title: Crystal structures of the carborane dianions [1,4-(PhCB₁₀H₁₀C)₂C₆H₄]²⁻ and [1,4-(PhCB₁₀H₁₀C)₂C₆F₄]²⁻ and the stabilizing role of the para-phenylene unit on 2n+3 skeletal electron clusters.
abstract: While carboranes with 2 n+2 and 2 n+4 (n=number of skeletal atoms) skeletal electrons (SE) are widely known, little has been reported on carboranes with odd SE numbers. Electrochemical measurements on two-cage assemblies, where two C-phenyl-ortho-carboranyl groups are linked by a para-phenylene or a para-tetrafluorophenylene bridge, revealed two well separated and reversible two-electron reduction waves indicating formation of stable dianions and tetraanions. The salts of the dianions were isolated by reduction with sodium metal and their unusual structures were determined by X-ray crystallography. The diamagnetic dianions contain two 2 n+3 SE clusters where each cluster has a notably long carborane C-carborane C distance of ca 2.4 Å. The π conjugation within the phenylene bridge plays an important role in the stabilization of these carboranes with odd SE counts.
authors.affiliation: Fakultät für Chemie der Universität Bielefeld, 33615 Bielefeld (Germany).
authors.forename: Jan
authors.initials: J
authors.lastname: Kahlert
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Stammler
authors.forename: Beate
authors.initials: B
authors.lastname: Neumann
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Harder
authors.forename: Lothar
authors.initials: L
authors.lastname: Weber
authors.forename: Mark A
authors.initials: MA
authors.lastname: Fox
keywords: carborane; conjugation; electrochemistry; phenylene; quinoidal structures