Helmut Beckers

Elusive diazirinone, N2CO.

viewed as dimers of the very stable diatomic molecules CO and N2. Thus, they represent a very special class of molecules. The consequent metastability also serves to make their preparation and detection challenging. However, experimental detection of such species affords an opportunity to study molecules at the limit of chemical stability. N2CO (1) was calculated to be 400 kJmol 1 higher in energy than N2 and CO, but a significant dissociation barrier of 108 kJmol 1 was also predicted at the coupled-cluster level of theory. 4] The cyclic isomer 1 was calculated to be the most stable of the N2CO species on the singlet potential energy surface (PES); it is thermodynamically more stable than NCNO (2), CNNO (3), and NCON (4), all of which have been observed in cryogenic Ar matrices at 15 K. Formation of triplet NNCO (5) has been claimed in a neutralization–reionization mass spectrometry study starting from mixtures of N2 + + CO or N2 + CO . Observation of 1 in the reaction of p-nitrophenoxychlorodiazirine with halide salts was recently reported. However, subsequent work strongly suggested that an IR feature attributed in the previous study to cyclic N2CO was in fact due to condensed-phase CO. Thus, to date, diazirinone remains an undetected species. Our recent studies of pure carbonyl diazide, OC(N3)2, [13] stimulated investigations of its photolytic decomposition reactions. UV photolysis (l = 255 nm) of low-temperature matrix-isolated OC(N3)2 results in carbonyl nitrene N3C(O)N, which undergoes a Curtius rearrangement to give the N6 analogue N3 NCO upon visible-light (l 455 nm) irradiation. N3 NCO decomposed to CO and N2 when irradiated with UV/Vis light (l 335 nm). In these experiments, none of the N2CO isomers were observed, probably because of their photolytic destruction under the experimental conditions. Herein, we report on the thermal decomposition of gaseous OC(N3)2 through low-pressure pyrolysis, both in the pure form and diluted with noble gases. In the low-pressure pyrolysis of the pure diazide at 400 8C, the pyrolysis products were directed through two U-traps held at 173 and 77 K (liquid nitrogen). Unreacted diazide remained in the former trap, while the trap at 77 K contained a small amount of a yellow solid. Its gas-phase IR spectrum displays two prominent bands in the region from 1800 to 2100 cm 1 (Figure 1). The positions (Q centers) at 2044 and 1865 cm 1 and relative intensities are in excellent agreement with values predicted for the most intense vibrational bands of cyclic 1 (Table 1). Furthermore they exhibit the expected A-type band contour with a P–R separation of 25 cm 1 (calc.: 24.7 cm ). At room temperature in an IR cell, the intensities of these bands Scheme 1. Isomers of N2CO.

Fluorine-Rich Fluorides: New Insights into the Chemistry of Polyfluoride Anions.

Polyfluoride anions have been investigated by matrix-isolation spectroscopy and quantum-chemical methods. For the first time the higher polyfluoride anion [F5 ](-) has been observed under cryogenic conditions in neon matrices at 850 cm(-1) . In addition, a new band for the Cs(+) [F3 ](-) complex in neon is reported.

Thermally persistent fluorosulfonyl nitrene and unexpected formation of the fluorosulfonyl radical.

Thermally persistent triplet sulfonyl nitrene, FSO(2)N, was produced in the gas phase in high yields (up to 66%) by flash vacuum pyrolysis of FSO(2)N(3). Surprisingly, no rearrangement of FSO(2)N was observed, but the long-sought radical FSO(2) (22%) and traces of SO(2) (3%) were identified by IR ((15)N, (18)O, (34)S) spectroscopy. The photoinduced Curtius rearrangement of the nitrene to FNSO(2) was observed in solid noble gas matrices, and reactions of the nitrene with O(2), NO, and CO were studied.

Intermediates Involved in the Oxidation of Nitrogen Monoxide: Photochemistry of the cis-N2O2·O2 complex and of sym-N2O4 in Solid Ne Matrices

Pure sym-N(2)O(4) isolated in solid Ne was obtained by passing cold neon gas over solid N(2)O(4) at -115 degrees C and quenching the resulting gaseous mixture at 6.3 K. Filtered UV irradiation (260-400 nm) converts sym-N(2)O(4) into trans-ONONO(2), a weakly interacting (NO(2))(2) radical pair, and traces of the cis-N(2)O(2)O(2) complex. Besides the weakly bound ONO(2) complex, cis-N(2)O(2)O(2) was also obtained by co-deposition of NO and O(2) in solid Ne at 6.3 K, and both complexes were characterised by their matrix IR spectra. Concomitantly formed cis-N(2)O(2) dissociated on exposure to filtered IR irradiation (400-8000 cm(-1)), and the cis-N(2)O(2)O(2) complex rearranged to sym-N(2)O(4) and trans-ONONO(2). Experiments using (18)O(2) in place of (16)O(2) revealed a non-concerted conversion of cis-N(2)O(2)O(2) into these species, and gave access to four selectively di-(18)O-substituted trans-ONONO(2) isotopomers. No isotopic scrambling occurred. The IR spectra of sym-N(2)O(4) and of trans-ONONO(2) in solid Ne were recorded. IR fundamentals of trans-ONONO(2) were assigned based on experimental (16/18)O isotopic shifts and guided by DFT calculations. Previously reported contradictory measurements on cis- and trans-ONONO(2) are discussed. Dinitroso peroxide, ONOONO, a proposed intermediate in the IR photoinduced rearrangement of cis-N(2)O(2)O(2) to the various N(2)O(4) species, was not detected. Its absence in the photolysis products indicates a low barrier (<or=10 kJ mol(-1)) for its exothermic O-O bond homolysis into a (NO(2))(2) radical pair.

The Bis(pentafluoroethyl)phosphinous Acid (C2F5)2POH

The industrial product (C(2)F(5))(3)PF(2) is transformed into the phosphinic acid chloride (C(2)F(5))(2)P(O)Cl, which reacts with an excess of Bu(3)SnH in a clean, multistep reaction to give the stannyl derivative (C(2)F(5))(2)POSnBu(3). Subsequent treatment with gaseous HBr leads to the formation of (C(2)F(5))(2)POH, which is isolated in 70 % yield. Besides (CF(3))(2)POH, bis(pentafluoroethyl)phosphinous acid, (C(2)F(5))(2)POH, represents the second known example of a phosphinous acid that is predicted by using density functional theory calculations at the B3PW91/6-311G(3d,p) level to be more stable than the phosphane oxide tautomer, the energy difference being 11.7 kJ mol(-1). Only the phosphinous acid isomer is detectable in the gas phase and in solution. However, investigations of the neat liquid reveal a temperature-dependent tautomeric equilibrium with the phosphane oxide isomer (C(2)F(5))(2)P(O)H, which is characterized by vibrational and multinuclear NMR spectroscopic methods in combination with quantum-chemical calculations.

Difluoro‐λ5‐Phosphinonitrile F2PN: Matrix Isolation and Photoisomerization into FPNF

Splendid isolation: Monomeric phosphazene F(2)PN ((1)A(1)) was prepared for the first time through irradiation of F(2)PN(3) in an argon matrix with an ArF excimer laser (lambda=193 nm). Upon subsequent irradiation with a high-pressure mercury arc lamp (lambda=255 nm), F(2)PN undergoes a 1,2-fluorine shift to give iminophosphane cis-FP=NF.

Thermally Persistent Carbonyl Nitrene: FC(O)N

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.

Experimental Observation of the 16-Electron Molecules SPN, SNP, and Cyclic PSN†

16-Electron triatomic ring: novel thiazylidynephosphane (SNP) was produced by either flash vacuum pyrolysis (ca. 1000 °C) or laser photolysis (193 nm) of SP(N(3))(3). Its photointerconversion to cyclic thiazaphosphirine (cyc-PSN) and thiophosphoryl nitride (SPN) was found in Ar matrix at 16 K. Cyc-PSN is the first experimentally observed 16-electron cyclic triatomic molecule.

Synthesis and Characterization of the Phosphorus Triazides OP(N3)3 and SP(N3)3

Two explosive triazides of phosphorus(V), OP(N(3))(3) and SP(N(3))(3), have been prepared as neat substances and structurally characterized. Both compounds can be handled in gas, liquid, and solid states in submillimolar quantities. The melting points of OP(N(3))(3) and SP(N(3))(3) are +22 and -30 °C, respectively. The two triazides have been characterized by IR (Ar matrix and gas phase) and Raman (solid) spectroscopies. Their single-crystal structures were obtained by X-ray diffraction and found to be significantly distorted from the predicted ideal C(3) symmetry because of intermolecular interactions. The spectroscopic and structural properties are discussed in combination with density functional theory calculations.

Detailed study of fine and hyperfine structures in rotational spectra of the free fluoroformyloxyl radical FCO2

More than 160 new hyperfine components of rotational transitions of the free fluoroformyloxyl radical FCO(2) have been measured using the Prague millimeter wave high resolution spectrometer. The frequencies of these transitions together with the previously measured data were analyzed in detail and precise values of magnetic hyperfine and fine parameters were obtained. These new parameters significantly improve the values of previously determined hyperfine parameters which were rather unreliable. The new fine and hyperfine parameters obtained in this study are compatible with those of the simultaneously electron paramagnetic resonance study. Besides that, significantly improved ground state rotational and centrifugal distortion constants of the fluoroformyloxyl radical were derived.