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; Lelli, Moreno; Salvadori, Piero. - In: CHEMISTRY-A EUROPEAN JOURNAL. - ISSN 0947-6539. - STAMPA. - 10:(2004), pp. 4594-4598. [10.1002/chem.200400302]
Ligand lability and chirality inversion in Yb heterobimetallic catalysts
LELLI, MORENOWriting – Original Draft Preparation
;
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.File | Dimensione | Formato | |
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