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Abstract

The first part (Chapter 1) of this dissertation focuses on designing functional metal-organic frameworks (MOFs) by decorating the bridging ligand with orthogonal moieties terminated with succinic acid (MOF-SA) and maleic acid (MOF-MA). Structural analysis of MOF-SA provides the first direct evidence for 8-connected secondary building units (SBUs) in UiO-type MOFs. In contrast, MOF-MA contains 12-connected SBUs as seen in the traditional UiO MOF topology. The reduced connectivity results in MOF-SA with a larger pore aperture and more accessible metal-binding sites located at the termini of the orthogonal functionalities. The highly porous MOF-SA is an excellent fluorescence sensor for metal ions with a detection limit of <0.5 ppb for Mn2+ and three to four orders of magnitude greater sensitivity for metal ions than previously reported luminescent MOFs. , The second part (Chapters 2 and 3) of this dissertation focuses on designing MOFs with multiple precisely-spaced catalytic sites for cooperative catalysis. In Chapter 2, we synthesized porous and interpenetrating In-MOFs with strategically placed CoIII(porphyrin) active sites for efficient cooperative hydration of terminal alkynes via dual substrate activation. In Chapter 3, we encapsulated a Ni-containing polyoxometalate (POM) into two highly stable and porous phosphorescent MOFs. The proximity of POM to multiple photosensitizers in POM@MOFs allows for facile multi-electron transfer to enable efficient visible-light driven hydrogen evolution reaction (HER) with turnover numbers (TONs) as high as 1476. Photophysical and electrochemical studies established the oxidative quenching of the photosensitizer excited state by POM as the initiating step of HER, explaining the drastic catalytic activity difference between the two POM@MOF systems., The third part (Chapters 4 and 5) of this dissertation focuses on the development and use of two-dimensional (2D) metal-organic layers (MOLs) as single-site solid catalysts for various organic transformations. Although many research efforts have been devoted to designing MOF catalysts with interesting catalytic activities and selectivities by taking advantage of the site-isolation effect, the diffusion of substrates and products through the framework remains a significant issue for MOF catalysts. This diffusion constraint can be relieved by reducing one dimension of the MOF crystals to afford a new category of 2D materials, MOLs, that are only a few nanometers thick, minimizing diffusion distance. In Chapter 4, we developed a highly scalable bottom-up strategy to assemble MOLs directly from molecular building blocks in one-pot solvothermal reactions. The MOLs were functionalized with Fe-terpyridine catalytic centers to give diffusion-free single-site solid catalysts for the hydrosilylation of terminal olefins. In Chapter 5, we synthesized a terpyridine-based TPY-MOL and metalated TPY-MOL with CoCl2 and FeBr2 to generate M•TPY-MOL (M = Co or Fe) catalysts for benzylic C-H borylation and Csp3-H amination reactions. Interestingly, M•TPY-MOL catalysts showed significantly higher activity and different chemo-selectivity than homogeneous MOF controls. Spectroscopic studies and DFT calculations indicated the formation of unprecedented MOL-stabilized MII-(TPY••)2- species featuring divalent metals and TPY diradical dianions. We believe that the formation of novel MII-TPY•• species endows them with unique and enhanced catalytic activities in Csp3-H borylation and intramolecular Csp3-H amination reactions.

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