Olefin-oxygen complex

Although solutions of molybdenum complexes A in methylcyclohexane or benzene are stable for several weeks at room temperature [416], these complexes are sensitive towards oxygen and protic solvents [813,814]. Aldehydes are quickly olefinated by complexes A, whereas variable reactivity is observed towards ketones [416,736]. With carboxylic esters usually no reaction occurs. 

VII. Olefinic Oxygen, Sulphut and Selenium Complexes of Transition Metals... 

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... 

Until recently, the hypothesis that the termination reaction of type II photooxygenation reactions occurs between the substrate and an excited light absorber-oxygen complex seemed to be well established. The typical products obtained from cyclic 1,3-dienes and olefins (see Fig. 1 and Sect. IV) could only be made by photochemical reactions. 

The second intermediate proposed is a Cu-olefin jr-complex with an additional interaction of Mg + with the carbonyl oxygen of the enone (enoate). The formation of a jr-complex is presumably followed by intramolecular rearrangement to a Cu(III) intermediate, where Cu forms a a-bond with the -carbon of the enone (enoate), in fast equilibrium with the jr-complex. 

When the catalyst was used for simple olefin systems, it was not as active as with the amino acid precursors. Table III shows the relative rates for a variety of substrates, special care being taken in each case to purge oxygen. The slow rate of a-phenylacrylic acid was unexpected, but, it may be the result of a stable olefin-rhodium complex similar to the one Wilkinson (15) experienced with ethylene. Such a contention is consistent with the increased speed of hydrogenation with increased pressure. 

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 ... 

In addition to the complexes of platinum(II), a number of olefin complexes of platinum(O) have been prepared. Chatt, Shaw, and Williams (103) have described the complex (olefin)bis(triphenylphosphine)-platinum(O) prepared by reaction of the olefin at 60°C with cis-dichloro-bis(triphenylphosphine)platinum(Il) in ethyl alcohol containing hydrazine hydrate. The complex was formed only with ethylene complex (C2H4)Pt[P(CgH5)3]2 has been prepared (121) by reduction of the corresponding oxygen complex with sodium borohydride in the presence of the olefin. 

The identification of a complex is not proof that the reaction path is by way of that particular complex, as a more unstable intermediate is likely to be involved. The reports that aluminum halides alone are not catalysts for n-butane unless a trace of olefin, oxygen, or water is present even when HX, the corresponding halogen acid, is present (Pines and Wachher, 128), lead one to suspect that both a nucleophilic and an electrophilic reagent are needed and that the role of the solvent in solvat-... 

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. 

In the case of lead ruthenate, the oxygen non-stoichiometry concept can be developed further by combining it with the known reactions of the variable valence ruthenium. It has been shown in this work that these same catalysts can cleave carbon-carbon double bonds (3) in a manner analogous to that of osmium and ruthenium tetroxiHe (1,1). It is known (12) that OSO4 (and presumably RUO4) cleave olefins via complexes with the structure ... 

Gustorf and co-workers (264-266) have prepared complexes of the type (7r-CH2=CHX)Fe(CO)4 [X = OCOCH3 (266), Cl, CH3, CeHs, or OCH3 (265)] by irradiation of Fe(CO)5 with the corresponding olefin. The complexes are very oxygen-sensitive and thermally unstable. At room temperature they decompose to yield the olefin and Fe3(CO)i2. The order of thermal stability is vinyl chloride > styrene > propylene > vinyl methyl ether. The vinyl chloride and styrene complexes show catalytic activity for polymerization of methyl methacrylate in the presence of a small amount of halogenated hydrocarbon, e.g., CCI4, at room temperature (265). 

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. 

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]. 

Table 6.3 Product ratios and 0 labeling data of the catalytic olefin oxygenation with bispidine-ferryl complexes (cyclooctene, MeCN, HjOj, TON" = 10) [7b, 35],...

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). 

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