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)­(OO)] and cis-trans-[M­(CO)2(P)2(OO)] (M = Re, 99mTc), 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, 99mTc) 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 β-amyloid plaques of Alzheimer’s disease. At the 99mTc tracer level, the same type of complexes, fac-[99mTc­(CO)3(P)­(OO)] and cis-trans-[99mTc­(CO)2(P)2(OO)], are formed introducing new donor combinations for 99mTc­(I). Overall, β-diketonate and phosphine constitute a versatile ligand combination for Re­(I) and 99mTc­(I), and the successful employment of the multipotent curcumin as β-diketone provides a solid example of the pharmacological potential of this system.