The main goal of master's thesis was the optimization of the synthesis of a planar
palladium complex, bearing two Py-tzNHC ligands. In the first step the starting azide was
formed, which reacted in a ‘click’ reaction with desired alkyne into the appropriated
triazole. In the next step pyridine nitrogen was oxidized into N-oxide using biphasic system
chloroform-water. Peroxyacetic acid was used as an oxidant, which was formed in situ
between hydrogen peroxide and acetic acid in the presence of catalytic amounts of
sulphuric(VI) acid. Oxidation was followed by methylation of the triazole ring at position
N3. In addition to the nitrogen at the triazole ring, pyridine N-oxide atom was also
methylated. N–O bond cleavage in the subsequent step was achieved by using activated
zinc in the presence of NH4BF4 to afford a pyridine-functionalized triazolium
tetrafluoroborate, which served as a ligand in the preparation of the desired mesoionic
palladium complex. For the preparation of targeted complex, PdCl2 was chosen as the
palladium source in the presence of Cs2CO3 as a base. One ligand coordinated in a
bidentate, and the other in monodentate fashion. To achieve bidentate coordination of both
ligands, the abstraction of chloride ion from the metal centre had to be performed, which
was achieved by using AgBF4. With that the desired mesoionic palladium(II) complex,
broadly used as a versatile catalyst for various cross-coupling reactions, was successfully
synthesized under optimized reaction conditions.
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