Small Molecule Activation by Metalloporphyrin Complexes Isolated within Metal-Organic Frameworks

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Contained in the following dissertation are detailed investigations regarding the thermodynamics of small molecule activation by metalloporphyrin complexes isolated within metal-organic frameworks (MOFs). Chapter 1 provides a description of the role metalloporphyrin complexes play in biological systems and the challenges associated with studying small molecule activation by metalloporphryin sites in both the protein’s native structure as well as molecular model complexes. This chapter culminates with a description of how an alternative material platform, a MOF, offers the opportunity to access species that have confounded isolation and thorough investigations in molecular form. Chapters 2 and 3 focus on the study and characterization of low-coordinate metalloporphyrin O2 adducts featuring iron and cobalt, respectively. Importantly, these results provide the first structurally-characterized five coordinate Fe–O2 and Co–O2 porphyrin species, further highlight the importance of axial ligation in biological O2 transport and storage, and demonstrate the ability of a MOF to enable isolation and study of species that are highly unstable in molecular form. Chapter 4 employs the same approach to isolate a four-coordinate manganese(II) porphyrin complex and examine its reactivity with O2 using a myriad of characterization techniques. X-ray diffraction experiments reveal for the first time a peroxomonaganese(IV) porphyrin species, which exhibits a side-on, 2 binding mode. Further, quantification of the interaction of O2 with manganese(II), iron(II), and cobalt(II) porphyrin complexes demonstrate that O2 binding enthalpy increases with increasing reductive capacity of the MII/III redox couple. Chapter 5 details the comprehensive characterization of highly-labile carbonyl adducts of cobalt porphyrin complexes. Importantly, this work provides the first crystallographic characterized example of a noniron first-row transition metal porphyrin complex. The combination of these four chapters provides not only key biological insight regarding the thermodynamics of small molecule activation by metalloporphryin centers, but also, unprecedented characterization, particularly in the form of single crystal X-ray diffraction analysis, of species that have only been observed transiently in molecular form. Chapters 6 and 7 suggest next directions in the form of potential synthetic-pathways that can lead to the isolation and study of reactive metalloporphyrin complexes capable of carrying out group atom transfer chemistry. The combination of the results reported herein demonstrate that the sequestration of metalloporphyrin moieties within the solid-state architecture of MOFs provides access to a wide a range of novel coordination complexes.

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  • 01/10/2019
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