Cationic Bis(η^<b>6</b>-arene) Cobalt(I) Complexes: Enabling Catalyst Discovery by High-Throughput Experimentation

Cationic, 20-electron bis(η6-arene)Co(I) complexes have been synthesized and evaluated as precursors for the generation of bis(phosphine) cobalt(I) η6-arene precatalysts. The arenes and anions in the precursors were varied, with isolated examples, including [Al(pftb)4]− (pftb = (CF3)3CO), [BArF4]− (tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), and [SbF6]−. Treatment of the isolated precursors with a series bis(phosphines) resulted in arene displacement and isolation of well-defined [(bis(phosphine))Co(η6-arene)][X] (X = Al(pftb)4– and SbF6–; arene = C6H6, C6H5Me, and C6H5Et) complexes in 84–99% yield. This ligand substitution enabled unprecedented generation of catalyst libraries using high-throughput experimentation (HTE) for asymmetric alkene hydrogenation, as well as formal [2 + 2] cycloaddition, hydroboration, and C(sp2)–H functionalization. These versatile precursors simplify increasingly complex chemical transformations by introducing single-component, well-defined precatalysts through general ligand substitution.