Multistep π dimerization of tetrakis(n-decyl)heptathienoaceneradical cations: a combined experimental and theoretical study (original) (raw)
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We have investigated the impact of the functionalization and the chemical nature of counterions on the p-dimer dications formation in two end-capped heptathienoacenes. Radical cations of an a-substituted heptathienoacene with triisopropylsilyl groups do not p-dimerize, while those of an a,b-substituted heptathienoacene with four n-decyl side chains show a high propensity toward p-dimerization, increased by PF 6 À counterions. w In Memoriam of Prof. Dr Rafael Suau . z Electronic supplementary information (ESI) available: Additional experimental data (cyclic voltammograms), topologies of the frontiers MO's of D4T7 and TIPS-T7-TIPS and p-dimer dication of D4T7, side and top views of selected optimum structures of the p-dimer dication, calculated vertical one-electron excitations of D4T7 + and [D4T7 + ] 2 (CH 2 Cl 2 ) 8 and [D4T7 + ] 2 (PF 6 À ) 2 aggregates as well as experimental and computational details. See
We have investigated the impact of the functionalization and the chemical nature of counterions on the p-dimer dications formation in two end-capped heptathienoacenes. Radical cations of an a-substituted heptathienoacene with triisopropylsilyl groups do not p-dimerize, while those of an a,b-substituted heptathienoacene with four n-decyl side chains show a high propensity toward p-dimerization, increased by PF 6 À counterions. w In Memoriam of Prof. Dr Rafael Suau . z Electronic supplementary information (ESI) available: Additional experimental data (cyclic voltammograms), topologies of the frontiers MO's of D4T7 and TIPS-T7-TIPS and p-dimer dication of D4T7, side and top views of selected optimum structures of the p-dimer dication, calculated vertical one-electron excitations of D4T7 + and [D4T7 + ] 2 (CH 2 Cl 2 ) 8 and [D4T7 + ] 2 (PF 6 À ) 2 aggregates as well as experimental and computational details. See
2013
Radical cations of a soluble rigid tetrathienoacene are capable of forming stable p-dimer dications at ambient temperature when the short backbone becomes extended with conjugated thiophene-2-yl substituents in the a-positions. On the other hand, simple attachment of methyl groups on the a-carbon of the external thiophen-2-yl rings proved sufficient to inhibit the dimerization. Stable radical cations were also exclusively formed for tetrathienoacene derivatives end-capped with bulky TIPS and phenyl substituents. † Electronic supplementary information (ESI) available: Additional experimental data (the cyclic voltammogram of 4, UV-Vis spectra of 1-4, EPR spectra of 1_ + , 2_ + and 4_ + , UV-Vis spectroelectrochemistry of 3), calculated topologies of frontier MO's of 1-4, spin densities in 1_ + -4_ + , lateral and top views of the selected (3_ + ) 2 (CH 2 Cl 2 ) 4 and (3_ + ) 2 (PF 6 À ) 2 conformations with potential curve parameters, vertical excitations of 1-4, 1_ + -4_ + and d-d/d-d anti (3_ + ) 2 (CH 2 Cl 2 ) 4 and (3_ + ) 2 (PF 6 À ) 2 aggregates, as well as all experimental and computational details, including syntheses and characterisation of 2-4. See
Journal of the American Chemical Society, 1985
A curve-crossing diagram model is used to conceptualize the stability trends in delocalized clusters X,' ( n = 3, 4, 6; z = 0, -1; X = H, Li, Na, K, F, CI, Br, I). The size of the diagram's gap ( G ) appears to be the decisive stability factor. Large gaps result in unstable (distortive) clusters with a high percentage of bond stretching and large quantum mechanical resonance energies (QMRE), e.g., H6. Since G is related to the strength of the two-center X-X bond it follows that only atoms which form very weak bonds will generate stable delocalized clusters. Such clusters will possess slightly stretched bonds (on a percentage basis) and small Q M R E s (e.g., Li3,Li6). The strength of the a-bond between carbon atoms indicates that a-components, of conjugated a-u-systems, are distortive. This is confirmed by ab initio u-a energy partitions for benzene and allyl radical. The results show that the species involve distortive *-transition states which are forced to be delocalized by the a-frames. In accord with the general trend, the distortive a-components also possess large QMRE. It is shown that the Huckel 4n/(4n + 2) dichotomy is reflected in the corresponding QMRE values but not in the a-distortivity, and that the connection between "aromaticity-antiaromaticity" and geometry is not necessary. These conclusions carry over to other u-a-systems, X, (X = CH, SiH, N, P n = 4, 6 ) . The QMRE and the a-distortivities are two distinct molecular properties which must be probed by different experiments. Measurements of rotational barriers (in allyl) and thermochemical resonance energies are shown to be QMRE-related properties. Measurements of the a-distortivity are rare.
Journal of The American Chemical Society, 1976
. (3) Similar results have been obtained by anodic oxidation in acetonitrile containing fluoroboric acid as supporting electrolyte [E. Kotani, N. Takeuchi, and S. Tobinaga, J. Chem. Soc., Chem. Commun., 380 (1973)]. (41 M. A. Schwartz. E. F. Rose, and B. Vishnuvaiiala, J. Am. Chem. SOC., 95, 612 (1973). B 30. 89 11976) (5) 0. Hammerich, V. D. Parker, and A. Ronlan, Acta Chem. Scand., Ser. I -. -I -, _~. ~. (6) €,., (phenol ) ,> €,*Jphenol ether) for phenols with not more than one &alkyl substituent and €,.Jphenol) < E,.Jphenol ether) for 2,6dialkylphenols. (7) The diarylalkanes containing terf-butyl groups (6 and 8) looses one tertbutyl group in the presence of TFMS. Cyclic voltammograms run at various times alter the preparation of a 1 mM solution of 6 in CH2C12-TFMS (1 % ) at -50 OC showed that the rate constant for this dealkylation is about 4 X s-' under these conditions. In a preparative oxidation of 8 in CHpCIz-TFMS at -50 OC, compound 35 was obtained in 60 % yield with 100 % conversion (two stereoisomeric spirbdienones should be obtained from the diarylpropane with one tert-butyl group. However the same product (35) is formed by dienone-phenol rearrangement of these spirodienones). From this we conclude that 35 is formed by cyclization of the mono-terf-butyl compound. (8) U. Svanholm. A. Ronlan, and V. D. Parker, J. Am. Chem. SOC., 96, 5108 (1974). (9) A. Ronlan, 0. Hammerich, and V. D. Parker, J. Am. Chem. SOC., 95, 7132 (1973). (10) This appears a reasonable assumption since our measurements in CH2Cl2-FSO3H (ref 5) have shown that the oxidation potential for the oxidation of a cation radical of a phenol or a phenol ether is at least 300-400 mV more anodic than the oxidation potential for the oxidation of the phenol or phenol ether to the cation radical. Preparative experiments were carried out at the latter potential. (1 1) In our preliminary communication (ref 2) we argued on the basis of the difference in oxidation potential between a phenol and its methyl ether that the initial one-electron transfer from a phenol to an anode with for-mation of a cation radical is generally followed by rapid deprotonation to a phenoxy radical which can dimerize (path e in Scheme I), react as an electrophile (path d), or become further oxidized to a phenoxonium ion (path f). Our finding ref 5) that the reversible potential (in CHpClp-FS03H) for the redox reaction -e phenol phenol cation radical +e is about the same as for the reversible redox reaction (also in CHpCIp-FS03H), -e phenol ether +phenol ether cation radical +e of the corresponding methyl ether supports this hypothesis. (12) A. Ronlan. J. Coleman, 0. Hammerich, and V. D. Parker, J. Am. Chem. SOC., 96, 845 (1974). (13) This very rough estimate is obtained by applying the Tafel equation assuming that the phenol and its methyl ether have the same transfer coefficient (0.5) and the same exchange current. (14) U. Palmquist and A. Ronlan, to be submitted for publication. (15) V. D. Parker, U. Palmquist. and A. Ronlan. Acta Chem. Scand., Ser. 8. 28, 1241 (1974); V. D. Parker and A. Ronlan, J. Am. Chem. SOC., 97, 4714 (1975). (16) We assume that phydroxy-and pmethoxyphenyl groups are equally efficient nucleophiles. (17) E. Kotani, F. Miyazaki, and S. Tobinaga, J. Chem. SOC., Chem. Com mun., 300 (1974). (18) Our previous investigations of the anodic coupling and cyclization reactions of phenol ethers (ref 15) have shown that phenol ether cation radicals preferentially couple or cyclize through positions para to methoxy groups and that coupling or cyclization does not occur if these positions are substituted. Abstract: Reactions of benzylic fluorides and chlorides with lithium naphthalene in THF have been found to give dimers in 61 -79%
The Journal of Physical Chemistry A, 2012
The redox behavior of the series of 7substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinolines and 8-substituted 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-f ]quinolines with R 7 , R 8 = H, COOC 2 H 5 , COOCH 3 , COOH, COCH 3 , and CN has been studied by in situ EPR and EPR/UV−vis spectroelectrochemistry in dimethylsulfoxide. All selenadiazoloquinolones undergo a one-electron reduction process to form the corresponding radical anions. Their stability strongly depends on substitution at the nitrogen atom of the 4-pyridone ring. The primary generated radical anions from N-ethyl-substituted quinolones are stable, whereas for the quinolones with imino hydrogen, the initial radical anions rapidly dimerize to produce unusually stable sigmadimer (σ-dimer) dianions. These are reversibly oxidized to the initial compounds at potentials considerably less negative than the original reduction process in the back voltammetric scan. The dimer dianion can be further reduced to the stable paramagnetic dimer radical trianion in the region of the second reversible reduction step. The proposed complex reaction mechanism was confirmed by in situ EPR/UV−vis cyclovoltammetric experiments. The site of the dimerization in the σ-dimer and the mapping of the unpaired spin density both for radical anions and σ-dimer radical trianions with unusual unpaired spin distribution have been assigned by means of density functional theory calculations.
New benzene dimers: an MRMP2 study
Theoretical Chemistry Accounts, 2020
The reaction energies of one cis-fused and four new trans-fused benzene dimers have been studied with state-specific multi-reference Møller-Plesset perturbation theory of the second order (MRMP2) based on reference CASSCF(12,12) wavefunctions. The cis-fused dimer 1, the product of symmetry-allowed [4 + 2] cycloaddition process, has been previously characterized experimentally and theoretically and, in this study, was used as reference. Dimer 1 lies 45 kcal/mol above two isolated benzene molecules, and its retro-dimerization activation energy is ~ 8 kcal/mol. In contrast, the [4 + 2] formation of trans-fused dimer 2 is symmetry-forbidden with an energetic driving force (E rel) of 57.6 kcal/mol. An activation barrier for corresponding retro-dimerization calculated to be 31.0 kcal/mol. The thermal [2 + 2] formation of dimers 3 and 4 are also symmetry-forbidden. They have been calculated to be 79.0 kcal/mol and 105.1 kcal/mol higher in energy than two isolated benzene molecules, respectively. However, the activation energies of 23.2 and 20.5 kcal/mol could allow for kinetic persistence of these compounds. Dimer 5 is the only symmetry-allowed [2 + 2] cycloaddition product. With E rel of 67.5 kcal/ mol and E a for retro-dimerization reaction of 19.2 kcal/mol, it shows high similarity with the symmetry-forbidden dimers. The wave function for each of the dimers at their local minimum geometry contains greater than 80% of the configuration 4 8 * 0 * 0. The transition state for the retro-dimerization of 1 (1TS) also contains more than 80% of the closed-shell configuration 4 8 * 0 * 0. For 2TS-5TS systems, the wavefunctions exhibit significant biradical character (20%, 20%, 14% and 26%, respectively).