Oxidative addition, metal atom-organic

The ability of transition metals to bind and activate organic molecules, and to release the transformed organic product with turnover, forms the basis of the vast catalytic chemistry of transition metal complexes. In addition, metal atoms play a key role at the catalytic center of many enzymes. For example, metalloenzymes play key roles in hydrolysis, oxidation, reduction, electron-transfer chemistry, and many other remarkable processes such as nitrogen fixation. The long-term development of synthetic polymers that perform catalytic chemistry in a manner analogous to enzymes, is a goal of profound interest. 

The oxidative addition of alkyl halides can proceed in different ways, although the result is usually atrans addition independent of the mechanism. In certain cases the reaction proceeds as an SN2 reaction as in organic chemistry. That is to say that the electron-rich metal nucleophile attacks the carbon atom of the alkyl halide, the halide being the leaving group. This process leads to inversion of the stereochemistry of the carbon atom (only when the carbon atom is asymmetric can this be observed). There are also examples in which racemisation occurs. This has been explained on the basis of a radical chain... 

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. 

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. 

In summary, the triplet (do po) excited states of the d -d metal dimers [Ir(p-pz)(C0D)]2 and Pt2(pop)4 " undergo a variety of photochemical reactions. Electron transfer to one-electron quenchers such as pyridinium cations or halocarbons readily occurs with acceptors that have reduction potentials as negative as -2.0 V. With the latter reagents, net two-electron, photoinduced electron transfer yields d -d oxidative addition products. Additionally, the triplet (da pa) excited state of Pt2(pop)4 apparently is able to react by extracting a hydrogen atom from a C-H bond of an organic substrate. 

Abstraction, reductive coupling, electron transfer, bond activation, oxidative addition, n-complexation, disproportionation and metal cluster formation are some of the reactions that occur when metal atoms interact with organic polymers and small molecules. Examples of these reactions are provided from the literature on the organometallic chemistry of free atoms and coordination-deficient molecules. Past uses of model compound studies to understand the early stages of chromium metallization on polyimide are critiqued. New evidence for reactions of chromium atoms with compounds related to polyimides is given. 

Scheme 1 depicts some of the outcomes possible (5) when a metal atom reacts with an organic molecule, which might be a monomer or a substituent on a polymer. Some of the more common reactions are generalized. Oxidative addition is relevant to insertion of a metal atom into a carbon-halogen bond, such as might be found in polyvinyl chloride or the monomer, allyl chloride, or... 

Oxidative addition of H—C bonds to transition metals, which also is referred to as an activation of the H—C bond, is of scientific and technological importance. " (See 1.10.2 for activation of H—C bonds by metal-atom vapors.) Intramolecular oxidative addition of H—C bonds (cyclometallation) occurs, but organic functional... 

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