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Deprotonation of cationic azo dyes results in the formation of aminyl biradicals., The synthesis of the industrially important polymer parylene is achieved by polymerization of p-quinodimethane (p-QDM). The polymerization is thought to proceed via a biradical p-QDM dimer, but isolation or characterization of such a biradical has remained elusive. Here, we describe the synthesis of an aza-analogue of this p-QDM dimer. The biradical is formed by base-induced dimerization of an azoimidazolium dye. Due to the presence of sterically shielded aminyl radicals instead of terminal H2Ċ groups, the stability of this dimer is sufficient for analyses by ESR spectroscopy and X-ray crystallography. A similar Csp3–Csp3 coupling was observed for an azotriazolium dye, suggesting that base-induced C–C coupling reactions can be realized for different types of azo dyes.

We report the use of two earth abundant molybdenum sulfide-based cocatalysts, Mo(3)S(13)(2-)clusters and 1T-MoS2 nanoparticles (NPs), in combination with the visible-light active metal-organic framework (MOF) MIL-125-NH2 for the photocatalytic generation of hydrogen (H-2) from water splitting. Upon irradiation (lambda >= 420 nm), the best-performing mixtures of Mo3S132-/MIL-125-NH2 and 1T-MoS2/MIL-125-NH2 exhibit high catalytic activity, producing H-2 with evolution rates of 2094 and 1454 mu mol h(-1) g(MOF)(-1) and apparent quantum yields of 11.0 and 5.8% at 450 nm, respectively, which are among the highest values reported to date for visible-light-driven photocatalysis with MOFs. The high performance of Mo3S132- can be attributed to the good contact between these clusters and the MOF and the large number of catalytically active sites, while the high activity of 1T-MoS2 NPs is due to their high electrical conductivity leading to fast electron transfer processes. Recycling experiments revealed that although the Mo3S132-/MIL-125-NH2 slowly loses its activity, the 1T-MoS2/MIL-125-NH2 retains its activity for at least 72 h. This work indicates that earth-abundant compounds can be stable and highly catalytically active for photocatalytic water splitting, and should be considered as promising cocatalysts with new MOFs besides the traditional noble metal NPs.

This thesis describes the syntheses of novel boronate ester-capped clathrochelate complexes and their application in supramolecular chemistry, materials science, and chemical biology. Chapter 2 shows the synthesis of long Fe(II) dinuclear clathrochelates, up to 3 nm, with low synthetic effort. Their ability to be used as building blocks in supramolecular chemistry is evidenced by the formation of a Cu4L4-type coordination cage, and by the formation of a 2-dimensional metal-organic framework (MOF). The incorporation of clathrochelate complexes with terminal pyridyl groups into pillared MOFs by using solvent-assisted ligand exchange is described in Chapter 3. The strong basicity of clathrochelates with pyridyl groups makes them particularly suited for this approach. In Chapter 4, the structural characterization of novel cobalt clathrochelates is described. A first example of a Co(II) clathrochelate with potentially redox non-innocent phenanthrenequinone dioximato groups is reported. Chemical reductions of cobalt clathrochelates were carried out, and ligand effects are investigated by crystallography. Moreover, in the Chapter 5, clathrochelates with elongated π–dioximate groups are described, along with preliminary attempts of using them as three-way junction (TWJ) stabilizers. The synthesis of clathrochelate complexes with a chiral dioximato ligand and terminal pyridyl, bromo or carboxylic acid groups are described in Chapter 6. Potential applications of this new metalloligand in supramolecular chemistry are investigated.