Pyrazolat-liganden mit zwei facial tridentaten Koordinationstaschen - Metallkomplexe und erste Reaktivitätsuntersuchungen

Abstract

In the aim of synthesis of model complexes for active core of type 3 copper proteins a novel ligand system was developed. Chief characteristic are two facial tridentate coordination pockets of this pyrazolate based ligands. In 3- and 5-position of the pyrazole ring are functionalized side arms with two substituted imidazole rings. A better imitation of the (His)3-coordination of copper ions in biological systems should be guaranteed. During the present work six different ligands and also numerous copper(II) complexes were synthesized and their structure clarified by X-ray crystallography. In use of copper acetate a dinuclear copper complex LCu2(OH)(OAc)2 was built. One imidazole ring is turned away and so coordination to the metal ion isn´ t possible. Out of this square planar coordination environment results for both copper(II) ions which are bridged by the pyrazolate unit and a hydroxyl function. If copper sulfate was used a staircase like tetranuclear complex was formed. The same coordination behavior was observed. Again one imidazole ring each ligand side is turned away and didn´t coordinate to the corresponding copper ion. In the case of the inner copper ions ligands are crossed and so an imidazole ring is connected to the neighboring copper ion. This motif can also be found if copper nitrate, copper perchlorate or copper tetrafluoroborate are used. But in those cases tetranuclear copper(II) complexes with square arrangement of the metal ions are formed. On both ligand sides free imidazole rings bound to the neighboring metal ions. Magnetic investigation of all copper(II) complexes shows a very strong antiferromagnetic coupling of the pyrazolate bridged copper ions. Besides first synthesis of copper(I) complexes of this ligand was done and by use of co ligands (X) like PMe3, n-butylisonitrile or 2,6-dimethylphenylisonitrile complex structure could be solved by x-ray crystallography. Always tetranuclear complexes of type [(LCu2X)2]2+ are formed and the copper(I) ions have a trigonal planar coordinati! on envir onment. By means of in situ generated copper(I) complexes investigations of the reactivity towards oxygen and carbon dioxide were carried out and followed be UV/Vis spectroscopy. The formation of intermediate stages couldn´t be detected and so no reactivity was observed. For all investigations at various conditions the corresponding copper(II) complexes are formed. Novel ligands were also used for the complex synthesis with various nickel salts. Some nickel complexes of the type L2Ni3X4 are formed where the central nickel ion has an octahedral coordination environment. Outer nickel ions shows different coordinations like octahedral, square bipyramidal or tetrahedral. In case of nickel complex with tetrahedral coordination environment ferromagnetic coupling between two pyrazolate bridged nickel ions was observed for the first time.