Unique phosphine ligand synergy in asymmetric hydroformylation of styrene over the Rh@MOF-5 heterogeneous catalysis system

Abstract

For the heterogeneous reaction of asymmetric hydroformylation (AHF), a highly decentralized active Rh site played a key role in enhancing the yield of chiral isomeric aldehydes. Herein, the mesoporous Rh-loaded catalyst (Rh@MOF-5) was prepared using a zinc-based metal–organic framework (MOF-5) to serve as a carrier. During the AHF reaction, the HRh(BINAP)(CO)₂ component was formed by the combination of active Rh in Rh@MOF-5 and (R)-BINAP under a syngas atmosphere (H₂/CO = 1). The Rh@MOF-5 showed a higher yield of iso-aldehydes (Y_iso = 86.71%) and enantioselectivity (ee = 25.01%) of S-iso-aldehydes, which was attributed to the synergy of BINAP and the highly dispersed active Rh sites. Furthermore, density functional theory (DFT) calculation results show the feasible mechanism of HRh(BINAP)(CO)₂ catalyzed with 6 steps, and the Rh–H insertion step determined the type of product. The higher enantioselectivity and regioselectivity of S-iso-aldehydes using this catalyst were due to the lower barrier of the S-iso-aldehyde precursor than other product precursors in the step of Rh–H insertion.