We have investigated the exchange dynamics between the free and bound ligand in K-3[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)-bi-naphthol, 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, K-3[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.

Ligand Lability and Chirality Inversion in Yb Heterobimetallic Catalysts

DI BARI, LORENZO;SALVADORI, PIERO
2004

Abstract

We have investigated the exchange dynamics between the free and bound ligand in K-3[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)-bi-naphthol, 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, K-3[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; Lelli, M.; Salvadori, Piero
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/187975
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