- Vinylic, allylic and homoallylic oxidations of alkenes via π- and σ-organopalladium complexes
-
The stoichiometric and catalytic pathways of oxidative esterification of alkenes via intermediate organopalladium complexes are discussed. The oxidation of propylene, hex-1-ene and cyclohexene by PdII acido complexes containing achiral, racemic and chiral carboxylate ligands was first studied in a series of solvents other than acetic acid. Significant changes in the selectivity of the PdII-promoted reaction with changes in the solvent nature and ligand chirality were observed. A way to allylic esters based on low-valence Pd nanoclusters provide highly selective oxidation of acyclic alkenes into allylic esters, whereas cycloalkenes undergo mostly redox disproportionation. The role of π-alkene, σ-alkenyl and π-allyl complexes in the mechanism of the alkene oxidative esterification with PdII complexes and low-valence Pd clusters is discussed.
- Kozitsyna, N.Yu.,Vargaftik,Moiseev
-
p. 274 - 291
(2007/10/03)
-
- The effects of the solvent and the ligand chirality on the regioselectivity of alkene oxidative esterification by PdII carboxylates
-
The effects of the solvent and the ligand chirality on the regioselectivity of oxidative esterificanon of propylene and cyclohexene by PdII carboxylates were studied using achiral (MeCO2-, Me2CHCH2CO2-), racemic ((±)-CF3CF2CF2OC*F(CF3) CO2-) and chiral ((S)-(+)-MeC*H(Et)CO2-, (+)-CF3CF2CF2OC*F(CF3)CO2 -) carboxylate ligands. The oxidation of alkenes in aprotic media (CHCl3, CH2C12, CO2, THF) affords mainly allylic esters (in the case of cyclohexene also homoallylic esters) and the oxidative esterification at the vinylic position is absent. In weakly solvating media (CHCl3, CH2Cl2) the regioselectivity of cyclohexene oxidation (the allyl to homoallyl ratio) increases substantially on going from achiral or racemic acido ligands to chiral acido ligands. In a more donor medium (THF) the ligand chirality effect almost vanishes. The effects of the ligand chirality and the nature of the solvent on the mechanism of alkene oxidation by PdII complexes are discussed.
- Kozitsyna,Martens,Stolyarov,Gekhman,Vargaftik,Moiseev
-
p. 1673 - 1681
(2007/10/03)
-
- Structure-reactivity dependence in the rearrangements of a family of alkylacetoxycarbenes
-
Absolute rate constants and activation parameters are presented for the 1,2-H and 1,2-acetyl migrations of a family of alkylacetoxycarbenes.
- Moss, Robert A.,Merrer, Dina C.
-
p. 8067 - 8070
(2007/10/03)
-
- Formation of Glycol Monoacetates in the Oxidation of Olefins Catalyzed by Metal Nitro Complexes: Mono- vs. Bimetallic System
-
The oxidation of terminal olefins by bis(acetonitrile)chloronitropalladium(II) (1) in acetic acid leads to a mixture of glycol monoacetate isomers as the main products.Various amounts of ketones and unsaturated acetates are also formed.The rate of formation and the yield of glycol monoacetate decrease with increasing chain length.Cyclic olefins yield no glycol monoacetates.Replacement of acetic acid by stronger or sterically hindered carboxylic acids completely eliminates the formation of glycol monocarboxylates.Introduction of oxygen converts this stoichiometric reaction into a catalytic system.Our studies, including those carried out with complex 1 labeled with 18O in the nitro ligand, suggest that the glycol monoacetates and most of the ketones are the product of oxygen atom transfer from the nitro group, while the unsaturated acetates are the result of a Wacker-type reaction.In the glycol monoacetate, the 18O label is found exclusively in the acetate group.A mechanism which is in agreement with the above observations as well as a comparison of the above reaction with the oxidation of olefins by nitrate ions in the presence of palladium(II) salts is offered.The formation of glycol monoacetates in the monometallic system represented by complex 1 is to be compared with the results obtained in the bimetallic systems consisting of a combination of py(TPP)CoNO2 and either (CH3CN)2PdCl2 or Pd(OAc)2.In the latter systems, ketones or vinyl acetates are found as the predominant products.This fact underlines the difference between the mono- and bimetallic systems and strongly argues against alternative mechanisms involving nitro group transfer from cobalt to palladium before the olefin oxidation takes place.Additional evidence underlining the difference between these two systems is presented.
- Mares, Frank,Diamond, Steven E.,Regina, Francis J.,Solar, Jeffrey P.
-
p. 3545 - 3552
(2007/10/02)
-