Pentamethylcyclopentadienyl iridium-aqua complexes can be employed as catalysts for a variety of transformations in both aqueous and organic solvents to aid in the catalytic synthesis of molecular fuels. Traditional methods to access the iridium-aqua complexes from their halide precursors rely on solubility-driven halide removal using silver salts. Typically, an excess of the silver salt is required for complete conversion from the iridium-halide complex to the desired iridium-aqua product. The residual, redox-active silver frequently bedevils electrochemical experiments, as it overlaps with the iridium-aqua complex’s cyclic voltametric response. To avoid this interference, we developed a new solid-phase synthetic approach to synthesize the iridium-aqua complexes directly from their iridium-halide precursor, completely bypassing the use of silver. This new pathway is less expensive than utilizing silver salts and does not compromise yields of, or conversions to, the iridium-aqua complexes. We have optimized and expanded the versatility of this method by substantially reducing the volume of the conversion reagent (water) needed and expanding the ligand screen to include bipyridine ligands with methyl (4,4’-Dimethyl-2,2’-bipyridine) and methoxy (4,4’-Dimethoxy-2,2’-bipyridine) substituents in addition to unsubstituted 2,2’-bipyridine ligand. Our method results in the successful conversion of three halide ligands (chloride, bromide, or iodide) to an aqua ligand. Product characterization by ¹H NMR spectroscopy and cyclic voltammetry confirms successful conversion of the iridium-halide to the desired iridium-aqua complex and the absence of any adventitious silver.

Melanie Oliva

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