Redox Isomerization of Allylic Alcohols to Carbonyl Compounds Catalyzed by Ruthenium(IV) Complexes Containing N-Heterocyclic Ligands in Ionic Liquids
Francisco J. Suarez, Cristian Vidal and Joaquin Garcia-Alvarez
Affiliation: Laboratorio de Compuestos Organometalicos y Catalisis (Unidad Asociada al CSIC). Departamento de Quimica Organica e Inorganica, Instituto Universitario de Quimica Organometalica Enrique Moles, Facultad de Quimica, Universidad de Oviedo, Julian Claveria 8, E-33006, Oviedo, Spain.
Keywords: Allylic alcohols, ionic liquids, recovery, redox isomerizations, ruthenium catalyst.
Bis-allyl ruthenium(IV) complexes containing N-heterocyclic ligands [Ru(η3:η3-C10H16)Cl2(κ1-N-L)] (L =
pyrazole (1a), benzimidazole (1b)) are active catalysts in the redox isomerization of allylic alcohols into saturated carbonyl
compounds using the ionic liquid [BMIM][BF4] (BMIM = 1-butyl-3-methylimidazolium) as a non-conventional reaction
media in the absence of additional base. Complex 1b has been found to be the most efficient catalyst for the isomerization
of a series of primary and secondary allylic alcohols (9 substrates). In addition, we have studied the effect of
the counter anion in the ionic liquid finding that non coordinating anions (BF4-, PF6- and SbF6-) led to the best reactions
times and conversion, when compared with the coordinating chloride anion (Cl-). It is important to note that the catalytic
system could be recovered through seven catalytic cycles with only partial loss of the initial activity in the first five cycles.
Since this catalytic system: i) shows high efficiency and selectivity, ii) involves no presence of phosphines or any
base as co-catalyst, iii) proceeds without the formation of by-products (atom economy), and iii) is readily recovered, it can
be considered as a genuine example of a Green chemical process.
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