Carbon-hydrogen bonds oxidative addition

In addition to olefin oxidation, carbon-hydrogen bond oxidation has also been extensively investigated. Thus, the group of Que Jr. and by Costas have... 

On the basis of the fact that (R)-BMPP coordinated to the metal center can induce asymmetric addition of methyldichlorosilane across the carbon-carbon double bond of 2-substituted propenes to afford an enantiomeric excess of (R)-2-substituted propylmethyldichlorosilanes, the following processes should be involved in these reactions (a) insertion of the metal center into the silicon-hydrogen bond (oxidative addition of the hydrosilane) (b) addition of the resulting hydridometal moiety to the coordinated olefin preferentially from its re face (in a cis manner) to convert the olefin into an alkyl-metal species and (c) transfer of the silyl group from the metal center to the alkyl carbon to form the product. Since process (b) most likely involves diastereomeric transition states or intermediates, the overall asymmetric bias onto the R configuration at the chiral carbon would have already been determined prior to process (c). A schematic view of such a process is given in Scheme 1. 

Ca.ta.lysis, Iridium compounds do not have industrial appHcations as catalysts. However, these compounds have been studied to model fundamental catalytic steps (174), such as substrate binding of unsaturated molecules and dioxygen oxidative addition of hydrogen, alkyl haHdes, and the carbon—hydrogen bond reductive elimination and important metal-centered transformations such as carbonylation, -elimination, CO reduction, and... 

Presumably, the heterolytic scission of the carbon-sulfur bond in the oxide is assisted by the hydrogen bonding, in addition to the inherent strain of the three-membered ring. 

Organometals and metal hydrides as electron donors in addition reactions 245 Oxidative cleavage of carbon-carbon and carbon-hydrogen bonds 253 Electron-transfer activation in cycloaddition reactions 264 Osmylation of arene donors 270... 

The entries into transition metal catalysis discussed so far, required the presence of a specific bond (a polar carbon-heteroatom bond for oxidative addition or a carbon-carbon multiple bond for coordination-addition processes) that was sacrificed during the process. If we were able to use selected carbon-hydrogen bonds as sacrificial bonds, then we could not only save a lot of trouble in the preparation of starting materials but we would also provide environmentally benign alternatives to several existing processes. In spite of the progress made in this field the number of such transformations is still scarce compared to the aforementioned reactions. 

Further chemistry of alkenes and alkynes is described in this chapter, with emphasis on addition reactions that lead to reduction and oxidation of carbon-carbon multiple bonds. First we explain what is meant by the terms reduction and oxidation as applied to carbon compounds. Then we emphasize hydrogenation, which is reduction through addition of hydrogen, and oxidative addition reactions with reagents such as ozone, peroxides, permanganate, and osmium tetroxide. We conclude with a section on the special nature of 1-alkynes— their acidic behavior and how the conjugate bases of alkynes can be used in synthesis to form carbon-carbon bonds. 

Hoyano JK, Graham WAG. Oxidative addition of the carbon-hydrogen bonds of neopentane and cyclohexane to a photochemically generated iridium(I) complex. J Am Chem Soc 1982 104(13) 3723-3725. 

J. K. Hoyano, and W. A. G. Graham, Oxidative Addition of the Carbon-Hydrogen Bonds of Neopentane and Cyclohexane to a Photochemically Generated Iridium(I) Complex, J. Am. Chem. Soc. 104, 3723-3725 (1982). 

With the development of powerful methods for molecular orbital calculations (e.g. DFT) (see Molecular Orbital Theory), several computational studies of the C-H oxidative addition (see Alkane Carbon-Hydrogen Bond Activation) process have been undertaken. One has used CpRh(PH3) to model the reactive intermediate Cp Rh(PMe3) proposed for the reaction shown in equation (13). The results... 

The oxidative addition of an allylic carbon-hydrogen bond to a transition-metal complex has been frequently invoked in the mechanism of the catalytic isomerization of olefins under hydride-free conditions. 

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