Shape-Persistent Multimetallic Cartwheel Complexes: Design, Catalysis and Recycling

Abstract

An important new research area in the field of homogeneous catalysis is the development of catalytic processes which combine the advantages of homogeneous (high activity/selectivity, mild conditions, reproducibility, good catalyst description) and heterogeneous catalysis (easy catalyst recycling, low catalyst quantities, high total turnover number (ttn)). A promising approach to achieve this, is by applying nanofiltration technology: adjusted homogeneous catalysts are applied in a membrane reactor and recycled in situ, even allowing catalytic reactions under continuously operating conditions. This leads to a significant increase in the total turnover number of the catalyst. Due to the very small pore-sizes in the membranes, macromolecules with sizes between 0.5 and 8 nanometers can be retained in solution by applying nanofiltration technology. To create homogeneous catalysts which possess the dimensions needed for efficient retainment by nanofiltration membranes, it is necessary to anchor catalytically active transition-metal complexes to soluble macromolecular supports. This thesis describes the design and synthesis of shape-persistent nanosize multi(pincer-metal) complexes containing linear, flat or three-dimensional geometries. In particular, these complexes were studied in a nanofiltration membrane reactor in order to investigate the influences of shape-persistence, dimension and geometry on the retention of these compounds by nanofiltration membranes. Furthermore, these macromolecular complexes were tested as homogeneous catalysts in different organic transformations. One example is given in which a shape-persistent nanosize complex is applied as a homogeneous catalyst in a nanofiltration membrane reactor under continuous reaction conditions. In this research, aromatic supports were chosen for the macromolecular complexes since it assures a high rigidity (shape-persistence) as well as a high inertness toward many reagents, allowing a versatile use as homogeneous catalyst for diverse organic reactions. A further objective of this work was to investigate whether these highly symmetric (C3- or D3-symmetry, as a result of the aromatic backbone and the substitution pattern) macromolecular materials could be used as supramolecular templates in the selective construction of large heterocycles, using olefin metathesis as the ring-closing reaction.