Oxidative addition homolytic

Like dicyclopentadienyltin, it undergoes oxidative addition-reactions with alkyl halides, and, again, there is evidence for a homolytic chain-mechanism (330, 331). 

M H (M = Si, Ge, Sn) bonds are reactive to undergo oxidative addition of transition metals, homolytic cleavage giving group 14 metal radicals, and so on. Some studies have been reported on the formation of M E (M = Si, Ge, Sn E = S, Se, Te) bonds by using the group 14 metal hydrides. 

Hence, the copper surface catalyzes the following reactions (a) decomposition of hydroperoxide to free radicals, (b) generation of free radicals by dioxygen, (c) reaction of hydroperoxide with amine, and (d) heterogeneous reaction of dioxygen with amine with free radical formation. All these reactions occur homolytically [13]. The products of amines oxidation additionally retard the oxidation of hydrocarbons after induction period. The kinetic characteristics of these reactions (T-6, T = 398 K, [13]) are presented below. 

A common, quite general route for activation of hydrogen is the oxidative addition by homolytic cleavage to form a dihydride complex24,124,125 [Eq. (11.21)]. It involves an increase of 2 in the formal oxidation state of the metal. In turn, monohydrido complexes can be formed through both homolytic [Eq. (11.22)] and heterolytic [Eq. (11.23)] cleavages of hydrogen 109... 

A second process that has been invoked is heterolytic fission of H2.49 Examples are shown in equations (15) and (16). Although the overall process certainly involves heterolysis, some or all of these reactions may well go via initial oxidative addition followed by fast deprotonation or reductive elimination (equation 17). A third variant closely related to heterolytic fission is the addition of hydrogen across a metal-ligand or metal-metal bond. Examples are shown in equations (18) and (19). Here too, homolytic addition via equation (1) followed by fast reductive elimination may be taking place in some cases. In d° systems, the homolytic fission reaction of equation (1) is unlikely as the metal is already at its maximum valency, so examples of heterolytic fission and addition to... 

Homolytic cleavage. There are two versions of this process. The most important is oxidative addition (below). Rhodium(I) complexes exemplify this reaction. A di-dihydride is formed with an increase of two in the formal oxidation state of the metal. The second form of homolytic cleavage involves two metal centres (equation 2). This is common for cobalt complexes. 

Homolytic catalysis is observed with both organometallic and coordination complexes. It is involved in a wide variety of metal-mediated transformations, often in competition with electrophilic or nucleophilic catalysis [11], For example, many metal-catalyzed oxidations involve substrate activation by homolytic catalysis (Eq. 5) [12], Similarly, oxidative additions (Eq. 6) and dioxygen activation (Eq. 7) can proceed via two-step homolytic mechanisms. 

Reaction (414) is formally analogous to the oxidative addition of alkyl halides to noble metal complexes described earlier, and both homolytic and heterolytic processes can be envisaged. Heterolytic cleavage of C—H bonds represented in Eq. (415) is analogous to the interaction of the powerful oxidant Co3+ with alkanes in TFA in reaction (229). 

The term homolytic splitting of Hj by metal complexes, in contrast to heterolytic cleavage (H2 H + H" ) to be discussed in the following section, is generally used synonymously with oxidative addition. Equation (a) illustrates an oxidative addition reaction of Hj to a univalent metal center ... 

The synonymity of H2 homolytic splitting with oxidative addition is clear upon examination of equations (a) and (e), and the examples discussed above. Some hydrides,... 

Aside from loss of H2, reactions of M-H2 complexes are dominated by homolytic cleavage of H2 (oxidative addition) and heterolytic cleavage, essentially deprotonation of bound H2 on electrophilic metal centers (Scheme 5.9).10... 

The above examples have shown how complexes having a-bonds can be synthesized by oxidative addition reactions. An important factor to be considered in applying these oxidative reactions to organic synthesis is the reactivity of the a-bond thus created. (Homolytic fragmentation, coupling and elimination reactions of a-bonds are discussed in Chapt. IV.) Carbon on the electropositive... 

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