Methane homolytic bond cleavage

One of the more unusual examples of hydrocarbon activation was reported by Wayland involving an example of radical homolytic cleavage of the C-H bond of methane (Fig. lb). In this reaction, the methyl group is transferred to one porphyrin metal center and the hydrogen to a second metal center. The reaction follows termolecular kinetics, which suggests a linear transition state for the cleavage (Eq. 21) [88]. In addition to methane, only the benzylic C-H bonds of tolu-... 

However, the more careful analysis indicates that all the schemes discussed above suffer from one intrinsic contradiction. Indeed, if the main process of activation of the initial hydrocarbon (e.g., methane) is a homolytic C H bond cleavage on an oxidative surface center... 

The addition of radical scavengers, such as TEMPO, suppressed the formation of ethane, methane, and methyl chloride, instead leading rally to the observation of TEMPO-Me (35) and Pd(II) complex 34 (Fig. 19). The observed reaction with radical scavengers is consistent with photo-induced homolytic Pd-C bond cleavage... 

Homolytic cleavage of one carbon-hydrogen bond in methane... 

FIGURE 2.8 Two ways of showing homolytic cleavage of one carbon—hydrogen bond in methane. Each single-barbed arrow represents movement of one electron. 

The thermolysis of 2-methoxyphenol in the presence of cumene as a radical scavenger occurs via two possible pathways. A homolytic cleavage of the methoxyl 0-C bond leads to methane and 1,2-dihydroxybenzene whereas an induced route starting with abstraction of the phenolic hydrogen by cumyl radicals leads, after a cascade of reactions, to phenol, 2-hydroxybenzaldehyde, and 2-hydroxybenzyl alcohol. ... 

The Te—Te bond in diorgano ditellurium compounds is rather weak with a tendency to homolytic cleavage. Species that act as diradicals may insert into the Te —Te bond. Dialkyl or diaryl ditellurium compounds and diazomethane in diethyl ether solution produce bis[organotelluro]methanes ... 

Experimental observation. Chlorination occurs when a mixture of CH4 and CI2 is either heated to 300°C or irradiated with light, as mentioned earlier. Under such conditions, methane by itself is completely stable, but CI2 undergoes homolysis to two atoms of chlorine. Interpretation. The first step in the mechanism of chlorination of methane is the heat- or light-induced homolytic cleavage of the Cl-Cl bond (which happens to be the weakest bond... 

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