US EPA

3072767 

Journal Article 

Asymmetric hydroformylation catalyzed by RhH(CO)₂[(R,S)-Yanphos]: mechanism and origin of enantioselectivity 

Lei, M; Wang, Z; Du, X; Zhang, X; Tang, Y 

2014 

1 

Journal of Physical Chemistry A
ISSN: 1089-5639
EISSN: 1520-5215 

118 

39 

8960-8970 

English 

24735053 

10.1021/jp501941b 

WOS:000342651200010 

Asymmetric hydroformylation (AHF) catalyzed by transition metal (TM) complexes bearing chiral phosphorus ligands is one of the most powerful synthetic ways that could provide chiral aldehydes directly from alkenes and syngas in one step. Experiments have proved the efficiency of Rh catalyst with hybrid phosphorus ligands owning two different phosphorus moieties in AHF. Herein the origin of enantioselectivity of AHF catalyzed by RhH(CO)2[(R,S)-Yanphos] was studied at M06/BSI level using the density functional theory (DFT) method to unveil a fundamental understanding on factors contributing to the efficiency in AHF. The alkene insertion step is supposed to be the chirality-determining step in the whole catalytic cycle of the Rh-Yanphos system. Four possible pathways of styrene (Sub1) insertion step (pathways R1, S1, R2, and S2) were discussed; the calculated results indicate that pathways R1 and S2 are proposed to be two dominant alkene insertion pathways and that styrene tends to adopt apical coordination mode (A mode) to Rh center in pathways R1 and S2 compared to equatorial coordination mode (E mode) in pathways R2 and S1. The enantioselectivity of AHFs of ten alkene substrates (CH2═CH-R, R═Ph, C(═O)OCH3, Ph-(p)-Me, Ph-(p)-OMe, Ph-(p)-(i)Bu, Ph-(p)-F, Ph-(p)-Cl, Ph-(o)-F, OC(═O)-Ph and O-Ph, corresponding alkenes are abbreviated as Sub1 to Sub10, respectively) were also investigated. The predicted chiralities agree well with experimental results. The present work suggests that the relative stabilities of coordination modes (A/E mode) of alkene to 2 (RhH(CO)[(R,S)-Yanphos]) might be of importance in the enantioselectivity of AHF catalyzed by Rh-Yanphos.