title: n-Doping of organic electronic materials using air-stable organometallics: a mechanistic study of reduction by dimeric sandwich compounds.
abstract: Several 19-electron sandwich compounds are known to exist as "2×18-electron" dimers. Recently it has been shown that, despite their air stability in the solid state, some of these dimers act as powerful reductants when co-deposited from either the gas phase or from solution and that this behavior can be useful in n-doping materials for organic electronics, including compounds with moderate electron affinities, such as 6,13-bis[tri(isopropyl)silylethynyl]pentacene (3). This paper addresses the mechanisms by which the dimers of 1,2,3,4,5-pentamethylrhodocene (1 b(2)), (pentamethylcyclopentadienyl)(1,3,5-trialkylbenzene)ruthenium (alkyl=Me, 2 a(2); alkyl=Et, 2 b(2)), and (pentamethylcyclopentadienyl)(benzene)iron (2 c(2)) react with 3 in solution. Vis/NIR and NMR spectroscopy, and X-ray crystallography indicate that the products of these solution reactions are 3(·-) salts of the monomeric sandwich cations. Vis/NIR kinetic studies for the Group 8 dimers are consistent with a mechanism whereby an endergonic electron transfer from the dimer to 3 is followed by rapid cleavage of the dimer cation. NMR crossover experiments with partially deuterated derivatives suggest that the C-C bond in the 1 b(2) dimer is much more readily broken than that in 2 a(2); consistent with this observation, Vis/NIR kinetic measurements suggest that the solution reduction of 3 by 1 b(2) can occur by both the mechanism established for the Group 8 species and by a mechanism in which an endergonic dissociation of the dimer is followed by rapid electron transfer from monomeric 1 b to 3.
authors.affiliation: School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, 30332-0400, USA.
authors.forename: Song
authors.initials: S
authors.lastname: Guo
authors.forename: Swagat K
authors.initials: SK
authors.lastname: Mohapatra
authors.forename: Alexander
authors.initials: A
authors.lastname: Romanov
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Timofeeva
authors.forename: Kenneth I
authors.initials: KI
authors.lastname: Hardcastle
authors.forename: Kada
authors.initials: K
authors.lastname: Yesudas
authors.forename: Chad
authors.initials: C
authors.lastname: Risko
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Brédas
authors.forename: Seth R
authors.initials: SR
authors.lastname: Marder
authors.forename: Stephen
authors.initials: S
authors.lastname: Barlow