Pyrazolone-based metal complexes: synthesis, characterization and theoretical study of Zn(II), Cu(II) and Mo(IV) derivatives

4-acyl-5-pyrazolones are a class of compounds that combine the properties of the pyrazolone ring with that of diketones, affording an O,O-chelating ligand with biological features. Since the first synthesis by Jensen in 1959 they have been the subject of a multitude of studies concerning their tautomeric forms, their biological properties, and their coordination chemistry towards a variety of metal centres. Furthermore, the readiness of the structural modifications they can undergo pushed researchers to explore many different variations tailoring the substituents to optimize their coordination with the metals and to vary their properties. In particular, one interesting variant of 4-acyl-5-pyrazolones is obtained by condensation with hydrazine or amine to afford N,O-chelating Schiff base ligands. This class of ligands retains all the characteristics of their synthon and additionally, they show enhanced coordination features due to the presence of one or more nitrogen atoms. In Chapter 1 an introduction to these compounds is reported together with a comprehensive state-of-the-art of their metal complexes, involving zinc, copper, and molybdenum. Chapter 2 deals with the synthesis and characterization of Schiff base ligands and the study of their tautomerism in solid state and solution. The ligands have then been utilized to synthesize the respective zinc(II) complexes of composition [Zn(HLn )2], they were fully characterized and the structures of two ligands and three complexes were determined by X-ray diffraction, showing that complexes 1 and 2 have a monomeric nature, while complex 4 exists as one-dimensional coordination polymer. DFT calculations on proligands, anions and complexes were exploited to confirm the experimental result and rationalized the polymeric nature of complex 4 and the presence of two water molecules coordinated on complexes 3 and 5. The antimicrobial activity of the compounds was investigated against Escherichia coli and Staphylococcus aureus. Complexes 4 and 5 demonstrated good efficiency, the latter probably for its ligand containing aliphatic and fluorinated substituents. Similarly, in Chapter 3 two hydrazone ligands were synthesized, characterized and reacted with Zn(II) and Cu(II) affording four complexes of formula [Zn(HL1 )2(MeOH)2], [Cu(HL1 )2], and [M(HL2 )2]. DFT and XRD studies determined that the free proligands exist in the NH,NH tautomeric form, [Zn(HL1 )2(MeOH)2] has an octahedral geometry with two apical methanol molecules, [Cu(HL1 )2] adopts a square planar geometry, and the two [M(HL2 )2] are octahedral with the ligands acting as tridentate O,N,N-donors in planar conformation. All the compounds were tested against the parasite Trypanosoma brucei and Balb3T3 cells obtaining powerful results, from the ligand H2L 1 and its Zn complex, showing a high selectivity index. For this reason, the mechanism of action of these two compounds has been investigated, indicating a strong impact on the CTP (cytidine triphosphate) pools, making it likely that CTP synthetase is the targeted enzyme. Chapter 4 is focused on the theoretical study of the mechanism of molybdenum-catalyzed deoxydehydration (DODH) of vicinal diols to alkenes. The mechanism has been investigated employing DFT calculations and considering [Mo(O)2(QMe)2] as a catalyst, where QMe is an O,O-donor pyrazolone-based ligand, and PMe3 as a reductant. Two different pathways have been analysed differing in the order of the main steps of the reaction. The lowest energy profiles were calculated for both, and the data obtained suggest that the second pathway is energetically preferred. Finally, In Chapter 5, a list of activities aimed at improving the efficiency of the processes of TechPol srl, a company active in the field of technopolymer molding, is reported. The activities carried out have optimized the use of recycled materials in a circular economy perspective, investigating the nature of the problems encountered and confirming that the main cause was the material used.