Unsymmetrical Iron P-NH-P' Catalysts for the Asymmetric Pressure Hydrogenation of Aryl Ketones.
The reductive amination of α-dialkylphosphine acetaldehydes with enantiopure β-aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P'. Four new ligands PR2CH2CH2NHCHR'CHR''PPh2(R=iPr, Cy, R'=Ph, CH(CH3)2, R''=Ph, H) prepared in this way are used to make the iron(II) complexes mer-FeCl2(CO)(P-NH-P') and mer-FeCl(H)(CO)(P-NH-P'). The hydride complex with the rigid ligand with R'=R''=Ph is an efficient and highly enantioselective homogeneous asymmetric pressure hydrogenation (APH) catalyst. Prochiral aryl ketones are reduced under mild conditions (THF, 0.1 mol % catalyst, 1 mol % KOtBu, 5-10 bar, 50 °C) to the (S)-alcohols, usually in enantiomeric excess (ee) greater than 90 %. DFT calculations provided transition-state structures for the enantiodetermining hydride-transfer step.
Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario, M5S3H6, Canada.
Samantha A M
SAM
Smith
Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario, M5S3H6, Canada.
Paraskevi O
PO
Lagaditis
Department of Chemistry, Johannes Gutenberg University, Mainz, Saarstraße 21, 55122, Mainz, Germany.
Anne
A
Lüpke
Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario, M5S3H6, Canada.
Alan J
AJ
Lough
Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario, M5S3H6, Canada.
Robert H
http://orcid.org/0000-0002-7574-9388
RH
Morris
asymmetric synthesis; hydrogenation; iron catalysts; ketone reduction; pincer ligand synthesis