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Room temperature asymmetric Pd-catalyzed methoxycarbonylation of norbornene: highly selective catalysis and HP-NMR studies.

Authors
  • Blanco, Carolina
  • Godard, Cyril
  • Zangrando, Ennio
  • Ruiz, Aurora
  • Claver, Carmen
Type
Published Article
Journal
Dalton Transactions
Publisher
The Royal Society of Chemistry
Publication Date
Jun 21, 2012
Volume
41
Issue
23
Pages
6980–6991
Identifiers
DOI: 10.1039/c2dt30267e
PMID: 22535338
Source
Medline
License
Unknown

Abstract

Palladium complexes bearing monodentate and bidentate phosphine ligands (1-7) were synthesised and used as catalyst precursors in the methoxycarbonylation of norbornene. The catalytic systems bearing ligands 1, 3 and 4 afforded excellent conversions (>99%) and selectivity of the ester (>99%). NMR investigations showed that using complex 1a as the precursor resulted in the protonated phosphine, 1-H(+), being formed under catalytic conditions and thus the addition of acid is not required for the activation of this system since the reaction involving the precursor with methanol under CO pressure produces 2 equivalents of HCl and leads to the formation of the active species. The protonation of ligand 4 under methoxycarbonylation conditions was also observed and the diprotonated diphosphine was isolated and characterised. This compound was tested as a ligand and acid source in a catalysis and provided excellent conversion and high selectivity to the ester.

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