Cycloheptatrienyl dicarbollyl zirconium complexes: Building blocks for the preparation of multidecker sandwich complexes

Abstract

The reaction of [(η7-C7H7)ZrCl(tmeda)] (1, tmeda = N,N,N',N'-tetramethylethylene-1,2-diamine) with the sodium dicarbollide Na2(C2B9H11) afforded the cycloheptatrienyl-dicarbollyl (Cht-Dcb) complex [Na(tmeda)][(η7-Cht)Zr(η5-Dcb)], [Na(tmeda)][2]. In the solid state, the sodium cations act as bridging units between the sandwich anions by η2-and η3-interaction with the Cht and Dcb ligands, respectively. The reaction of [Na(tmeda)][2] with BaI2 resulted in the formation of [Ba(thf)5(μ-η7:η7-C7H7)Zr(η5-C2B9H11)][(η7-C7H7)Zr(η5-C2B9H11)], [Ba(thf)5(2)][2], in which the cation exhibits an unusual bridging μ-η7:η7-C7H7 unit between the Dcb-Zr and the Ba(thf)5 fragments. An analogous reaction could not be effected by the salt metathesis reaction between [Na(tmeda)][2] and 0.25 equivalents of [(η5-C5Me5)Ru(μ3-Cl)]4, since the ion pair [(η5-C5Me5)Ru(tmeda)][2] containing the 16-electron half-sandwich tmeda complex was formed instead. The tetramethylammonium salt [NMe4][2] was prepared via an acid-base reaction between the amido complex [(η7-C7H7)Zr{N(SiMe3)2}(thf)] and [NMe4][C2B9H12]. [NMe4][2] is more stable than its sodium congener [Na(tmeda)][2] and might therefore act as a suitable transfer reagent for the construction of multidecker sandwich transition metal complexes in the future.