eta-6-Arene metal complexes. Synthesis, reactivity and crystal and molecular structure of [V(eta-6-1,3,5-Me3C6H3)2]AlCl4 and the one-pot synthesis of V(eta-6-1,3,5-MeC6H5)2 and Mo(eta-6-MeC6H5)2.

The products of the reduction of VX3 by the Al/AlX3 (X = Cl, Br, I) system in 1,3,5-Me3C6H3 (mes), [Vmes2]AlX4, have been isolated and structurally characterized for X = Cl. Crystal data: C18H24AlCl4V; M = 460.1; orthorhombic, space group Pnnm, a = 15.078(1); b = 14.391(3); c = 10.481(3) angstrom; U = 2274(1) angstrom3; Z = 4; D, = 1.344 Mg m-3; lambda(Mo-K(alpha1)) = 0.70930 angstrom; mu = 0.93 mm-1; F(000) = 944; T = 294 K. The structure consists of the discrete VMes2+ and AlCl4- ions, the former containing sandwiched, eclipsed arene ligands. In the parent hydrocarbon as medium, no further reduction of the vanadium(I) complex occurred even over long reaction times: in the presence of tetrahydrofuran, the crude primary product of the reaction was further reduced by the excess of aluminium affording bismesitylenevanadium(0), VmeS2, in good yields. The slight solubility of [VmeS2]AlCl4 in mesitylene has been found to increase enormously by addition of one equivalent of AlCl3: this adduct clathrates additional mesitylene up to a critical ratio of the mesitylene/vanadium molar value, further addition of mesitylene giving a biphasic system. The new synthetic method used for Vmes2 has been extended to the preparation of the chromium(0) and molybdenum(0) complexes, Cr(eta6-MeC6H5)2 and Mo(eta6-MeC6H5)2, respectively