Synthesis and characterization of chromium(I) bis(η6-toluene) derivatives containing sterically demanding anions

The reaction of Cr(eta(6)-CH3C6H5)(2) with 1-benzoyl-6-hydroxy-6-phenyl fulvene, dbcpH, and with pentakis(methoxycarbonyl)cyclopentadiene, pcmcpH, proceeds with evolution of dihydrogen and the formation of the ionic derivatives [Cr(eta(6)-CH3C6H5)(2)][X] ([X](-) = 1,2-dibenzoylcyclopentadienyl, [dbcp](-), pentakis(methoxycarbonyl)cyclopentadienyl, [pcmcp](-)), which have been characterized by IR and EPR spectroscopies, X-ray diffraction and electrochemical techniques. The sterically demanding anions do not affect the structural and electronic properties of the Cr(eta(6)-CH3C6H5)(2)(+) cations in solution but strongly influence crystal packing. In fact, a rare cis-eclipsed conformation of the toluene rings is found for [Cr(eta(6)-CH3C6H5)(2)][dbcp] center dot THF, whereas two independent complexes are observed in the unit cell of [Cr(eta(6)-CH3C6H5)(2)][pcmcp], one with toluene rings in a cis-eclipsed conformation and the other in a staggered conformation (projections of methyl groups form an angle of 151 degrees). (c) 2005 Elsevier B.V. All rights reserved.