Ligand lability and chirality inversion in yb heterobimetallic catalysts.
We have investigated the exchange dynamics between the free and bound ligand in K3[Yb[(R)-binol]3], the most active heterobimetallic lanthanoid catalyst for cyclic imine hydrophosphonylation; we found that the Yb-binol bond is labile. The rate constant for this exchange was determined through NMR saturation transfer experiments. Upon addition of (S)-binaphthol, ligand exchange leads to the formation of a small quantity of heterochiral complexes and, in the presence of a molar excess of (S)-binaphthol, to chirality inversion of the whole complex. This demonstrates that, in contrast to other analogous systems, K3[Yb(binol)3] displays a strong chiral discrimination, with the overwhelming preference for ligands of the same configuration. The lability of Yb-binol bond in THF may suggest a ligand-to-substrate exchange as a key step in the catalytic process.
Di Bari
Lorenzo
L
CNR-ICCOM sez. di Pisa, Dipartimento di Chimica e Chimica Industriale via Risorgimento 35, 56126 Pisa, Italy.
Lelli
Moreno
M
Salvadori
Piero
P
D002384:Catalysis; D007097:Imines / Q000138:chemical synthesis; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008672:Metals, Alkali / Q000737:chemistry*; D015394:Molecular Structure; D009284:Naphthols / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D015018:Ytterbium / Q000737:chemistry*
D007097:Imines; D008024:Ligands; D008672:Metals, Alkali; D009284:Naphthols; D009942:Organometallic Compounds; D015018:Ytterbium