Cationic Bis(η<sup><b>6</b></sup>‑arene)\nCobalt(I) Complexes: Enabling Catalyst Discovery by High-Throughput\nExperimentation

Cationic,\n20-electron bis(η<sup>6</sup>-arene)Co(I)\ncomplexes\nhave been synthesized and evaluated as precursors for the generation\nof bis(phosphine) cobalt(I) η<sup>6</sup>-arene precatalysts.\nThe arenes and anions in the precursors were varied, with isolated\nexamples, including [Al(<i>pftb</i>)<sub>4</sub>]<sup>−</sup> (<i>pftb</i> = (CF<sub>3</sub>)<sub>3</sub>CO), [BAr<sup>F</sup><sub>4</sub>]<sup>−</sup> (tetrakis[3,5-bis(trifluoromethyl)phenyl]borate),\nand [SbF<sub>6</sub>]<sup>−</sup>. Treatment of the isolated\nprecursors with a series bis(phosphines) resulted in arene displacement\nand isolation of well-defined [(bis(phosphine))Co(η<sup>6</sup>-arene)][<i>X</i>] (<i>X</i> = Al(<i>pftb</i>)<sub>4</sub><sup>–</sup> and SbF<sub>6</sub><sup>–</sup>; arene = C<sub>6</sub>H<sub>6</sub>, C<sub>6</sub>H<sub>5</sub>Me,\nand C<sub>6</sub>H<sub>5</sub>Et) complexes in 84–99% yield.\nThis ligand substitution enabled unprecedented generation of catalyst\nlibraries using high-throughput experimentation (HTE) for asymmetric\nalkene hydrogenation, as well as formal [2 + 2] cycloaddition, hydroboration,\nand C(<i>sp</i><sup>2</sup>)–H functionalization.\nThese versatile precursors simplify increasingly complex chemical\ntransformations by introducing single-component, well-defined precatalysts\nthrough general ligand substitution.