PUB - Publikationen an der Universität Bielefeld

The first organometallic zinc hydroxylamides [Zn(RZn)(4)(ONMe2)(6)] (1:R = Me; 2:R = iPr) and [Zn(EtZn)(4)(ONEt2)(6)] (3) have been prepared by alkane elimination from dialkylzinc solutions upon treatment with N,N-dialkylhydroxylamines. The molecular structures of 1 and 2 reveal that a subtle change in the constitution of the aggregates can make a striking difference. By the simple exchange of the MeZn+ groups with iPrZn(+) groups, the coordination number of the central Zn2+ nucleus increases from four (1) to six (2). The two cluster types are unprecedented in both hydroxylamine and organometallic chemistry. Compounds 1 and 3 adopt a doubly bridged fenestrane-like Zn5N6O6 core with two dangling NR2 moieties, whereas iPrZn species 2 comprises an octahedroid backbone with all donor atoms attached to the five Zn nuclei with the maintenance of the same heteroatom composition as 1 and 3. Variable-temperature C-13 NMR experiments of all-ethyl cluster 3 reveal that the R2NO- ligands rapidly exchange between the RZn+ and Zn2+ cations. This process is rationalised by a plausible model which also points out that the core structure of 3 could be an intermediate motif in the observed heteroatom connectivity exchange. In line with this, computational investigations reveal that both skeletons are very similar in energy. In sum, the coordination flexibility of the hydroxylamide ligand makes this group of organometallic zinc complexes a highly dynamic family of cluster compounds. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).