Diazonium salts, aryl reduction, reagents

Photochemical arylation 4-24 Reduction of diazonium salts 4-29 Dimerization of diazonium salts 4-30 Methylation of diazonium salts 4-33 Coupling of Grignard reagents 4-34 Coupling of arylboranes 4-35 Coupling of other organometallic compounds... 

Aryl radicals may also be prepared from the respective diazonium salts by electrochemical reduction. The radicals obtained from this single electron transfer then react with the diamond surface, arylating it in the course of the process. Varying a bit with the reagent chosen, the resultant surface covering is about 13% of a monolayer. Depending on the substitution pattern of the aromatic compound, the most different functionalizations of diamond films can be achieved this way. For example, doubly meta-chlorinated or para-nitrated diazonium salts can be... 

The carbodiazenylation of olefins is related to the Meerwein arylation. In this case, the aryl radical addition intermediates are not halogenated (as in the original Meerwein protocol) but are trapped with a diazonium salt so as to provide the corresponding radical cation. Reduction finally leads to aryl diazenes. Fe(ll)-salts, Ti(III)chloride and Cu(l)-salts or mixtures of these reducing reagents have been used to conduct carbodiazenylations, some reported examples of which are presented in Equation 13.12 [146]. 

The reaction apparently involves free-radical mechanism, but arylcopper compounds take a part, at least under certain reaction conditions, as clearly demonstrated through Cohen s concise results [99,100]. The reaction was discovered as a side-reaction during probes of the Gatterman synthesis of aryl halides from diazonium salts and copper(l) halides. Probably the most known example is very practical preparation of diphenic acid (57) starting from anthranilic acid (58). The reaction is usually conducted by adding an aqueous diazotized anthranilic acid solution (diazonium salt 59) to the copper(l) reagent, in situ obtained by reduction of CUSO4 with an equimolar amount of hydroxylaminc in aqueous sodium hydroxide solution, to produce diphenic acid with a 80-90% yield [99,100], Scheme 25. 

We have found that SWNTs can be functionalized by electrochemical reduction of aryl diazonium salts in their presence. Using this method, about 1 in 20 carbon atoms of the nanotube framework are reacted. We have also found that the SWNTs can be functionalized by direct treatment with aryl diazonium tetrafluoroborate salts in solution, or by in situ generation of the diazonium moiety using an alkyl nitrite reagent. These functional groups give us handles with which we can direct further, more selective derivatization (Figure 5.2) and we recently reviewed the area of covalent sidewall derivatization of SWNTs. 

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