Magnetically Bistable Nitrenes: Matrix Isolation of Furoylnitrenes in Both Singlet and Triplet States and Triplet 3-Furylnitrene

Abstract

Two simple acylnitrenes, 2-furoylnitrene (2) and 3-furoylnitrene (6), were generated through 266 nm laser photolysis of the corresponding azides. Both are magnetically bistable in cryogenic matrices, as evidenced by the direct observation of the closed-shell singlet state with IR spectroscopy in solid Ne, Ar, Kr, Xe, and N matrices (3-40 K) and the triplet state in toluene (10 K) with EPR spectroscopy (2: |D/hc| = 1.48 cm and |E/hc| = 0.029 cm; 6: |D/hc| = 1.39 cm and |E/hc|c = 0.039 cm). Subsequent visible-light and UV laser irradiations led to the formation of furyl isocyanates (3 and 7) and ring-opening product 3-cyanoacrolein (9-E and 9-Z), respectively, in which the elusive 3-furylnitrene (8) was also identified by IR and EPR spectroscopy (|D/hc| = 1.12 cm and |E/hc| = 0.005 cm).

Trimethylsilylnitrene and Its Surprising Rearrangement to N‐(Dimethylsilyl)methanimine via Silaziridine and Silaazomethine Ylide

“…The silanimine 3 a was not characterized. We have confirmed Ferrante's assignments by calculating the IR spectra of 2 aT , 3 a , and 5 (see Supporting Information) at the B3LYP/6–311++G(d,p) level, which has given excellent results for a variety of nitrenes . The experimental IR spectra ascribed to 2 aT and 5 are in excellent agreement with the calculations.…”

The Simplest, Isolable, Alkynyl Isocyanate HC≡CNCO: Synthesis and Characterization

“…As expected, only the band for ν (CN) displays a noticeable 15 N isotopic shift (Δ ν ( 14/15 N)=9.4 cm −1 ). The frequency and the associated 15 N isotopic shift are similar to those in other oxazirine‐like singlet carbonyl nitrenes such as 2‐furoylnitrene (1752.3 cm −1 , Δ ν ( 14/15 N)=8.5 cm −1 , Ne matrix) . Nitrene 2 was not observed among the pyrolysis products of 1 (Figure C) owing to immediate rearrangement to 3 under the pyrolysis conditions.…”

“…The resulting IR difference spectrum (Figure A) demonstrates the formation of 3 and a new species 2 . Similar to the photochemistry of other carbonyl nitrenes, 2 can be selectively depleted with subsequent visible‐light irradiation (532 nm, Figure B). As expected, mainly 3 forms together with traces of 1 via the recombination of 2 with neighboring N 2 molecules in the solid matrix.…”

“…Thefrequency and the associated 15 Ni sotopic shift are similar to those in other oxazirine-like singlet carbonyl nitrenes such as 2-furoylnitrene (1752.3 cm À1 , Dn( 14/15 N) = 8.5 cm À1 ,N em atrix). [23] Nitrene 2 was not observed among the pyrolysis products of 1 ( Figure 2C) owing to immediate rearrangement to 3 under the pyrolysis conditions. Thef acile generation of 3 enables as tudy of its photochemistry in the N 2 matrix (15 K).…”

Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry

“…Recently,itwas found that the 2-and 3-furoylnitrenes (64 and 65)a re magnetically bistable in cryogenic matrices (Ne, Ar, Kr,Xe, and N 2 at 3-40 K), where the closed-shell singlets were observed by IR spectroscopy,a nd the triplets by ESR spectroscopy in at oluene matrix at 10 K( 64: j D/hc j= 1.48, j E/hc j= 0.029 cm À1 ; 65: j D/hc j= 1.39, j E/hc j= 0.039 cm À1 ). [72] Irradiation of the nitrenes with UV or visible light caused rearrangement to the furyl isocyanates (66 and 67;S cheme 17). Photolysis of the isocyanates generated the furylnitrenes,w hich underwent ring-opening to 3-cyanoacrolein (69), but only the triplet 3-furylnitrene (68)was detected by ESR spectroscopy (j D/hc j= 1.12, j E/hc j= 0.005 cm À1 ).…”