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Article

Synthesis and Characterization of a Highly Reducing Neutral “Extended Viologen” and the Isostructural Hydrocarbon 4,4‘ ‘‘ ‘-Di-n-octyl-p-quaterphenyl

Supporting Info

William W. Porter III,^† Thomas P. Vaid,*^† and Arnold L. Rheingold^‡

Contribution from the Center for Materials Innovation and Department of Chemistry, Washington University, St. Louis, Missouri 63130, and Department of Chemistry, University of California, San Diego, La Jolla, California 92093

J. Am. Chem. Soc., 2005, 127 (47), pp 16559–16566

DOI: 10.1021/ja053084q

Publication Date (Web): November 8, 2005

†

Washington University in St. Louis.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

‡

University of California, San Diego.

, vaid@wustl.edu

Abstract

The molecule 4,4‘ ‘‘ ‘-di-n-octyl-p-quaterphenyl was synthesized in one step by a nickel-catalyzed cross-coupling reaction. Powder X-ray diffraction shows that it crystallizes in a layered structure with the long axis of the molecule nearly perpendicular to the layer plane. Differential scanning calorimetry indicates a transition to a liquid−crystalline phase at 81 °C. Reaction of 4,4‘-bis(4-pyridyl)biphenyl with 1-bromooctane yields the dication 2²⁺2Br^-, an “extended viologen” isostructural with 4,4‘ ‘‘ ‘-di-n-octyl-p-quaterphenyl. Reduction of 2²⁺2Br^- with sodium amalgam in DMF yields 2, the first neutral extended viologen to be isolated. The molecule 2 is, to the best of our knowledge, the most reducing neutral organic molecule that has been synthesized. Single-crystal X-ray diffraction shows that a diradical form, either singlet or triplet, makes an important contribution to the electronic structure of 2. The broadened ¹H NMR spectrum of 2 indicates the presence of a triplet, but it has not been possible to observe the triplet by ESR spectroscopy. The electronic structure of 2 appears to be closely related to that of a classic molecule, Chichibabin's hydrocarbon.