Existence and Properties of [TcH(CO)5]

A preparation of [⁹⁹TcH(CO)₅] as a neat liquid or as a solution in a hydrocarbon solvent by treatment of [⁹⁹TcBr(CO)₅] with Na[BH₄] in an organic solvent–water mixture is presented. [⁹⁹TcH(CO)₅] was characterized by ¹H and ⁹⁹Tc NMR spectroscopy, IR spectroscopy, and EI MS. The reactivity of [⁹⁹TcH(CO)₅] was studied. It reacts readily with strong acids such as HClO₄ and F₃CCOOH to form [⁹⁹Tc(ClO₄)(CO)₅] and [⁹⁹Tc(O₂C–CF₃)(CO)₅], respectively, but does not react with weak acids such as HCOOH. [⁹⁹TcH(CO)₅] is moderately resistant to atmospheric oxygen in solution and is more air-sensitive in the neat form, gradually transforming into [⁹⁹Tc₃H(CO)₁₄]. The metal–hydrogen bond in [⁹⁹TcH(CO)₅] is oxidized with I₂ to form [⁹⁹TcI(CO)₅]. The oxidation pathway with molecular iodine differs from the ones observed for typical hydrides or acids and is rather characteristic for low-polarity covalent compounds. The carbonyl groups of [⁹⁹TcH(CO)₅] are quite resistant to substitutions by σ-donor ligands. To promote such substitutions, the Tc–H bond should be oxidatively cleaved. Unusual technetium carbonyl complexes, [(μ₃-CO₃)(⁹⁹Tc(bipy)(CO)₃)₃]⁹⁹TcO₄ and [⁹⁹Tc(phen)₂(CO)₂]⁹⁹TcO₄, are formed in the reactions of [⁹⁹TcH(CO)₅] with 2,2′-bipyridine and 1,10-phenanthroline in air. [⁹⁹Tc(phen)₂(CO)₂]⁺ is the first example of a technetium(I) dicarbonyl complex stabilized by ligands with weak π-acceptor properties.