Oxidation carbon-metal bonds

Carbon-Metal Bond Oxidations. In MeOH and under O2 atmosphere, a catalytic amount of Cu(OAc)2 promotes the cleavage of the Si-C bond of (F)-alkenylpentafluorosihcates to give alkenyl ethers (eq 9). The reaction is highly stereoselective and leads to the ( )-enol ethers. In the presence of H2O the corresponding aldehydes are obtained. ... 

The first step is carbon-metal bond formation via coordination. This process may be followed by one or more steps, leading to transformation of ligands and/or reaction between ligands. In a final step, the metal is removed from the organic moiety. Reactions are catalytic or stoichiometric, depending on whether or not the metal is eliminated in its original oxidation state. The following is a broad classification of these processes. 

This special feature arises from the combination of the transition metal behavior such as the coordination of a carbon-carbon multiple bond, oxidative addition, reductive elimination, P-hydride elimination, addition reactions and the behavior of classical c-carbanion towards electrophiles. 

A large number of cyclopropanated derivatives of Cgo in which the bridging atom is an electron rich transition metal (see Fig. 16) such as Pt, Pd, Ni, Ir, W, Mo, and Rh has been reported. Their electrochemical properties have been reviewed [83, 141, 142] and, in general, reductions are Cgo centered and negatively shifted with respect to those of pure Cgo, while oxidations are metal centered. In most cases, however, the first reduction is accompanied by breakage of the carbon-metal bonds and recovery of the pristine [60] fullerene. In multiadduct derivatives, the breakage occurs in a stepwise manner. 

By far the most common way for organic molecules to enter late transition metal catalyzed reactions is oxidative addition. In this process a low valent palladium(O)3 or nickel(O) atom inserts into a carbon-heteroatom bond, usually of an aryl halide or sulfonate (Figure 1-2). The formation of the carbon-metal bond is accompanied by an increase in the oxidation number of the metal by 2. There are a series of factors determining the speed of the process. 

A. Heterolysis of the Metal-Carbon a-Bond Homolysis of the Metal-Carbon a-Bond Oxidation of Lm iM +1-R Followed by Homolysis P-Hydride Shift Reactions P-Elimination Reactions P-Elimination of Carboxylates CO Insertion/Methyl Migration... 

Sachtler [270] notes that the 7r-allyl complex can be attached to a metal ion or to an oxygen anion but doubts that a 7r-allyl metal complex can be stable at the high temperatures normally used. He draws attention to the fact that, in the case of aromatic oxidations, benzoates, maleinates, etc. are observed spectroscopically, indicating that a carbon—metal bond is not formed. 

Once complexed to palladium(II), the alkene is generally activated towards nucleophilic attack, with nucleophiles ranging from chloride to phenyllithium undergoing reaction. The reaction is, however, quite sensitive to conditions and displacement of the alkene by the nucleophile (path a) or oxidative destruction of the nucleophile can become an important competing reaction. Nucleophilic attack occurs predominately to exclusively at the more-substituted position of the alkene (the position best able to stabilize positive charge) and from the face opposite the metal (trans attack, path b) to produce a new carbon-nucleophile bond and a new carbon-metal bond. This newly formed a-alkylmetal complex (2) is... 

Organometallic compounds which contain a carbon-metal bond are the most reactive carbon nucleophiles. In most cases they are also powerful bases and must be prepared and used under strictly anhydrous and aprotic conditions. A very common way to produce organometallic compounds is to reduce alkyl halides with active metals. Grignard reagents and organolithium compounds are routinely produced in this manner. The transformation is a two-electron reduction of the alkyl halide to a carbanion equivalent the metal is oxidized. 

Burchill and Hickling, 1970). Organic radicals have been shown to be oxidized by a variety of other inorganic ions. The most commonly used oxidants were Cu2 + and Fe(CN)6 (see e.g. Garrison, 1968 Haysom et al., 1972 Bhatia and Schuler, 1974). However, evidence has been presented also for the reduction of such radicals by Fe2 + and Ti3 + (Behar et al., 1973) and the process has been suggested to involve intermediate formation of a carbon-metal bond [reactions (60) and (61)]. Intermediates containing carbon-metal bonds have... 

The difference in reactivity between the a-stannyl sulfide 16A and the a-silyl sulfide 16B can be explained by comparing the two-center energies of their carbon-metal bonds. Semiempirical molecular orbital calculation revealed that the bond energies decrease in the order of 2-silyl, 2-germyl, and 2-stannyl-1,3-dithiane cation radicals. As the silyl dithiane was completely consumed by the oxidation under the... 

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