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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Abstract
The
synthesis and characterization of neutral mixed ligand complexes <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)] (M = Re, <sup>99m</sup>Tc),
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 <i>fac-</i>[M(CO)<sub>3</sub>(H<sub>2</sub>O)(OO)] (M = Re, <sup>99m</sup>Tc) intermediate aqua complex.
In the presence of phosphine, replacement of the H<sub>2</sub>O molecule
of the intermediate complex at room temperature generates the neutral
tricarbonyl monophosphine <i>fac</i>-[Re(CO)<sub>3</sub>(P)(OO)] complex, while under reflux conditions further replacement
of the trans to the phosphine carbonyl generates the new stable dicarbonyl
bisphosphine complex <i>cis-trans</i>-[Re(CO)<sub>2</sub>(P)<sub>2</sub>(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 <sup>99m</sup>Tc tracer level, the same type of complexes, <i>fac</i>-[<sup>99m</sup>Tc(CO)<sub>3</sub>(P)(OO)] and <i>cis-trans</i>-[<sup>99m</sup>Tc(CO)<sub>2</sub>(P)<sub>2</sub>(OO)], are formed
introducing new donor combinations for <sup>99m</sup>Tc(I). Overall,
β-diketonate and phosphine constitute a versatile ligand combination
for Re(I) and <sup>99m</sup>Tc(I), and the successful employment of
the multipotent curcumin as β-diketone provides a solid example
of the pharmacological potential of this system
