Bis(triphenylphosphine)iminium Salts of the Low-Valent Carbonyltechnetates [Tc2(CO)9Cl]− and [Tc(CO)3Cl3]2−

Reduction of [Tc(CO)5Br] with sodium amalgam, sodium naphthalenide, or potassium graphite in THF and subsequent addition of bis(triphenylphosphine)iminium chloride, (PPN)Cl, gave mixtures of the orange-yellow Tc(0) compound (PPN)[Tc(CO)9Cl], (PPN)[1], and the colorless Tc(I) complex (PPN)2[Tc(CO)3Cl3], (PPN)2[2]. The products have been studied by X-ray diffraction and NMR spectroscopy. The dimeric compound [1]− represents the first example of an anionic technetium(0) complex with only one halide ligand in its coordination sphere. The equatorial carbonyl (and chlorido) ligands at the two technetium atoms show the expected staggered conformation around the (CO)Tc–Tc(CO) axis. The Tc–Tc bond is 3.0269(7) Å. The different nature of the two technetium atoms in compound [1]− is reflected by the appearance of two different 99Tc NMR signals in CD2Cl2 at −1770 and −2487 ppm, while the corresponding signal of the technetium(I) anion [2]2− appears at −953 ppm in the same solvent. Anion [2]2− shows the expected facial arrangement of the carbonyl and chlorido ligands. The use of the bulky PPN+ cation allowed the first determination of the [Tc(CO)3Cl3]2− structure by X-ray diffraction without significant interference due to disorder effects in the coordination sphere of the transition metal.