Aminyle, 6. tert.‐Butyl‐substituierte 9‐Carbazolyl‐Radikale, Carbazol‐Radikalkationen und Carbazol‐9‐oxyl‐Radikale

Abstract

Aminyle, 61)tert.-Butyl-substituierte 9-Carbazolyl-Radikale, Carbazol-Radikalkationen und Carbazol-9-oxyl-Radikale Die chemischen und spektroskopischen Eigenschaften der Titelverbindungen werden beschrieben. tert.-Butylgruppen erhohen die Stabilitat der 9-Carbazolyl-Radikale und der Carbazol-Radikalkationen: 1.3.6.8-Tetra-tert.-butyl-9-carbazolyl (10) ist eine stabile kristallisierte Substanz. GroBen und Vorzeichen der ESR-Kopplungskonstanten von 10 wurden aus den ESR-, IH-NMR-und ZH-NMR-Spektren erhalten. Verschiedene Radikal-Dimere wurden isoliert und identifiziert. Eines dieser Dimeren (13) besitzt eine Struktur, die der Konstitution des Triphenylmethyl-Dimeren sehr ahnlich ist. Aminyls, 6 l ) rerf-Butyl-Substituted 9-Carbazolyl Radicals, Carbazol Radical Cations and Carbazol-9-oxyl RadicalsChemical and spectroscopic data for the title compounds are reported. tert-Butyl groups increase the stability of 9-carbazolyl radicals and carbazol radical cations: 1.3.6.8-tetratert-butyl-9-carbazolyl (10) is a stable crystalline solid. The magnitudes and signs of the e.s.r. coupling constants in 10 were evaluated from the e.s.r., 1 H n.m.r. and 2H n.m.r. spectra. Various radical dimers were isolated and identified. One of these dimers (13) has a structure similiar to that of the triphenylmethyl dimer.Die direkte Verknupfung von zwei o-Positionen im Diphenylaminyl ergibt ein eingeebnetes Aminyl-System, das 9-Carbazolyl-Radikal. Das Auftreten dieses Radikals als kurzlebige Zwischenstufe wird fur eine Reihe von Reaktionen postuliert, z. B. fur die Pyrolyse des Bis-biphenylen-tetrazens 2). Die Lebensdauer von 9-Carbazolyl-Radikalen sollte sich erheblich verlangern lassen, wenn es gelingt, die reaktiven Positionen 1, 3, 6, 8 und 9 sterisch abzuschirmen. Wie das monomere, isolierbare 1) 5.

Isolation of the Triplet Ground State Aminyl Diradical

“…Nitrogen‐centered (aminyl) radicals are typically short‐lived, and have been detected as intermediates in a variety of chemical and biological processes 1. 2 To the best of our knowledge, only two known stable aminyl radicals have been reported (more than 30 years ago),3, 4 while a few others have recently been isolated as aminyl metal complexes and as heteroatom (e.g., O, S) stabilized aminyls 5–7…”

A Benzene‐1,3,5‐Triaminyl Radical Fused with ZnII‐Porphyrins: Remarkable Stability and a High‐Spin Quartet Ground State

“…[2] Along these lines,Rajca et al have developed meta-phenylene-bridged di-and tetra-aminyl radicals (1)(2)(3)(4) that display high-spin (triplet and quintet) ground states due to strong intramolecular ferromagnetic interactions and reasonable stability owing to designed steric protection. [4] Theradical-stabilizing abilities of porphyrins were recognized during the study of heme catabolism, in which meso-oxy heme acts as an important intermediate.I nr elation to this, aZ n II -octaethylporphyrin meso-oxy radical was reported to be stable when coordinated with pyridine. Actually,most of the stable aminyl radicals reported so far are stabilized by resonance stabilization of neighboring heteroatoms and there are only limited examples without such stabilization in the scientific literature.…”

“…[1] Among many candidates, meta-phenylene-bridged oligoradicals are promising candidates as high-spin species owing to their intrinsic large intramolecular ferromagnetic interactions. [2] Along these lines,Rajca et al have developed meta-phenylene-bridged di-and tetra-aminyl radicals (1)(2)(3)(4) that display high-spin (triplet and quintet) ground states due to strong intramolecular ferromagnetic interactions and reasonable stability owing to designed steric protection. [3] These radicals are persistent but short-lived even under strictly controlled inert conditions,a si ndicated in Figure 1.…”

“…Actually,most of the stable aminyl radicals reported so far are stabilized by resonance stabilization of neighboring heteroatoms and there are only limited examples without such stabilization in the scientific literature. [4] Theradical-stabilizing abilities of porphyrins were recognized during the study of heme catabolism, in which meso-oxy heme acts as an important intermediate.I nr elation to this, aZ n II -octaethylporphyrin meso-oxy radical was reported to be stable when coordinated with pyridine. [5] Recently,w e have explored stable porphyrinoid radicals such as meso-oxy radicals and diarylmethyl-fused porphyrins.…”

Stable Subporphyrin meso‐Aminyl Radicals without Resonance Stabilization by a Neighboring Heteroatom

“…Nitrogen-atom-centeredneutralradicals(aminylradicals) [1] play important roles in many synthetic [2] and biological [3] processes as reactive intermediates.E xtensive studies have been carried out on stable aminyl radicals, [4] such as hydrazinyl, [5] oxyaminyl, [6] and thioaminyl [7] radicals,w hich are stabilized by effective spin sharing between the nitrogen atom and the neighboring heteroatom (Scheme 1, top). In contrast, aminyl radicals without such stabilization are usually shortlived and reactive.T ot he best of our knowledge,alimited number of aminyl radicals have been isolated under rigorously controlled conditions by using ag love box, af ramesealed tube,aninert atmosphere,and/or distilled solvents, [8][9][10] and only two aminyl radicals,1 ,3,6,8-tetra-tert-butyl-9-carbazoyl (1) [11] and decachlorodiphenylaminyl (2; [12] Scheme 1) have been isolated under ambient conditions without such care.…”