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

摘要

The simplest acryloylnitrene, CH2=CHC(O)N (1b), and two halogenated derivatives, CH2=CFC(O)N (2b) and CH2=CBrC(O)N (3b), were generated through the 266 nm laser photolysis of the corresponding azide precursors in solid N-2-matrices at 15 K. The IR spectroscopic characterization of these new acylnitrenes is supported by N-15-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 (Delta E-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 CH2=CXNCO (X = H, F, Br), for which the IR spectra have also been obtained. According to the calculations on the alpha,beta-fluorinated acryloylnitrenes at the CBS-QB3 level, their spin multiplicities can be switched from singlet CH2=CFC(O)N (DEBT = -0.86 kcal mol(-1)) to triplet CF2=CFC(O)N (Delta E-ST = +0.61 kcal mol(-1)), whereas CFH=CFC(O)N is magnetically bistable due to a rather small Delta E-ST (+0.09 kcal mol(-1)).