Acryloylnitrenes: Spectroscopic Characterization, Spin Multiplicities, and Rearrangement to Vinyl Isocyanates

Abstract

The simplest acryloylnitrene, CH 2 CHC(O)N (1b), and two halogenated derivatives, CH 2 CFC(O)N (2b) and CH 2 CBrC(O)N (3b), were generated through the 266 nm laser photolysis of the corresponding azide precursors in solid N 2matrices at 15 K. The IR spectroscopic characterization of these new acylnitrenes is supported by 15 N-labeling and quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) level of theory. For the three nitrenes 1b, 2b, and 3b, two conformers exhibiting syn and anti configurations between the CC and C O bonds with respect to the C−C bonds have been identified. Consistent with the CBS-QB3 calculated singlet−triplet energy gaps (ΔE ST < 0 kcal mol −1 ), the IR spectral analysis suggests that all these acryloylnitrenes adopt oxazirine-like structures with closed-shell singlet spin multiplicity. Upon subsequent green light (532 nm) irradiation, these acryloylnitrenes rearrange to form vinyl isocyanates CH 2 CXNCO (X = H, F, Br), for which the IR spectra have also been obtained. According to the calculations on the α,β-fluorinated acryloylnitrenes at the CBS-QB3 level, their spin multiplicities can be switched from singlet CH 2 CFC(O)N (ΔE ST = −0.86 kcal mol −1 ) to triplet CF 2 CFC(O)N (ΔE ST = +0.61 kcal mol −1 ), whereas CFHCFC(O)N is magnetically bistable due to a rather small ΔE ST (+0.09 kcal mol −1 ).

3-Fluoro-2H-azirine: Generation, Characterization, and Photochemistry

“…According to the IR spectrum of the N 2 -matrix-isolated pyrolysis products at 10 K (Figure B), the azide decomposes completely, as evidenced by the absence of its IR bands. Strong IR bands for CH 2 CFNCO ( b , 2248.8/2266.4, 1705.7, 1437.5/1462.0, 1203.0, 915.1/931.5, 839.1/833.4, 827.3, 665.8, 560.0, and 511.4 cm –1 ), HF ( d , 3880.1 cm –1 ), and NCC­(H)­CO ( c , 3076.7, 2240.2, 2162.8, and 1364.4 cm –1 ) − can be identified, indicating further dissociation of CH 2 CFNCO by the elimination of HF (CH 2 CFNCO → HCCNCO + HF) followed by immediate isomerization of HCCNCO to the cyanoketene isomer under the pyrolysis conditions. This intramolecular isomerization has been previously observed for matrix-isolated HCCNCO under irradiation at 266 nm .…”

“…Acryloyl azide, CH 2 CFC(O)N 3 , was prepared according to published protocols. 45 Vinyl isocyanate CH 2 CFNCO was prepared by the low-pressure flash pyrolysis of CH 2 CFC(O)N 3 and purified with vacuum distillation. Briefly, CH 2 CFC(O)N 3 was extracted from a flask and passed through a quartz tube (o.d.…”

Hydrogen‐Bonded Complex of the Parent Phosphinidene

“…[1] Like the nitrene analogues, [2] most phosphinidenes have triplet ground state in which the two non-bonding electrons at the phosphorus atom prefer occupation of two different orbitals with parallel spins. [3] Therefore, free phosphinidenes are very reactive, and many triplet phosphinidenes have only been spectroscopically detected in cryogenic noble gas matrices [4] or chemically inferred by the trapping products in solutions. [5] For instance, the parent phenylphosphinidene has been recently identified among the photolysis products of the corresponding phenylphosphirane in cryogenic matrices.…”

Stable Room Temperature Nitrenes Created by Photolysis of Crystalline 4-Azido-2,3,5,6-tetrafluorobenzoic Acid

“…Though the possibility of using nitrenes in quantum information science has been highlighted, their instability has prevented any significant experimental efforts in this direction. Nitrene species, typically created by photolysis of an azide, often have a sub-second lifetime at room temperature in condensed phase environments because of reactions with oxygen, hydrogen abstraction, or other molecular rearrangement. , A nitrene is often regarded as “stable” or “persistent” if it survives temperatures above the boiling point of liquid nitrogen , or beyond a few microseconds at room temperature . However, practical applications require much longer lifetimes.…”