טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMarina Malka Raizman
SubjectMolybdenum Corroles
DepartmentDepartment of Chemistry
Supervisor Full Professor Gross Zeev


Abstract

Corroles are tetra-pyrrolic macrocycles of potential biological importance, due to their similarity to porphyrins in hemoglobin, chlorins in chlorophylls and corrins in vitamin B12. There are many recent reports about applications based on  5, 10, 15 - tris(pentafluorophenyl)corrole, H3(tpfc), among them catalytic activities and affinity to carcinogenic cells. 

The first part of this research deals with application of corroles as photo-catalysts. The TON (mol of product / mol of catalyst) value of cyclohexene oxidation by the combination of molecular oxygen and light was selected as a model reaction for estimating the effectiveness of the complexes to serve as catalysts. The influence of different metals (transition and non-transition) and modifications on the corrole ring was the focus of the investigations. All results were successfully explained by the “heavy atom effect”, affecting intersystem crossing from singlet to triplet excited states.

During this research, a new complex of corrole was prepared: the (oxo)molybdenum corrole - (tpfc)Mo(O). Molybdenum enzymes participate in reduction and oxidation of sulfur containing compounds and nitrogen reduction to ammonia (nitrogenase). Chemical research in this field is aimed to produce nitrogenase activity by inorganic molybdenum complexes. In light of this, the second goal of this research was the rational synthesis and full characterization of the new molybdenum corrole complexes. The  (oxo)molybdenum(V) corroles - (tpfc)Mo(O) (3) and (tdcc)Mo(O) (4) were successfully characterized by a variety of methods, including the structural characterization of 3 by X-ray crystallography. This revealed a highly domed corrole with a very large out of plane displacement (0.73 Å) of the metal.

 The d1 electron configuration of the (oxo)molybdenum(V) complexes enables easy characterization by EPR.  The electrochemical research (cyclic voltammetery) of the molybdenum complexes led to the conclusion that the reduction is metal- centered. Several attempts to produce molybdenum complexes in lower oxidation state were performed, which were not successful because of demetalation of the reduced complex. But, the reaction of (oxo)molybdenum(V) corroles with hydrochloric acid led to new complexes:  [(cor)MoV(OH)]+ and (cor)MoV(Cl)(OH).

All together, this work uncovered the variables important for applying metallocorroles as photo-catalysts and some unique chemistry of molybdenum corroles.