Oxidation organometallic intermediates

The success of these reactions was intriguing because, under normal reaction conditions, group 14 organometallic compounds serve as carbanion synthons. The anodic oxidation reaction successfully reversed this polarity thereby expanding the overall synthetic utihty of group 14 organometallic intermediates. 

The homolysis of a metal alkyl may be regarded as a reductive elimination however, it is convenient to consider such reactions separately (Section V,B). Electron-transfer mechanisms for organometallic intermediates in catalytic reactions have been reviewed (129) examples are in the formation of transient RCu(I) or RCr(III) in oxidation (by Cu(II)) or reduction (by Cr (II)) of R, and in the role of Fe in the Kharasch-Grignard... 

Clearly, to clarify Co(III) oxidation mechanisms a great deal of further work is needed e.g. looking for organometallic intermediates and elucidating the role of charge-transfer complexes between Co(III) and aromatics (Szymanska-Buzar and Ziolkowski, 1979). 

Methods for the oxidation of arylic and vinylic C—bonds which do not proceed via organometallic intermediates have already been referred to in the proceeding sections when it was appropriate to make comparisons. 

A common pathway in palladium-catalyzed oxidation reactions is that the 7r-olefin complex formed reacts with a nucleophile, either external or coordinated, and the new organometallic intermediate may then undergo a number of different reactions (Scheme l) (i) an intramolecular hydride shift leads to ketone formation (ii) a )6-elimination results in the formation of a vinyl functionalized olefin (iii) an oxidative cleavage of the palladium-carbon bond produces a 1,2-functionalized olefin and (iv) an insertion reaction, exemplified by insertion of an olefin, leads to formation of a new palladium-carbon bond, which may be cleaved according to one of the previous processes ()6-elimination or oxidative cleavage). In all cases palladium has removed 2 electrons from the organic molecule, which becomes oxidized. These electrons, which end up on Pd(0), are in turn transferred to the oxidant and Pd(II) is regenerated, in this way a palladium(II)-catalyzed oxidation is realized. 

K. B. Sharpless, A. Y. Teranishi, J.-E. Backvall, Chromyl chloride oxidations of olefins. Possible role of organometallic intermediates in the oxidations of olefins by oxo transition metal species, J. Am. Chem. Soc. 99 (1977) 3120. 

The Metal-mediated Oxidation of Organic Substrates via Organometallic Intermediates Recent Developments and Questions of Dispute... 

On the other hand a coordinatively unsaturated paramagnetic d metal center could oxidatively add the allyl radical at the metal center to form a labile d° n-aWyl oxo species as organometallic intermediate (step B). The latter may rearrange via a ff-allyl intermediate to a d allyloxy species (step D). The latter is believed to convert to acrolein and a reduced metal center via an /0-hydrogen abstraction by the metal center. In an attempt to gain insight into fundamental reactions involved in this catalytic cycle, some authentic d° allyl 0X0 complexes of rhenium [23] and tungsten... 

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