| Abstract |
Two new dicopper(II) aminoalcoholate compounds, namely a discrete 0D complex [\Cu(Hdea)(H(2)dea)\(2)(mu(2)-H(2)pma)]center dot 3H(2)O (1) and a 1D coordination polymer [Cu-2(mu(2)-H(2)tea)(2)(mu(2)-nda)](n)center dot 2nH(2)O (2), were self-assembled from copper(II) nitrate, an aminoalcohol \diethanolamine (H(2)dea) or triethanolamine (H(3)tea)\ and carboxylic acid \pyromellitic (H(4)pma) or 2,6-naphthalenedicarboxylic (H(2)nda)\ building blocks. Both products were isolated as stable and water-soluble microcrystalline solids and fully characterized by IR spectroscopy, ESI-MS(+/-), elemental analysis and single-crystal X-ray diffraction, revealing distinct types of dicopper(II) units. The structures of 1 and 2 are further extended by intermolecular hydrogen bonds giving rise to 3D or 2D H-bonded nets with a pcu and sql topology, respectively. Both compounds act as efficient pre-catalysts for the mild homogeneous oxidation, by aqueous H2O2 in MeCN/H2O medium, of different cycloalkanes to the corresponding cyclic alcohols and ketones, which are obtained in up to 34\% total yields (based on alkanes). The influence of various reaction parameters such as the amount and type of pre-catalyst and acid promoter, solvent composition and substrate scope were investigated, which also show that the oxidation of cycloalkanes and the activity of a catalytic system can be restarted upon addition of new portions of oxidant and substrate. Besides, an unusual promoting role of water was found when using both pre-catalysts 1 and 2. The bond-, regio- and stereoselectivity parameters were established using different alkane substrates, supporting a free radical oxidation mechanism. The model 1/H+/H2O2 and 2/H+/H2O2 solutions were investigated by ESI-MS(+/-), allowing us to propose some possible catalytically active species. |
