Carbon diazonium cation

The photolysis of arenediazonium salts has been widely used for intramolecular cyclizations in the synthesis of 1-phenylethylisoquinoline alkaloids by Kametani and Fukumoto (review 1972). An example is the photolysis of the diazonium ion 10.73, which resulted in the formation of O-benzylandrocymbine (10.74) (Kametani et al., 1971). The mechanism of this cyclization is obviously quite complex, since the carbon (as cation or radical ) to which the diazonio group is attached in 10.73 does not react with the aromatic CH group, but with the tertiary carbon (dot in 10.73), forming a quinone-like ring (10.74). In our opinion the methyl cation released is likely to react with the counter-ion X- or the solvent. 

The carbon dioxide anion radical was used for one-electron reductions of nitrobenzene diazonium cations, nitrobenzene itself, quinones, aliphatic nitro compounds, acetaldehyde, acetone and other carbonyl compounds, maleimide, riboflavin, and certain dyes (Morkovnik Okhlobystin 1979). This anion radical reduces organic complexes of Com and Rum into appropriate complexes of the metals in the valence 2 state (Morkovnik Okhlobystin 1979). In the case of the pentammino-p-nitrobenzoato-cobalt(III) complex, the electron-transfer reaction passes a stage of the formation of the Co(III) complex with the p-nitrophenyl anion radical fragment. This intermediate complex transforms into the final Co(II) complex with the p-nitrobenzoate ligand as a result of an intramolecular electron transfer. Scheme 1-89 illustrates this sequence of transformations ... 

Displacement of carboxyl groups by other electrophiles such as halogens or under nitrating conditions, or with aryl diazonium cations occurs more readily than at a carbon carrying hydrogen. 

Reaction mechanism for chemical modification of carbon by spontaneous reduction of anthro-quinone diazonium cations. (Source Pognon, G. et al. 2011. Journal of Power Sources, 196,4117-4122. With permission.)... 

The existence of S /ace-N=N-aryl bonds are more difficult to establish because azo bonds are also formed during the growth of the film. A C(OH)-C-N=N-C6H5 has been observed by TOF-SIMS [126] and assigned to an electrophilic attack of the diazonium cation on an -OH-substituted aromatic ring at the surface of carbon. This is the well-known azo coupling reaction between diazonium salts and, for example, naphthol that has been the basis of the dye chemistry. It is different from the reaction of Figure 3.1 that involves a radical. 

Dne to the bifnnctionality of substituted aryl diazonium cations, they have been employed for polymer grafting from the early years of their modern surface chemistry when an epoxy resin was grafted to 4-aminophenyl-modified carbon fibers [288]. Becanse the dediazonation provides reactive radical species toward surfaces, one can take advantage of the functional group in the para position to attach polymers and, therefore, design new materials [6,118,289]. 

Baranton, S. and D. Belanger. Electrochemical derivatization of carbon surface by reduction of in situ generated diazonium cations. J. Phys. Chem. B 109, 2005 24401-24410. 

ShuL G., C. A. Castro Ruiz, D. Rochefort, P. A. Brooksby, D. Belanger. Electrochemical functionalization of glassy carbon electrode by reduction of diazonium cations in protic ionic liquid. Electrochim. Acta 106, 2013 378-385. 

Abstract Diazonium salts have been previously used to cleave DNA via generation of carbon centered radicals and cations. Efforts have been made in the past decade or so to develop diazo compounds and a-diazoketones for physiologically relevant DNA cleavage. These efforts, coupled with their relevance to the mechanism of action of kinamycin and lomaiviticin antibiotics and other naturally occurring diazo compounds, will be discussed. 

The cation 18 did not show any DNA cleavage, due probably to its inherent stability (18 would be more stable than a benzyl cation [66], relatively stable ions that do not alkylate the heterocyclic bases in DNA). The 9-diazofluorene 19 would not undergo reduction like the corresponding diazonium salts (17) because of the presence of a negative charge on the fluorenyl carbon. 

More recently, cationic intermediates have been observed in the Heck reactions of arene diazonium salts catalyzed by triolefinic macrocycle Pd(0) complexes [17,59], o-iodophenols and enoates to form new lactones [60], and o-iodophenols with olefins (the oxa-Heck reaction) [61 ]. In the first case ions were formed by oxidation of the analyte at the capillary, or by association of [NH4] or Na". In the two other cases ionization occurred through the more typical loss of a halide ligand. The oxa-Heck reaction provides a good example of how these experiments are typically performed and the type of information that can be obtained. The oxyarylations of olefins were performed in acetone, catalyzed by palladium, and required the presence of sodium carbonate as base. Samples from the reaction mixtures were diluted with acetonitrile and analyzed by ESI(+)-MS. Loss of iodide after oxidative addition of o-iodophenol to palladium afforded positively-charged intermediates. Species consistent with oxidative addition, such as [Pd(PPh3)2(C6H50)], and the formation of palladacycles of the type seen in Scheme 8 were observed. Based on this, a mechanism for the reaction was proposed (Scheme 8). 

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