Chalcogen controlled redox behaviour in peri-substituted S, Se and Te naphthalene derivatives

Roemmele, Tracey L. and Knight, Fergus R. and Crawford, Ellis and Robertson, Stuart D. and Bode, Bela E. and Bühl, Michael and Slawin, Alexandra M. Z. and Woollins, J. Derek and Boeré, René T. (2022) Chalcogen controlled redox behaviour in peri-substituted S, Se and Te naphthalene derivatives. New Journal of Chemistry, 2022 (46). pp. 22363-22383. ISSN 1144-0546 (https://doi.org/10.1039/d2nj04737c)

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Abstract

Cyclic and square wave voltammetry of (PhE) 2peri-disubstituted naphthalene[1,8-cd]dichalcoganyls and acenaphthene[5,6-diyl]dichalcoganyls (E = S, Se, Te, 12 compounds) is reported. Mixed (E 1 = Se, Te; E 2 = Br, I) naphthalene[1,8-cd]halochalcoganyls were also investigated, as well as an exemplar bearing two PhS(=O) groups and another bearing one PhSe and one Ph 2P( S) substituent. The voltammetry, in CH 2Cl 2/0.4 M [ nBu 4N][PF 6] at both platinum and glassy carbon macro-disk working electrodes, shows two sequential chemically reversible and electrochemically quasi-reversible oxidation processes, and the lack of accessible reductions. Additional oxidations above +1.5 V vs. Fc +/0 have not been investigated in detail. In situ and ex situ EPR spectroscopy conclusively demonstrate that both anodic processes are 1e transfers; persistent radical cations could be generated for all the dichalcoganyls except when E 1 = E 2 = Te; for the latter case thermally stable dications are generated instead. The complex possible solution conformations of these compounds in 0, +1 and +2 charge states were modelled with DFT at the B3LYP-D3(BJ)/6-31+G(d) level of theory in a CH 2Cl 2 PCM continuum solution model and adiabatic ionisation energies calculated, which correlate linearly (R = 0.88) with the E a1 p values. Crystal structures of four solvolysis and hydrolysis products of the ditellurium dications are reported and were modelled computationally. Interpretative comparisons to unsubstituted naphthalene[1,8-cd]dichalcogenoles are reported and the crystal structure of naphtho(1,8-cd)(1,2-dithiolium) tetrafluoroborate has been obtained. This is the first structure reported for any salt of this cation radical. Electron transfer mechanisms of both the (PhE) 2 and E 2peri-disubstituted naphthalene series are correlated using a redox molecular orbital interpretative framework.

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