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1,3-Dimethyl-2,3-dihydrobenzo[
d ]imidazoles,1H , and 1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d ]imidazoles,1 2 , are of interest as n-dopants for organic electron-transport materials. Salts of 2-(4-(dimethylamino)phenyl)-4,7-dimethoxy-, 2-cyclohexyl-4,7-dimethoxy-, and 2-(5-(dimethylamino)thiophen-2-yl)benzo[d ]imidazolium (1g–i + , respectively) have been synthesized and reduced with NaBH4to1gH ,1hH , and1iH , and with Na:Hg to1g 2 and1h 2 . Their electrochemistry and reactivity were compared to those derived from 2-(4-(dimethylamino)phenyl)- (1b + ) and 2-cyclohexylbenzo[d ]imidazolium (1e + ) salts.E (1 + /1 • ) values for 2-aryl species are less reducing than for 2-alkyl analogues, i.e., the radicals are stabilized more by aryl groups than the cations, while 4,7-dimethoxy substitution leads to more reducingE (1 + /1 • ) values, as well as cathodic shifts inE (1 2 •+ /1 2 ) andE (1H •+ /1H ) values. Both the use of 3,4-dimethoxy and 2-aryl substituents accelerates the reaction of the1H species with PC61BM. Because 2-aryl groups stabilize radicals,1b 2 and1g 2 exhibit weaker bonds than1e 2 and1h 2 and thus react with 6,13-bis(triisopropylsilylethynyl)pentacene (VII ) via a “cleavage-first” pathway, while1e 2 and1h 2 react only via “electron-transfer-first”.1h 2 exhibits the most cathodicE (1 2 •+ /1 2 ) value of the dimers considered here and, therefore, reacts more rapidly than any of the other dimers withVII via “electron-transfer-first”. Crystal structures show rather long central C–C bonds for1b 2 (1.5899(11) and 1.6194(8) Å) and1h 2 (1.6299(13) Å). -
The molecular tetravalent oxidation state for praseodymium is observed in solution via oxidation of the anionic trivalent precursor [K][Pr 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (1-Pr(NP*)) with AgI at −35 °C. The Pr 4+ complex is characterized in solution via cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, and EPR spectroscopy. Electrochemical analyses of [K][Ln 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (Ln = Nd and Dy) by cyclic voltammetry are reported and, in conjunction with theoretical modeling of electronic structure and oxidation potential, are indicative of principal ligand oxidations in contrast to the metal-centered oxidation observed for 1-Pr(NP*). The identification of a tetravalent praseodymium complex in in situ UV-vis and EPR experiments is further validated by theoretical modeling of the redox chemistry and the UV-vis spectrum. The latter study was performed by extended multistate pair-density functional theory (XMS-PDFT) and implicates a multiconfigurational ground state for the tetravalent praseodymium complex.more » « less