Sigma-bond cleavage

This process is known as sigma-bond cleavage or simply o-cleavage. The favored charged fragment will be the one that can better stabilize the positive charge. For... 

The results can be rationalized in terms of an oxidative addition-reductive elimination mechanism as illustrated with XXII. A similar mechanism has been proposed for the acid cleavage of Pt(II)-C sigma bond (57, 58). 

Photochemical Cleavage Reactions of Benzyl-Heteroatom Sigma Bonds... 

Photochemical Cleavage Reactions of Benzyl-Heteroatom Sigma Bonds Steven A. Fleming and James A. Pincock... 

There are much fewer examples in the literature of the heterolytic cleavage of Si H bonds compared to H-H and even fewer other examples in which a cr-silane complex was observed as an intermediate in the activation. We have synthesized alkyl-substituted diimine ligands with sidearms containing labile functional groups that reserve a vacant site for binding and activation of sigma bonds as shown in Eq. (32) (108,109). 

The mass spectrum of octane is shown in Figure 15.8. The molecular ion appears at m/z 114. Cleavage of the sigma bond between C-l and C-2 would lead to the fragments shown in the following equations ... 

Cleavage of the sigma bond between C-2 and C-3 leads to the fragments shown in the following equations ... 

The experiments with the varioug —M-Re(CO)3L species establishes that population of the a level is not required to achieve sufficient M-M bond lability to yield homolytic cleavage within the lifetime of the excited state. However, when the sigma bond order is reduced from one to approximately one-half by the depopulation of the level, the rate constant for M-M bond cleavage appears to be only 105 s-1. By way of contrast, M-M bond cleavage seems to occur with a rate of >1010 s 1 for species... 

Photochemical Cleavage Reactions of Benzyl-Heteroatom Sigma Bonds. Fleming, S. A. Pincock, J. A. In Organic Molecular Photochemistry Ramamur-thy, V., Schanze, K, S., Eds, Dekker New York, 1999 Vol. 3, pp 211 -281. 

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