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Abstract:
The investigations conducted in this master thesis have led to the finding of the ligand pzbpy, capable to promote the nickel-catalyzed OAT from the pollutant N2O to aryl halides generating phenols and environmentally benign N2 in high yields.
Exploration of a series of pzbpy derivatives revealed that position 3 of the pyrazolyl ring in pzbpy had to remain unsubstituted to deliver good yields in catalysis. The ligand’s performance was affected negatively when electron-withdrawing groups were introduced, as well as when the peripheral pyridine was eliminated and when the pyrazole ring was substituted by a thiophene ring.
X-ray analysis of Ni(pzbpy)Br2 showed pzbpy coordinating to the nickel center in a tridentate mode. This compound was moreover found capable to catalyze the OAT from N2O to 4-iodofluorobenzene.
The synthesis of the pzbpy ligand was improved to an overnight reaction and reliable purification via column chromatography. Thus, the ligand can be accessed in a shorter period of time in higher purity from affordable commercial reagents.
The presence of impurities in the originally used batch of commercial terpy was confirmed. OPPh3 and a pyridine-tetramer isomer were detected, while an unidentified impurity with a mass weight of 228, and unknown aluminium and silicon species were also found.
Formation of N2 was confirmed via GC analysis of the headspace of the reaction. The phenol yield of a series of substrates was found to correlate linearly with the produced N2.
The salt metathesis reaction of Ni(terpy)Br with NaOMes afforded one set of paramagnetic signals in the 1H NMR spectrum. Unfortunately, such a species could not be observed for the reaction of [Ni(terpy)Mes]Br with the tested reductants. Nonetheless, it might be accessible using zinc as the reductant from a related [Ni(terpy)Mes]X species bearing a non-coordinating counterion.
