Oxidation olefin-oxygen complex

The palladium chloride process for oxidizing olefins to aldehydes in aqueous solution (Wacker process) apparendy involves an intermediate anionic complex such as dichloro(ethylene)hydroxopalladate(II) or else a neutral aqua complex PdCl2 (CH2=CH2)(H2 0). The coordinated PdCl2 is reduced to Pd during the olefin oxidation and is reoxidized by the cupric—cuprous chloride couple, which in turn is reoxidized by oxygen, and the net reaction for any olefin (RCH=CH2) is then... 

The olefin oxygenations carried out with dioxygen seem to be metal-centered processes, which thus require the coordination of both substrates to the metal. Consequently, complexes containing the framework M (peroxo)(olefin) represent key intermediates able to promote the desired C-0 bond formation, which is supposed to give 3-metalla -l,2-dioxolane compounds (Scheme 6) from a 1,3-dipolar cycloinsertion. This situation is quite different from that observed in similar reactions involving middle transition metals for which the direct interaction of the olefin and the oxygen coordinated to the metal, which is the concerted oxygen transfer mechanism proposed by Sharpless, seems to be a more reasonable pathway [64] without the need for prior olefin coordination. In principle, there are two ways to produce the M (peroxo)(olefin) species, shown in Scheme 6, both based on the easy switch between the M and M oxidation states for... 

The gas phase oxidation of ethylene to ethylene oxide over silver catalysts has been studied extensively.49 la-c It has been suggested that epoxide formation involves transfer of oxygen from a silver-oxygen complex to the olefin on the catalyst surface.4913 Silver-on-silica also catalyzes the liquid phase oxidation of cumene to cumene hydroperoxide. A mechanism that involved insertion of coordinated oxygen into a C—H bond was proposed630 ... 

G. Yin, M. Buchalova, A. M. Danby, C. M. Perkins, D. Kitko, J. D. Carter, W. M. Scheper, D. H. Busch, Olefin oxygenation by the hydroperoxide adduct of a nonheme Manganese(lV) complex Epoxidations by a metallo-peracid produces gentle selective oxidations, /. Am. Chem. Soc. 127 (2005) 17170. 

Many oxygenated complexes of transition metals have now been isolated and used as catalysts for the oxidation of olefins and recent evidence supports the initiation of autoxidation through the formation of a metal hydroperoxide catalyst complex. 

With the hard base water, oxidative olefin substitution leads to acetaldehyde with acetic acid, vinyl acetate is formed. Finally, the metallic palladium is oxidized by atmospheric oxygen in the presence of Cu ", re-forming the starting complex. 

In 1989, Volz reported the isolation of an iodosylbenzene complex of [(TDCPP) MnCl] from the reaction of the components at —78°C (Scheme 9) [35]. The crystalline compound could epoxidize olefins, oxygenate cyclohexane, and oxidize triphenylphosphine. Interestingly, reaction of this material with ammonia led to the formation of the manganese(V) nitrido complex [(TDCPP)Mn=Nj. In 1992, Volz reported details for related CgFsIO complexes [36]. 

Thus the rate is determined by the equilibrium between monomer and dimer which is itself dependent on the amount of free phosphine present. The dimer is the more reactive form of the complex, in contrast to reactions with olefins and oxygen where the intermediate [RhCKPPha) is the most active. The observed rate constant for the oxidative addition of hydrogen to the olefin-substituted complex, equation (14),... 

The addition of an oxygen atom to an olefin to generate an epoxide is often catalyzed by soluble molybdenum complexes. The use of alkyl hydroperoxides such as tert-huty hydroperoxide leads to the efficient production of propylene oxide (qv) from propylene in the so-called Oxirane (Halcon or ARCO) process (79). 

T[[dotb]he nature of the initial attack by the water (eq. 10) is a matter of some controversy (205,206). Stereochemical and kinetic studies of model systems have been reported that support trans addition of external water (207,208) or internal addition of cis-coordinated water (209), depending on the particular model system under study. Other paHadium-cataly2ed oxidations of olefins ia various oxygen donor solvents produce a variety of products including aldehydes (qv), ketones (qv), vinyl acetate, acetals, and vinyl ethers (204). However the product mixtures are complex and very sensitive to conditions. 

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