We
demonstrate, for the first time, that pentamethylcyclopentadienyl
(Cp*) iridium pyridinecarboxamidate complexes (<b>5</b>) can
promote <i>catalytic</i> hydride transfer from nicotinamide
adenine dinucleotide to aldehydes in pH 7.4 buffered cell growth media
at 37 °C and in the presence of various biomolecules and metal
ions. Stoichiometric hydride transfer studies suggest that the unique
reactivity of <b>5</b>, compared to other common Cp*Ir complexes,
is at least in part due to the increased hydride transfer efficiency
of its iridium hydride species <b>5-H</b>. Complex <b>5</b> exhibits excellent reductase enzyme-like activity in the hydrogenation
of cytotoxic aldehydes that have been implicated in a variety of diseases
