Carbon-metal bonds oxidative formation

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. 

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. 

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 reactions between C-H compounds and metal complexes in a low oxidation state, which produce organometallic derivatives (i.e., compounds containing direct carbon-metal bonds) will be considered in this chapter, hi some cases the intermediate o-organyl and organyl hydride complexes can not be isolated, although the evidence for their formation is obtained. Reactions of such type (often-catalytic processes) will be considered in this chapter. 

This section mainly deals with Pd-catalyzed reactions of aryl, alkenyl, benzyl, alkyl, and acyl electrophiles with metal nucleophiles M = Si, Ge, Sn, B, and transition metals) leading to carbon-metal bond formation (Scheme 1). Allylic and related metallations are described in Sect. V.2.3.3, The reaction mechanism is generally believed to involve, firstly, oxidative addition of R—X to a Pd(0) species second, transmetallation of the resulting Pd(II) species with M—M and finally, reductive elimination forming R—M and the active Pd(0) species. However, another catalytic cycle via oxidative addition of M—M to Pd(0) species is also proposed. ... 

Two possible reasons may be noted by which just the coordinatively insufficient ions of the low oxidation state are necessary to provide the catalytic activity in olefin polymerization. First, the formation of the transition metal-carbon bond in the case of one-component catalysts seems to be realized through the oxidative addition of olefin to the transition metal ion that should possess the ability for a concurrent increase of degree of oxidation and coordination number (177). Second, a strong enough interaction of the monomer with the propagation center resulting in monomer activation is possible by 7r-back-donation of electrons into the antibonding orbitals of olefin that may take place only with the participation of low-valency ions of the transition metal in the formation of intermediate 71-complexes. 

E.O. Fischer s discovery of (CO)sW[C(Ph)(OMe)D in 1964 marks the beginning of the development of the chemistry of metal-carbon double bonds (1). At about this same time the olefin metathesis reaction was discovered (2), but It was not until about five years later that Chauvln proposed (3) that the catalyst contained an alkylidene ligand and that the mechanism consisted of the random reversible formation of all possible metallacyclobutane rings. Yet low oxidation state Fischer-type carbene complexes were found not to be catalysts for the metathesis of simple olefins. It is now... 

While the alkoxymetallation process has typically been affected by highly electrophilic metal salts, high-valent metal species generated by an oxidative addition have also been used to activate alkynes through the formation of 7r-complexes. In such cases, the metal-carbon emerging from the attack of an oxygen nucleophile may enter a reaction manifold that leads to an additional C-G bond formation rather than a simple protic quench. This approach, pioneered by Arcadi and Cacci, has proved to be a powerful strategy for the synthesis of structurally diverse substituted... 

Transition metal complex-catalyzed carbon-nitrogen bond formations have been developed as fundamentally important reactions. This chapter highlights the allylic amination and its asymmetric version as well as all other possible aminations such as crosscoupling reactions, oxidative addition-/3-elimination, and hydroamination, except for nitrene reactions. This chapter has been organized according to the different types of reactions and references to literature from 1993 to 2004 have been used. 

In relation to the mechanistic proposal, an interesting reactivity of (boryl)(silyl)platinum(n) complex has been reported.223 The complex is prepared by the reaction of silylborane with Pt(cod)2 complex via oxidative addition (Scheme 46). The (boryl)(silyl)platinum complex undergoes insertion of alkynes at the B-Pt bond to give (/3-borylalkenyl)(silyl)platinum(n) complex in high yield. Importantly, the insertion takes place regioselectively, with Pt-G bond formation at the internal. -carbon atom. This result may indicate that the boron-transition metal bond is more prone to undergo insertion of unsaturated molecules. 

In some cases pulse-radiolysis techniques were employed to study the effect of pressure on inorganic reactions. For instance the oxidation of [CuI(phen)2] by dioxygen via the formation of a C -C transient species was studied using this technique (see Section III,A). Other examples include the formation and cleavage of metal-carbon (7-bonds, which formally involve a change in the oxidation state of the metal. A typical example of a volume profile for the formation and cleavage of a Co-CH3 bond is reported in Fig. 21 for the reaction (162)... 

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