Search

A new and efficient system for the allylic acetoxylation of olefins has been developed, which consists of a palladium (II) catalyst and hydrogen peroxide as oxidant in acetic acid. The acetoxylation reaction competes with the epoxidation by the peracetic acid generated in situ in this system. Increase of the concentration of palladium catalyst and addition of benzoquinone (BQ), enhance the acetoxylation considerably. For the Pd(OAc)2BQH2O2 system, more than 1000 turnover number could be achieved in the acetoxylation of cyclohexene. Most internal and cyclic olefins tested gave the corresponding allylic acetates in fair to high yields. 1,3-Cyclohexadiene gave 1,4-diacetoxy-cyclohex-2-ene while 1,5-hexadiene afforded 3-acetoxy-methylenecyclopentane; 1,7-octadiene produced 1-octen-7-one and octan-2,7-dione. Terminal olefins gave methyl ketones in good yield with high turnover number both in the presence and absence of BQ. Possible mechanisms and involvement of palladium peroxidic species in both the catalytic acetoxylation and ketonization of olefins are discussed.

Novel manganese (III) μ-oxo complexes with the formula Mn2IIIO(C3F7CO2)4(bipy)2 ( 1 ) were synthesized from the oxidation of

Die Pd(II)-aoetate (I) reagieren mit tert.-Butylhydroperoxid (II) zu den tetrameren Titelkomplexen (III).

New oxygen-activating systems for hydroxylation of hydrocarbons in organic solvents at ambient temperature are described. These systems are composed of a transition metal and an electron donating ligand, giving a strongly polarised peroxidic form active in hydroxylation. The most active systems are FeCl 2 /DH 2 /AH/O 2 (DH 2 = hydrazobenzene or orthophenylene diamine, AH = carboxylic acid).

Novel oxoperoxomolybdenum(VI) complexes with the general formula MoO(O2)L2X2 (III, L = DMF, HMPT) and MoO(O2)Cl(ON)L(IV, ON) = pyridin-2-carboxylate (Pic), 8-hydroxyquinolinate (Quin) were prepared from the reaction of Ph3COOH or H2O2 with the corresponding cis-dioxo complexes. In the reaction with Ph3COOH both oxygen atoms of the peroxo moiety were found, by 18O labeling experiments, to come from the hydroperoxide. The X-ray crystal structure of MoO(O2)Cl(Pic)(HMPT) revealed a bipyramidal pentagonal surounding with a rather short OO distance (1.41 A). Complexes III were found to be more reactive than MoO(O2)2,HMPT for the epoxidation of olefins (oxidative cleavage products are consecutively formed) but react by the same cyclic peroxymetalation mechanism. The absence of reaction in the case of complexes IV illustrates the necessity for the metal to possess an equatorial releasable coordination site adjacent to the peroxo group for the oxygen transfer to occur. Catalytic oxidation of olefins using Ph3COOH gave a selectivity in oxygenated products very different from that using t-BuOOH, and 18O labeling studies showed that alkyl-peroxidic rather than peroxo species are intermediates in this latter reaction. The mechanism of epoxidation of olefins by alkyl hydroperoxides catalyzed by d0 metal complexes is discussed.

A practical procedure for the epoxidation of alkenes is described. The reaction is performed between 30 and 50°C in 1,2-dichloroethane with 30% hydrogen peroxide and a catalytic amount of a quaternary phosphonium or ammonium pertungstate. Allylic alcohols are very reactive and require lower temperatures for their epoxidation.

Resume Les complexes peroxydiques covalents du molybdene VI de formule generale [Mo(O 2 ) 2 O] L 1 L 2 reagissent selectivement avec les olefines pour donner des epoxydes avec un rendement eleve. Les resultats cinetiques de la reaction conduisent a supposer l'existence intermediaire de complexes olefiniques. Un mecanisme aprotique 1–3 dipolaire de la formation d'epoxyde est propose.