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Date of Award
Thesis-ISU Access Only
Master of Science (MS)
Department of Chemistry
Timothy D. Lash
Porphyrins have been the focus of a great deal of research for over a century. Their importance is highlighted by their wide distribution in nature and their countless applications. Porphyrin analogues have also been the target for many investigations due to their potential to provide a greater understanding of porphyrinoid systems and because their modified properties may lead to new applications. With the goal of achieving new porphyrinoid systems, synthesis of a unique set of adj-dicarbaporphyrinoid systems were developed.
Two classes of dicarbaporphyrinoid systems were synthesized. adj-Oxo-dibenziphlorin were prepared by reacting a dipyrrylmethane dicarboxylic acid with a series of diarylketone dialdehydes using well known MacDonald `2+2' methods. The molecules were isolated as their TFA salts due to the instability of their free base structures. These unique molecules represent a cross between porphyrins and tetraoxacalixarenes. They are cross-conjugated by design and as a result do not possess 18 electron conjugation pathway. Although oxo-dibenziphlorins do not possess porphyrin-like spectral characteristics, these structures are potentially key intermediates in the synthesis of adj-dibenziporphyrins.
The second class of porphyrin analogue discussed in this study are adj-dicarbaporphyrins and a related adj-dicarbachlorin. These porphyrinoids were synthesized using a novel base-catalyzed MacDonald `2+2' route, where diindenylmethane or dicyclopentadienylmethane were reacted with a dipyrrylmethane dialdehyde in refluxing 1% potassium hydroxide in ethanol. The resulting condensation products were air oxidized to give the corresponding carbaporphyrinoid systems. Diindenylmethane gave a dibenzodicarbaporphyrin in 21% yield. This system retains highly diatropic character and a porphyrin-like UV-vis spectrum. Reaction of dicyclopentadienylmethane with a dipyrrylmethane dialdehyde gave a dicarbachlorin as the major product, and this also retained porphyrin-like characteristics and a stron diamagnetic ring current. The adj-dibenzodicarbaporphyrin also reacted with palladium(II) acetate to form an unprecedented tripalladium complex.
In addition, theoretical methods were applied to different porphyrinoid systems in order to gain a deeper understanding of their aromaticity and stability. DFT methods including B3LYP, M06-2X and B3LYP-D were deployed in order to assess the relative stability of the different porphyrinoid tautomers. In addition, NMR calculations were done using NICS (Nucleus Independent Chemical Shift) calculations. The results helped highlight aspects of porphyrinoid chemistry that were otherwise difficult to explain. The results also allowed conclusions to be drawn about the stability of porphyrin analogues and may be beneficial in assessing the feasibility of synthesizing new porphyrinoid systems.
AbuSalim, Deyaa, "Synthesis of Novel Adj-Dicarbaporphyrinoid Systems and Theoretical Investigations into Porphyrinoid Aromaticity and Stability" (2014). Theses and Dissertations. 207.