Journal article

Authors list: Rösel, S; Becker, J; Allen; WD; Schreiner, PR

Publication year: 2018

Pages: 14421-14432

Journal: Journal of the American Chemical Society

Volume number: 140

Issue number: 43

ISSN: 0002-7863

DOI Link: https://doi.org/10.1021/jacs.8b09145

Publisher: American Chemical Society

Abstract: 
The long-known, ubiquitously present, and always attractive London dispersion (LD) interaction was probed with hexaphenylethane (HPE) derivatives. A series of all-meta hydrocarbyl [Me, Pr-i, Bu-t, Cy, Ph, 1-adamantyl (Ad)]-substituted triphenylmethyl (TPM) derivatives [TPM-H, TPM-OH, (TPM-O)(2), TPM center dot] was synthesized en route, and several derivatives were characterized by single-crystal X-ray diffraction (SC-XRD). Multiple dimeric head-to-head SC-XRD structures feature an excellent geometric fit between the meta-substituents; this is particularly true for the sterically most demanding Bu-t and Ad substituents. NMR spectra of the Pr-i-, Bu-t-, and Cy-derived trityl radicals were obtained and reveal, together with EPR and UV-Vis spectroscopic data, that the effects of all-meta alkyl substitution on the electronic properties of the trityl scaffold are marginal. Therefore, we concluded that the most important factor for HPE stability arises from LD interactions. Beyond all-meta Bu-t-HPE we also identified the hitherto unreported all-meta Ad-HPE. An intricate mathematical analysis of the temperature-dependent dissociation constants allowed us to extract Delta G(d)(298)(exptl) = 0.3(5) kcal mol(-1) from NMR experiments for all-meta Bu-t-HPE, in good agreement with previous experimental values and B3LYP-D3(BJ)/def2-TZVPP(C-PCM) computations. These computations show a stabilizing trend with substituent size in line with all-meta Ad-HPE (Delta G(d)(298)(exptl) = 2.1(6) kcal mol(-1)) being more stable than its Bu-t congener. That is, large, rigid, and symmetric hydrocarbon moieties act as excellent dispersion energy donors. Provided a good geometric fit, they are able to stabilize labile molecules such as HPE via strong intramolecular LD interactions, even in solution.

Harvard Citation style: Rösel, S., Becker, J., Allen, WD and Schreiner, P. (2018) Probing the Delicate Balance between Pauli Repulsion and London Dispersion with Triphenylmethyl Derivatives, Journal of the American Chemical Society, 140(43), pp. 14421-14432. https://doi.org/10.1021/jacs.8b09145

APA Citation style: Rösel, S., Becker, J., Allen, WD, & Schreiner, P. (2018). Probing the Delicate Balance between Pauli Repulsion and London Dispersion with Triphenylmethyl Derivatives. Journal of the American Chemical Society. 140(43), 14421-14432. https://doi.org/10.1021/jacs.8b09145