Advances in the Chemistry of Stable Hydrocarbon Radicals

Sholle, V. D.; Rozantsev, É. G.

doi:10.1070/rc1973v042n12abeh002781

Cited by 30 publications

(10 citation statements)

References 45 publications

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“…A dissociation enthalpy of Δ H diss = 11 kcal/mol for 5b to give 3l was obtained from the van't Hoff equation. This Δ H diss value is much smaller than that reported for the silicon benzopinacolate (Me 3 SiOC(Ph) 2 C(Ph) 2 OSiMe 3 (31 kcal/mol), but comparable with that reported for the C α −C para bonds in the trityl dimer [Ph 3 C] 2 (11−12 kcal/mol) (Scheme ) and that for the dimeric titanium(IV) alkoxide/enolate complex [( t Bu 3 SiO) 3 TiOCPh 2 )] 2 (18 kcal/mol) 4a).…”

Section: Resultssupporting

confidence: 71%

One-Electron Reduction of Aromatic Ketones by Low-Valent Lanthanides. Isolation, Structural Characterization, and Reactivity of Lanthanide Ketyl Complexes

et al. 1998

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In this paper we report on the isolation, structural characterization, and reactivity of a series of lanthanide ketyl complexes, which are generated by reactions of benzophenone and fluorenone with several different types of lanthanide reducing agents including Ln(OAr) 2 (L) x (Ar ) C 6 H 2 -t Bu 2 -2,6-Me-4; 1a: Ln ) Sm, L ) THF, x ) 3; 1b: Ln ) Yb, L ) THF, x ) 3; 1c: Ln ) Sm, L ) HMPA, x ) 2; 1d: Ln ) Yb, L ) HMPA, x ) 2), (C 5 Me 5 ) 2 Ln(THF) 2 (Ln ) Sm, Yb), (C 5 Me 5 )Sm(OAr)(HMPA) 2 , Sm(N(SiMe 3 ) 2 ) 2 (THF) 2 , and Ln/HMPA (Ln ) Sm, Yb) (HMPA ) hexamethylphosphoric triamide). Reactions of 1a-d with 1 equiv of fluorenone in THF afforded the corresponding ketyl complexes Ln(OAr) 2 (ketyl)(L) 2 (3a-d) in 85-90% isolated yields. Hydrolysis of 3a (Ln ) Sm, L ) THF) gave the corresponding pinacol-coupling product, 1,2-bis(biphenyl-2,2′-diyl)ethane-1,2-diol (4), while air oxidation of 3a yielded fluorenone almost quantitatively. Reaction of 3a with 1 equiv of 1a followed by hydrolysis afforded fluorenol quantitatively. When 3a was dissolved in hexane/ether, pinacol-coupling of the ketyl unit occurred to give the OEt 2 -coordinated pinacolate complex [Sm(OAr) 2 (OEt 2 )] 2 [µ-pinacolate] (5a, pinacolate ) 1,2-bis(biphenyl-2,2′-diyl)ethane-1,2-diolate). Dissolving 5a in THF regenerated 3a via C-C bond cleavage of the pinacolate unit, showing that the pinacolcoupling process was reversible. Addition of 2 equiv of HMPA (per Sm) to a THF solution of 3a or 5a gave the corresponding HMPA-coordinated ketyl complex 3c. Complex 3c was more stable than 3a, and no reaction was observed when 3c was treated similarly with hexane/ether. Reactions of fluorenone with (C 5 Me 5 ) 2 Ln-(THF) 2 (Ln ) Sm, Yb) and (C 5 Me 5 )Sm(OAr)(HMPA) 2 gave the corresponding ketyl complexes (C 5 Me 5 ) 2 -Ln(ketyl)(THF) (3e: Ln ) Sm, 3f: Ln ) Yb) and (C 5 Me 5 )Sm(OAr)(ketyl)(HMPA) (3i), respectively. In contrast, the similar reaction of Sm(N(SiMe 3 ) 2 ) 2 (THF) 2 with fluorenone in THF yielded the pinacolate complex [Sm(N(SiMe 3 ) 2 ) 2 (THF)] 2 [µ-pinacolate] (5b) as the only isolable product, although the formation of a ketyl species was evident in THF solution. Reaction of 4 equiv of HMPA with 5b in THF gave a mixture of Sm(N(SiMe 3 ) 2 ) 2 (ketyl)(HMPA) 2 (3k) and [Sm(N(SiMe 3 ) 2 ) 2 (HMPA)] 2 [µ-pinacolate] (5c), while reactions of 5b with 4 equiv of ArOH (Ar ) C 6 H 2 -t Bu 2 -2,6-Me-4) in THF and THF/HMPA produced the corresponding ArO-ligated ketyl complexes 3a and 3c, respectively. A variable-temperature UV-vis spectroscopic study in toluene derived a dissociation enthalpy of 11 kcal/mol for 5b. Reactions of metallic Ln (Ln ) Sm, Yb) with 3 equiv of fluorenone and 3 equiv of HMPA in THF yielded the corresponding tris(ketyl)metal complexes Ln(ketyl) 3 (HMPA) 3 (7a: Ln ) Sm, 7b: Ln ) Yb). Hydrolysis of 7a,b afforded the pinacol 4, while reaction of 7a with 0.5 equiv of 4 or benzopinacol produced the fluorenoxide/pinacolate complex 6. Reaction of 4 with Sm(N(SiMe 3 ) 2 ) 3 in THF/HMPA also afforded 6. In contrast to the reactions of ...

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Section: Resultssupporting

confidence: 71%

One-Electron Reduction of Aromatic Ketones by Low-Valent Lanthanides. Isolation, Structural Characterization, and Reactivity of Lanthanide Ketyl Complexes

et al. 1998

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“…The loss in this absorbance at 425 nm under subsequent oxidation conditions suggests it is unlikely to be from a nitrophenyl species. On the other hand the trityl radical, Ph 3 C • , is known to be fairly stable and absorb at these wavelengths, but a mechanism for its formation has not been determined. The two observed products have a different behavior over time and appear to form separately, the absorbance at 320 nm decays first but does not increase the absorbance at 420 nm.…”

Section: Resultsmentioning

confidence: 99%

Interrelationships between Conformational Dynamics and the Redox Chemistry of S-Nitrosothiols

et al. 1999

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An increasing number of biological roles are ascribed to S-nitrosothiol compounds. Their inherent instability in multicomponent solutions is recognized as forming the basis for their physiological effects, such as the release of nitric oxide or the posttranslational modification of protein cysteine residues. This reactivity also contributes to the lack of fundamental physical and spectroscopic data that have been reported. We have addressed this issue through characterization of the physical and spectroscopic properties of a group of commonly used S-nitrosothiols. The S-nitrosothiol Ph3CSNO, which is readily prepared by the biphasic nitrosation of Ph3CSH, is characterized by X-ray diffraction, vibrational spectroscopy, electrochemistry, and spectroelectrochemistry. Its behavior is contrasted with that of known S-nitrosothiols derived from glutathione and N-acetyl-d,l-penicillamine, which also are demonstrated to undergo facile electrochemical and chemical denitrosylation. The structure and vibrational data are contrasted with ab initio results calculated with density functional theory, B3LYP/6-311+G*, which indicates that electron transfer populates an orbital that is strongly ON−SR antibonding in character. The bond lengths observed for Ph3CSNO (N−O 1.18 Å, S−N 1.79 Å) indicate a formal nitrogen-to-oxygen double bond and sulfur−oxygen single bond. However, theoretical calculations show a measure of delocalization over the −CSNO framework. This is supported by experimental results that show low ν(NO) vibrational frequencies (1470−1515 cm-1) and a large ΔG ⧧ (10.7 kcal/mol) for syn−anti interconversion determined by variable-temperature 15N NMR. Together these results demonstrate an important new reactivity pattern for this biologically critical class of compounds.

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“…As is well-known, the class of triarylmethyl radicals is stable because the unpaired electron can be delocalized onto the ortho and para positions of the phenyl rings. Dimerizations of these radicals take place at the para ring position due to steric hindrance at the ortho position.…”

Section: Introductionmentioning

confidence: 99%

Novel Heteroatom-Linked Analogues of Trityl Radicals: Diaryl(benzotriazol-1-yl)methyl Radical Dimers

1998

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The lithiation of diaryl(benzotriazol-1-yl)methanes followed by addition of iodine generates phenanthridines and dimers of hitherto unknown trityl analogues in which the radical center is directly attached to a heteroatom. These dimers differ from those of triarylmethyl radicals by not dissociating in solution, but variable temperature ESR measurements provided direct evidence for the formation of the corresponding diaryl(benzotriazol-1-yl)methyl radicals as intermediates in solution.

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Advances in the Chemistry of Stable Hydrocarbon Radicals

Cited by 30 publications

References 45 publications

One-Electron Reduction of Aromatic Ketones by Low-Valent Lanthanides. Isolation, Structural Characterization, and Reactivity of Lanthanide Ketyl Complexes

One-Electron Reduction of Aromatic Ketones by Low-Valent Lanthanides. Isolation, Structural Characterization, and Reactivity of Lanthanide Ketyl Complexes

Interrelationships between Conformational Dynamics and the Redox Chemistry of S-Nitrosothiols

Novel Heteroatom-Linked Analogues of Trityl Radicals: Diaryl(benzotriazol-1-yl)methyl Radical Dimers

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