title: Dimers of nineteen-electron sandwich compounds: crystal and electronic structures, and comparison of reducing strengths.
abstract: The dimers of some Group 8 metal cyclopentadienyl/arene complexes and Group 9 metallocenes can be handled in air, yet are strongly reducing, making them useful n-dopants in organic electronics. In this work, the X-ray molecular structures are shown to resemble those of Group 8 metal cyclopentadienyl/pentadienyl or Group 9 metal cyclopentadienyl/diene model compounds. Compared to those of the model compounds, the DFT HOMOs of the dimers are significantly destabilized by interactions between the metal and the central CC σ-bonding orbital, accounting for the facile oxidation of the dimers. The lengths of these CC bonds (X-ray or DFT) do not correlate with DFT dissociation energies, the latter depending strongly on the monomer stabilities. Ru and Ir monomers are more reducing than their Fe and Rh analogues, but the corresponding dimers also exhibit much higher dissociation energies, so the estimated monomer cation/neutral dimer potentials are, with the exception of that of [RhCp2 ]2 , rather similar (-1.97 to -2.15 V vs. FeCp2 (+/0) in THF). The consequences of the variations in bond strength and redox potentials for the reactivity of the dimers are discussed.
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA); Present address: KIIT University, Bhubaneswar, Orissa 751024 (India).
authors.forename: Swagat K
authors.initials: SK
authors.lastname: Mohapatra
authors.forename: Alexandr
authors.initials: A
authors.lastname: Fonari
authors.forename: Chad
authors.initials: C
authors.lastname: Risko
authors.forename: Kada
authors.initials: K
authors.lastname: Yesudas
authors.forename: Karttikay
authors.initials: K
authors.lastname: Moudgil
authors.forename: Jared H
authors.initials: JH
authors.lastname: Delcamp
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Timofeeva
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
keywords: density functional calculations; doping; redox chemistry; sandwich complexes; structure elucidation