Ferrocenyl(trihydro)borates: building blocks for the synthesis of heterooligonuclear metallocene complexes.

The reaction of [Cp(2)ZrCl(2)] with the lithium salt Li[FcBH(3)] in stoichiometric ratios of 1.5 : 1 or 0.4 : 1 furnishes the mixed-metallocene complexes [Cp(2)(Cl)Zr(H(3)BFc)] (1) and [Cp(2)Zr(H(3)BFc)(2)] (3), respectively (Cp = cyclopentadienyl; Fc = ferrocenyl). When the two reagents are combined in a ratio of 0.6 : 1, complex 1 is formed together with the zirconium hydride species [Cp(2)(H)Zr(H(3)BFc)] (2). Compound 2 can be obtained in pure form from [Cp(2)Zr(H)Cl] and Li[FcBH(3)]. Treatment of the half-sandwich complexes [(C(5)R(5))ZrCl(3)] with 3 equivalents of Li[FcBH(3)] leads to the heterotetranuclear aggregates [(C(5)R(5))Zr(H(3)BFc)(3)] (4: R = H; 5: R = CH(3)). Li(2)[fc(BH(3))(2)] and 3 equivalents of [Cp(2)ZrCl(2)] give the heterotrinuclear compound [fc(BH(3)Zr(Cl)Cp(2))(2)] (6) with bridging ferrocenylene core (fc = 1,1'-ferrocenylene). According to X-ray crystallography, the trihydroborate ions are coordinated in a [Zr(μ-H)(2)B(H)-] fashion in 1, 2, 3 and 6, whereas 4 and 5 are carrying tridentate trihydroborate ligands.