Arenediazonium o -benzenedisulfonimides 3 (20 examples, yield >90%) were prepared in the dry state by diazotization of aromatic amines with i -pentyl nitrite and o -benzenedisulfonimide in glacial acetic acid or formic acid at 0-5°C. Unlike most diazonium salts in the dry state, salts 3 are very highly stable.

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The diaryldiazenes (19 examples) and aryl( tertbutyl)diazenes (3 examples) 3 were prepared by electrophilic C-coupling reactions of dry arenediazonium o-benzenedisulfonimides 1 with Grignard reagents. The reactions were carried out in anhyd THF at -78°C under nitrogen and gave diazenes in 66-91% yield with few exceptions. In all cases the anion precursor of salts 1 , i.e. the o-benzenedisulfonimide, was recovered easily, in greater than 90% yield.It is known 1 that most dry-state arenediazonium salts are a high risk from the point of view of storage and handling, as many physical stimuli such as heat, light, shock, static electricity etc. can lead to their rapid decomposition, occasionally explosively. Such instability has certainly limited the use of these salts in synthetic applications, both on a laboratory scale and, even more so, on an industrial scale. Despite this, three classes of dry-state arenediazonium salts, viz., most tetrafluoroborates and some zinc double chlorides and sulfonates , are considered low risk reagents and are used, though with great caution, both in the laboratory and industrially. From a synthetic point of view one of the advantageous features of dry arenediazonium salts is certainly that of being able to realize reactions in aprotic solvents with various reagents, for example carbanions incompatible with protic solvents. On this subject, among the methods used in the past to prepare azo compounds, various reactions were studied, though not in-depth, using different combinations of dry arenediazonium salts and organometallic reagents, precursors of aryl and tert -butyl carbanions. Reactions specifically studied were those between arenediazonium tetrafluoroborates and Grignard reagents, or organocadmium, -mercury, -lithium, and -zinc reagents, 2, 3 or also between arenediazonium zinc double chlorides and Grignard reagents. [4][5][6][7] The best synthetic results obtained are those related to various reactions between the arenediazonium tetrafluoroborates and diphenylzinc (4 examples, 40-70% yield) 3 or di-tert -butylzinc (1 example, 97% yield), 3 and various reactions between arenediazonium zinc double chlorides and Grignard reagents (4 examples, 72-99% yield). 4 In other cases the reactions either failed completely or gave a maximum yield of 60%; the azo compound yield for most of the considered examples was 1 to 10%.In the course of recent research, we prepared a representative series of dry arenediazonium salts 1 , that were stabilized to an exceptionally high degree by the anion of o -benzenedisulfonimide. Most of these salts can be stored without decomposition for extended periods and are ready for use.In a wide-ranging investigation of the possible synthetic uses of salts 1 , we aimed to prepare azo compounds 3 [diaryldiazenes and aryl( tert -butyl)diazenes] by electrophilic C-coupling reactions of dry salts 1 with Grignard reagents 2 . The reactions were performed by adding equimolar amounts of Grignard reagents to suspensions of salts 1 in anhyd THF at -78°C, under stirring and...

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