Halogen-lead bonds

Platinum removes a halogen atom from the halide, causing homolytic fission of the C-halogen bond. The resulting Pt -XR radical pair can either react to form Ptn(R)X or separate, with subsequent reaction with RX leading to either PtX2 or PtRX species or reaction with solvent molecules. 

Fig. 4 Halogen-bonded adducts are pre-reactive complexes, which, under convenient conditions, can lead to covalent bonds breaking and forming. Perfluoroalkylation occurs when the complexes between iodoperfluoroalkanes and anilines are heated or irradiated in certain solvents...

Prior to 1958 only nitrile-adducts were reported to result from the reaction of nitriles with trihaloboranes (c.f. 36)). The first reported example of the 1,2-addition of boron-halogen bonds to a C=N group involves the reaction of tri-fluoroacetonitrile with trichloroborane or tribromoborane 4) and leads to dimeric derivatives. A 1 1 ratio of the cis-trans isomers is obtained as indicated on the basis of 19F n.m.r. studies. 

Halogen bonded to boron or carbon of the CNB grouping of the molecule seems to be of similar activity. Reactions of monomeric iminoboranes with organothiols lead to C-S substituted iminoboranes which will be discussed later (c.f. Sect. VI). 

Carbon monoxide and low valent transition metals are known to give various quite well described complexes. However, due to the strong coordination to CO, these metal carbonyl compounds are not very reactive towards carbon-halogen bonds. Thus the carbonylation of organic halides remains a difficult reaction since the presence of CO leads to the deactivation of the catalytic system. Various attempts to overcome this drawback have however been reported. 

As assumed, the small and positive valne of H/D kinetic isotope effect may be used as a criterion for an electron-transfer pathway. For example, anion-radicals of a-benzoyl-co-haloalkanes can react in two routes (Kimura and Takamnkn 1994). The first ronte is the common one—an electron is transferred from the oxygen anion of the carbonyl gronp to a terminal halogen. The transfer provokes fission of the carbon-halogen bond. The second ronte is the S 2 reaction, leading to a cyclic product as shown in Scheme 2.37. 

Electrochemical oxidation of alkyl bromides and iodides leads to loss of a nonbonding electron from the halogen substituent, followed by cleavage of the carbon-halogen bond to form a carbonium ion and a halogen atom. The products isolated are formed by further reactions of the carbonium ion while two of the halogen at-... 

Oxidation of sulphonamides in the presence of bromide or iodide ions and sodium methoxide in methanol also leads to formation of the N-halogeno intermediate. The nitrogen-halogen bond in these intermediates is weak and will undergo themiolysis. At -10 °C, reaction proceeds by base catalysed elimination of hydrogen halide and ftirther steps lead to an a-amino acetal 20. The reaction is carried out in an undivided cell and renders a-aminoacetals readily available for the iso-... 

The pentacarbonylmanganese halides have been known for some time1 2 but are still the subject of intense interest. Numerous vibrational analyses h- ve been carried out,3 as well as synthetic and kinetic studies of carbonyl substitution reactions.4 Halide substitution, which requires elevated temperatures,5 leads to charged species. Diazocyclopentadienes insert into the manganese-halogen bond.6... 

The reductions of halogenated organic compounds (RX) involve the cleavage of carbon-halogen bonds [62]. Depending on the solvent, supporting electrolyte, electrode material and potential, it is possible to electrogenerate either alkyl radicals (R ) or carbanions (R ), which then can lead to the fonnation of dimers (R-R), alkanes (RH) and olefins [R(-H)] ... 

The corrinoid-mediated reduction of polyhaloethenes has been the subject of a recent study, which reports reaction via homolytic C-halogen bond fission. The elimination of a further halogen radical affords haloalkynes, which lead to acetylene itself.56 The electron transfer-induced reductive cleavage of alkyl phenyl ethers with lithium naphthalenide has been re-examined in a study which showed that it is possible to reverse regioselectivity of the cleavage (i.e. ArOR to ArH or ArOH) by introduction of a positive charge adjacent to the alkyl ether bond.57 A radical intermediate has been detected by ESR spectroscopy in the reduction of imines to amines with formic acid58 which infers reacts takes place via Lukasiewicz s mechanism.59... 

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