Nucleophilic aromatic substitution approach to phosphanyl-substituted diboraanthracenes: biphilic compounds with tunable electron affinities

Abstract

9,10-Dimesityl-9,10-dihydro-9,10-diboraanthracenes (Mes₂DBAs) bearing one (1), two (2), or four (3) Ph₂P substituents were prepared from Ph₂PSiMe₃ and tetrafluorinated Mes₂DBAs via a nucleophilic aromatic substitution protocol. Using compound 1 as the model system, it was shown that P-oxidation (4), -sulfurization (5), or -methylation ([6]OTf) leads to a gradual anodic shift in the redox potentials of the compounds to an E_1/2 value of ultimately −1.24 V (CH₂Cl₂; vs. FcH/FcH⁺). An exhaustive P-sulfurization is also possible for 2 and 3, and affords the Ph₂P(S)-substituted species 7 and 8 with E_1/2 values of −1.33 and −1.23 V, respectively. Fourfold P-methylation of 3 with MeOSO₂CF₃ (MeOTf) furnishes the salt [10](OTf)₂, in which each of the two Mes substituents previously bonded to the B centers is replaced by two [OTf]⁻ ligands. Late-stage P derivatization of Ph₂P-carrying Mes₂DBAs is thus a simple and effective means of tuning their redox properties and Lewis acidities.