Multifunctional Cyclopentadienes as a Scaffold for Combinatorial Bioorganometallics in [(5-C5H2R1R2R3)M(CO)3] (M=Re, 99mTc) Piano-Stool Complexes

Multifunctional cyclopentadiene (Cp) ligands and their rhenium and Tc-99m complexes were prepared by a versatile synthetic route. The properties of these Cp ligands can be tuned on demand, either during their synthesis (variation of R-1) or through post-synthetic functionalization with two equal or different vectors (V-1 and V-2). Variation of these groups enables a combinatorial approach in the synthesis of bioorganometallic complexes. This is demonstrated by the preparation of Cp ligands containing both electron-donating and electron-withdrawing groups at the R-1 position and their subsequent homo- or heterofunctionalization with biovector models (benzylamine and phenylalanine) under standard amide bond-formation conditions. All ligands can be coordinated to the fac-[Re(CO)(3)](+) and fac-[Tc-99m(CO)(3)](+) cores to give tetrafunctional complexes in straightforward and functional-group-tolerant procedures. The Tc-99m complexes were prepared in one step, in 30min, and under aqueous conditions from generator-eluted [(TcO4)-Tc-99m](-).