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

The attachment of an ethyne substituent in the para position of phenylisocyanide, CNPh pC≡CH , enables the isocyanide to replace carbonyl ligands in the coordination sphere of common technetium(I) starting materials such as (NBu 4 )[Tc 2 (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(CNPh azole ) 6 ] + cation. The free, uncoordinated "Click" product is obtained from a reaction of the corresponding tetrakis(CNPh azole )copper(I) complex and NaCN. It readily reacts with mer -[Tc(CO) 3 (tht)(PPh 3 ) 2 ](BF 4 ) (tht = tetrahydrothiophene) under exchange of the thioether ligand. Alternatively, [Cu(CNPh azole ) 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 99m Tc, and a corresponding protocol for [ 99m Tc(CNPh azole ) 6 ] + is reported. The 99 Tc and copper complexes have been studied by single-crystal X-ray diffraction and/or spectroscopic methods including IR and multinuclear NMR spectroscopy.