Synthesis and Photodimerization of 2- and 2,3-Disubstituted Anthracenes: Influence of Steric Interactions and London Dispersion on Diastereoselectivity

Abstract

There is increased evidence that the effect of bulky groups in organic, organometallic, and inorganic chemistry is not only repulsive but can be attractive because of London dispersion interactions. The influence of the size of primary alkyl substituents in 2- and 2,3-positions of anthracenes on the diastereoselectivity (anti vs syn dimer) of the [π4s + π4s] photoinduced dimerization is investigated. The synthesis of the anthracene derivatives was achieved by Suzuki–Miyaura reaction of 2,3-dibromoanthracene with alkylboronic acids as well as by reduction of anthraquinones that were obtained from 2,3-disubstituted 1,3-butadienes and naphthoquinone followed by dehydrogenation. The mixtures of dianthracene isomers were analyzed with respect to the anti/syn-ratio of the products by X-ray crystallography and nuclear Overhauser effect spectroscopy. While for the 2,3-dimethylanthracene the anti and syn isomers were formed in equal amounts, the anti dimers are the major products in all other cases. A linear correlation (R 2 = 0.98) between the steric size (Charton parameter) and the isomeric ratio suggests that the selectivity is dominated by classical repulsive steric effects. An exception is the iso-butyl substituent that produces an increased amount of the syn isomer. It is suggested that this is due to an exalted effect of London dispersion interactions.

Modulating the Electronic and Solid‐State Structure of Organic Semiconductors by Site‐Specific Substitution: The Case of Tetrafluoropentacenes

“…Mass spectrometric investigation of 13 was precluded due to its instability under electron‐impact (EI) conditions. Similar to the observations we have made investigating anthracene dimers, only the mass of the monomer was detected, exhibiting the same fragmentation pattern as an authentic sample of the monomer. Given that the material is too insoluble, electrospray ionization (see the Supporting Information) could not be employed.…”

“…After 3 h of heating to 120 °C, all pentacene 1 H NMR signals had completely disappeared (Figure ) and a new set of three signals (integration ratio 8:8:4) had formed, indicative of a single reaction product with the same symmetry. Correlation of chemical shifts with data for pentacene endoperoxide (PcEP), an authentic sample of dianthracene prepared following our general method for preparation of substituted dianthracenes, the thermal dimer of 1,2,3,4‐tetrafluoropentacene, and diheptacene (see Supporting Information, Table S1) strongly indicates formation of the covalent dimer 13 .…”

“…Only the relevant reaction products are shown, the byproducts of the reaction have been discussed and characterized in previous publications. [31,33] symmetry.C orrelation of chemical shifts with data for pentacene endoperoxide (PcEP), [46] an authentic sample of dianthracene prepared following our generalm ethod for preparation of substituted dianthracenes, [47] the thermald imer of 1,2,3,4tetrafluoropentacene, [29] and diheptacene [48] (see Supporting Information,T able S1)s trongly indicates formation of the covalent dimer 13.…”

Recent advances in the syntheses of anthracene derivatives

“…In this review, a more detailed discussion of different types of anthracene derivatives (e.g., anthracenophanes) that have been the subject of research interest for some time [ 1 ] cannot be included. Nevertheless, readers interested in this area should refer to several interesting articles on this subject such as the work of the research groups of Bettinger [ 83 – 84 ], Ohmori [ 85 ], and Novak [ 86 ].…”

Photoreactivity of an Exemplary Anthracene Mixture Revealed by NMR Studies, including a Kinetic Approach

“…Furthermore, different isomers of the dimer can be formed [9,22,23]. Therefore, the regio-and enantioselectivity of anthracene photodimerization has been investigated comprehensively, both via experiment and quantum chemistry calculations [24][25][26][27][28].…”