Versatile Strategy for Organic Surface Modification of Cobalt Phosphide Using Iodonium Salts Enables Systematic Tuning for Hydrogenation Catalysis

Ligand-directed catalysis is a powerful tool to tune catalytic reactions. While this has been demonstrated for metal-based catalysts, versatile and controllable approaches for surface modification are lacking for emerging transition metal phosphide-based catalysts. Herein, we report a novel method for the surface functionalization of cobalt phosphide (<b>CoP</b>) using iodonium salts and compare it to an adapted literature method using diazonium salts. We show that the method using iodonium salts offers distinct advantages. A range of aryl and alkyl groups with varied steric and electronic properties can be introduced to the <b>CoP</b> surface using iodonium salts, while diazonium salt-based approaches are usually limited to aryl groups. Our method using iodonium salts further allowed control and quantification of surface coverage using the organo-iodines formed during modification. This is more challenging with highly reactive diazonium salts that often lead to multilayers. The utility of our surface modification approach for <b>CoP</b> is demonstrated for catalysis by testing a series of modified <b>CoP</b> materials with systematically varied steric and electronic properties and with varied surface coverage as catalysts for the hydrogenation of α,β-unsaturated aldehydes. A pronounced selectivity enhancement to the desired unsaturated alcohol was observed with surface-modified <b>CoP</b>. Our results show that the best selectivity can be obtained with dense, sterically demanding, and electron-donating organic surface ligands. Overall, our work significantly expands the chemical space accessible for modified transition metal phosphides and paves the way for the development of these materials for new catalytic applications.