Hydroformylation of Olefins With Paraformaldehyde Catalyzed by a Rhodium(I)/Diphosphine/Diphosphoramidite System

A new dual-ligand rhodium catalytic system based on [RhCl(cod)]2 and BINAP or BIPHEP in combination with a readily accessible diphosphoramidite ligand has been developed for the hydroformylation of olefins using paraformaldehyde as a syngas surrogate. The catalytic system efficiently hydroformylates a broad range of substrates, including vinyl arenes, alkyl olefins, cyclopentene, and allyl acetate. High regioselectivity toward the linear aldehyde (up to 80%) was achieved for several aryl alkenes, with performances comparable to those obtained under conventional hydroformylation conditions. Hydroformylation of 1-decene revealed a strong influence of reaction temperature, reflecting competition between hydroformylation and olefin isomerization. 31P and 1H nuclear magnetic resonance (NMR) studies identified a trigonal bipyramidal rhodium dicarbonyl hydride complex containing an equatorially coordinated diphosphoramidite ligand, providing evidence that this species is involved in the catalytic cycle. These results demonstrate the potential of inexpensive diphosphoramidite ligands for syngas-free rhodium-catalyzed hydroformylation.