Multifunctional Cyclopentadienes as a Scaffold for Combinatorial Bioorganometallics in [(η 5 ‐C 5 H 2 R 1 R 2 R 3 )M(CO) 3 ] (M=Re, 99m Tc) Piano‐Stool Complexes

Multifunctional cyclopentadiene (Cp) ligands and their rhenium and 99m Tc 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 ‐[ 99m Tc(CO) 3 ] + cores to give tetrafunctional complexes in straightforward and functional‐group‐tolerant procedures. The 99m Tc complexes were prepared in one step, in 30 min, and under aqueous conditions from generator‐eluted [ 99m TcO 4 ] − .