Transition metal peroxides hydrocarbons

In the earlier volume of this book, the chapter dedicated to transition metal peroxides, written by Mimoun , gave a detailed description of the features of the identified peroxo species and a survey of their reactivity toward hydrocarbons. Here we begin from the point where Mimoun ended, thus we shall analyze the achievements made in the field in the last 20 years. In the first part of our chapter we shall review the newest species identified and characterized as an example we shall discuss in detail an important breakthrough, made more than ten years ago by Herrmann and coworkers who identified mono- and di-peroxo derivatives of methyl-trioxorhenium. With this catalyst, as we shall see in detail later on in the chapter, several remarkable oxidative processes have been developed. Attention will be paid to peroxy and hydroperoxide derivatives, very nnconunon species in 1982. Interesting aspects of the speciation of peroxo and peroxy complexes in solntion, made with the aid of spectroscopic and spectrometric techniqnes, will be also considered. The mechanistic aspects of the metal catalyzed oxidations with peroxides will be only shortly reviewed, with particular attention to some achievements obtained mainly with theoretical calculations. Indeed, for quite a long time there was an active debate in the literature regarding the possible mechanisms operating in particular with nucleophilic substrates. This central theme has been already very well described and discussed, so interested readers are referred to published reviews and book chapters . 

Catalytic Decomposition of Hydrogen Peroxide by Ferrous Ions Catalysis by Transition Metal Ions and Complexes in Liquid-Phase Oxidation of Hydrocarbons and Aldehydes by Dioxygen... 

This paper presents the results of an investigation of the oxidation of substituted olefins in the presence of hydrocarbon-soluble transition metal complexes. Results indicate that the initial interaction of oxygen with the olefin probably does not occur within the coordination sphere of the metal. The best interpretation appears to be autoxidation of the olefin, initiated either by the metal or by metal catalyzed decomposition of peroxidic impurities. The initial product of an olefin having allylic hydrogens is an allylic hydroperoxide species this is usually the case in radical initiated autoxidations. Nonetheless, with some metal complexes the product profile differs markedly from that observed when radical initiators are used. In the presence of several complexes, oxidation is... 

In general, the catalytic properties of transition metals for the oxidation of hydrocarbons are strongly governed by the existence and nature of the metal-oxygen intermediates. Among the various possible reactive intermediates, two families of metal-oxygen species emerge as the most important ones, i.e. metal peroxides and metal-oxo compounds. 

Similarly, a recent study141 of the homogeneous oxidation of cyclohexene by various low-valent phosphine complexes of Group VIII transition metals yielded no definite proof for initiation by oxygen activation. Results were consistent with reactions involving chain initiation via the usual redox reactions of the metal complexes with traces of hydroperoxides. Long induction periods were observed with peroxide-free hydrocarbons. 

BQDI 53 is the principal product of both sacrificial and depleting transformations of PD in model hydrocarbons, PO and rubbers and is formed via oxidation with ROO , oxygen, ozone, ozonides, organic peroxides or ions of transition metals. BQDI have therefore been found in PD doped polymers degraded under various conditions [3-5,58]. They are formed in high preparative yield by oxidation with femcyanide and also result in interactions of PD with some rubber chemicals, e.g, with benzothiazolyl-2-sulfenemorpholide. 

The oxidation of hydrocarbons by molecular oxygen in the absence of metal complexes has been discussed in Chapter II. The oxidation of hydrocarbons with molecular oxygen, as well as with donors of an oxygen atom (hydrogen peroxide, alkyl hydroperoxides and some other compounds), is a very important field since many industrial processes are based on these reactions [1], In many cases, chain radical non-catalyzed autoxidation of samrated hydrocarbons is not very selective and the yields of valuable products are often low. The use of salts and complexes of transition metals creates great possibilities for solving problems of selective oxidation, as has been demonstrated for a number of important processes. 

Various metal complexes catalyze efficient oxygenations of organic compounds with hydrogen peroxide (see, e.g., [8]). Tables X.I and X.2 summarize some examples of hydrocarbon oxidations with hydrogen peroxide catalyzed by transition metal complexes. 

Oxidation of saturated hydrocarbons, the main feedstocks for the chemical industry, is extremely important. With simple substrates such as cyclohexane or adaman-tane, selective oxidation can be achieved, typically by using hydrogen peroxide or peroxycarboxylic acids in combination with strong acids or transition metal... 

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