Cationic Bis(η⁶-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), [BAr^F₄]⁻ (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.