PUB - Publikationen an der Universität Bielefeld

The reactions of zinc dialkyls, R2Zn (1a-d; R = Me (a), Et (b), iPr (c) and tBu (d)), with N,N-dialkylhydroxylamines, HO-NR2' (2a-c; R' = Me (a), Et (b) and iPr (c)), afford organozinc hydroxylamides under alkane extrusion. Species of different nuclearity are observed, depending on the hydroxylamine 2 employed. The smaller 2a and 2b give pentanuclear complexes of the general formula Zn(RZn)(4)O-NR2')(6) (R = Me, Et, iPr and tBu; R' = Me and Et), whereas the derivatives of 2c are tetramers of the general formula (RZn)(4)(O-NR2')(4) (R = Me, Et and iPr; R' = iPr) as governed by bulk issues about the N-donor. Due to the ability of the double-donor unit O-NR2 to change its bridging mode, two coordination isomers exist for both types of compounds. The pentanuclear species crystallise either in a heterofenestrane or an octahedroid motif. For these species, the central Zn atom exhibits either coordination number 4 or 6; in solution, a rapid change between coordination isomers is observed. Due to the absence of a central Zn atom in the tetranuclear species, these aggregate in heterocubane geometries or such derived thereof. They display the O-N units in either kappa O-3 or kappa O-2;kappa N-1 mode. The tetranuclear species are also yielded with the less sterically encumbered precursors under thermodynamic conditions (i.e. reflux), as exemplified by the reaction of Me2Zn (1a) with HO-NEt2 (2b). They are non-dynamic in solution, showing that a central cation is mandatory for the fluxional behaviour observed for the pentanuclear derivatives. DFT studies on the O-NMe2 series reveal that the relative energies of the pentazinc isomers become more similar with increasing RZn group size; possible conversions of these to their tetrazinc counterparts were also scrutinised. Two kappa O-3-bridged degradation products of hydroxylamide complexes could be structurally characterised. They were formed either by partial product hydrolysis, or by in situ oxygenation of the starting zinc dialkyl.