Time-Resolved Infrared (TRIR) Studies of Oxycarbonylnitrenes

Abstract

N-Ethyloxycarbonyl-S,S-dibenzothiphene sulfilimine and N-t-butyloxycarbonyl-S,S-dibenzothiphene sulfilimine have been utilized as precursors to ethoxycarbonylnitrene and t-butyloxycarbonylnitrene. B3LYP/6-31G(d) calculations predict triplet ground states for both oxycarbonylnitrenes, albeit by small margins. Triplet ethoxycarbonylnitrene and triplet t-butyloxycarbonylnitrene have been observed following photolysis of these sulfilimine precursors by time-resolved infrared (TRIR) spectroscopy. Kinetic studies show that ethoxycarbonylnitrene reacts with solvents such as acetonitrile and cyclohexane, while t-butyloxycarbonylnitrene undergoes an intramolecular insertion reaction to produce 5,5-dimethyl oxazolidinone. Product analysis following photolysis of N-t-butyloxycarbonyl-S,S-dibenzothiphene sulfilimine confirms that the oxazolidinone is the major product with an estimated yield of 90%. The products from these two nitrenes are derived from the corresponding singlet nitrene, either directly or via thermal repopulation of the singlet from the lower-energy triplet nitrene.

Contrasting Photolytic and Thermal Decomposition of Phenyl Azidoformate: The Curtius Rearrangement Versus Intramolecular C–H Amination

“…Considering its formation from PhOC(O)N and the associated IR band at 2200.6 cm −1 , the carrier should belong to the Curtius rearrangement product PhONCO. This assignment is confirmed by the agreement with the calculated IR spectrum (Table S3), especially for the IR band at 909.3 cm −1 (ν calcd : 928 cm −1 ), which associates with the characteristic O−N stretching vibration with an observed 15 N isotopic shift of 7.1 cm −1 (Figure S2). Similarly, the band at 2200.6 cm −1 exhibits a 15 N isotopic shift of 7.8 cm −1 .…”

“…The calculated strongest IR bands for PhOC(O)N in the singlet state (syn: 1777 cm −1 ; anti: 1764 cm −1 ) mainly belong to the C−N stretching vibration with large 15 N isotopic shifts (syn: 14 cm −1 ; anti: 12 cm −1 ). In contrast, the C−N stretching vibration in the triplet nitrene is symmetrically coupled with the C−O stretching and appears at 953.5 cm −1 with a well-resolved 15 N isotopic shift of 5.6 cm −1 . The asymmetrically coupled stretching mode locates at 1195.6 cm −1 .…”

“…14 Both triplet ethoxycarbonylnitrene and t-butyloxycarbonylnitrene, generated from laser photolysis of nonazide sulfilimine precursors in solution, have also been directly detected by time-resolved IR spectroscopy. 15 Comparing to the extensively explored mechanisms for the decomposition of alkylcarbonyl azides [5][6][7]16 and alkoxycarbonyl azides, [8][9][10][11][12][13][14]17 the corresponding studies of aryl-substituted azidoformates are limited, although their applications as nitrene transfer reagents have been frequently reported. 18−20 According to the early studies in solutions, 21,22 the parent phenyl azidoformate PhO−C(O)N 3 splits off molecular N 2 upon heating (250 °C) and yields aziridines as the formal intermolecular nitrene trapping products.…”

Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry

“…[50,85] Electron-withdrawing substituents stabilize the triplet nitrenes and result in triplet ground states for phosphoryl- [42b, 43] and sulfonylnitrenes [45, 47b] with D values on the order of 1.6 cm À1 (Table S1). These nitrenes largely fit the D-1 correlation, but alkoxycarbonylnitrenes [62,86,87] and carbamoylnitrenes [63b] have D values 12-14 %h igher than expected from the spin densities ( Figure 5a nd Table S1). This suggests the presence of SOC,and in fact our ORCAcalculations indicate aS OC contribution of about 10 %t ot he value of D,w hich brings D into agreement with experiment and explains the significant E values.I tc an be understood in terms of mixing with the low-lying oxazirine-type CSS state,which has adirect NÀOc ontact [Eq.…”

Photodecomposition of Thienylsulfonyl Azides: Generation and Spectroscopic Characterization of Triplet Thienylsulfonyl Nitrenes and 3-Thienylnitrene

“…Generally, nitrenes can be generated by either thermally or photolytically initiated N 2 -elimination in covalent azides. 34 Since azides are energetic compounds and, particularly, both 2and 3-thienyl azides are highly explosive as neat substances, 35 more stable compounds such as isocyanates 36 and sulfilimines 37,38 have also been utilized as nitrene precursors. Recently, we have demonstrated that phenylnitrene can be efficiently generated in the stepwise decomposition of sulfonyl azide PhS(O) 2 N 3 through SO 2 -elimination in the pseudo-Curtius rearrangement product N-sulfonyl imine PhNSO 2 via the intermediacy of sulfonyl nitrene PhS(O) 2 N. 17 Continuing our interest in the decomposition of sulfonyl azides and the distinct photochemistry of the involved sufonyl nitrene intermediates, 39−41 herein, we report the photodecomposition of two thienylsulfonyl azides (1 and 6) in cryogenic matrixes, in which the formation and photochemistry of thienylsulfonyl nitrenes (2 and 7) as well as 3-thienylnitrene (8) have been observed for the first time (Scheme 2).…”