Organometallic hydride-transfer agents as reductants for organic semiconductor molecules

Abstract

Both organic hydride donors, DH, and the dimers formed by some organic radicals and by some 19-electron organometallic sandwich compounds, D2, have recently been examined extensively as n-dopants for organic semiconductors. This properties of two classes of organometallic DH derivatives – organic DH derivatives with metallocenyl substituents and species obtained by hydride reduction of 18-electron D+ sandwich cations – are discussed and compared to those of the corresponding D2 molecules. 1,3-Dimethyl-2-metallocenyl-2,3-dihydro-1H-benzo[d]imidazoles, Mc-DMBI-H (Mc = ferrocenyl [Fc], ruthenocenyl [Rc]), and 1,3-dimethyl-2-phenyl-1H-benzo[d]imidazolium tetrakis(3,5-bis(trifluoromethyl))borates, Mc-DMBI+BAr'4– (Mc = Fc, Rc), have recently been reported as intermediates in the synthesis of the dimers (Mc-DMBI)2; here their crystal structures are reported and compared to those of related molecules. The solution reactivity of the Mc-DMBI-H derivatives with a fullerene acceptor is similar to that of purely organic aryl-DMBI-H species. Previously reported (exo-H-η4-pentamethylcyclopentadiene)(η5-cyclopentadienyl)metal complexes, M(exo-H-Cp*H)Cp (M = Rh, Ir) and the new (η5-pentamethylcyclopentadienyl)(η5-1,3,5-trimethylcyclohexa-1,3-dien-5-yl)ruthenium, RuCp*(mesH), have also been examined as potential reductants for organic semiconductors; RuCp*(mesH) is particularly reactive, affording the radical anions of perylene diimide and 6,13-bis(tri(isopropyl)silylethynyl)pentacene. The electrochemistry of DH, D+, and D2 species is compared for the five compounds. Density-functional theory calculations are used to gain insight into the trends in electrochemistry and reactivity.