of this system.