Organometallic chemistry of metalloporphyrins and their applications in aqueous controlled radical polymerization

Cobalt, rhodium, iridium porphyrins react with dihydrogen, carbon monoxide and olefins to form a diverse range of complexes including metal hydrides, metaloformyl and organometallic species. One of the central objectives of this project has been to explore the scope of organometallic transformation mediated by cobalt, rhodium and iridium porphyrins.; The first part of this thesis describes the reaction of cobalt porphyrins with dihydrogen, alkyl halide and radicals in aqueous media. A series of water-soluble cobalt porphyrin and their organometallic derivatives are synthesized and utilized in the investigation of controlled radical polymerization. The equilibrium between (TMPS)Co_II• and methacrylic type radicals successfully controls the radical polymerization of acrylic acid in water and (TMPS)CoII• catalyzes the chain transfer radical polymerization of methyl methacrylic acid and 2-hydroxyl ethyl methylacrylate in water media. The relationship between the ligand systems and the ability to catalyze chain transfer is investigated and discussed.; The second part of this thesis is focused on mechanistic investigations of chain transfer radical polymerization in water and in organic media. An increase in the average degree of polymerization that is observed during polymerization process is inconsistent with currently accepted CCT mechanism. A series of factors related to the kinetics of chain transfer radical polymerization are studied and the kinetic origin is explored experimentally and from kinetic simulations.; The third part of this thesis focuses on the formation of iridium/rhodium porphyrin metal-centered radicals and the investigations of their reactions with olefin and alcohol substrates and the relationship of reaction products with ligand environment. A series of iridium(II) porphyrin metallo-radicals with various steric requirements are synthesized from photolysis of methyl iridium porphyrin compounds. The dependence of their reactivity with olefins to form bridge or π-complexes on steric demands is evaluated. A series of cationic rhodium porphyrin with weak coordinating anions were prepared and observed to react with olefin rapidly to form alkyl or π-complexes. The reaction product is related to the counter anions. Reaction of β-hydroxyl alkyl rhodium porphyrin complexes with “super acid” is another facile pathway to form π-complexes.