Synthesis and Characterization of Chromium(I) Bis(h6-toluene) Derivatives Containing Sterically Demanding Anions

The reaction of Cr(h6-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(h6-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(h6-CH3C6H5)+2 cations in solution but strongly influence crystal packing. In fact, a rare ciseclipsed conformation of the toluene rings is found for [Cr(h6-CH3C6H5)2][dbcp]. THF, whereas two independent complexes are observed in the unit cell of [Cr(h6-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).