Zur Existenz nichtklassischer, cyclisch delokalisierter 4N/5e-Radikalanionen und 4N/6e-Dianionen – Ein- und Zweielektronen-Reduktion nahgeordneter, synperiplanarer Bisdiazene

Exner, Kai S.; Hunkler, Dieter; Gescheidt, Georg; Prinzbach, Horst

doi:10.1002/(sici)1521-3757(19980703)110:13/14<2013::aid-ange2013>3.0.co;2-m

Angewandte Chemie

1998

DOI: 10.1002/(sici)1521-3757(19980703)110:13/14<2013::aid-ange2013>3.0.co;2-m

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Zur Existenz nichtklassischer, cyclisch delokalisierter 4N/5e-Radikalanionen und 4N/6e-Dianionen – Ein- und Zweielektronen-Reduktion nahgeordneter, synperiplanarer Bisdiazene

Kai S. Exner

Dieter Hunkler

Georg Gescheidt

et al.

Abstract: Delokalisiert in der N,N,N,N‐Ebene sind die fünf bzw. sechs Elektronen der aus rigiden, nahgeordneten Bisdiazenen durch Ein‐ bzw. Zweielektronen‐Reduktion erhaltenen, äußerst beständigen 4N/5e‐Radikalanionen (tiefgrün) und σ‐bishomoaromatischen 4N/6e‐Dianionen (rot) (siehe unten). Deren längstwellige Absorption hängt stark vom Gegenion ab.

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Cited by 9 publications

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References 21 publications

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“…[1] In order to assess the geometrical prerequisites of these novel bonding motifs, [2] modification of the cage structures has been pursued in three directions: a) by formal rotation of a molecular ªhalfº (3ªisopagodanesº), [3] b) by homologation at the X-and/or Y-positions (3[2.2.1.1]/[2.2.2.2](iso)pagodanes), [3] and c) by bridging the X,Y positions (3(homo)dodecahedradienes). [4] A particularly attractive triad of this latter series consists of the parent bisseco-(1), seco-(2), and 1,16-dodecahedradienes (3) (Scheme 1).…”

mentioning

confidence: 99%

σ-Bishomoconjugation (σ-Bishomoaromaticity) in 4C/3(2)e Cations—Scope and Limitations

Prinzbach

Reinbold

Bertau

et al. 2001

Angew. Chem. Int. Ed.

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For the seco‐dodecahedradiene 1, in which the distance dππ between the carbon atoms of the two double bonds ranges from 2.90 to 3.20 Å and pyramidalization angles Φ range from 14.9 to 35.5°, the geometrical prerequisites for in‐plane (σ)‐homoconjugative (σ‐bishomoaromatic) electron delocalization in 4C/3(2)e cations could be better defined. Whilst the 4C/3e radical cation is persistent in a matrix, the 4C/2e dication in superacid medium is, at best, an intermediate en route to the stable bisallylic dication.

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mentioning

confidence: 99%

σ-Bishomoconjugation (σ-Bishomoaromaticity) in 4C/3(2)e Cations—Scope and Limitations

Prinzbach

Reinbold

Bertau

et al. 2001

Angew. Chem. Int. Ed.

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Proximate,syn-Periplanar Bisdiazene Skeletons: Syntheses, Structures, Homoconjugate Reactivity and Photochemistry

Exner¹,

Fischer

Bahr

et al. 2000

Eur. J. Org. Chem.

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Rigid NN/NN (diazene/diazene) systems (F) consisting of more or less alkylated DBH and DBO chromophoric units (1, 2, X‐ray structures), with very short π,π distances [d = 2.849 (1a, av.), 2.822 Å (2)] and almost perfect syn‐periplanar π,π alignments [ω = 168.6 (1a), 174.2° (2)] as well as the more flexible, less “proximate” metathesis isomers (3a,c, 27a,c, d >4.6 Å, ω = 90‐100°) have been synthesized. Homoconjugate π,π interaction (in 1, 2, not in 3, 27) is deduced from UV spectroscopic measurements [π → π* maxima at 239 (234) nm (sh, 260)], while PE analyses furnished only small interaction parameters (1a: <0.3 eV). The potential of the novel syn‐periplanar NN/NN motif in 1 and 2 for the synthesis of somewhat exotic polyheterocycles has been explored by calculation (B3LYP) as well as experimentally: i.a. kinetically stabilized, all‐cis‐peralkylated tetrazolidines (38, 44) and perhydro‐1,2,4,5‐tetrazines (41, 47) have become accessible (i.a. via novel azomethine/diazene and azomethine/azomethine cycloadditions). In 1a with its unreactive DBO chromophoric subunits, in the “buttressed” derivatives 1b‐d, as well as in the DBH/DBO combination 2, and likewise in more ‘distant’ 27 (differently from the analogous CC/CC and NN/CC systems), irrespective of the excitation conditions employed (light of λ ≥≥ 280, 254 nm, low temperature matrix irradiation, acetone sensitization) no [2+2]photocycloaddition was observed. Instead exclusively N2‐elimination took place. It is argued that unproductive NN/NN photocycloaddition would have become observable through metathesis isomerization of the respective tetrazetidines.

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Proximate,syn-Periplanar Diazene/Diazene(di)oxy, Diazeneoxy/Diazene(di)oxy, and Diazenedioxy/Diazenedioxy Skeletons: Syntheses, [2+2]Photocycloadditions, Metathesis

et al. 2000

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Of two very proximate syn‐periplanar bisdiazenes (1,2) mono‐, di‐, tri‐ and tetra‐N‐oxides were prepared, representing six combinations of the individual NN/NNO/ONNO chromophores. According to DFT calculations (B3LYP/6‐31G*), [2+2]photocycloaddition to the respective oxidized tetrazetidines is significantly to moderately endothermic. The metathesis isomerization of the oxidized tetrazetidines is generally highly exothermic and kinetically increasingly favorable with increasing oxidation state. In practice, four out of the six bichromophoric combinations undergo selectively, in competition with N2 elimination from a DBH unit (13) still partially, metathesis isomerization upon π → π* excitation (monochromatic 254 nm light). In the case of the syn‐NNO/NNO combinations (5/6, 14), the photoaddition is thermally reversed. For a ONNO/NN combination (30), internal electron transfer is responsible for a complex reaction pattern. The preparative value of the metathesis reactions, though, is limited: The metathesis‐derived bis[diazene mono(di)oxides] undergo relatively fast secondary photoreactions, while the tri(tetra)oxides undergo rapid thermal transformations. For the NN/NNO systems (12), of three potential pathways for its metathesis isomerization, the one that takes place via σ‐symmetric intermediates (63, 64) is excluded by virtue of the retention of optical purity in the photometathesis of a highly enriched enantiomer [(−)‐12]. Matrix irradiation experiments (12 K, IR control) with 12 result in the appearance of a kinetically highly labile transient. Supported by DFT calculations it is concluded that in the metathesis reactions, the respective tetrazetidine oxides (increasingly destabilized by interactions between oxygen lone pairs and NNσ* orbitals) function as vibrationally excited transients. That thermal reversion of these transients might be a general, nonproductive competition, is suggested by the experimental verification of a “reversed photometathesis” (51 → 15) and by the generally low rates in product formation upon irradiation. The question remains to be answered why in structurally analogous molecular skeletons, [2+2]photocycloaddition occurs in the CC/NN and variously oxidized NN/NN, and not, however, in the parent NN/NN combinations.

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Zur Existenz nichtklassischer, cyclisch delokalisierter 4N/5e-Radikalanionen und 4N/6e-Dianionen – Ein- und Zweielektronen-Reduktion nahgeordneter, synperiplanarer Bisdiazene

Cited by 9 publications

References 21 publications

σ-Bishomoconjugation (σ-Bishomoaromaticity) in 4C/3(2)e Cations—Scope and Limitations

σ-Bishomoconjugation (σ-Bishomoaromaticity) in 4C/3(2)e Cations—Scope and Limitations

Proximate,syn-Periplanar Bisdiazene Skeletons: Syntheses, Structures, Homoconjugate Reactivity and Photochemistry

Proximate,syn-Periplanar Diazene/Diazene(di)oxy, Diazeneoxy/Diazene(di)oxy, and Diazenedioxy/Diazenedioxy Skeletons: Syntheses, [2+2]Photocycloadditions, Metathesis

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