|Ph.D Student||Aviv Iris|
|Subject||Catalysis Based on Unique Coordination|
Chemistry of Metallocorroles
|Department||Department of Chemistry||Supervisor||Professor Zeev Gross|
|Full Thesis text|
Corroles are tetrapyrrolic macrocycles, who belong to the pophyrinoid family that includes also porphyrins, corrins and chlorins. The 1999 discoveries of facile methodologies for the synthesis of 5,10,15-triarylcorroles and the corresponding metal complexes allowed for their utilization in various fields: catalysis, sensing of gaseous molecules and medicine-oriented research. This thesis uncovered the capability of rhodium and iron corrole complexes as catalysts for the insertion of a carbene moiety from diazo compound into the C-H bonds of allylic hydrocarbons, the O-H bonds of alcohols, and the N-H bonds of amines. The most unique results were obtained for insertion of diazo compound into the N-H bonds of various amines, leading to doubly protected a-amino acid derivatives. Iron corroles and iron porphyrins were found to display most unique features: full and very fast conversion was obtained by simultaneous addition of equimolar amounts of the substrates to the catalysts (0.1 mol%); the selectivity toward activation of the NH bonds was absolute; and the reaction was complete within seconds. Iron complexes were used for this application for the first time (all previously reported catalysts are based on Rh, Ru, Cu, and Au), and discovered to be truly outstanding catalysts for N-H insertion reactions. The success with amines served as the basis of a much more challenging reaction: the use of ammonia as the nitrogen atom source in the synthesis of the two smallest amino acids; glycine and alanine. This may be considered as a N-H activation process, which is extremely rare for ammonia. The success was limited with the iron corrole, but iron porphyrins were found to be excellent catalysts for that purpose. This is indeed the first reported catalytic system for the synthesis of non-protected amino acid esters from diazoacetates. In an attempt to extent the reactions toward asymmetric catalysis, the heme-containing protein, myoglobin, and albumin-conjugated iron-corrole were utilized. Both approaches worked in the sense of catalyzing the reactions of amines with diazo compounds in aqueous solutions at physiological pH. Enantiomerically enriched products were however not obtained, most likely because of mechanism-based reasons and not because of poor chiral induction by the protein. Quite detailed mechanistic investigations were carried out and the results suggest that the commonly proposed metallocarbene intermediates are not involved in catalysis.