Dingqing Li

Simplest N-Sulfonylamine HNSO2.

The simplest N-sulfonylamine HNSO2 has been generated in the gas phase through flash vacuum pyrolysis of methoxysulfonyl azide CH3OS(O)2N3. Its identification was accomplished by combining matrix-isolation IR spectroscopy and quantum chemical calculations. Both experimental and theoretical evidence suggest a stepwise decomposition of the azide via the methoxysulfonyl nitrene CH3OS(O)2N, observed in the 193 nm laser photolysis of the azide, with concerted fragmentation into CH2O and HNSO2. Upon the 193 nm laser irradiation, HNSO2 isomerizes into the novel N-hydroxysulfinylamine HONSO.

Toward Understanding the Decomposition of Carbonyl Diazide (N3)2C═O and Formation of Diazirinone cycl-N2CO: Experiment and Computations

Carbonyl diazide, (N3)2CO (I), is a highly explosive compound. The isolation of the substance in a neat form was found to provide unique access to two other high-energy molecules, namely, N3-NCO (III) and cycl-N2CO (IV), among the decomposition products of (I). To understand the underlying reaction mechanism, the decomposition reactions including the thermal conversion of two conformers of (I) were revisited, and the potential energy surface (PES) was computationally explored by using the methods of B3LYP/6-311+G(3df) and CBS-QB3. The most stable syn-syn structure (I) readily converts into the syn-anti conformer (ΔHexptl = 1.1 ± 0.5 kcal mol(-1)), which undergoes decomposition in two competing pathways: a concerted path to N3-NCO (III) or a stepwise route to (III) via the nitrene intermediate N3C(O)N (1)(II). The calculated activation barriers (Ea) are almost the same (∼33 kcal mol(-1), B3LYP/6-311+G(3df)). Further decomposition of (III) occurs through a concerted fragmentation into 2 N2 + CO with a moderate Ea of 22 kcal mol(-1), and this process is compared to the isoelectronic species N3-N3 → 3 N2 (Ea = 17 kcal mol(-1)) and OCN-NCO → N2 + 2 CO (61 kcal mol(-1)). No low-energy pathway leading to (IV) was found on the singlet PES. However, the intervention of triplet ground-state (3)(II) from the initially generated (1)(II) through an intersystem crossing (ISC) offers a likely approach to (IV); that is, (3)(II) can decompose in a concerted process (Ea = 30 kcal mol(-1)) by eliminating one N2 to yield the disfavored OCNN (3)(VI). A careful intrinsic reaction coordinate analysis and a combined energy scan of the N-C-N angle reveals a bifurcation point on this triplet PES, which allows a spin crossover to the singlet PES along the reaction coordinate and eventually leads to the formation of the metastable diazirinone (IV).

Methanesulfonyl Azide: Molecular Structure and Photolysis in Solid Noble Gas Matrices.

The parent sulfonyl azide CH3SO2N3 has been characterized in a neat form by IR (gas, matrix-isolation) and Raman (solid) spectroscopy, and its structure has been established by X-ray crystallography. In both gas phase and solid state, the azide exhibits single conformation with the azido ligand being synperiplanar to one of the two S═O groups. In the crystal molecules of CH3SO2N3 are interconnected through three-dimensional O···H-C-H···O hydrogen bonds. Upon an ArF laser (193 nm) photolysis, the azide in solid noble gas matrices splits off N2 and yields the sulfonyl nitrene CH3SO2N in the triplet ground state. Subsequent photolysis with UV light (266 nm) causes the transformation from the nitrene to the pseudo-Curtius rearrangement product CH3NSO2. The identification of the photolysis intermediates by matrix-isolation IR spectroscopy is supported by quantum chemical calculations with DFT methods.

A Singlet Thiophosphoryl Nitrene and Its Interconversion with Thiazyl and Thionitroso Isomers.

Thiophosphoryl nitrenes, R2P(S)N, are thiazirine-like intermediates that have been chemically inferred from trapping products in early solution studies. In this work, photolysis of the simplest thiophosphoryl azide, F2P(S)N3, in solid noble-gas matrices enabled a first-time spectroscopic (IR and UV-vis) identification of the thiophosphoryl nitrene F2P(S)N in its singlet ground state. Upon visible-light irradiation (≥495 nm), it converts into the thionitroso isomer F2P-N═S, which can also be produced in the gas phase from flash vacuum pyrolysis of F2P(S)N3. Further irradiation of F2P-NS with 365 nm UV light leads to the reformation of F2P(S)N and isomerization to the thiazyl species F2P-S≡N.

Heterocumulene Sulfinyl Radical OCNSO

Neutral five-atomic cumulenes formally consisting of two pseudohalogens (e.g., NCO, NNN, NSO) by sharing the central nitrogen atom are exotic species that have been barely studied. Through flash vacuum pyrolysis of CF3 S(O)NCO at ca. 1200 K, sulfinyl isocyanate, bearing resonance structures of O=C-N=S=O and O=C=N-S=O, has been generated in the gas phase and subsequently characterized in cryogenic matrices (Ar and N2 ). Its reversible conformational (syn and anti) interconversion and photodecomposition were observed.

Dichlorophosphanyl isocyanate – spectroscopy, conformation and molecular structure in the gas phase and the solid state

Dichlorophosphanyl isocyanate, Cl2PNCO, was synthesized and characterized by IR, Raman and 31P NMR spectroscopy. The conformational properties and molecular structures were studied by using gas electron diffraction (GED), X-ray crystallography and quantum-chemical calculations. Extensive DFT and ab initio calculations show that the potential energy surface of Cl2PNCO upon rotating the P-N bond is rather flat; three conformers, namely syn, anti and gauche between the NCO group and the bisector of the ClPCl angle, were theoretically predicted. Experimentally, only one conformer was indicated by gas-phase IR spectroscopy and the preference for a gauche conformation in both gas phase and solid state was unambiguously ascertained by gas electron diffraction and X-ray crystallographic data. In the solid state, the Cl2PNCO molecules adopt a gauche conformation with two distinct dihedral angles Cl-P-N-C of -121.3(2) and 137.4(2)° and form polymeric chains through weak intermolecular CO contacts. Additionally, the dynamic character of the position of the isocyanate group of Cl2PNCO was examined in the gas phase.