I thank the members of the Roberts group, past and present, for the many long discussions and outings. Review of Electrophilic Reactions of £.-Toluenesulfonyl Azide The electrophilic reactions of .E_-toluenesulfonyl azide are reviewed using the principle of hard and soft acids and bases (HSAB). A number of simultaneous reactions of _g_-toluenesulfonyl azide-3l5N (I-3!5 .N) with the sodium salt of .e_-toluenesulfonamide were followed by 15N NMR.
The reaction of p-toluenesulfonyl azide with potassium azide The reaction of .e.-toluenesulfonyl azide with potassium azide-1-15N was investigated in toluene and dichloromethane by 15N NMR. The effect of solvent on the positions of the 15N and 13c resonances of E_-(!!_-butyl)benzenediazonium fluoborate is small. THE ELECTRONIC STRUCTURE OF THE NUCLEOPHILIC ATTACK OF Q-TOLUENESULFONYL AZIDE TO THE TERMINAL NITROGEN OF .E_-TOLUENESULFONYL AZIDE.
The reaction between Q-toluenesulfonyl azide and potassium azide-1-15N in toluene. The reaction of Q-toluenesulfonyl azide.
PART II
PART I
SECTION 1
The chemistry of I with nucleophiles is of particular interest because I is an ambidextrous electrophile that can react at both sulfur and terminal nitrogen. In the teninology of the theory of hard and soft acids and bases. This leads to a duality of reaction pathways$ where the nature of the nucleophile determines which site it is in. When the anionic nucleophile lacks a labile a-hydrogen, decomposition of the triazenyl anion yields a new azide and an excellent leaving group, the .e_-toluenesulfinate anion.
The products are a consequence of the preference for the soft terminal nitrogen in I to attack the softer carbon site rather than the harder nitrogen site on. Anselme and Fischer 22 have reported the isolation of an adduct from the reaction of the chloromagnesium salt of aniline with I~, which decomposed on heating to give phenylazide. There have been no reports of the hard oxybases attacking the soft terminal nitrogen in I.
Most sulfonyl sulfur substitutions occur by an addition-elimination process, but there is disagreement about the details of the mechanism. For an excellent discussion of the application of the HSAB principle in organic chemistry, see: T.-L Ho.
SECTION 2
To increase understanding of the reactions of £_-toluenesulfonyl azide (I) with nucleophiles, the reaction of I with the sodium salt of £_-toluenesulfonamide in dimethyl sulfoxide was investigated. The 15N-spectra of I-3-15N in the presence of the sodium salt of p-toluenesulfonamide, in dimethylsulfoxide, show that I is completely mixed within two hours and in addition many new 15. However, it is not necessary to call reaction of the open form to explain Equation 9, because this reaction follows naturally from Equation 5.
This 15N-labeled sulfonyl azide polymer could be prepared by diazotization of the poly(styrenesulfonylhydrazine) reported by Emerson and co-workers 18. N spectrum of potassium azide-1-15N and I in dimethyl sulfoxide after 8 hours showed no distortion of the potassium azide. The 15N NMR of I-3- 15N in the presence of small concentrations of the sodium salt of p-toluenesulfinic acid (dihydrate) in dimethyl sulfoxide.
If an excess of the sulfinate salt is added to I-3-15N in dimethyl sulfoxide, a concentration of the triazene salt builds up. 15N NMR of multilabeled I with an excess of the sulfinate salt (as the dihydrate) in dimethylsulfoxide shows that no I remains and only 15N signals attributed to Nl (24.2 ppm) and N2 (-160.3 ppm) of X are . Triazenyl Anions and Reaction of Azides with Sulfinate Salts The formation of diary1 32a, dia1ky1 33 and su1fony1triazeny1 32b anions by deprotonation of the parent triazene is well documented.
A 15N spectrum of a mixture of multilabeled I in dimethylsulfoxide treated with an equimolar amount of the sodium salt of p-. The source of the azide ion is very likely the slow reaction of the sodium salt of p-toluenesulfinate with the sulfonyl sulfur in I. In this case, because the sulfonyl in I is a hard acid, the harder oxygen in the surrounding anion is the attack center 37 (Eq. 28) .
A precedent for reaction 28 is found in studies by Corson and Pews 38 of the reaction of the sodium salt of p-toluenesulfinate with p-. When the sulfinate salt is formed in situ, as in the reaction of I with azide ion, the equilibrium of reaction 28 should lie far to the left because of the large excess of azide ion, In. These acid-induced decompositions are the reverse of the coupling procedures for the preparation of the triazenes.
Instead, it appears that the highly delocalized anion (X} is favorably protonated at the sulfonyl oxygen hard site. The combined pentane extracts were washed three times with water, first dried over anhydrous sodium sulfate, then over calcium sulfate.the solvent was removed under reduced pressure and the 15N spectrum of the remaining mixture of 15N-labeled Q_-toluenesulfonyl azides showed no other 15N-labeled compounds.
SECTION 3
The signals at 154.0 and 295.6 ppm result from a product of a side reaction of the azide ion with the solvent and will be discussed later. 3, no triazenyl di(E._-toluenesulfonyl) anion or products from the reaction of the sulfinate with chloromethyl azide are visible in the presence of iodide. A possible source of £_-toluenesulfonylnitrene in the presence of ion I and azide, is the decomposition of the £_-pentazole derivative {II} discussed in Scheme 1.
Products of the insertion of the single nitrene 39 into the C-H bonds of the solvent or crown ether should therefore be visible in the 15N NMR. Iodide ion prevents the formation of I-2-15N in dichloromethane by causing the decomposition of the hexene derivative before further reaction can take place. Commercially available spectrophotometric grade dichloromethane was used in these studies. a) The trimer of dinitrogen (N6) is also thought to be involved in the oxidation of azide ion to dinitrogen. Both a cyclic and linear form of N6 are consistent with the 15N labeling studies.
Evidence for I includes the importance of cavity size of the crown 3, steric effects of ortho ring substituents 4. In addition to improving the solubility of aryldiazonium salts in non-polar solvents, crown ethers also have a strong effect on the electronic structure of the cations. This was clearly demonstrated by changes in the spectral and chemical properties of the complex cations.
The upfield shift of N2 with basic solvents is likely due to diamagnetic shielding of the terminal nitrogen upon interaction with the basic solvent. Replacement of the fluoroborate counterion of a 1.2 M solution of II in dichloromethane by chloride ion induces downfield shifts of both nitrogens. The 15N shifts of the aryldiazonium chloride are also consistent 24 with some covalent interaction between the diazonium cation and chloride ion (IV).
The anion of the diazonium salt in dilute solutions of H2so4 and HCl has no appreciable effect on the rate of thermal decomposition 26• The counterion also has no significant effect on the rate of azo coupling in polar aprotic solvents. in nonpolar solutions was recently given by Juri and Bartsch 5. The importance of the diazo-resonance structures (Vb,Vc) in the delocalization of the positive charge of the N~ group is also demonstrated by 15N NMR. The equilibrium and rate of coupling of N2 with nucleophiles gives good Hammett plots versus common values o 33• Half-wave potential for one-electron reduction.
The diminished delocalization of the positive charge on the ring upon crown ether complexation is also evident in the chemistry of complexed aryldiazonium salts. For example, the 15N shifts of the azo nitrogens of l-phenyl-3,3-dimethyltriazene are considerably lower than aryldiazonium 15 .
