Radical Ions in the Pentalene Series. Part III. Three Paramagnetic Redox Stages of a Dicyclopenta[a,e]pentalene

Five redox stages have been observed for the recently synthesized 1,3,5,7-tetra(tert-butyl) derivative 1 of the dicyclopenta[a,e]pentalene, a novel non-alternant hydrocarbon: the radical cation 1 , the neutral compound 1, the radical anion Is, the dianion 1²-, and the radical trianion 1³. Information about the electronic structure of the three paramagnetic stages, 1, 1⁻, and 1³⁻ is provided by the use of ESR, ENDOR, and TRIPLE resonance spectroscopy. The unpaired electron in the trianion resides mainly on the ‘inner’ butadiene-π-system, whereas in the cation and the anion, it is largely localized on the two ‘outer’ five-membered rings

Synthesis and Properties of the First [4.4]Ferrocenophane-1,3,15,17-tetrayne

Building butadiyne bridges: The kinetically stabilized 1,1′-diethynylferrocene, readily prepared from the pentafulvenoid allene 1, can be transformed into the [4.4]ferrocenophane 2 by oxidative coupling. This compound exhibits a remarkably symmetrical structure in which the electrons are delocalized through the butadiyne bridges; in the crystalline state 2 exists in a helical-chiral conformation

Synthese und Eigenschaften des ersten [4.4]Ferrocenophan-1,3,15,17-tetrains

Das aus dem pentafulvenoiden Allen 1 leicht zugängliche, kinetisch stabilisierte 1,1′-Diethinylferrocen lässt sich durch oxidative Kupplung in das [4.4]Ferrocenophan 2 überführen. Diese Verbindung hat eine bemerkenswert symmetrische Struktur, die Elektronen sind über die Butadiinbrücken hinweg delokalisiert, und im Kristall liegt 2 in einer helical-chiralen Konformation vor

Synthesis, Structure and Reactivity of Cyclopenta-annulated 1,2,3,4-Tetrazines

The 2-aryl-2H-cyclopenta[e]-1,2,3,4-tetrazines 3a-n are formed by coupling of the diazocyclopentadienes 1a and 1b with arenediazonium salts and subsequent reversible electrocyclization of the primary coupling products 2a-n. From the solutions of the equilibrium mixtures of 2a ⇌ 3a - 2n ⇌ 3n the tetrazines 3a-d, h-k and the arylazo-diazocyclopentadienes 2e-g and 21-n crystallize. The 2-methyl-2H-cyclopenta[e]-1,2,3,4-tetrazines 3o and 3p are obtained by addition of methyllithium to 1a and 1b followed by a diazo transfer reaction and cyclization. In solutions of 3o and 3p the ring-opened isomers 2o and 2p could not be detected. X-ray analyses of 3h and 3p prove their bicyclic planar geometry in the solid state. ¹⁵N-NMR and temperature-dependent ¹H-NMR spectroscopy have enabled a detailed study of the reversible ring closure reaction in the case of 2d ⇌ 3d. Reaction of 2-phenyl-2H-cyclopenta[e]-1,2,3,4-tetrazine (3b) with tetrafluoroboric acid results in the formation of the protonated monocyclic salt 4. Furthermore 3b undergoes electrophilic substitution reactions preferably at C-7, as demonstrated by bromination, formylation, and trifluoroacetylation. Photolysis of solutions of 2i/3i, 2k/3k, and 21/31 leads to the ketene imines 11a-c. The structure of 11c has been determined by X-ray crystallography

Synthesis, Structure and Reactivity of Cyclopenta-annulated 1,2,3,4-Tetrazines

The 2-aryl-2H-cyclopenta[e]-1,2,3,4-tetrazines 3a-n are formed by coupling of the diazocyclopentadienes 1a and 1b with arenediazonium salts and subsequent reversible electrocyclization of the primary coupling products 2a-n. From the solutions of the equilibrium mixtures of 2a ⇌ 3a - 2n ⇌ 3n the tetrazines 3a-d, h-k and the arylazo-diazocyclopentadienes 2e-g and 21-n crystallize. The 2-methyl-2H-cyclopenta[e]-1,2,3,4-tetrazines 3o and 3p are obtained by addition of methyllithium to 1a and 1b followed by a diazo transfer reaction and cyclization. In solutions of 3o and 3p the ring-opened isomers 2o and 2p could not be detected. X-ray analyses of 3h and 3p prove their bicyclic planar geometry in the solid state. ¹⁵N-NMR and temperature-dependent ¹H-NMR spectroscopy have enabled a detailed study of the reversible ring closure reaction in the case of 2d ⇌ 3d. Reaction of 2-phenyl-2H-cyclopenta[e]-1,2,3,4-tetrazine (3b) with tetrafluoroboric acid results in the formation of the protonated monocyclic salt 4. Furthermore 3b undergoes electrophilic substitution reactions preferably at C-7, as demonstrated by bromination, formylation, and trifluoroacetylation. Photolysis of solutions of 2i/3i, 2k/3k, and 21/31 leads to the ketene imines 11a-c. The structure of 11c has been determined by X-ray crystallography

Radical Ions in the Pentalene Series. Part III. Three Paramagnetic Redox Stages of a Dicyclopenta[a,e]pentalene

Five redox stages have been observed for the recently synthesized 1,3,5,7-tetra(tert-butyl) derivative 1 of the dicyclopenta[a,e]pentalene, a novel non-alternant hydrocarbon: the radical cation 1 , the neutral compound 1, the radical anion Is, the dianion 1²-, and the radical trianion 1³. Information about the electronic structure of the three paramagnetic stages, 1, 1⁻, and 1³⁻ is provided by the use of ESR, ENDOR, and TRIPLE resonance spectroscopy. The unpaired electron in the trianion resides mainly on the ‘inner’ butadiene-π-system, whereas in the cation and the anion, it is largely localized on the two ‘outer’ five-membered rings

Synthesis and Properties of the First [4.4]Ferrocenophane-1,3,15,17-tetrayne

Building butadiyne bridges: The kinetically stabilized 1,1′-diethynylferrocene, readily prepared from the pentafulvenoid allene 1, can be transformed into the [4.4]ferrocenophane 2 by oxidative coupling. This compound exhibits a remarkably symmetrical structure in which the electrons are delocalized through the butadiyne bridges; in the crystalline state 2 exists in a helical-chiral conformation

Synthese und Eigenschaften des ersten [4.4]Ferrocenophan-1,3,15,17-tetrains

Das aus dem pentafulvenoiden Allen 1 leicht zugängliche, kinetisch stabilisierte 1,1′-Diethinylferrocen lässt sich durch oxidative Kupplung in das [4.4]Ferrocenophan 2 überführen. Diese Verbindung hat eine bemerkenswert symmetrische Struktur, die Elektronen sind über die Butadiinbrücken hinweg delokalisiert, und im Kristall liegt 2 in einer helical-chiralen Konformation vor