Synthesis and characterization of novel metal complexes modified by O,N,O'-ligands and applications in C-C bond formation reactions

In the first part of the dissertation the synthesis and characterization of new transition metal complexes using 5-hydroxypyrayoline ligand was investigated. The 5-hydroxypyrazolines have been synthesized in good yields and characterized, and were reacted with different metal precursors (Ni, Fe, Zn, Mo and Cu) to form metal complexes, which have different coordination modes. These complexes were characterized and investigated by various techniques to clarify the coordination mode of the ligands. Most notably, in the case of a Ni complex, X-ray crystallography determined a O, N, O´-coordination in which the ligand is planar and the oxygen donors are placed in a trans-position with respect to each other, while the nitrogen donor is cis-positioned. The other coordination sites on the nickel center are occupied by the added base molecules (NH3, DMAP or phosphanes). Noteworthy, the number of the NH3, DMAP or phosphane ligands depends on the nature of the base; i. e. in the case of ammonia or phosphanes one molecule is coordinated to the nickel forming a diamagnetic square planar complex, while with DMAP an octahedral paramagnetic complex coordinated by three additional DMAP ligands was observed. On the other hand the 5-hydroxypyrazoline ligands were reacted with dimethyl zinc in a 1:1 molar ratio to form zinc complexes with a RO-Zn-Me motif. Moreover, the addition of N, N, N’, N’-tetramethylethylenediamine (tmeda) showed the formation of the first zinc-based seven-membered system with covalent bonding in the solid state. Furthermore the coordination mode of Fe, Cu and Mo complexes was also studied and flexible coordination chemistry of 5-hydroxypyrazoline ligand was investigated. In the second part of the dissertation, catalytic experiments have been performed by using Ni complexes where the structures and electronic properties were investigated. Applying the complexes as pre-catalysts in the nickel-catalyzed C(sp2)–C(sp3) cross coupling of aryl halides with benzylzinc bromides or dialkyl zinc reagents excellent yields and selectivities have been achieved. Moreover, various experiments and DFT calculations were performed to shed light on the underlying reaction mechanism. The diamagnetic nickel complexes modified by 5-hydroxypyrazoline ligand had useful NMR probes (1H, 31P and 19F) for the investigation of the reaction mechanism. Furthermore for improvement of catalytic properties of Ni complexes we have set up a straightforward catalytic system based on the Ni complex containing O, N, O’-ligands and aromatic anilines. Interestingly, by addition of primary amines the catalyst activity can be easily tuned and a significant improvement was observed. Finally the nickel-catalyzed C(sp2)–C(sp2) bond formation of a range of sulfur containing substrates with Grignard reagents via desulfurization has been explored. With a well-defined nickel complex an excellent and easy-accessible pre-catalyst was found. The obtained system was capable to convert a broad scope of substrates under mild reaction conditions.