Heterolytic Cleavage of a Bonds Involving C or

Similarly, one may ask how A het would be expected to change in the series C—F, C—Cl, C—Br, and C—I. The situation is more complicated for this series, since both 

The last approximation in equation (4.1) is only really valid for the small-overlap regime, which this is not, but it serves to remind us of the approximately inverse energy dependence of the stabilization. One may ask how AEhGt would be expected to change in the series C— , C—N, C—O, and C—F or the series H— , H—N, H—O, and 

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In the bimolecular concerted beta elimination reaction, E2, heterolytic cleavage of the C—X and C—H bonds takes place within the same reaction step, without formation of an intermediate (see Vol. 9). It appears that the energy barrier for the concerted process is lower than each of the barriers for the separate steps involving either a carbanion or a carbonium ion intermediate. 

The C-O reductive elimination reaction shown in Fig. 14 can be viewed as a intramolecular version of nucleophilic elimination reactions with one of the Pt atoms as a leaving group Z (Fig. 9). As in the case of S iv2 processes discussed above, one can consider a mechanism involving an attack of the nucleophile upon a six coordinate Pt atom (Fig. 9, dashed line) or a dissociation - elimination mechanism involving a formally five coordinate Pt transient (Fig. 9, solid line) that forms upon a heterolytic cleavage of the Pt -Pt bond. 

The next reasonable step involves cleavage of the O—O bond. This is envisioned as proceeding in the manner shown in Fig. 10. Here cleavage of the 0—0 bond of the /i-peroxobisiron(III) complex A must occur without the entry of electrons into the distal Cu-Fe pair (no low energy pathway across the /x-peroxo bridge), and consequently must be achieved by an heterolytic process. This could occur uninfluenced by electron pressure from cytochrome c (A —> B —> C) or under the influence of electron pressure (A — D —> E —> C). To go from A to B can be thought of... 

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