Computational study of singlet and triplet sulfonylnitrenes insertion into the C―C or C―H bonds of ethylene

Abstract

Formation of N‐sulfonylaziridines, N‐ethylidenesulfonamides, N‐vinylsulfonamides and 4,5‐dihydro‐1,2,3‐oxathiazole 2‐oxides by the reaction of singlet and triplet trifluoromethyl‐, methyl‐ and tosylnitrenes with ethylene is studied computationally at the B3LYP/6‐311++G(d,p) level of theory in both gas phase and in solution. Singlet sulfonylnitrenes react with ethylene via [1 + 2]‐cycloaddition exothermically to give N‐sulfonylaziridines. Triplet sulfonylnitrenes are formed from the singlet ones by the intersystem crossing with the energy barrier not exceeding 2.5 kcal/mol and react in a stepwise fashion by C‐addition or H‐abstraction. The C‐addition gives rise to the formation of N‐sulfonylaziridines or N‐ethylidenesulfonamides depending on the S―N―Csp3―Csp2 dihedral angle, with the barrier to rotation about the N―Csp3 bond not exceeding 2.5 kcal/mol. The H‐abstraction results in N‐vinylsulfonamides. Transformation of N‐sulfonylaziridines to N‐ethylidenesulfonamides requires to overcome the barrier of 57–60 kcal/mol, N‐ethylidenesulfonamides to 4,5‐dihydro‐1,2,3‐oxathiazole 2‐oxides—74–80 kcal/mol and N‐vinylsulfonamides to N‐ethylidenesulfonamides—about 64 kcal/mol. The use of the polarizable continuum model does not lead to a change of the course of the reaction of trifluoromethanesulfonylnitrene with ethylene and only slightly affects the relative energies of the products, intermediates and transition states. Copyright © 2014 John Wiley & Sons, Ltd.

Exploring photochemistry of p-bromophenylsulfonyl, p-tolylsulfonyl and methylsulfonyl azides by ultrafast UV-pump–IR-probe spectroscopy and computations

“…6,23 Recently, we confirmed that such transformation has an activation barrier of as low as 2 kcal mol À1 . 21 That means that the formation of triplet nitrene is, apparently, the predominant if not the only process of transformation of the singlet nitrene and the two processes should occur with the 3b and 4). A 'rise-decayrise' profile of the 1323 cm À1 curve in Fig.…”

“…6 This S 1 state decays to produce the singlet nitrene 1 (2-C 10 H 7 SO 2 N) as a short-lived species (t S E 0.70 AE 0.30 ns in CCl 4 ) that decays to the lower-energy and longer-lived triplet nitrene 3 (2-C 10 H 7 SO 2 N). The triplet spin state is the ground state for sulfonyl nitrenes which has been proved both theoretically 6,19,21 and experimentally by ESR and IR spectroscopy in matrices at low temperature. 16,17,20 However, neither singlet nor triplet sulfonylnitrenes are global minima, because the most stable species are N-sulfonylimines RNSO 2 , which are formed with a large energy gain.…”