Synthesis and Characterization of <i>fac</i>-[M(CO)<sub>3</sub>(P)(OO)] and <i>cis-trans</i>-[M(CO)<sub>2</sub>(P)<sub>2</sub>(OO)] Complexes (M = Re, <sup>99m</sup>Tc) with Acetylacetone and Curcumin as OO Donor Bidentate Ligands
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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.
