The reaction of [Cp2ZrCl2] with the lithium salt Li[FcBH3] in stoichiometric ratios of 1.5 : 1 or 0.4 : 1 furnishes the mixed-metallocene complexes [Cp2(Cl)Zr(H3BFc)] (1) and [Cp2Zr(H3BFc)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 [Cp2(H)Zr(H3BFc)] (2). Compound 2 can be obtained in pure form from [Cp2Zr(H)Cl] and Li[FcBH3]. Treatment of the half-sandwich complexes [(C5R5)ZrCl3] with 3 equivalents of Li[FcBH3] leads to the heterotetranuclear aggregates [(C5R5)Zr(H3BFc)3] (4: R = H; 5: R = CH3). Li2[fc(BH3)2] and 3 equivalents of [Cp2ZrCl2] give the heterotrinuclear compound [fc(BH3Zr(Cl)Cp2)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)2B(H)–] fashion in 1, 2, 3 and 6, whereas 4 and 5 are carrying tridentate trihydroborate ligands.
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