Co-reporter:Hongmin Li;Zhuang Wu;Dingqing Li;Huabin Wan;Jian Xu;Manabu Abe
Chemical Communications 2017 vol. 53(Issue 35) pp:4783-4786
Publication Date(Web):2017/04/27
DOI:10.1039/C7CC01926B
The simplest alkoxycarbonylnitrene, CH3OC(O)N, has been generated through laser (266 and 193 nm) photolysis of CH3OC(O)N3 and CH3OC(O)NCO and subsequently characterized by IR (15N, D-labelling) and EPR (|D/hc| = 1.66 cm−1 and |E/hc| = 0.020 cm−1) spectroscopy in cryogenic matrices. Two conformers of the nitrene, with the CH3 group being in syn or anti configuration to the CO bond, have been unambiguously identified. Further UV light irradiation (365 nm) of the nitrene results in isomerization to CH3ONCO, completing the frequently explored mechanism for the Curtius-rearrangement of CH3OC(O)N3.
Co-reporter:Huabin Wan;Hongmin Li;Jian Xu;Zhuang Wu;Qifan Liu;Xianxu Chu;Manabu Abe;Didier Bégué
Organic Chemistry Frontiers 2017 vol. 4(Issue 9) pp:1839-1848
Publication Date(Web):2017/08/22
DOI:10.1039/C7QO00277G
N-Methylcarbamoyl azide Me(H)NC(O)N3 has been synthesized and structurally characterized. Both N3 and CH3 groups in the molecule adopt a syn conformation with the CO bond. Upon flash vacuum pyrolysis at 800 K, the azide mainly decomposes into Me(H)NNCO/N2 and MeNCO/HN3 through Curtius-rearrangement and a retro-ene reaction, respectively. In contrast, 193 and 266 nm laser photolysis of Me(H)NC(O)N3 in cryogenic matrices (Ar, Ne, and N2) leads to stepwise Curtius-rearrangement via the intermediacy of carbamoylnitrene Me(H)NC(O)N, for which two conformers with the CH3 group being in syn and anti conformations to the CO bond have been unambiguously identified by matrix-isolation IR spectroscopy. Triplet multiplicity of Me(H)NC(O)N (|D/hc| = 1.57 cm−1 and |E/hc| = 0.012 cm−1) and another two carbamoylnitrenes H2NC(O)N (|D/hc| = 1.59 cm−1 and |E/hc| = 0.018 cm−1) and Me2NC(O)N (|D/hc| = 1.55 cm−1 and |E/hc| = 0.016 cm−1) has been further established by matrix-isolation EPR spectroscopy. Subsequent visible light irradiation (420–460 nm) of Me(H)NC(O)N results in the exclusive formation of Me(H)NNCO. The molecular structures of Me(H)NC(O)N3 and Me(H)NC(O)N, multiplicities of the nitrene, and the underlying mechanism for the decomposition of the azide are reasonably explained with quantum chemical calculations by utilizing the B3LYP, CBS-QB3, CCSD(T), and CASPT2 methods.
Co-reporter:Zhuang Wu;Jian Xu;Qifan Liu;Xuelin Dong;Dingqing Li;Nicole Holzmann;Gernot Frenking;Tarek Trabelsi;Joseph S. Francisco
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 25) pp:16713-16720
Publication Date(Web):2017/06/28
DOI:10.1039/C7CP02774E
A biologically relevant reactive sulfur species (RSS), the hypothiocyanite radical OSCN, is generated in the gas phase through flash vacuum pyrolysis (FVP) of trifluoromethyl sulfinyl cyanide CF3S(O)CN at ca. 1000 K. Upon UV light irradiation (365 nm), OSCN rearranges to novel isomers OSNC and SOCN, and further visible light irradiation (400 ± 20 nm) leads to reverse isomerization. The identification of OSCN, OSNC, and SOCN in cryogenic matrices (Ar and N2, 2.8 K) with IR spectroscopy is supported by quantum chemical calculations up to the CCSD(T)-F12/VTZ-F12 level. The potential energy surface for the interconversion of OSCN isomers and their bonding properties are computationally explored by using the CCSD(T)-F12/VTZ-F12 and EDA–NOCV methods, respectively.
Co-reporter:Guohai Deng;Xuelin Dong;Qifan Liu;Dingqing Li;Hongmin Li;Qiao Sun
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 5) pp:3792-3799
Publication Date(Web):2017/02/01
DOI:10.1039/C6CP08125H
The thermal-decomposition and photo-decomposition of benzenesulfonyl azide, PhS(O)2N3, have been studied by combining matrix-isolation IR spectroscopy and quantum chemical calculations. Upon flash vacuum pyrolysis at 800 K, the azide splits off molecular nitrogen and exclusively furnishes phenylnitrene (PhN) and SO2 in the gas phase. In contrast, the azide favors stepwise photodecomposition in solid Ar and Ne matrices at 2.8 K. Specifically, the UV laser photolysis (193 and 266 nm) of PhS(O)2N3 results in the formation of the key nitrene intermediate PhS(O)2N in the triplet ground state, which undergoes pseudo-Curtius rearrangement into N-sulfonyl imine PhNSO2 under subsequent visible light irradiation (380–450 nm). Further fragmentation of PhNSO2 into SO2 and PhN followed by ring-expansion to didehydroazepine also occurs upon visible light irradiation. The preference of the stepwise mechanism for the decomposition of PhS(O)2N3 is supported by quantum chemical calculations using DFT B3LYP/6-311++G(3df,3pd) and CBS-QB3 methods.
Co-reporter:Zhuang Wu, Qifan Liu, Dingqing Li, Ruijuan Feng, Xiaoqing Zeng
Journal of Analytical and Applied Pyrolysis 2017 Volume 124(Volume 124) pp:
Publication Date(Web):1 March 2017
DOI:10.1016/j.jaap.2017.01.001
•The synthesis and properties of methoxysulfinyl azide are described.•The flash vacuum pyrolysis of methoxysulfinyl azide is reported.•The key intermediate methoxysulfinyl nitrene in two conformations is observed.•A stepwise decomposition mechanism of the azide is supported by quantum chemical calculations.Methoxysulfinyl azide, CH3OS(O)N3, which is unstable at room temperature, has been synthesized and characterized as neat substance for the first time. Its decomposition in the gas phase has been studied by combining flash vacuum pyrolysis (FVP) and matrix isolation IR spectroscopy. The novel dipolar nitrene intermediate, CH3OS(O)N, in the singlet ground state with two distinct conformations (syn and anti) has been identified among the FVP products at 600 K. At higher FVP temperature (800 K) the nitrene undergoes further fragmentation into HNSO and H2CO. The stepwise decomposition mechanism of CH3OS(O)N3 is supported by the quantum chemical calculations.Download high-res image (125KB)Download full-size image
Co-reporter:Ruijuan Feng, Zhuang Wu, Jian Xu, Qifan Liu, Xiaoqing Zeng
Journal of Analytical and Applied Pyrolysis 2017 Volume 125(Volume 125) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.jaap.2017.03.021
•The synthesis, characterization, and conformation of difluoroacetyl azide and its Curtius-rearrangement product difluoromethyl isocyanate are studied.•The photo-induced Curtius-rearrangement of difluoroacetyl azide is explored in solid Ne matrix.•The unexpected formation of novel carbonyl isocyanide from the flash vacuum pyrolysis of difluoroacetyl azide is observed.•The mechanism for the concerted and stepwise decomposition of difluoroacetyl azide is analyzed with the aid of quantum chemical calculations.Difluoroacetyl azide, CHF2C(O)N3, has been synthesized and characterized. The azide decomposes slowly at room temperature (300 K) into N2 and difluoromethyl isocyanate CHF2NCO, which has also been isolated as neat substance and fully characterized. The elusive nitrene intermediate CHF2C(O)N in the stepwise Curtius-rearrangement of the azide is tentatively identified by IR spectroscopy during the 193 nm laser photolysis of the azide in solid Ne matrix at 2.8 K. Unexpectedly, flash vacuum pyrolysis (FVP) of CHF2C(O)N3 at 500 K yields a novel carbonyl isocyanide FC(O)NC with N2, HF, FCN, CO, and traces of CHF2NCO. Subsequent irradiation (193 nm) of the pyrolysis products results in the rearrangement of FC(O)NC to FC(O)CN. According to the quantum chemical calculations (B3LYP and CCSD(T)), the azide CHF2C(O)N3 prefers concerted Curtius rearrangement with minor contribution of the stepwise decomposition. The thermally generated CHF2NCO eliminates HF and forms FC(O)NC solely under the pyrolysis conditions, whereas, no HF-elimination occurs to isolated CHF2NCO even at 1000 K due to a formidable activation barrier.Download high-res image (128KB)Download full-size image
Co-reporter:Zhuang Wu;Ruijuan Feng;Hongmin Li;Jian Xu;Guohai Deng; Dr. Manabu Abe; Dr. Didier Bégué; Dr. Kun Liu; Dr. Xiaoqing Zeng
Angewandte Chemie 2017 Volume 129(Issue 49) pp:15878-15882
Publication Date(Web):2017/12/04
DOI:10.1002/ange.201710307
AbstractChemical reactions involving quantum mechanical tunneling (QMT) increasingly attract the attention of scientists. In contrast to the hydrogen-tunneling as frequently observed in chemistry and biology, tunneling solely by heavy atoms is rare. Herein, we report heavy-atom tunneling in trifluoroacetyl nitrene, CF3C(O)N. The carbonyl nitrene CF3C(O)N in the triplet ground state was generated in cryogenic matrices by laser (193 or 266 nm) photolysis of CF3C(O)N3 and characterized by IR and EPR spectroscopy. In contrast to the theoretically predicted activation barriers (>10 kcal mol−1), CF3C(O)N undergoes rapid rearrangement into CF3NCO with half-life times of less than 10 min and unprecedentedly large 14N/15N kinetic isotope effects (1.18–1.33) in solid Ar, Ne, and N2 matrices even at 2.8 K. The tunneling disappearance of CF3C(O)N becomes much slower in the chemically active toluene and in 2-methyltetrahydrofuran at 5 K.
Co-reporter:Zhuang Wu;Ruijuan Feng;Hongmin Li;Jian Xu;Guohai Deng; Dr. Manabu Abe; Dr. Didier Bégué; Dr. Kun Liu; Dr. Xiaoqing Zeng
Angewandte Chemie International Edition 2017 Volume 56(Issue 49) pp:15672-15676
Publication Date(Web):2017/12/04
DOI:10.1002/anie.201710307
AbstractChemical reactions involving quantum mechanical tunneling (QMT) increasingly attract the attention of scientists. In contrast to the hydrogen-tunneling as frequently observed in chemistry and biology, tunneling solely by heavy atoms is rare. Herein, we report heavy-atom tunneling in trifluoroacetyl nitrene, CF3C(O)N. The carbonyl nitrene CF3C(O)N in the triplet ground state was generated in cryogenic matrices by laser (193 or 266 nm) photolysis of CF3C(O)N3 and characterized by IR and EPR spectroscopy. In contrast to the theoretically predicted activation barriers (>10 kcal mol−1), CF3C(O)N undergoes rapid rearrangement into CF3NCO with half-life times of less than 10 min and unprecedentedly large 14N/15N kinetic isotope effects (1.18–1.33) in solid Ar, Ne, and N2 matrices even at 2.8 K. The tunneling disappearance of CF3C(O)N becomes much slower in the chemically active toluene and in 2-methyltetrahydrofuran at 5 K.
Co-reporter:Guohai Deng, Zhuang Wu, Dingqing Li, Roberto Linguerri, Joseph S. Francisco, and Xiaoqing Zeng
Journal of the American Chemical Society 2016 Volume 138(Issue 36) pp:11509-11512
Publication Date(Web):August 30, 2016
DOI:10.1021/jacs.6b07966
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.
Co-reporter:Guohai Deng, Dingqing Li, Zhuang Wu, Hongmin Li, Eduard Bernhardt, and Xiaoqing Zeng
The Journal of Physical Chemistry A 2016 Volume 120(Issue 28) pp:5590-5597
Publication Date(Web):July 6, 2016
DOI:10.1021/acs.jpca.6b05533
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.
Co-reporter:Zhuang Wu;Dingqing Li;Hongmin Li;Bifeng Zhu;Hailong Sun;Dr. Joseph S. Francisco;Dr. Xiaoqing Zeng
Angewandte Chemie 2016 Volume 128( Issue 4) pp:1529-1532
Publication Date(Web):
DOI:10.1002/ange.201510105
Abstract
The dipolar oxathiazyne-like sulfinylnitrene RS(O)N, a highly reactive α-oxo nitrene, has been rarely investigated. Upon flash vacuum pyrolysis of sulfinyl azide CF3S(O)N3 at 350 °C, an elusive sulfinylnitrene CF3S(O)N was generated in the gas phase in its singlet ground state and was characterized by matrix-isolation IR spectroscopy. Further fragmentation of CF3S(O)N at 600 °C produced CF3 and a novel iminyl radical OSN, an SO2 analogue, which were unambiguously identified by IR spectroscopy. Consistent with the experimental observations, DFT calculations clearly support a stepwise decomposition mechanism of CF3S(O)N3.
Co-reporter:Zhuang Wu;Dingqing Li;Hongmin Li;Bifeng Zhu;Hailong Sun;Dr. Joseph S. Francisco;Dr. Xiaoqing Zeng
Angewandte Chemie International Edition 2016 Volume 55( Issue 4) pp:1507-1510
Publication Date(Web):
DOI:10.1002/anie.201510105
Abstract
The dipolar oxathiazyne-like sulfinylnitrene RS(O)N, a highly reactive α-oxo nitrene, has been rarely investigated. Upon flash vacuum pyrolysis of sulfinyl azide CF3S(O)N3 at 350 °C, an elusive sulfinylnitrene CF3S(O)N was generated in the gas phase in its singlet ground state and was characterized by matrix-isolation IR spectroscopy. Further fragmentation of CF3S(O)N at 600 °C produced CF3 and a novel iminyl radical OSN, an SO2 analogue, which were unambiguously identified by IR spectroscopy. Consistent with the experimental observations, DFT calculations clearly support a stepwise decomposition mechanism of CF3S(O)N3.
Co-reporter:Hongmin Li; Zhuang Wu; Dingqing Li; Xiaoqing Zeng; Helmut Beckers;Joseph S. Francisco
Journal of the American Chemical Society 2015 Volume 137(Issue 34) pp:10942-10945
Publication Date(Web):August 14, 2015
DOI:10.1021/jacs.5b07302
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.
Co-reporter:Dingqing Li, Hongmin Li, Bifeng Zhu, Xiaoqing Zeng, Helge Willner, Helmut Beckers, Patrik Neuhaus, Dirk Grote and Wolfram Sander
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 9) pp:6433-6439
Publication Date(Web):28 Jan 2015
DOI:10.1039/C4CP05694A
The photolytic and thermal decomposition of fluorophosphoryl diazide, FP(O)(N3)2, was studied using matrix isolation spectroscopy. Upon ArF laser photolysis (λ = 193 nm), FPO and a new geminal azido nitrene FP(O)(N3)N were identified using matrix IR spectroscopy. The nitrene shows a triplet ground state with the zero-field parameters |D/hc| = 1.566 cm−1 and |E/hc| = 0.005 cm−1. Further decomposition of the nitrene into FPO was observed under an irradiation of λ > 335 nm. In contrast, no nitrene but only FPO was identified after flash vacuum pyrolysis of the diazide. To reveal the decomposition mechanism, quantum chemical calculations on the potential energy surface (PES) of the diazide using DFT methods were performed. On the singlet PES four conformers of the nitrene were predicted. The two conformers (syn and anti) showing intramolecular Nnitrene⋯Nα,azide interactions are much lower in energy (ca. 40 kJ mol−1, B3LYP/6-311+G(3df)) than the other two exhibiting Nnitrene⋯O interactions. syn/anti refers to the relative orientation of the PO bond and the N3 group. The interconversion of these species and the decomposition into FPO via a novel three-membered ring diazo intermediate cyclo-FP(O)N2 were computationally explored. The calculated low dissociation barrier of 45 kJ mol−1 (B3LYP/6-311+G(3df)) of this cyclic intermediate rationalizes why it could not be detected in our experiments.
Co-reporter:Zhuang Wu, Hongmin Li, Bifeng Zhu, Xiaoqing Zeng, Stuart A. Hayes, Norbert W. Mitzel, Helmut Beckers and Raphael J. F. Berger
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 14) pp:8784-8791
Publication Date(Web):23 Feb 2015
DOI:10.1039/C5CP00850F
The conformational composition, molecular structure and decomposition of difluorophosphoryl azide F2P(O)N3 in the gas phase were studied using gas electron diffraction (GED), matrix isolation IR spectroscopy, and quantum-chemical calculations, respectively. While computational methods predict only minor differences in the total energy between the two possible conformers (syn and anti), the analysis of electron diffraction data reveals the dominating abundance of the syn conformer in the gas phase at room temperature. Ab initio frequency analyses suggest that a low-frequency large-amplitude motion of the N3 group with respect to the P–N–N–N torsion is to be expected for the syn conformer. The large amplitude motion was included explicitly into the GED structure refinement procedure. It presumably contributes to a thermodynamic stabilization of the syn-conformer with respect to the anti-conformer in the gas phase at ambient temperature. Upon flash vacuum pyrolysis, this syn conformer undergoes a stepwise decomposition via the difluorophosphoryl nitrene, F2P(O)N, which features as the first experimentally observed phosphoryl nitrene that can be thermally produced in the gas phase. To reveal the reaction mechanism, quantum-chemical calculations on the potential energy surface (PES) of F2P(O)N3 were performed. Both B3LYP/6-311+G(3df) and CBS-QB3 calculation results strongly support a stepwise decomposition into the singlet F2P(O)N, which prefers intersystem crossing to the thermally persistent triplet ground state instead of a Curtius rearrangement into FP(O)NF.
Co-reporter:Hongmin Li, Dingqing Li, Xiaoqing Zeng, Kun Liu, Helmut Beckers, Henry F. Schaefer III, Brian J. Esselman, and Robert J. McMahon
The Journal of Physical Chemistry A 2015 Volume 119(Issue 33) pp:8903-8911
Publication Date(Web):July 28, 2015
DOI:10.1021/acs.jpca.5b04586
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).
Co-reporter:Hailong Sun, Bifeng Zhu, Zhuang Wu, Xiaoqing Zeng, Helmut Beckers, and William S. Jenks
The Journal of Organic Chemistry 2015 Volume 80(Issue 3) pp:2006-2009
Publication Date(Web):January 13, 2015
DOI:10.1021/jo502821y
Transient carbonyl nitrenes RC(O)N, formed during thermal- or photoinduced decomposition of carbonyl azides RC(O)N3, are highly liable to the Curtius rearrangement, producing isocyanates RNCO in almost quantitative yield. Contrary to common belief, we found a thermally persistent triplet carbonyl nitrene, FC(O)N, that can be produced by flash pyrolysis of FC(O)N3 in 49% yield. The computed CBS-QB3 activation barrier for the thermal decomposition of FC(O)N3 to FC(O)N is 29 kJ mol–1 lower than that for a concerted pathway producing FNCO.
Co-reporter:Bifeng Zhu;Dr. Xiaoqing Zeng;Dr. Helmut Beckers;Dr. Joseph S. Francisco;Dr. Helge Willner
Angewandte Chemie 2015 Volume 127( Issue 39) pp:
Publication Date(Web):
DOI:10.1002/ange.201583961
Co-reporter:Bifeng Zhu;Dr. Xiaoqing Zeng;Dr. Helmut Beckers;Dr. Joseph S. Francisco;Dr. Helge Willner
Angewandte Chemie 2015 Volume 127( Issue 39) pp:11566-11570
Publication Date(Web):
DOI:10.1002/ange.201503776
Abstract
Das Methylsulfonyloxyl-Radikal, CH3SO3, ein Schlüsselintermediat der atmosphärischen Oxidation von Dimethylsulfid (DMS), wurde durch Blitzpyrolyse von CH3SO2OOSO2CH3 erzeugt und nachfolgend in festen Edelgas-Matrizen isoliert. Das Radikal wurde charakterisiert über seine UV/Vis- und IR-Spektren, sowie seine Tautomerisierung zum CH2SO3H unter Bestrahlung mit Licht von λ≥360 nm.
Co-reporter:Dr. Xiaoqing Zeng;Dr. Andrea FloresAntognini;Dr. Helmut Beckers;Dr. Helge Willner
Angewandte Chemie 2015 Volume 127( Issue 9) pp:2797-2800
Publication Date(Web):
DOI:10.1002/ange.201407538
Abstract
Die UV-Photolyse (λ=248 oder 255 nm) von cyclischem S2N2, das in fester Argonmatrix isoliert wurde, ergibt zwei offenschalige S2N2-Isomere, trans-SNSN (3A′′) und cis-SNSN (3A′′), sowie das geschlossenschalige C2v-symmetrische Dimer (SN)2 (1A1). Die neuartigen Isomere wurden über ihre IR-Spektren und ihre wechselseitige photolytische Umwandlung charakterisiert. Quantenchemische Rechnungen stützen die experimentellen Ergebnisse und bieten Einblicke in die komplexe Potentialhyperfläche von S2N2.
Co-reporter:Dr. Xiaoqing Zeng;Hongmin Li;Hailong Sun;Dr. Helmut Beckers;Dr. Helge Willner;Dr. Henry F. Schaefer III
Angewandte Chemie 2015 Volume 127( Issue 4) pp:1343-1346
Publication Date(Web):
DOI:10.1002/ange.201409868
Abstract
Die neuartige aromatische Ringverbindung 2,4-Diphospha-3,5-diazathiol (cyclo-SNPNP) wurde durch Blitzpyrolyse von SP(N3)3 und nachfolgende Matrixisolierung der Produkte erhalten und über ihr IR-Spektrum und 15N-Isotopenmarkierung nachgewiesen. Quantenchemische Rechnungen lassen auf eine Bildung dieser Verbindung durch Kopf-zu-Schwanz-Dimerisierung von SNP mit anschließender Abspaltung eines Schwefelatoms aus dem sehr instabilen, bootförmigen, sechsgliedrigen Ring cyclo-SNPSNP schließen.
Co-reporter:Bifeng Zhu;Dr. Xiaoqing Zeng;Dr. Helmut Beckers;Dr. Joseph S. Francisco;Dr. Helge Willner
Angewandte Chemie International Edition 2015 Volume 54( Issue 39) pp:
Publication Date(Web):
DOI:10.1002/anie.201583961
Co-reporter:Bifeng Zhu;Dr. Xiaoqing Zeng;Dr. Helmut Beckers;Dr. Joseph S. Francisco;Dr. Helge Willner
Angewandte Chemie International Edition 2015 Volume 54( Issue 39) pp:11404-11408
Publication Date(Web):
DOI:10.1002/anie.201503776
Abstract
The methylsulfonyloxyl radical, CH3SO3, one of the key intermediates in the atmospheric oxidation of dimethyl sulfide (DMS), was generated by flash pyrolysis of CH3SO2OOSO2CH3 and subsequently isolated in solid noble-gas matrices. The radical has been characterized by UV/Vis and IR spectroscopy and its tautomerization to CH2SO3H observed upon irradiation with light of λ≥360 nm.
Co-reporter:Dr. Xiaoqing Zeng;Dr. Andrea FloresAntognini;Dr. Helmut Beckers;Dr. Helge Willner
Angewandte Chemie International Edition 2015 Volume 54( Issue 9) pp:2758-2761
Publication Date(Web):
DOI:10.1002/anie.201407538
Abstract
UV photolysis (λ=248 or 255 nm) of cyclic S2N2 isolated in solid argon matrices yields two open-shell S2N2 isomers, trans SNSN (3A′′) and cis SNSN (3A′′), as well as a closed-shell C2v dimer (SN)2 (1A1). These novel isomers have been characterized by their IR spectra and mutual photo-interconversion reactions. Quantum chemical calculations support the experimental results and also provide insight into the complex potential energy surface of S2N2.
Co-reporter:Dr. Xiaoqing Zeng;Hongmin Li;Hailong Sun;Dr. Helmut Beckers;Dr. Helge Willner;Dr. Henry F. Schaefer III
Angewandte Chemie International Edition 2015 Volume 54( Issue 4) pp:1327-1330
Publication Date(Web):
DOI:10.1002/anie.201409868
Abstract
The novel aromatic ring compound 2,4-diphospha-3,5-diaza-thiole (cyclo-SNPNP) was synthesized via flash pyrolysis of SP(N3)3 and characterized by IR spectroscopy and 15N isotope labeling. Quantum chemical computations indicate its formation by head-to-tail dimerization of SNP and subsequent elimination of a sulfur atom from the highly unstable boatlike six-membered-ring compound cyclo-SNPSNP.
Co-reporter:Xiaoqing Zeng;Helmut Beckers;Jennifer Seifert;Klaus Banert
European Journal of Organic Chemistry 2014 Volume 2014( Issue 19) pp:4077-4082
Publication Date(Web):
DOI:10.1002/ejoc.201402153
Abstract
Decomposition of the extremely explosive and unstable parent compound of 1-azidoalkynes, HCCN3 (azidoacetylene), was studied in the gas phase, solid argon matrix, and solutions. In the gas phase, this azide decomposes quickly at room temperature with a half-life time (t1/2) of 20 min at an initial pressure (p0) of 0.8 mbar. The decay (p0 = 1.0 mbar) is significantly increased in an atmosphere of O2 with t1/2 of 3 min, in which HC(O)CN was identified as the trapping product of the cyanocarbene intermediate HCCN. Trapping products of this carbene by solvent molecules (CH2Cl2 and CHCl3) were also found during decomposition of the azide in solution, whereas the reaction with a solution of bromine to form dibromoacetonitrile is interpreted as taking place by nucleophilic attack of the alkyne itself. The intermediary formation of triplet HCCN by flash vacuum pyrolysis and photolysis (255 nm) of the azide in the gas phase and in solid argon matrices, respectively, was confirmed by IR spectroscopy and mutual photo-interconversion of HCCN with isomeric cyclo-C(H)CN (azirinylidene) and HCNC by selective irradiations at 16 K.
Co-reporter:Dr. Xiaoqing Zeng;Dr. Helmut Beckers;Dr. Helge Willner
Angewandte Chemie International Edition 2013 Volume 52( Issue 31) pp:7981-7984
Publication Date(Web):
DOI:10.1002/anie.201302968
Co-reporter:Dr. Xiaoqing Zeng;Dr. Helmut Beckers;Dr. Helge Willner
Angewandte Chemie 2013 Volume 125( Issue 31) pp:8139-8142
Publication Date(Web):
DOI:10.1002/ange.201302968
Co-reporter:Jon B. Nielsen, Petra Zylka, Marc Kronberg, Xiaoqing Zeng, Kerry D. Robinson, Simon G. Bott, Hongming Zhang, Jerry L. Atwood, Heinz Oberhammer, Helge Willner, Joseph S. Thrasher
Journal of Molecular Structure (15 March 2017) Volume 1132() pp:
Publication Date(Web):15 March 2017
DOI:10.1016/j.molstruc.2016.05.089
•Mechanism of formation and thermal decay of N(SF5)3 and N(SF5)2.•Gas electron diffraction of N(SF5)3 and N(SF5)2.•Single crystal X-ray diffraction of N(SF5)3.•Vibrational and UV–vis spectra of N(SF5)3 and N(SF5)2.•Quantum chemical calculations of N(SF5)3 and N(SF5)2.Tris(pentafluorosulfanyl)amine, N(SF5)3, and the bis(pentafluorosulfanyl)aminyl radical, N(SF5)2, have been synthesized and characterized by gas electron diffraction, single crystal XRD, NMR, EPR, FT-IR, Raman, and UV–vis spectroscopy, and by their thermal decompositions. The amine possesses a planar molecular structure of D3 symmetry with an unusually long NS bond of 1.829(6) Å. The long NS bonds are in accordance with the small Arrhenius activation barrier for the decay into N(SF5)2 and SF5 radicals of 6.9 kcal mol−1, and its half-life at room temperature is only 50 min. The aminyl radical possesses C2 symmetry with NS = 1.692(4) Å and SNS = 135.1(5)°, and its structure is similar to that of FN(SF5)2. This radical is much more stable than the amine (half-life at room temperature is 130 min). Dimerization and formation of the corresponding hydrazine, (SF5)2NN(SF5)2, was not observed, nor was the nitrene:NSF5 or its isomer FNSF4.
Co-reporter:Hongmin Li, Zhuang Wu, Dingqing Li, Huabin Wan, Jian Xu, Manabu Abe and Xiaoqing Zeng
Chemical Communications 2017 - vol. 53(Issue 35) pp:NaN4786-4786
Publication Date(Web):2017/04/07
DOI:10.1039/C7CC01926B
The simplest alkoxycarbonylnitrene, CH3OC(O)N, has been generated through laser (266 and 193 nm) photolysis of CH3OC(O)N3 and CH3OC(O)NCO and subsequently characterized by IR (15N, D-labelling) and EPR (|D/hc| = 1.66 cm−1 and |E/hc| = 0.020 cm−1) spectroscopy in cryogenic matrices. Two conformers of the nitrene, with the CH3 group being in syn or anti configuration to the CO bond, have been unambiguously identified. Further UV light irradiation (365 nm) of the nitrene results in isomerization to CH3ONCO, completing the frequently explored mechanism for the Curtius-rearrangement of CH3OC(O)N3.
Co-reporter:Dingqing Li, Hongmin Li, Bifeng Zhu, Xiaoqing Zeng, Helge Willner, Helmut Beckers, Patrik Neuhaus, Dirk Grote and Wolfram Sander
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 9) pp:NaN6439-6439
Publication Date(Web):2015/01/28
DOI:10.1039/C4CP05694A
The photolytic and thermal decomposition of fluorophosphoryl diazide, FP(O)(N3)2, was studied using matrix isolation spectroscopy. Upon ArF laser photolysis (λ = 193 nm), FPO and a new geminal azido nitrene FP(O)(N3)N were identified using matrix IR spectroscopy. The nitrene shows a triplet ground state with the zero-field parameters |D/hc| = 1.566 cm−1 and |E/hc| = 0.005 cm−1. Further decomposition of the nitrene into FPO was observed under an irradiation of λ > 335 nm. In contrast, no nitrene but only FPO was identified after flash vacuum pyrolysis of the diazide. To reveal the decomposition mechanism, quantum chemical calculations on the potential energy surface (PES) of the diazide using DFT methods were performed. On the singlet PES four conformers of the nitrene were predicted. The two conformers (syn and anti) showing intramolecular Nnitrene⋯Nα,azide interactions are much lower in energy (ca. 40 kJ mol−1, B3LYP/6-311+G(3df)) than the other two exhibiting Nnitrene⋯O interactions. syn/anti refers to the relative orientation of the PO bond and the N3 group. The interconversion of these species and the decomposition into FPO via a novel three-membered ring diazo intermediate cyclo-FP(O)N2 were computationally explored. The calculated low dissociation barrier of 45 kJ mol−1 (B3LYP/6-311+G(3df)) of this cyclic intermediate rationalizes why it could not be detected in our experiments.
Co-reporter:Zhuang Wu, Hongmin Li, Bifeng Zhu, Xiaoqing Zeng, Stuart A. Hayes, Norbert W. Mitzel, Helmut Beckers and Raphael J. F. Berger
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 14) pp:NaN8791-8791
Publication Date(Web):2015/02/23
DOI:10.1039/C5CP00850F
The conformational composition, molecular structure and decomposition of difluorophosphoryl azide F2P(O)N3 in the gas phase were studied using gas electron diffraction (GED), matrix isolation IR spectroscopy, and quantum-chemical calculations, respectively. While computational methods predict only minor differences in the total energy between the two possible conformers (syn and anti), the analysis of electron diffraction data reveals the dominating abundance of the syn conformer in the gas phase at room temperature. Ab initio frequency analyses suggest that a low-frequency large-amplitude motion of the N3 group with respect to the P–N–N–N torsion is to be expected for the syn conformer. The large amplitude motion was included explicitly into the GED structure refinement procedure. It presumably contributes to a thermodynamic stabilization of the syn-conformer with respect to the anti-conformer in the gas phase at ambient temperature. Upon flash vacuum pyrolysis, this syn conformer undergoes a stepwise decomposition via the difluorophosphoryl nitrene, F2P(O)N, which features as the first experimentally observed phosphoryl nitrene that can be thermally produced in the gas phase. To reveal the reaction mechanism, quantum-chemical calculations on the potential energy surface (PES) of F2P(O)N3 were performed. Both B3LYP/6-311+G(3df) and CBS-QB3 calculation results strongly support a stepwise decomposition into the singlet F2P(O)N, which prefers intersystem crossing to the thermally persistent triplet ground state instead of a Curtius rearrangement into FP(O)NF.
Co-reporter:Guohai Deng, Xuelin Dong, Qifan Liu, Dingqing Li, Hongmin Li, Qiao Sun and Xiaoqing Zeng
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 5) pp:NaN3799-3799
Publication Date(Web):2017/01/11
DOI:10.1039/C6CP08125H
The thermal-decomposition and photo-decomposition of benzenesulfonyl azide, PhS(O)2N3, have been studied by combining matrix-isolation IR spectroscopy and quantum chemical calculations. Upon flash vacuum pyrolysis at 800 K, the azide splits off molecular nitrogen and exclusively furnishes phenylnitrene (PhN) and SO2 in the gas phase. In contrast, the azide favors stepwise photodecomposition in solid Ar and Ne matrices at 2.8 K. Specifically, the UV laser photolysis (193 and 266 nm) of PhS(O)2N3 results in the formation of the key nitrene intermediate PhS(O)2N in the triplet ground state, which undergoes pseudo-Curtius rearrangement into N-sulfonyl imine PhNSO2 under subsequent visible light irradiation (380–450 nm). Further fragmentation of PhNSO2 into SO2 and PhN followed by ring-expansion to didehydroazepine also occurs upon visible light irradiation. The preference of the stepwise mechanism for the decomposition of PhS(O)2N3 is supported by quantum chemical calculations using DFT B3LYP/6-311++G(3df,3pd) and CBS-QB3 methods.
Co-reporter:Zhuang Wu, Jian Xu, Qifan Liu, Xuelin Dong, Dingqing Li, Nicole Holzmann, Gernot Frenking, Tarek Trabelsi, Joseph S. Francisco and Xiaoqing Zeng
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 25) pp:NaN16720-16720
Publication Date(Web):2017/05/31
DOI:10.1039/C7CP02774E
A biologically relevant reactive sulfur species (RSS), the hypothiocyanite radical OSCN, is generated in the gas phase through flash vacuum pyrolysis (FVP) of trifluoromethyl sulfinyl cyanide CF3S(O)CN at ca. 1000 K. Upon UV light irradiation (365 nm), OSCN rearranges to novel isomers OSNC and SOCN, and further visible light irradiation (400 ± 20 nm) leads to reverse isomerization. The identification of OSCN, OSNC, and SOCN in cryogenic matrices (Ar and N2, 2.8 K) with IR spectroscopy is supported by quantum chemical calculations up to the CCSD(T)-F12/VTZ-F12 level. The potential energy surface for the interconversion of OSCN isomers and their bonding properties are computationally explored by using the CCSD(T)-F12/VTZ-F12 and EDA–NOCV methods, respectively.
Co-reporter:Dingqing Li, Jan Schwabedissen, Hans-Georg Stammler, Norbert W. Mitzel, Helge Willner and Xiaoqing Zeng
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 37) pp:NaN26253-26253
Publication Date(Web):2016/09/01
DOI:10.1039/C6CP05377G
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 C⋯O contacts. Additionally, the dynamic character of the position of the isocyanate group of Cl2PNCO was examined in the gas phase.
![{[(methylsulfonyl)peroxy]sulfonyl}methane](http://img.cochemist.com/ccimg/1100/1001-62-3.png)
![{[(methylsulfonyl)peroxy]sulfonyl}methane](http://img.cochemist.com/ccimg/1100/1001-62-3_b.png)
