Redox reactions with bis(h6-arene) derivatives of early transition metals

The reactivity of M(h6{arene)2 derivatives of early transition metals (M = Ti, Cr, Mo, arene = MeC6H5; M = V, Nb, arene = 1,3,5-h6{Me3C6H3) has been investigated and the syntheses of new and known compounds are described. The derivatives M(CH3COO)3, M = Ti, V, Nb, Cr; M(CF3COO)3, M = Ti, Nb, Cr; M(acac)3, M = Ti, V, Mo, acac = acetylacetonato, and M(F6acac)3, F6acac = hexafluoroacetylacetonato, M = V, Nb have been prepared by reaction of the metal bis(arene) derivatives with the appropriate Lewis acid. The crystal and molecular structure of V(F6acac)3 has been determined. Hydrogen halides or halogens react with M(h6{arene)2 with formation of metal halides, a highly reactive form of VCl3 being obtained from V(h6{1,3,5-{Me3C6H3)2 and hydrogen chloride in heptane. TiCl4 oxidizes Ti(h6{arene)2 with complete loss of the arene ligands. An electron transfer process affording ionic derivatives of formula [M(h6{MeC6H5)2][TiCl4(THF)2], M = Cr (structurally characterized), Mo, has been observed between the THF-adduct of TiCl4 and the appropriate metal-arene derivative of Group 6.