Ferrocenyl naphthalenes: substituent- and substitution pattern-depending charge transfer studies

Andrea Preuss, Marcus Korb, Dominique Miesel, Tobias Rueffer, Alexander Hildebrandt, Heinrich Lang

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Abstract

The synthesis of a series of ferrocenyl-functionalized naphthalenes of type 2-Fc-C10H7 (3a), 1-Fc-2-R-C10H6 (3b, R = OMe; 3c, R = Me; 3d, R = H; 3e, R = CH(O)), 1,1 '-(C10H7)(2)Fc ' (4), 1-Br-4-Fc-C10H6 (6a), 1-Br-5-Fc-C10H6 (6b), 1-Br-8-Fc-C10H6 (6c), 2-Br-6-Fc-C10H6 (6d), 1,4-Fc(2)-C10H6 (7a), 1,5-Fc(2)-C10H6 (7b), 1,8-Fc(2)-C10H6 (7c) and 2,6-Fc(2)-C10H6 (7d) (Fc = Fe(eta(5)-C5H4)(eta(5)-C5H5), Fc ' = Fe(eta(5)-C5H4)(2)) is reported. They are accessible either by the Suzuki-Miyaura or Negishi C,C cross-coupling reaction of FcB(OH)(2) (1a) or FcZnCl (1b) with the appropriate bromo-naphthalenes 2a-e and 5a-d, respectively. The molecular structures of 3a-c, 3e, 4, 6b-d and 7a-d in the solid state were determined by single-crystal X-ray diffraction analysis. They show inter- (3b,c,e, 6b,d, 7a) and intramolecular (7c) pi-interactions in the form of T-shaped or parallel displaced pi arrangements (3c,e, 6b), whereby 3e displays a columnar stacking of the condensed aromatic unit with plane distances of 3.485(5) to 3.525(5) angstrom. The (spectro)electrochemical behaviour of 3-4 and 6-7 in dichloromethane in the presence of the weakly coordinating anion [B(C6F5)(4)](-) is discussed, showing reversible redox events in the range of -140-150 mV vs. FcH/FcH(+). The electrochemical response of 3a-e and 4 depends on the electron-withdrawing and -donating groups present. The redox processes of mono Fc-substituted 6a-d are affected by the naphthalene substitution pattern, which also influences the redox separations Delta E of Fc(2)-naphthalenes 7a-d, confirming a significant effect of the different electron transfer pathways through the aromatic core. The UV/vis/NIR spectra of mixed-valent [7a,b,d](+) show broad and weak absorptions in the NIR region, allowing a classification as weakly coupled class II systems according to Robin and Day.

Original languageEnglish
Pages (from-to)14418-14432
Number of pages15
JournalDalton Transactions
Volume48
Issue number38
DOIs
Publication statusPublished - 14 Oct 2019

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