From Ligand Design to Lactide Polymerisation Catalysis -A study on novel polydentate bis(pyrazolyl)methanes and their Fe(II), Cu(II) and Zn(II) complexes

On the long road of tridentate bis(pyrazolyl)methane ligand and complex design, this thesis goes one step further in tackling the issue of the bisfacial coordination mode, accompanied by possible 3,5-isomerisation processes in the ligands, and its influence on the catalytic abilities of bis(pyrazolyl)methane complexes. A number of different approaches in ligand development were tested to overcome the bisfacial coordination. A first successful approach was the implementation of a homogenous 3,5-functionalisation that solves the problem of isomerisation. The ligands HC(3,5-MePz)2(Py), HC(3,5-PhPz)2(Py) and HC(3,5-EtPz)2(Py) where synthesised by modulating the reaction conditions of already known synthetic routes. In addition, the ligand HC(3,5-iPrPz)2(Py) was designed and is the result of a novel route to bis(pyrazolyl)methane ligand synthesis. A large number of complexes with these ligands and Fe(II), Cu(I), Cu(II) and Zn(II) were obtained and fully characterised. The molecular structures show that the increasing sterical demand of the ligands leads to non-bisfacial complexes. Besides, interactions between the ligands' size and the spin state of the complexes, which influences the geometry in addition to sterical effects, were observed by SQUID measurements. NBO calculations were performed with bisfacial Fe(II) bis(pyrazolyl)pyridinylmethane complexes containing monofunctionalised pyrazolyl units. These calculations focus on the size and the position of the functional groups and the impact on ligand-metal interactions. The second successful approach was the establishment of tetradentate bis(pyrazolyl)bipyridinylmethane ligands as a new subgroup to this family of ligands. The newly developed ligands HC(Pz)2(Bipy), MeC(Pz)2(Bipy), HC(3,5-MePz)2(Bipy) and HC(3-tBuPz)2(Bipy) allow for two possible active sites, that cannot be occupied by a second ligand. Again, a large number of complexes with these ligands in combination with Fe(II), Cu(II) and Zn(II) were synthesised and characterised. In addition, the ligand MeC(Py)2(Bipy) was developed and successfully applied in complex syntheses. All obtained Fe(II) complexes are in the high spin state. A common feature of all these complexes is a bipyridinyl unit with various modes of distortion.A selection of Fe(II) and Zn(II) complexes with bis(pyrazolyl)bipyridinylmethane ligands were tested as successful catalysts in the solvent-free ring-opening polymerisation of rac-lactide. The selected Fe(II) complexes are the first Fe(II) catalysts with neutral ligands, that do not rely on alkoxide counterions. These catalytic tests include a range of investigated features. A higher water content leads to a faster polymerisation, but decreases the molecular masses of the obtained polymers. Furthermore, the methylation of the ligand and stronger coordinating counterions result in decelerated reaction rates. On the other hand, a switch from Fe(II) to Zn(II) does not exhibit any influence. Furthermore, steady state N and Fe K-edge XAS experiments as well as transient Fe K-edge XAS studies were conducted for the bisfacial ls complex [Fe{HC(3,5-MePz)2(Py)}2](CF3CO2)2 and the hs complex [Fe{HC(Pz)2(Bipy)}Cl2]