Reverting the effect of magnetic couplers in bridged di- and polyradicals

Baumgarten, Martin; Karabunarliev, Stoyan

doi:10.1016/s0301-0104(99)00090-7

Cited by 21 publications

(7 citation statements)

References 35 publications

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“…The spin density at the central C 9b and C 9b‘ atoms are low for all the species. These results are consistent with the literature spin density distribution for 7a and 12 . The absolute values of spin density in singlet E- 3 (ω = 44.8°) at the peri positions are considerably lower than the respective values in radical 7a (0.226−0.201 vs 0.309), except for the bridgehead C 1 and C 1‘ atoms (0.284 vs 0.309).…”

Section: Resultssupporting

confidence: 92%

“…These results are consistent with the literature spin density distribution for 7a and 12. 58 The absolute values of spin density in singlet E-3 (ω ) 44.8°) at the peri positions are considerably lower than the respective values in radical 7a (0.226-0.201 vs 0.309), except for the bridgehead C 1 and C 1′ atoms (0.284 vs 0.309). Increasing the pure twist in singlets Z-3 (57.8°) and TS-3 (87.5°) and in triplet Z-3 (77.0°) breaks the π-conjugation along the C 1 -C 1′ bond, thus eliminating the spin exchange between two halves of the molecules.…”

Section: Synthesis Of Peropyrene (5) By Reductive Coupling Of Phenale...mentioning

confidence: 84%

“…54,55 In contrast to 3, its constitutional isomers 2,2′-biphenalenylidene (12) and 1,2′-biphenalenylidene (13) diradicals are concealed and nonconcealed non-Kekule ´hydrocarbons, respectively. 57 The AM1-ROHF CI calculations of diradicals 12 and 13 (Chart 3) have been reported: 58 the triplet of nonconcealed 13(ω ) 50°) was more stable than the singlet (ω ) 80°) by 10.4 kJ/mol, whereas the singlet of concealed 12 (ω ) 44°) was more stable than the triplet (ω ) 44°) by 7.2 kJ/mol. 58 Figure 3 shows the relative energies of the optimized conforma- tions of 12.…”

Section: Synthesis Of Peropyrene (5) By Reductive Coupling Of Phenale...mentioning

confidence: 99%

“…57 The AM1-ROHF CI calculations of diradicals 12 and 13 (Chart 3) have been reported: 58 the triplet of nonconcealed 13(ω ) 50°) was more stable than the singlet (ω ) 80°) by 10.4 kJ/mol, whereas the singlet of concealed 12 (ω ) 44°) was more stable than the triplet (ω ) 44°) by 7.2 kJ/mol. 58 Figure 3 shows the relative energies of the optimized conforma- tions of 12. The DFT relative and total energies of 12 are given in Table S1 and Table S2 (see the Supporting Information).…”

Section: Synthesis Of Peropyrene (5) By Reductive Coupling Of Phenale...mentioning

confidence: 99%

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Biphenalenylidene: The Forgotten Bistricyclic Aromatic Ene. A Theoretical Study

Pogodin

Agranat

2003

J. Am. Chem. Soc.

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The Lawesson reagent and P(2)S(5) mediated reductive coupling of phenalenone (6) gives LPAH peropyrene (5) in 47% and 54% yields. The mechanism of the reaction involves the formation of phenalenethione (10), Z- and E-1,1'-biphenalenylidene (3), and 9 as intermediates. The electrocyclization reaction of Z-3 to 9, followed by aromatization, gives 5. The results of an ab initio and DFT study of 3 and 2,2'-biphenalenylidene (12) are reported. E-3 and Z-3 have a diradical character with twist angles of 44.8 degrees and 57.8 degrees (at UB3LYP/6-311G**). Delta E(++)(Tot) = 10.2 kJ/mol and Delta G(++)(298) = 10.6 kJ/mol for E-3 <==> Z-3 diastereomerization. These unusually low energy barriers are due to the ground-state diradical destabilization and the aromatic stabilization of the transition state TS-3. Triplet Z-3 is higher in energy than singlets E-3 and Z-3 by 10.4 and 3.1 kJ/mol. In the concealed non-Kekulé 12, singlet 12 is more stable than the triplet by 1.3 kJ/mol. Singlet 12 is more stable than singlet E-3 by 2.0 kJ/mol, and orthogonal singlet TS-12 is lower in energy than singlet TS-3 by 6.0 kJ/mol. The energy barriers for the hexatriene-cyclohexadiene electrocyclization Z-3 --> 9 are Delta E(++)(Tot) = 94.8 and Delta G(++)(298) = 98.3 kJ/mol (at (U)B3LYP/6-31G). The reaction occurs thermally in a conrotatory mode.

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Section: Resultssupporting

confidence: 92%

Section: Synthesis Of Peropyrene (5) By Reductive Coupling Of Phenale...mentioning

confidence: 84%

Section: Synthesis Of Peropyrene (5) By Reductive Coupling Of Phenale...mentioning

confidence: 99%

Section: Synthesis Of Peropyrene (5) By Reductive Coupling Of Phenale...mentioning

confidence: 99%

See 2 more Smart Citations

Biphenalenylidene: The Forgotten Bistricyclic Aromatic Ene. A Theoretical Study

Pogodin

Agranat

2003

J. Am. Chem. Soc.

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“…The mode of coupling of two phenalenyl units, however, has a significant impact on the relative stabilities of the resulting diions. Joining two phenalenyl radicals at the 2,2‘ positions yields the non-Kekulé hydrocarbon 2,2‘-biphenalenylidene ( 20 ), a constitutional isomer of BAEs 1 and 2 . In spite of its diradical character, it is more stable than 1 by 21.1 kJ/mol (Table ).…”

Section: Resultsmentioning

confidence: 99%

Theoretical Notions of Aromaticity and Antiaromaticity: Phenalenyl Ions versus Fluorenyl Ions

Pogodin

Agranat

2007

J. Org. Chem.

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The dications 6, 7, and 8 and dianions 9, 10, and 11 of the bistricyclic aromatic enes bifluorenylidene (1), 1,1'-biphenalenylidene (2), and 9-(9H-fluoren-9-ylidene)-1H-phenalene (4), as well as monocations 12a and 13a and monoanions 14a and 15a of phenalene (3) and fluorene (5), were subjected to a systematic DFT and ab initio study. B3LYP and MP2 methods were employed to estimate the relative aromaticity/antiaromaticity of these ions, using energetic, magnetic, and structural criteria. The couplings of monoions 12a-15a to give the respective diions 6-11 result in a similar destabilization in both the fluorene and phenalene series. The interactions between the C13H8 units in diions 6-11 are weak and are not expected to result in a significant loss of aromaticity/gain of antiaromaticity, as compared with the respective monoions. The antiaromaticity of bifluorenylidene dication (6), relative to that of two fluorenyl cations (12a), is only slightly enhanced as compared with the aromaticity of biphenalenylidene dication ((E)-7)) relative to that of two phenalenyl cations (13a). In particular, the homodesmotic reaction 6 + 2.13a = (E)-7 + 2.12a is only slightly exothermic, DeltaE(Tot) = -6.0 kJ/mol. The energetic effect of the analogous reaction involving anions 9 + 2.15a = (E)-10 + 2.14a is even smaller, DeltaE(Tot) = -3.4 kJ/mol. Bifluorenylidene dianion (9) and 1,1'-biphenalenylidene dianion ((E)-10) are aromatic, but the employed criteria disagree about their relative aromaticity. The electronic and structural properties of heteromerous dication 8 and dianion 11 lie between those of the homomerous diions. Thus, dications 6-8 and dianions 9-11 form a continuum of aromaticity/antiaromaticity.

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Intramolecular Magnetic Interaction of Spin‐Delocalized Neutral Radicals through m‐Phenylene Spacers

et al. 2019

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A new diradical having two 4,8,10‐trioxotriangulene (TOT) neutral radical units linked through an m‐phenylene moiety was synthesized and characterized by ESR measurements. An electrochemical study showed that the diradical undergoes two one‐electron reductions to generate corresponding dianion species, suggesting the electronic interaction between two TOT units through the π‐conjugated spacer. A strong intramolecular interaction between the two TOT units gives rise to the spin‐projected small hyperfine couplings in comparison with those of the monomer. Furthermore, the temperature dependent ESR measurement revealed that the dimer behaves as an S=1 species in the ground state with a ferromagnetic interaction of 2 J/kB=+7±3 K.

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Reverting the effect of magnetic couplers in bridged di- and polyradicals

Cited by 21 publications

References 35 publications

Biphenalenylidene: The Forgotten Bistricyclic Aromatic Ene. A Theoretical Study

Biphenalenylidene: The Forgotten Bistricyclic Aromatic Ene. A Theoretical Study

Theoretical Notions of Aromaticity and Antiaromaticity: Phenalenyl Ions versus Fluorenyl Ions

Intramolecular Magnetic Interaction of Spin‐Delocalized Neutral Radicals through m‐Phenylene Spacers

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