title: Novel iron-pybisulidine catalysts for the selective aerobic oxidation and C-O/C-C cleavage of organic substrates
Creators: name: Gonzalez De Castro, Angela
Publisher: name: University of Liverpool Repository
Year: 2015

description: The selective oxidation of organic compounds is one of the most attractive transformations for both, industry and academia. Industrial interest stems from the potential application of such oxidation methodologies in the economic, greener synthesis of valuable products, whereas academic research is challenged by the difficulties in achieving specific, direct functionalisation of the “inert” CH bonds in complex molecules. In this Ph. D. thesis, our contribution to the selective oxidation of organic substrates using a novel class of iron catalysts is presented. A general introduction covering the major challenges in the area of iron-catalysed selective oxidation of organic compounds is described in Chapter 1. Chapter 2 covers the design, synthesis and coordination properties of the novel PyBisulidine type ligands, which we have conceived for their potential use in selective oxidation, attempting to overcome some of the limitations of current methods. The efficiency of such PyBisulidine ligands is demonstrated in Chapter 3, where iron-PyBisulidine complexes are used for catalysing the aerobic α-oxidation of functionalised ethers. High catalytic efficiency, very good mass balance and excellent functional group tolerance were achieved with these catalysts under mild conditions. Such advantages stem from an unconventional reaction mechanism, involving the dehydrogenative oxygenation of the ether substrate to give a peroxobisether, followed by the cleavage of the peroxy bond to form two ester molecules. Unlike metalloenzymes and biomimetic iron complexes, H2 is released as the sole byproduct during the catalytic cycle. The oxidation mechanism is discussed in Chapter 4. Like natural dioxygenases, iron-PyBisulidine catalysts were found capable of promoting the aerobic cleavage of aliphatic C-C and C-O bonds. Even though biomimetic complexes are often seen as simplified models to study enzymatic processes, a more synthetic perspective of the selective aerobic cleavage of ethereal C-C and C-O bonds is described in Chapter 5.The great potential of such cleavages in organic synthesis is well exemplified in the iron-PyBisulidine catalysed direct conversion of natural isochromans into biologically active isochromanones with excellent selectivity. The ability of the iron-PyBisulidine complexes in catalysing aerobic C-C cleavages is further expanded in Chapter 6, where the oxidative cleavage of olefinic C=C bonds to carbonyl compounds is demonstrated. The catalytic reactions proceeded efficiently, showing a broad scope and a mechanism that involves the formation of dioxetane intermediates is postulated. Chapter 7 is an extension of Chapter 6, in which iron-PyBisulidine complexes were found to catalyse α-methylstyrene linear dimerisation under an inert atmosphere. Moreover, control in the regioselectivity of the double bond in the dimers can be achieved by modifications in the PyBisulidine ligands. Final conclusions and a perspective of the research covered in this Ph.D. thesis are provided in Chapter 8.