Reactions of the alkyl isocyanide fac-[Tc­(CO)3(CNR)2Cl] complexes (2) (CNR = CN n Bu or CN t Bu) with the sterically encumbered isocyanide CNp-FArDarF2 [DArF = 3,5-(CF3)2C6H3] allow a selective exchange of the carbonyl ligands of 2 and the isolation of the mixed-isocyanide complexes mer,trans-[Tc­(CNp-FArDarF2)3(CNR)2Cl] (3). Depending on the steric requirements of the residues R, the remaining chlorido ligand can be replaced by another isocyanide ligand. Cationic complexes such as mer-[Tc­(CNp-FArDarF2)3(CN n Bu)3]+ (4a) or mer,trans-[Tc­(CNp-FArDarF2)3(CN n Bu)2(CN t Bu)]+ (6) have been prepared in this way and isolated as their PF6 – salts. mer,trans-[Tc­(CNp-FArDarF2)3(CN n Bu)2(CN t Bu)]­(PF6) represents to the best of our knowledge the first transition-metal complex with three different isocyanides in its coordination sphere. Since the degree of the ligand exchange seems to be controlled both by the electronic and steric measures of the incoming isocyanides, we undertook similar reactions with the sterically less demanding p-fluorophenyl isocyanide, CNPhpF, which indeed readily led to the hexakis­(isocyanide)­technetium­(I) cation through an exchange of all ligands in the staring materials [Tc2(CO)6(μ-Cl)3]− or fac-[Tc­(CO)3(CNR)2Cl]. The influence of the substituents at the isocyanide ligands in such reactions has been reasoned with the density functional theory-derived electrostatic potential at the accessible surface of the corresponding isocyanide carbon atoms.

Organometallic approaches are of ongoing interest for the development of novel functional 99mTc radiopharmaceuticals, while the basic organotechnetium chemistry seems frequently to be little explored. Thus, structural and reactivity studies with the long-lived isotope 99Tc are of permanent interest as the foundation for further progress in the related radiopharmaceutical research with this artificial element. Particularly the knowledge about the organometallic chemistry of high-valent technetium compounds is scarcely developed. Here, phenylimido complexes of technetium(V) with different isocyanides are introduced. They have been synthesized by ligand-exchange procedures starting from [Tc(NPh)Cl3(PPh3)2]. Different reactivity patterns and products have been obtained depending on the steric and electronic properties of the individual ligands. This involves the formation of 1:1 and 1:2 exchange products of Tc(V) with the general formulae [Tc(NPh)Cl3(PPh3)(isocyanide)], cis- or trans-[Tc(NPh)Cl3(isocyanide)2], but also the reduction in the metal and the formation of cationic technetium(I) complex of the formula [Tc(isocyanide)6]+ when p-fluorophenyl isocyanide is used. The products have been studied by single-crystal X-ray diffraction and spectroscopic methods, including IR and multinuclear NMR spectroscopy. DFT calculations on the different isocyanides allow the prediction of their reactivity towards electron-rich and electron-deficient metal centers by means of the empirical SADAP parameter, which has been derived from the potential energy surface of the electron density on their potentially coordinating carbon atoms.

A series of technetium complexes with the sterically encumbered m-terphenyl isocyanides CNAr Dipp2 (Dipp = 2,6diisopropylphenyl) and CNAr Mes2 (Mes = 2,4,6-trimethylphenyl) has been prepared. The products span three different oxidation states (+1, +3, and +5) of the radioactive transition metal and comprise carbonyl, nitrosyl, chloride, and nitrido complexes. All members of this series (trans,mer-[Tc I (CO) 3 Cl(CNAr Dipp2 )], trans-[Tcand trans-[Tc V (NPh)X 2 (CNAr Dipp2 ) 2 ] (X = Cl, Br)) are stable under ambient conditions. The ν CN IR frequencies measured for the complexes frequently appear at wavenumbers higher than those for the uncoordinated isocyanides, which suggests a low degree of back-donation into the CN π* orbitals of these ligands.

p‐Fluorophenylisocyanide (CNPhpF) reacts with [Re(CO)5Br] under stepwise exchange of the carbonyl ligands depending on the conditions applied. The reaction stops with the formation of fac‐[Re(CO)3Br(CNPhpF)2] in boiling THF. An ongoing carbonyl exchange is observed at higher temperatures, e. g. in refluxing toluene, with the final formation of the [Re(CNPhpF)6]+ cation. The progress of the reactions has been studied by 19F NMR spectroscopy and the structures of [Re(CO)Br(CNPhpF)4] and [Re(CNPhpF)6](BPh4) have been elucidated by X‐ray diffraction.

Calix­[4]­arene-analogous technetium supramolecules (1 and 2) were assembled using (NBu4)­[Tc2(μ-Cl)3(CO)6] and neutral flexible bidentate nitrogen-donor ligands (L1 and L2) consisting of four arene units covalently joined via methylene units. The neutral homoleptic technetium macrocycles adopt a partial cone/cone-shaped conformation in the solid state. These supramolecules are the first example of fac-[Tc­(CO)3]+ core-based metallocalix[4]­arenes and second example of fac-[Tc­(CO)3]+ core-based metallomacrocycles. Structurally similar fac-[Re­(CO)3]+ core-based macrocycles (3 and 4) were also prepared using [Re­(CO)5X] (where X = Cl or Br) and L1 or L2. The products were characterized spectroscopically and by X-ray analysis.