Covalent Capture of Nitrous Oxide by N‐Heterocyclic Carbenes

Abstract

A good catch: N‐Heterocyclic carbenes (NHCs) form stable adducts with nitrous oxide (N2O) under mild reaction conditions. The adducts display unique reactivity as evidenced by an alkylation reaction which leads to a rupture of the NN bond.

The 1 : 1 Adduct of 1,3-Diisopropyl-4,5-dimethyl-2,3-dihydroimidazol-2- ylidene and Nitrous Oxide

“…In cross-over experiments between the adducts 6a/b and the complementary free carbenes 5b/a, no transfer of N 2 O was observed [26]. Similarly, the syn/anti mixture 8/9 shows no N 2 O transfer when mixed with the nucleophilic carbene 5a in [D 8 ]THF, although, because of the lack of resonance, the bond between C-2 of the imidazolium unit and the diazotate N atom is expected to be weaker in 8/9 compared to 6a.…”

“…In [D 8 has been found for the analogous compound 6a [26]. To the best of our knowledge, the parallel formation of the syn-and anti-isomer in a single reaction step is unique in the chemistry of diazotates.…”

“…The N,N -dimesityl and N,N -diisopropylphenylsubstituted nucleophilic carbenes 5a, b react with N 2 O to give the anti-imidazolium diazotates 6a, b [26] (Scheme 6).…”

“…The orientation of the bulky aryl groups in 6a, b nearly perpendicular to the five-membered ring allows the introduced diazotate unit to adopt dihedral angles of 25.4 and 39.5 • , respectively [26]. Thus, resonance stabilization between the N 2 O unit and the imidazolium ring should still be possible to some extent.…”

“…In a recent communication Severin et al [26] described the covalent capture of nitrous oxide by the N-heterocyclic carbenes 5a, b. This article prompted us to report on our study concerning the reaction of 1,3-diisopropyl-4,5-dimethyl-2,3-dihydroimidazol-2-ylidene (7) with N 2 O.…”