Coordination–driven encapsulation of transition metal complexes in molecular capsules and their application in hydroformylation and proton reduction catalysis

Traditional homogeneous catalysis applies catalysts based on organometallic complexes which are tuned by changing the metal and/or the ligands that are coordinated to it. Catalyst-substrate interactions which dictate the outcome of a reaction occur solely on the metal, i.e. the ‘first coordination sphere’. Catalysts of nature, ‘enzymes’, serve as a source of inspiration due their inherently high activity and selectivity in selected catalytic transformations. The success of enzymes lies in their use of a larger toolbox to steer the outcome of reactions compared to traditional homogeneous catalysts. Confinement of the active site in a bulky second coordination sphere is key, resulting in a local microenvironment radically different from bulk solution. In this thesis, the effect of synthetic second coordination spheres on encapsulated rhodium-based catalysts and bio-inspired hydrogenase mimics is studied. Chapter 2 reports on the encapsulation of a rhodium complex in a supramolecular assembly, resulting in a catalyst that displays unprecedented branched selectivity in the hydroformylation of propene. Chapter 3 discusses the first example of substrate–selective hydroformylation of terminal alkenes by a rhodium catalyst encapsulated in a metal-organic cage. Chapter 4 elaborates on the design of a biomimetic and fully base–metal photocatalytic system for photocatalytic proton reduction. Chapter 5 reports a new tetrahedral porphyrin–based M₄L₆ cage that selectively encapsulates an iron-iron hydrogenase mimic and thereby decreases its catalytic overpotential by 150 mV. Chapter 6 shows the design and synthesis of a novel supramolecular cage-based functional rotaxane.