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Cyclic Enolates of Ni and Pd: Equilibrium between C‐ and O‐Bound Tautomers and Reactivity Studies
Author(s) -
Cámpora Juan,
Maya Celia M.,
Palma Pilar,
Carmona Ernesto,
Gutiérrez Enrique,
Ruiz Caridad,
Graiff Claudia,
Tiripicchio Antonio
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500622
Subject(s) - tautomer , chemistry , metallacycle , nickel , enol , medicinal chemistry , diphosphines , keto–enol tautomerism , reactivity (psychology) , carbon atom , stereochemistry , catalysis , organic chemistry , ring (chemistry) , x ray crystallography , physics , alternative medicine , medicine , pathology , diffraction , optics
2‐Acylaryl complexes of Ni and Pd containing chelating diphosphines react with K t BuO to give metallacyclic enolate complexes. While coordination through the carbon atom is preferred in the case of Pd, the nickel O ‐enolate compounds are formed as the corresponding O‐tautomers. Slow equilibration between O ‐ and C ‐enolate tautomers is observed for the nickel complex with an unsubstituted enolate function (MOCCH 2 ). Theoretical DFT calculations suggest that the barrier for the tautomer exchange has its origin in the rigidity of the metallacycle. Whilst the C ‐enolate tautomer is unreactive towards aldehydes, the corresponding O ‐enolate adds to MeCHO and PhCHO, giving rise to products that retain the enolate functionality. The carbonylation of these products cleanly leads to the formation of enol lactones in a highly selective manner.