Polynitrogens

A great deal of information exists on the syntheses of macrocyclic polynitrogen compounds and it would be redundant to present it here. Outside of the rather specific examples chosen for inclusion here, the reader is directed to the book edited by Melson " and to any of the other numerous reviews cited at the end of this chapter . ... 

Analogous to other N-oxides of polynitrogen heterocyclic bases, quinoxaline 1-oxide and phenazine 9-oxides undergo quater-... 

Keywords Valence electron rule, Metal ring, Metal cluster, AN +2 valence electron rule, 8/V +6 valence electron rule, 6N +14 valence electron rule, Pentagon stability, Cyclopentaphosphane, Hydronitrogen, Polynitrogen, Triazene, 2-Tetrazene, Tetrazadiene, Pentazole, Hexazine, Nitrogen Oxide, Disiloxane, Disilaoxirane, 1,3-Cyclodisiloxane, Metallacycle, Inorganic heterocycle... 

Analysis suggested that cyclic delocalization could, however, occur in 17 and 18 to a lesser extent than in pyrrole and benzene, respectively [97], This suggests low aromaticity of 17 and 18. Donation from sp lone pairs (Scheme 9) weakens the N-N sp -sp ) single bonds in the cyclic conjugated hydronitrogens and polynitrogens. 

Notable in the series of homoleptic polynitrogen systems is the absence of the N ring. The structure of hexaazabenzene strongly depends on the choice of theoretical model and basis set [97] [112], van der Waals type structure of two... 

The introduction of powerful electron-withdrawing substituents (NO2, CN, a polynitrogen heterocycle) at the a-C atom of AN stabilize anions of AN, thus facilitating their generation. At the same time, stabilization of anions of AN leads to a decrease in their reactivity and such anions act as milder nucleophilic agents. It will be seen from the following that this leads to an increase in the contribution of C-alkylation. 

Debitus, C. Cesario, M. Guilhem, J. Pascard, C. Pa fe, M. (1989) Tetrahedron Lett., (1989) Corallistine, a new polynitrogen compound from the sponge Corallistes fulvodesmus. Tetrahedron Lett., 30, 1535-8. 

The pentazolate anion. Ns (11.2), is estimated to have a half-life of 2.2 days, whereas that of the parent pentazole HN5 is predicted to be only ca 10 min in methanol at 0 Although HN5 is unknown, the cyclic anion N5 has been detected by tandem mass spectrometric studies of 4-hydroxyphenylpentazole. Similarly to its congener P5 (Section 11.2), N5 (isoelectronic with cyclopenta-dienide [C5H5] ) has the potential to form metallocene-like complexes. The acyclic (V-shaped) cation Ns has been isolated as a hexafluoroantimonate salt, which decomposes at ca 70 °C. The estimated energy density of [N5] [N5] is approximately twice that of hydrazine, a well-known rocket propellant, suggesting that this ionic polynitrogen allotrope would be an excellent monopropellant... 

Gelbard, G. Vielfare-Joly, F. Polynitrogen Strong Bases 1-New Syntheses of Biguanides and Their Catalytic Properties in Transesterification Reactions, Tetrahedron Lett. 1998,39, 2743-2746. 

The nomenclature,particularly of complex compounds, is not always satisfactory in spite of the good work of the nomenclature commissions of the International Union of Pure and Applied Chemistry. Occasionally, a competent chemist would, not be able to write the correct structure based on a given name. This is particularly noticeable in the naming of open chain and cyclic polynitrogen compounds... 

When H2S is passed into a solution of a tnvalent Rh salt at lCKTC, the hydrosulfide, Rh(SH)3, is formed. This black precipitate is insoluble in (NH4)>S. Rh forms many complexes with NH3, amines, cyanide, chloride, bromide, and numerous polynitrogen and poly oxygen chelating agents. 

Christe and co-workers505 have reported the synthesis [Eq. (4.143)] and full characterization of the homoleptic N5+ polynitrogen cation. Both salts are surprisingly stable and decompose at —70°C. Crystal structure of the fluoroantimonate salt 217 is in excellent agreement with calculated values (MP2/6-31G 440 and B3LYP506). The N5+ cation has a V-shaped structure of C2v symmetry and its exceptional stability is largely due to resonance stabilization. 

Conversion of polysulfur polynitrogen heterocycles such as pyrazolotrithiadiazepines or tetrathiatriazepines by heating, either neat or in solvents, gives 1,2,3-dithiazoles nonfused and condensed. In some cases, the formation of 1,2,3-oxathiazoles and 1,2,3-dithiazoles has been explained by ring rearrangements <1996CHEC-II(4)409>. 

Other polynitrogen compounds containing the pentazole ring system 743... 

The availability of ever faster computers is responsible for the continuously improving quality in the calculations of the stability and the properties of pentazole compounds. Azidopentazole has been identified as the most stable of the known Ns polynitrogen compounds and considerable work has gone into the question whether a pentazole salt of the Ns+ ion would be stable. 

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