Electronic States of the Azoalkanes

Robin, M. B.; Hart, Robert R.; Kuebler, N. A.

doi:10.1021/ja00983a005

Cited by 88 publications

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“…Ammonia may also be prosome 2.8 eV higher (12). It also suggests that the duced (see below) but we have no positive evifirst excited singlet, also an n+ -t n* state, is dence for its formation.…”

Section: Magnetic Properties Of Di-inzidementioning

confidence: 64%

Di-imide: Some Physical and Chemical Properties, and the Kinetics and Stoichiometry of the Gas-phase Decomposition

Willis¹,

Back²

1973

Can. J. Chem.

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Preparation of di-imide by passing hydrazine vapor through a microwave discharge yields mixtures with NH, containing typically about 15% N2H2, estimated from the gases evolved on decomposition. The behavlor of the mixture (which melts at -65 "C) on warming from -196 to -30 "C suggests a strong interaction between the components. Measurements of magnetic susceptibility and e.p.r. experiments showed that N2H2 is not strongly paramagnetic, which with other observations points to a singlet rather than a triplet ground-state.Di-imide can be vaporized efficiently, together with NH,, by rapid warming, and the vapor is surprisingly long-lived, with a typical half-life of several minutes at room temperature. The near-U.V. (3200-4400 A) absorption spectrum of the vapor was photographed; it shows well-defined but diffuse bands, with E,,, = 6(f 3) at 3450 A.Di-imide decomposes at room temperature in two ways:Formation of NH, was not observed but cannot be ruled out. The decomposition of the vapor is complicated by a sizeable and variable decomposition that occurs rapidly during the vaporization. The stoichiometry of this and the vapor-phase decomposition depends on total pressure and di-imide con-I centration. The kinetics of the decomposition of the vapor were studied from 22 t o 200°C by following the disappearance of N2H2 by absorption of light at 3450 A, o r the formation of N2H4 by absorption at 2400 A, and by mass spectrometry. The kinetics are complex and can be either first-or second-order, 1 or mixed, depending on surface conditions. The effect of olefin additives on the decomposition was I studied, and is also complex. !Mechanisms for the decomposition are discussed, including the possible role of trons-cir isomerization. The relatively long lifetime found for di-imide in the gas phase suggests that it may be an important intermediate in many reactions of hydronitrogen systems. La di-imide se decompose a la temperature ambiante de deux faqonsLa formation de NH, n'a pas Cte observee mais n'a pas pu ttre Ccartee. La decomposition de la vapeur a Cte compliquCe par une autre, notable et variable, qui se produit rapidement lors de la vaporisation. La stoechiometrie de cette derniere et la decomposition en phase vapeur dependent de la pression totale et de la concentration en di-imide. Les cinetiques de dCcomposition de la vapeur ont Cte etudiees d e 22 a 200 "C en suivant la disparition de N2H2 par absorption de la lumiere a 3450 A et par spectromttrie Ide masse. Les cinetiques sont complexes et peuvent ttre soit d u premier ou du second ordre, o u un melange dzs deux dependant des conditions de la surface. L'effet de I'addition d'oltfines sur la decomposition a ete etudit et est Bgalement complexe bien qu'une legere reduction ait CtC observee. Les mecanismes de la decomposition ont kt6 discutis incluant le r81e possible d'une isomeration cis-trans. La durke de vie relativement longue trouvee pour la di-imide en phase gazeuse laisse penser a son importance en tant qu'intermediaire dans les nombreuses reactions de syste...

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Section: Magnetic Properties Of Di-inzidementioning

confidence: 64%

Di-imide: Some Physical and Chemical Properties, and the Kinetics and Stoichiometry of the Gas-phase Decomposition

Willis¹,

Back²

1973

Can. J. Chem.

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“…Walsh's prediction of the relative energies of the three highest orbitals for the observed H-N=N angle of 107" is not clear, but more recent calculations (8)(9)(10) show that the n+ orbital is undoubtedly the highest, with the n-orbital probably lying a t a lower energy than the K orbital. The lowest excited singlet state should then be ... n-(36,)'.…”

Section: Nature Of the Electronic Transitionmentioning

confidence: 95%

“…For N,H, and N,D, the N=N stretching frequencies in the excited state are 1550 and 1440 cm-' respectively; the isotope shift is similar to that for the C=C stretching frequencies of C,H, and C2D2 in the trans bent excited state, 1385 and 1299 cm-' respectively (14). Comparison with the ground-state N=N stretching frequencies (5) for N2H2 (1529 cm-') and N,D, (1539 cm-') is complicated by an 41t should be noted that the corresponding transition in cis diimide (point group C,,) is ' B , e ' A , , and is allowed by the electronic selection rules (8). The trans isomer is known to be the predominant form of diimide as prepared in the present experiments and there is no evidence for the presence of even low concentrations of the cis isomer in the gas phase.…”

Section: Geometry Of the Excited Statementioning

confidence: 99%

The Near-ultraviolet Absorption Spectrum of Diimide Vapor

Back¹,

Willis²,

Ramsay³

1974

Can. J. Chem.

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Absorption spectra of N2H2 and N2D2 in the gas phase have been obtained in the region 3000–4300 Å, consisting of about 30 diffuse bands for each compound. Long progressions in the spectra are attributed to excitation of the H—N=N bending mode, v2′, in the upper state, with much shorter progressions arising from the N=N stretching mode, v3′; values of v2′ = 1215 and 910 cm−1 and v3′ = 1550 and 1440 cm−1 were estimated for N2H2 and N2D2 respectively.The spectra are attributed to the 1Bg ← 1Ag(π* ← n+) transition of trans diimide, probably made allowed by vibronic interaction. From Franck–Condon calculations the H—N=N angle in the upper state was estimated to be 132 ± 2°, an increase of 25° from the ground-state value; the increase in the N=N bond length was estimated to be about 0.05 Å.

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“…Section 4.4). Such reactions thus correspond to transfer of the azo group to S; BSD thus acts as an "azo-ation agent" for S, and could therefore be used for the preparation of inorganic azo compounds (25) and (26). However, the substituted diimines expected according to equations (47) and (48) Thus the protolysis of BSD (S-B in Scheme 2 = H -X ; X=e.g.…”

Section: B S D + 4 S 0 + N 2 + S + (21)mentioning

confidence: 99%

Bis(trimethylsilyl)diimine: Preparation, Structure, and Reactivity

Wibeŕg¹

1971

Angew. Chem. Int. Ed. Engl.

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Dedicated to my father, Professor Egon Wiberg, on the occasion of his 70th birthdayThe highly reactive compound bis(trimethylsily1)diimine (BSD), which was first prepared by oxidation of lithium tris(trimethylsilyl)hydrazide, is light blue, sensitive to thermolysis and hydrolysis, and ignites spontaneously in air. On the basis of electron transfer, acid-base, or freeradical reactions, it acts in particular as a (preparatively useful) redox system and as an agent for the introduction of azo groups. Redox reactions lead by oxidation or reduction of the other reactant through two oxidation stages to hydrazine derivatives or molecular nitrogen, and in the case of electrochemical reduction, to BSD radical-anions. Azo-group transfers, on the other hand, yield new inorganic azo compounds with no change in the oxidation state of the diimine group. Introductionas the fist diimine completely substituted with silyl groups131, the unexpectedly long-wave light absorption and the resulting radiant blue color of the compound immediately aroused our particular interest. The investigation of this substance, which has lost none of its orig- inal fascination, has proved worth while ; it has revealed a varied, unusual, and interesting chemistry.Various investigators had attempted to prepare a bis-(sily1)diimine. The ability of carbon to fonn azo compounds (Z), which are often surprisingly stable (for example, azobenzene is stable up to 600°C[41), makes the synthesis of "azosilanes" (2) a challenge in view ofthe group relationship between carbon and silicon. A possible preparation method was seen in the oxidation of 1,2-bis(silyl)hydrazines (3).However, several attempts to verify this reactionc5-' I were initially unsuccessful because of failure to find an oxidizing agent that could oxidize bis(sily1)hydrazines (3) only to the stage of the readily oxidizable bis(sily1)-diimines ( 4 ) without oxidizing these further to nitrogen '']. By the action of p-toluenesulfonyl azide on lithium tris-(trimethylsily1)hydrazide (X = Li, Y = SiR, in (3)), we were able to obtain BSD as a readily sublimable product that crystallizes in .the form of needles and melts at -3 OC131. Including BSD and a bis(bory1)diimine that is obtainable from it["], there are now ten classes of isolable diimine derivatives X-N=N-X(counting diimine itself) in which ligands X are linked to the azo group via maingroup elements having various atomic numbers:The arenesulfonyl azide, as in its reactions with CH-acidic methylene derivatives"'], evidently adds first to the silylhydrazide to form a nitrogen chain compound R' SO,-N=N-N-N(SiR,)-N(SiR,),,which can decompose after migration of silyl groups to give the final reaction products.Instead of arenesulfonyl azides, arenesulfonyl chlorides may be used as the oxidizing agents[1g! In this case, however, the reaction no longer follows a single course:R'S0,Li + R,SiClSince BSD is also difficult to separate from trirnethylchlorosilane, the process is less suitable for the preparation of this diimine. However, it may offer advantag...

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Electronic States of the Azoalkanes

Cited by 88 publications

References 0 publications

Di-imide: Some Physical and Chemical Properties, and the Kinetics and Stoichiometry of the Gas-phase Decomposition

Di-imide: Some Physical and Chemical Properties, and the Kinetics and Stoichiometry of the Gas-phase Decomposition

The Near-ultraviolet Absorption Spectrum of Diimide Vapor

Bis(trimethylsilyl)diimine: Preparation, Structure, and Reactivity

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