Additional Oxygen Atom Transfer Reactions

Additional reactions of the general typeYO + X- Y + XO will now be described. The general conclusions arrived at from the thorough study of oxygen transfer from PyO to PR3, presented in Sections III and IV, will be valid for these reactions as well. In terms of detail, however, each reaction offers further insight which is the reason such research is rewarding. 

Oxygen Transfer from tert-butyl Hydroperoxide to Sulfides 

The same oxorhenium(V) compounds as used previously, such as 1, catalyze this transformation under mild conditions 

Provided an excess of the hydroperoxide is not used, sulfoxides are obtained in essentially quantitative yields in short reactions times, usually 0.7-2.5 h (42). The method is uncomplicated and can be carried out on the benchtop. The long shelf-life of 1 ( 3 months) adds to the convenience of this procedure. A wide variety of functional groups is tolerated on R and R. The reaction affords nearly pure sulfoxides without contamination from sulfones. The product is obtained simply be evaporating the solvent and tert-butyl alcohol. This method avoids aqueous workup, which is often required when peracids are used (43), and is thus convenient for water-soluble sulfoxides. 

The oxidation of methyl tolyl sulfoxide, a representative substrate, was monitored by the buildup of the sulfoxide as a function of time under many sets of conditions (42). A representative concentration time plot is presented in Pig. 1. In this case, and in all the others, the buildup curves showed similar features, the most noticeable of which is a distinct induction period. Its length depends on the concentrations, decreasing with increasing [Bu OOH] and [1], At the same time the rate itself was 

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Oxidation Catalyzed by Metalloporphyrins. Much attention has been devoted to the metal-catalyzed oxidation of unactivated C—H bonds in the homogeneous phase. The aim of these studies is to elucidate the molecular mechanism of enzyme-catalyzed oxygen atom transfer reactions. Additionally, such studies may eventually allow the development of simple catalytic systems useful in functionalization of organic compounds, especially in the oxidation of hydrocarbons. These methods should display high efficiency and specificity under mild conditions characteristic of enzymatic oxidations. 

An additional aspect in studying the half-reactions arises when a reaction is not treated as pseudo first order reaction. This is the case when the substrate is in approximately the same concentration as the metal complex. Caradonna et al. for instance studied the required treatment for such a case. Due to the accumulation of the product in the course of the reaction, the back reaction is not negligible anymore. To the best of our knowledge, analyses of the back reaction have never been mentioned in the literature with respect to oxygen atom transfer reactions of model complexes and this is due to several reasons. Either the reaction rate is too small compared to the forward reaction so that experimental difficulties in determining the reaction rate constant emerged. Or, as was emphasized by Enemark et No bis(dithi-olene) molybdenum or tungsten eomplex was observed to reduce PhjPO . ... 

Metal complexes as catalysts for oxygen, nitrogen and carbon-atom transfer reactions (Tsutomu Katsuki) Metal complexes as catalysts for H-X (X = B,CN, Si, N, P) addition to CC multiple bonds (M. Whittlesey) Metal complexes as catalysts for C-C cross-coupling reactions (I. Beletskaya, A.V. Cheprakov)... 

These PVP polymers provide a "proximal effect" without addition of free pyridine in the reaction mixture. Different studies have shown that only one pyridine per manganese catalyst is sufficient to enhance the rate of the catalytic oxygen atom transfer from the high-valent metal-oxo species to the organic substrate. The advantage of PVP polymer over a cationic Amberlite resin (see Scheme II for structures) have been recently illustrated in the modeling of ligninase (11). 

Intermolecular oxygen atom transfer from a metal complex to an organic substrate is an archetypical reaction step in oxidation catalysis. As the transformation of O2 into metal 0x0 groups by oxidative addition is a well-precedented process (Sect. 2.2), its combination with transfer of the oxygen atom to an oxidizable substrate ( S ) constitutes a catalytic cycle for aerobic oxidations (Eq. 21). Examples of such cycles exist in organometallic chemistry, by virtue of 0x0 complexes with carbon-based ancillary hgands. 

The Darzens reaction is the base-promoted generation of epoxides XIII from aldehydes (or ketones) XI and alkyl halides XII, the latter carrying an electron withdrawing group, for example the carbonyl, nitrile, or sulfonyl, in the a-position (Scheme 6.83) [188, 189]. It is, formally, addition of a carbene to the C=0 double bond (Scheme 6.83, path B) and thus complements oxygen atom transfer to olefins... 

The biochemistry of N02 oxidation is simpler than NH3 oxidation because it is only a two electron transfer and involves no intermediates. The additional oxygen atom in NOs is derived from water (Eq. 5.5), and the molecular oxygen that is involved in the net reaction (Eq. 5.7) results from electron transport involving cytochrome oxidase (Eq. 5.6). 

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