Synthesis, structures, and reactivity of isomers of [RuCp*(1,4-(Me2N)2C6H4)]2

Elena Longhi; Chad Risko; John Bacsa; Victor Khrustalev; Sergei Rigin; Karttikay Moudgil; Tatiana V Timofeeva; Seth R Marder; Stephen Barlow

doi:10.1039/d1dt02155a

Synthesis, structures, and reactivity of isomers of [RuCp*(1,4-(Me₂N)₂C₆H₄)]₂

Dalton Trans. 2021 Sep 28;50(37):13020-13030. doi: 10.1039/d1dt02155a.

Authors

Elena Longhi¹, Chad Risko², John Bacsa³, Victor Khrustalev^{4

5}, Sergei Rigin⁴, Karttikay Moudgil¹, Tatiana V Timofeeva⁴, Seth R Marder^{1

6

7

8

9}, Stephen Barlow^{1

6}

Affiliations

¹ School of Chemistry and Biochemistry & Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA.
² Department of Chemistry & Center for Applied Energy Research (CAER), University of Kentucky, 125 Chemistry-Physics Building, Lexington, KY 40506, USA.
³ Crystallography Lab, Emory University, 201 Dowman Drive, Atlanta, GA 30322, USA.
⁴ Department of Chemistry, New Mexico Highlands University, Las Vegas, NM 87701, USA.
⁵ Department of Inorganic Chemistry, Peoples' Friendship University of Russia, Moscow 117198, Russia.
⁶ Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, CO 80303, USA. stephen.barlow@colorado.edu.
⁷ Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO 80303, USA.
⁸ Department of Chemistry, University of Colorado Boulder, Boulder, CO 80303, USA.
⁹ Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.

PMID: 34581359
DOI: 10.1039/d1dt02155a

Abstract

[RuCp*(1,3,5-R₃C₆H₃)]₂ {Cp* = η⁵-pentamethylcyclopentadienyl, R = Me, Et} have previously been found to be moderately air stable, yet highly reducing, with estimated D⁺/0.5D₂ (where D₂ and D⁺ represent the dimer and the corresponding monomeric cation, respectively) redox potentials of ca. -2.0 V vs. FeCp₂^+/0. These properties have led to their use as n-dopants for organic semiconductors. Use of arenes substituted with π-electron donors is anticipated to lead to even more strongly reducing dimers. [RuCp*(1-(Me₂N)-3,5-Me₂C₆H₃)]⁺PF₆^- and [RuCp*(1,4-(Me₂N)₂C₆H₄)]⁺PF₆^- have been synthesized and electrochemically and crystallographically characterized; both exhibit D⁺/D potentials slightly more cathodic than [RuCp*(1,3,5-R₃C₆H₃)]⁺. Reduction of [RuCp*(1,4-(Me₂N)₂C₆H₄)]⁺PF₆^- using silica-supported sodium-potassium alloy leads to a mixture of isomers of [RuCp*(1,4-(Me₂N)₂C₆H₄)]₂, two of which have been crystallographically characterized. One of these isomers has a similar molecular structure to [RuCp*(1,3,5-Et₃C₆H₃)]₂; the central C-C bond is exo,exo, i.e., on the opposite face of both six-membered rings from the metals. A D⁺/0.5D₂ potential of -2.4 V is estimated for this exo,exo dimer, more reducing than that of [RuCp*(1,3,5-R₃C₆H₃)]₂ (-2.0 V). This isomer reacts much more rapidly with both air and electron acceptors than [RuCp*(1,3,5-R₃C₆H₃)]₂ due to a much more cathodic D₂˙⁺/D₂ potential. The other isomer to be crystallographically characterized, along with a third isomer, are both dimerized in an exo,endo fashion, representing the first examples of such dimers. Density functional theory calculations and reactivity studies indicate that the central bonds of these two isomers are weaker than those of the exo,exo isomer, or of [RuCp*(1,3,5-R₃C₆H₃)]₂, leading to estimated D⁺/0.5D₂ potentials of -2.5 and -2.6 V vs. FeCp₂^+/0. At the same time the D₂˙⁺/D₂ potentials for the exo,endo dimers are anodically shifted relative to those of [RuCp*(1,3,5-R₃C₆H₃)]₂, resulting in much greater air stability than for the exo,exo isomer.