Synthesis of Chromium(0) and Molybdenum(0) bis (eta(6)-arene) derivatives and their monoelectronic oxidation to [M(eta(6)-arene)2](+) cations

M(eta(6)-arene)(2) species (M = Cr, arene = 1,3,5-Me3C6H3; M = Mo, arene = 1,3,5-Me3C6H3, 1,3,5-(Pr3C6H3)-Pr-i), have been prepared by a modified Fischer-Hafner synthesis or by metal vapour techniques. The reaction of Cr(eta(6)-1,3,5-Me3C6H3)(2) with the fulvene derivatives pentacarbomethoxycyclopentadiene (pcmcpH), 1-benzoyl-6-hydroxy-6-phenylfulvene (dbcpH), or 1-benzoyl-3-nitro-6-hydroxy-6-phenylfulvene (dbncpH) proceeds with evolution of dihydrogen and formation of the ionic derivatives [Cr(eta(6)-1,3,5-Me3C6H3)(2)][E], where E = pcmcp, dbcp, or dbncp. Mo(eta(6)-arene)(2) derivatives (arene = toluene, 1,3,5-Me3C6H3, 1,3,5-(Pr3C6H3)-Pr-i) are oxidized to [Mo(eta(6)-arene)(2)](+) by pcmcpH. The crystal and molecular structures of [M(eta(6)-1,3,5-R3C6H3)(2)][pcmcp] (M = Cr, R = Me; M = Mo, R = Me, Pr-i) have been solved by X-ray single crystal diffraction.