4,5‐Bis(demethylamino)fluorene, a New “Proton Sponge”

Staab, Heinz A.; Saupe, Thomas; Krieger, Claus

doi:10.1002/anie.198307311

Cited by 52 publications

(20 citation statements)

References 5 publications

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“…The structural analysis showed a distortion of the naphthalene ring plane, pointing to a compromise between aromatic stabilization and conjugation with the amino group. 105 Later, compounds such as 4,5-bis(dialkylamino)-fluorene 106 (pK a = 12.8), and 4,5-bis(dialkylamino)-phenanthrene 107 (pK a = 11.5) were synthesized and also shown to be strong Brønsted bases and proton sponges. In these compounds, the orientation of the amino groups towards each other (Figure 8) increases the steric strain.…”

Section: Account Syn Lettmentioning

confidence: 99%

Guanidines as Reagents in Proton-Coupled Electron-Transfer Reactions and Redox Catalysts

Himmel

2018

Synlett

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Redox-active guanidines are ideal proton-coupled electron-transfer (PCET) reagents, since they combine a high Brønsted basicity with a low and tunable redox potential. In this article, the development of redox-active guanidines (especially guanidino-functionalized aromatics, GFAs) in the last ten years is summarized, and their properties compared to other organic Brønsted bases and organic electron donors. First, some applications in organic chemistry that purely use the redox activity (formation of organic donor–acceptor materials and photochemical reductive C–C coupling reactions) are presented. Then, reactions that involve both proton and electron transfer are reviewed. In stoichiometric reactions, redox-active guanidines are used for the dehydrogenative coupling of thiols and phosphanes. The first redox catalytic applications are discussed, using dioxygen as green oxidizing reagent.1 Introduction2 Redox-Active Amines and Guanidines3 Brønsted Basicity of Amines and Guanidines4 Variations of GFA Compounds5 GFA Compounds in Organic Donor–Acceptor Materials and as Reducing Reagents in Organic Synthesis6 Stoichiometric Dehydrogenative Coupling Reactions with Redox-Active Guanidines7 Guanidines as Redox Catalysts8 Conclusions and Outlook

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Section: Account Syn Lettmentioning

confidence: 99%

Guanidines as Reagents in Proton-Coupled Electron-Transfer Reactions and Redox Catalysts

Himmel

2018

Synlett

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“…Apart from varying the substituents of DMAN, several proton‐chelating compounds with backbones other than naphthalene have been synthesized. The interaction of two basicity centers has also been achieved by aromatic spacers such as fluorene,22 heterofluorene,23 phenantrene,24 biphenyl25 or helicene26 moieties. Potáček et al.…”

Section: Introductionmentioning

confidence: 99%

“… Alder’s proton sponge DMAN (a) [1] and aromatic sponges with quino[7,8‐ h ]quinoline (b),20 fluorene (c),22 phenantrene (d)24 and biphenyl (e)25 backbones as well as a proton sponge with a non‐aromatic skeleton 27…”

Section: Introductionmentioning

confidence: 99%

Superbasic Alkyl‐Substituted Bisphosphazene Proton Sponges: Synthesis, Structural Features, Thermodynamic and Kinetic Basicity, Nucleophilicity and Coordination Chemistry

Kögel

Xie

Baal

et al. 2014

Chemistry A European J

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Herein we describe an easily accessible class of superbasic proton sponges based on the 1,8-bisphosphazenylnaphthalene (PN) proton pincer motif and P-alkyl substituents ranging from methyl (TMPN) to n-butyl (TBPN), isopropyl (TiPrPN) and cyclopentyl (TcyPPN). These neutral bases with a pK(BH)(+) value (MeCN) of ~30 were accessible via a Kirsanov condensation using commercially available 1,8-diaminonaphthalene, and in case of TMPN and TBPN, simple one-pot procedures starting from trisalkylphosphanes can be performed. Furthermore, the known pyrrolidinyl-substituted superbase TPPN previously synthesized via a Staudinger reaction could also be prepared by the Kirsanov strategy allowing its preparation in a larger scale. The four alkyl-substituted proton sponges were structurally characterized in their protonated form; molecular XRD structures were also obtained for unprotonated TiPrPN and TcyPPN. Moreover, we present a detailed description of spectroscopic features of chelating bisphosphazenes including TPPN and its hyperbasic homologue P2-TPPN on which we reported recently. The four alkyl-substituted superbases were investigated with respect to their basic features by computational means and by NMR titration experiments revealing unexpectedly high experimental pK(BH)(+) values in acetonitrile between 29.3 for TMPN and 30.9 for TBPN. Besides their thermodynamic basicity, we exemplarily studied the kinetic basicity of TMPN and TPPN by means of NMR-spectroscopic methods. Furthermore, the competing nucleophilic versus basic properties were examined by reacting the proton sponges with ethyl iodide. Insight into the coordination chemistry of chelating superbases was provided by reacting TMPN with trimethylaluminum and trimethylgallium to give cationic complexes of Group XIII metal alkyls that were structurally characterized.

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“…Analogous but smaller effects are found in 4,5-dimethylamine fluorenium perchlorate (Staab, Saupe & Krieger, 1983;Staab & Saupe, 1988) which has twofold symmetry along the median molecular axis with the N atoms displaced above and below the mean molecular plane by 0.23 A.…”

Section: Perchlorofluorene-9-spirocyclohexa-2"5'-diene and Its Complmentioning

confidence: 73%

Crystal and molecular structures of overcrowded halogenated compounds. IX. Stereochemistry of molecules containing the perchlorofluorenyl and perchlorofluorenylidene moieties and of their hydrogen analogues

Herbstein¹

1991

Acta Crystallogr Sect B

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4,5‐Bis(demethylamino)fluorene, a New “Proton Sponge”

Cited by 52 publications

References 5 publications

Guanidines as Reagents in Proton-Coupled Electron-Transfer Reactions and Redox Catalysts

Guanidines as Reagents in Proton-Coupled Electron-Transfer Reactions and Redox Catalysts

Superbasic Alkyl‐Substituted Bisphosphazene Proton Sponges: Synthesis, Structural Features, Thermodynamic and Kinetic Basicity, Nucleophilicity and Coordination Chemistry

Crystal and molecular structures of overcrowded halogenated compounds. IX. Stereochemistry of molecules containing the perchlorofluorenyl and perchlorofluorenylidene moieties and of their hydrogen analogues

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