Technetium Complexes with an Isocyano-alkyne Ligand and Its Reaction Products

The attachment of an ethyne substituent in the para position of phenylisocyanide, CNPhpCCH, enables the isocyanide to replace carbonyl ligands in the coordination sphere of common technetium­(I) starting materials such as (NBu4)­[Tc2(μ-Cl)3(CO)6]. The ligand exchange proceeds under thermal conditions and finally forms the corresponding hexakis­(isocyanide)­technetium­(I) complex. The product undergoes a copper-catalyzed cycloaddition (“Click” reaction), e.g., with benzyl azide, which gives the [Tc­(CNPhazole)6]+ cation. The free, uncoordinated “Click” product is obtained from a reaction of the corresponding tetrakis­(CNPhazole)­copper­(I) complex and NaCN. It readily reacts with mer-[Tc­(CO)3(tht)­(PPh3)2]­(BF4) (tht = tetrahydrothiophene) under exchange of the thioether ligand. Alternatively, [Cu­(CNPhazole)4]+ can be used as a transmetalation reagent for the synthesis of the hexakis­(isocyanide)­technetium­(I) complex, which is the preferable approach for the synthesis of the technetium complex with the short-lived nuclear isomer 99mTc, and a corresponding protocol for [99mTc­(CNPhazole)6]+ is reported. The 99Tc and copper complexes have been studied by single-crystal X-ray diffraction and/or spectroscopic methods including IR and multinuclear NMR spectroscopy.