Anionic cleavage

The reductive dehalogenation of haloalkanes has also been achieved in high yield using polymer supported hydridoiron tetracarbonyl anion (Table 11.15). In reactions where the structure of the alkyl group is such that anionic cleavage is not favoured, carbonylation of the intermediate alkyl(hydrido)iron complex produces an aldehyde (see Chapter 8) [3]. 

The formation of RSSR from RS and RS species is particularly relevant in the present context because it is the reverse of the electro-induced radical anion cleavage (equation 76). Actually, the formation of RSSR from reaction (79) is as well studied as the reaction between aryl carbon radicals and anionic nucleophiles, the fundamental step of the SrnI. Equilibrium constants in the range 10 -10 M for reaction (79) were determined for a number of alkyl-type systems in water, although the corresponding values for aryl-type systems are smaller. The rate constants... 

A different type of anionic cleavage occurs with carbanions that are generated at a 2- (or 5-) carbon atom. In this case there are two possible modes of ring-opening, as shown in Scheme 2. The direction of ring-opening will depend... 

Cram, D. J. Langemann, A. Lwowski, W. Kopecky, K. R. Electrophilic substitution at saturated carbon. IV. Competing radical and anionic cleavage reactions./. Am. Chem. Soc. 1959, 81, 5760-5767. 

Silyl Anions (RjSi ). They have been generated by the following methods a) By the anionic cleavage of disilanes... 

In another study, the reductive C-F bond cleavage of fluoromethylarenes has been investigated in liquid ammonia and DMF by CV and/or redox catalysis [299]. Within a series of 4-cyanotoluenes where the a-carbon bears one, two or three fluorine atoms, the rate of radical anion cleavage increases on going from the trifluoro to the monofluoro derivative, a behavior which reflects the decrease in both C-F BDE and standard potential, °rx/rx.-, as the number of fluorine atoms is diminished (Table 14). 

Keywords electrochemical reduction, organofimctlonal silanes, anionic cleavage, hydrosilanes... 

We have now succeeded in the development of two new methods for the preparation of organofunctional silanes, both involving electroreductive coupling. The first synthesis concept comprises the anionic cleavage of electrochemically formed disilanes and subsequent reaction with organic halides, whereas the second even more general route involves the direct electrochemical Si-C bond formation. 

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