Co-catalysis for one-pot tandem hydroformylation-aldol condensation-hydrogenation with involvement of phosphino-phosphonium based bi-functional ligand and aniline

Co-catalysis in the way of synergetic catalysis and sequential catalysis has emerged as a powerful tool to achieve one-pot tandem reaction. Herein, a tri-functional catalytic system containing phosphino-phosphonium bi-functional ligand (L2) based Rh-catalyst and aniline was developed for three-step tandem hydroformylation-aldol condensation-hydrogenation to produce ketones from olefins. It was found that the intramolecular bi-functionalities of phosphino-fragment and phosphonium [P(V)⁺] in L2 greatly facilitated hydroformylation due to their synergetic effect on activation of carbonyl ([sbnd]C[dbnd]O) in Rh-acyl intermediate. In addition, the phosphonium in L2 also served as a Lewis acid to catalyse condensation of acetone with aniline to form enamine catalyst. The latter with more nucleophilicity was able to attack the aldehydes (formed from the preceding hydroformylation) to accomplish the subsequent aldol condensation along with the release of aniline. Finally, the obtained α,β-unsaturated ketones were hydrogenated to yield ketones over L2-based Rh-catalyst under the hydroformylation conditions. Such tri-functional catalytic system in combination of transition-metal catalysis, Lewis acid catalysis and enamine catalysis also exhibited good generality for the tandem hydroformylation-aldol condensation-hydrogenation of the different olefins to produce ketones.