To Sandwich Technetium: Highly Functionalized Bis‐Arene Complexes [99mTc(η6‐arene)2]+ Directly from Water and [99mTcO4]−.

The labeling of (bio)molecules with metallic radionuclides such as 99mTc demands conjugated, multidentate chelators. However, this is not always necessary since phenyl rings can directly serve as integrated, organometallic ligands. Bis‐arene sandwich complexes are generally prepared by the Fischer–Hafner reaction. In extension of this, we show that [99mTc(η6‐C6R6)2]+‐type complexes are directly accessible from water and [99mTcO4]−, even using arenes incompatible with Fischer–Hafner conditions. To unambiguously confirm the nature of these unprecedented 99mTc complexes, their rhenium homologous have been prepared by substituting naphthalene ligands in [Re(η6‐C10H8)2]+ with the corresponding phenyl groups. The ease with which highly stable [99mTc(η6‐C6R6)2]+ complexes are formed under standard labeling conditions enables a multitude of new potential imaging agents based on commercial pharmaceuticals or lead structures. [ABSTRACT FROM AUTHOR]