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.