abstract80

Ruthenium Complexes of C,C’-Bis(ethynyl)carboranes: An Investigation of Electronic Interactions Mediated by Spherical Pseudo-aromatic Spacers

Mark A. Fox, Rachel L. Roberts, Thomas E. Baines, Boris Le Guennic, Jean-François Halet, Frantiek Hartl, Dmitri S. Yufit, David Albesa-Jové, Judith A. K. Howard, and Paul J. Low*

Department of Chemistry, Durham University, South Rd, Durham, DH1 3LE, UK, Laboratoire des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1, 35042 Rennes cedex, France, Laboratoire de Chimie, UMR CNRS 5182, Ecole Normale Supérieure de Lyon, 46 allée d’Italie, 69364 Lyon cedex 07, France, and Van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018WV Amsterdam, The Netherlands

[email protected]

Received October 17, 2007

Abstract:

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The complexes [Ru(1-C  C-1,10-C₂B₈H₉)(dppe)Cp*] (3a), [Ru(1-C  C-1,12-C₂B₁₀H₁₁)(dppe)Cp*] (3b), [{Ru(dppe)Cp*}₂{  -1,10-(C  C)₂-1,10-C₂B₈H₈}] (4a) and [{Ru(dppe)Cp*}₂{  -1,12-(C  C)₂-1,12-C₂B₁₀H₁₀}] (4b), which form a representative series of mono- and bimetallic acetylide complexes featuring 10- and 12-vertex carboranes embedded within the diethynyl bridging ligand, have been prepared and structurally characterized. In addition, these compounds have been examined spectroscopically (UV-vis-NIR, IR) in all accessible redox states. The significant separation of the two, one-electron anodic waves observed in the cyclic voltammograms of the bimetallic complexes 4a and 4b is largely independent of the nature of the electrolyte and is attributed to stabilization of the intermediate redox products [4a]⁺ and [4b]⁺ through interactions between the metal centers across a distance of ca. 12.5 Å. The mono-oxidized bimetallic complexes [4a]⁺ and [4b]⁺ exhibit spectroscopic properties consistent with a description of these species in terms of valence-localized (class II) mixed-valence compounds, including a unique low-energy electronic absorption band, attributed to an IVCT-type transition that tails into the IR region. DFT calculations with model systems [4a-H]⁺ and [4b-H]⁺ featuring simplified ligand sets reproduce the observed spectroscopic data and localized electronic structures for the mixed-valence cations [4a]⁺ and [4b]⁺.

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