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 airsensitive
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.