Switchable synthesis of aldehydes and alcohols by hydroformylation with ligand-modified Rh single-atom catalyst

Controlling product selectivity in catalysis is fundamental for green synthesis, yet challenging, especially aiming for switchable outcomes between different products within a single catalytic system. This is exemplified in the industrially crucial hydroformylation reaction, where achieving controlled switching between aldehydes and alcohols remains difficult due to the inability of uniform active site to independently govern the hydrogenation and desorption steps of the aldehyde intermediate. Herein, we report CeO₂-supported single-atom Rh catalyst, in which triphenylphosphine (PPh₃) serves as molecular switch to precisely modulate the chemoselectivity between alcohols and aldehydes in alkene hydroformylation with broad substrate compatibility and excellent stability. The Rh/CeO₂ exhibits up to 99% chemoselectivity and 93% yield toward alcohols, while the PPh₃-Rh/CeO₂ shifts the chemoselectivity to aldehydes with up to 99% with 91% yield. Characterizations and theoretical calculations reveal that the coordination of PPh₃ modulates the electronic structure of Rh, increasing the electron density at Rh centers. This electronic modification alters the hydrogenation pathway from oxygen-then-carbon to carbon-then-oxygen, raising the Gibbs free energy barrier for the rate-determining step of aldehyde hydrogenation by 0.26 eV, thereby switching the chemoselectivity to aldehyde. This work establishes ligand-modified single-atom catalysts as a versatile platform for controlling reaction chemoselectivity.