טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentNigel-Etinger Izana
SubjectEarly Transition Metal Corrole Complexes
DepartmentDepartment of Chemistry
Supervisor Professor Zeev Gross
Full Thesis textFull thesis text - English Version


Abstract

Considering the strong reducing power of early transition metals in general, it is quite surprising that the chemistry of the corresponding corrole chelates remains quite unexplored. Examples that testify for the above are: sporadic reports on titanium and vanadium corroles in their most stable oxidation states, (oxo)titanium(IV) and (oxo)vanadium(IV). The same limitation holds for the heavier congeners of group 6: there are several publications on (oxo)molybdenum(V) corrole, and a trioxo-bridged binuclear tungsten(VI) corrole which  was reported recently.  Only the chemistry of chromium corroles has been developed beyond its most stable (oxo)chromium(V) state.


This thesis focused on Cr, Mo and W corroles, while some findings on V and Ti corroles are reported in a separated appendix. Molybdenum is a very important element in the biochemistry of animals, plans and microorganisms. It is actually the only second row transition metal that has natural biological functions. The most explored molybdenum containing enzymes are nitrogenases, which catalyze the reduction of nitrogen to ammonia by a coupled reaction of transferring electrons and protons. Considering the very important chemistry of low-valent molybdenum complexes, we have decided to start our research by  exploring the limited chemistry of molybdenum corroles. This was done by first exploring a variety of methodologies for reduction of the (oxo)chromium(V) complex (tpfc)CrV(O) [tpfc = trianion of tpfc]. These studies also included the previously reported brominated corrole and the introduction of the chromium complexes of a fully chlorinated corrole, which exhibits very unique properties in comparison to (tpfc)CrV(O). 

 The acquired knowledge was used for possible adoption for the (oxo)molybdenum(V) corrole (tpfc)MoV(O). This led to full identification of two novel molybdenum(IV)corrole complexes;  the mononuclear     (tpfc-Br8)MoIVOSi(CH3)3, and a binuclear molybdenum(IV) corrole dimer. These two new  molybdenum(IV) corrole complexes open new  perspectives regarding the chemistry of molybdenum corroles.  Also introduced was a new method for preparing a fully brominated  (tpfc-Br8)MoV(O), which displayed novel spectroscopic, electrochemical and catalytic properties compared to non-halogenated (tpfc)MoV(O). One promising application of that has been explored for  both (tpfc)MoV(O) and (tpfc-Br8)MoV(O)  is their potentials as  catalysts for  electrochemical reduction of protons to hydrogen gas.


We also introduced the first tungsten corrole via full characterization of a complex that appears to be novel by being  the first 5d early-transition-metal metallocorrole and the first binuclear tungsten complex with trioxo bridge. Oxygen atom transfer to very oxophilic reagents was found to be possible, suggesting that tungsten corroles could be used as catalysts for aerobic oxidation.