Radical cations and anions of s-tetrazines: an electron spin resonance study

Fischer, Hans; Umminger, Irmgard; Neugebauer, Franz A.; Chandra, Harish; Symons, Martyn C. R.

doi:10.1039/c39860000837

Cited by 16 publications

(2 citation statements)

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“…As to the last step of their synthesis it was generally of advantage to cyclize the substituted 2,2'-dinitrodiphenyl compounds using the lithium aluminium hydride reduction method of Corbett and his co-workers; 2 2 an example is given below. (2) (5) (6).-To a stirred suspension of 5,5'-dimethoxy-2,2'-dinitrobiphenyl (3.04 g, 10 mmol) in diethyl ether (300 cm3) and benzene (300 cm3) lithium aluminium hydride (2.28 g, 60 mmol) was added. Then the mixture was stirred under reflux for 2 h. After cooling to room temperature the excess of hydride was decomposed with water (ca.…”

Section: Methodsmentioning

confidence: 99%

Radical cations and anions of benzo[c]cinnolines: an electron spin resonance study

Fischer¹,

Neugebauer²,

Chandra³

et al. 1989

J. Chem. Soc., Perkin Trans. 2

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The radical cations of benzo[c]cinnoline and its four symmetrical dimethyl derivatives have been prepared by exposure of the parent compounds as dilute solutions in CFCI, t o 6oCo y-rays at 77 K.The e s r . spectra were all characterised by large hyperfine coupling t o t w o equivalent nitrogen atoms. Analysis of the data gave ca. 9% 2s and 44% 2p character o n each nitrogen, thereby establishing a o-structure. Clear deviation from axial symmetry shows that the orbital axes are tilted w i t h respect t o each other, an estimate of the angle between the two principle directions being ca. 40". This accords reasonably well with that derived from the p : s ratio of 4.9. The estimated total spin-density on nitrogen is 1.06, showing that the SOMO is strongly localised. Similar treatment of the 2,9-and 3,8-dimethoxy derivatives gave a broad unresolved singlet. This establishes that the SOMO has switched from the o-(N)-orbital to a .n-orbital. Clearly this has very low spin-density o n the t w o nitrogen atoms. We were not able t o detect any of the radical cations in the liquid phase. Exposure of dilute solutions of all six compounds as dilute solutions in CD,OD gave parallel features characteristic of t w o equivalent I4N nuclei. The perpendicular splittings were close t o zero, thus confirming that the SOMO is n, the estimated spin-density on the t w o nitrogen atoms being ca. 34% each. These anions were also prepared in liquid dimethoxyethane and hexamethylphosphoric triamide, and their e.s.r. and ENDOR spectra were recorded. Relative signs of the 'H coupling constants were obtained using general triple resonance. This has led to full assignments in all cases. Our assignment for the anion of the parent compound differs from that previously proposed.

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Section: Methodsmentioning

confidence: 99%

Radical cations and anions of benzo[c]cinnolines: an electron spin resonance study

Fischer¹,

Neugebauer²,

Chandra³

et al. 1989

J. Chem. Soc., Perkin Trans. 2

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“…On the other hand, s -tetrazines represent a class of electron-deficient aza-aromatic heterocycles, most noted as the 4-π electron component in the IEDDA reaction with electron-rich dienophiles; however, electron-poor alkenes and CN heterodienophiles such as amidines, carbamates, and nitriles also react in particular cases. Simple s -tetrazines are deeply colored, weakly basic compounds that can behave as reversible oxidizers and readily accept electrons, forming stable anion radicals. Being highly electron-deficient, s -tetrazines are prone to nucleophilic attack at the carbon atom (with S, N, O nucleophiles) and more rarely at nitrogen (with active C-nucleophiles).…”

Section: Introductionmentioning

confidence: 99%

Three-Component Reaction of 3,3-Difluorocyclopropenes, s-Tetrazines, and (benzo) Pyridines

Nechaev¹,

Cherkaev

Boev³

et al. 2020

J. Org. Chem.

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A new three-component reaction leading to 1-α-(pyridyl-2-[1,2,4]triazolyl)-2-alkyl-ethanones has been discovered while studying the reactivity of monosubstituted 3,3-difluorocyclopropenes in an inverse electronic demand Diels−Alder (IEDDA) cycloaddition−cycloreversion sequence with s-tetrazines. The reaction involving the above-mentioned reactants and (benzo)pyridine as a third component results in a complex transformation proceeding in mild conditions in a stoichiometric ratio of reactants and has high functional group tolerance (phenols, amides, ethers, carboxylic acids, ketones, and acrylic esters). As a result, simple pyridines are selectively functionalized at the α-position in good isolated yields. The reaction mechanism includes a rare azaphilic [4 + 2]cycloaddition step between s-tetrazine and intermediate 1-hydroxyindolizine, suggested after byproduct identification and tracked with a deuterium label. To date, it is only the third known example of skewed azaphilic cycloaddition of tetrazine. The reaction is truly three-component and cannot be effectively performed stepwise.

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Enhancing Magnetic Communication between Metal Centres: The Role of s‐Tetrazine Based Radicals as Ligands

Mavragani

Kitos

Brusso

et al. 2021

Chemistry A European J

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Although 1,2,4,5‐tetrazines or s‐tetrazines have been known in the literature for more than a century, their coordination chemistry has become increasingly popular in recent years due to their unique redox activity, multiple binding sites and their various applications. The electron‐poor character of the ring and stabilization of the radical anion through all four nitrogen atoms in their metal complexes provide new aspects in molecular magnetism towards the synthesis of new high performing Single Molecule Magnets (SMMs). The scope of this review is to examine the role of s‐tetrazine radical ligands in transition metal and lanthanide based SMMs and provide a critical overview of the progress thus far in this field. As well, general synthetic routes and new insights for the preparation of s‐tetrazines are discussed, along with their redox activity and applications in various fields. Concluding remarks along with the limitations and perspectives of these ligands are discussed.

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Radical cations and anions of s-tetrazines: an electron spin resonance study

Cited by 16 publications

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Radical cations and anions of benzo[c]cinnolines: an electron spin resonance study

Radical cations and anions of benzo[c]cinnolines: an electron spin resonance study

Three-Component Reaction of 3,3-Difluorocyclopropenes, s-Tetrazines, and (benzo) Pyridines

Enhancing Magnetic Communication between Metal Centres: The Role of s‐Tetrazine Based Radicals as Ligands

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