Protonation of CH3 N3 and CF3 N3 in Superacids: Isolation and Structural Characterization of Long-Lived Methyl- and Trifluoromethylamino Diazonium Ions.

The methylamino diazonium cations [CH3 N(H)N2 ]+ and [CF3 N(H)N2 ]+ were prepared as their low-temperature stable [AsF6 ]- salts by protonation of azidomethane and azidotrifluoromethane in superacidic systems. They were characterized by NMR and Raman spectroscopy. Unequivocal proof of the protonation site was obtained by the crystal structures of both salts, confirming the formation of alkylamino diazonium ions. The Lewis adducts CH3 N3 ⋅AsF5 and CF3 N3 ⋅AsF5 were also prepared and characterized by low-temperature NMR and Raman spectroscopy, and also by X-ray structure determination for CH3 N3 ⋅AsF5 . Electronic structure calculations were performed to provide additional insights. Attempted electrophilic amination of aromatics such as benzene and toluene with methyl- and trifluoromethylamino diazonium ions were unsuccessful.

Photochemistry of 2-Nitroarenes: 2-Nitrophenyl-α-trifluoromethyl Carbinols as Synthons for Fluoroorganics.

Facile synthesis of a new series of 2,2'-bis(trifluoroacetyl) azoxybenzene derivatives and trifluoromethylated benzo[c]isoxazoline systems, along with trifluoroacetyl nitrosobenzene derivatives was achieved by solvent controlled photolysis of appropriate 2-nitrobenzyl alcohols. Corresponding photoactive 2-nitrobenzyl chromophore plays a distinct role in this photosynthetic process, while, quite unprecedented, pertinent fluoromethyl substitution leads to high value fluoromethylated products, whose direct access is not feasible by common synthetic protocols. The significance of fluorine and fluoroalkyl substitution and its prominent biological effects makes this new photochemical approach an important discovery in synthetic methodology. Plausible mechanistic pathways involved in the formation of the products during steady-state photolysis are further established by picosecond laser flash photolysis experiments.

Studies on Long-Lived (Pentafluorosulfanyl)phenyl-Substituted Carbocations.

A variety of long-lived carbocations containing the p-(pentafluorosulfanyl)phenyl and m-(pentafluorosulfanyl)phenyl groups have been characterized by low-temperature NMR spectroscopy. In the case of potential nonclassical carbocations substituted with the p-(pentafluorosulfanyl)phenyl substituent, deviations from linearity when the Hammett parameter (σC+) is plotted versus 13C NMR shifts of the carbocationic center were observed. Plotting the experimentally derived 13C NMR shifts versus σC+ or σ+ of classical 4-phenyl-X substituted carbocations also provides a means to accurately back-calculate the σ+ and σC+ parameters of the -SF5 substituent.