Synthesis And Properties Of Manganese Corroles With Peculiar Electronic And Steric Features

Study on corrole macrocycle is one of the most active branches of modern porphyrinchemistry. The most extensively studied metallocorroles are the manganese corroles becauseof their ability to catalyze various chemical reactions such as azirdination, hydroxylation,asymmetric sulfoxidation, and oxygen atom transfer reactions. The most intriguing chemistryof manganese corroles is the nature of active intermediates responsible for oxygen atomtransfer in the catalytic oxidation of organic substrates. Importantly, the factors controlling thereactivity of manganese corroles are still not fully understood. To explore the effects ofelectronic and steric features of manganese corroles on the catalytic oxidation reactions, thispiece of research work is focused on the synthesis of electron-poor, electron-rich, andsterically hindered manganese corroles as well as the reactivity of their manganese(V)-oxocomplexes in oxygen atom transfer reactions to alkene. The main work of this thesis ishighlighted below:This work has developed a novel, efficient and easily reproducible method for thesynthesis of sterically encumbered multibrominated corroles in up to12%yields based on theuse of BF3Et2O catalyst. By using this method, multibromo corroles (3a,3b,3c) startingfrom2,6-dibromobenzaldehyde and2,6-dibromo-4-fluorobenzaldehyde have been prepared.An improvement for the synthesis of bulky bis-pocket corrole (TTPPC) based on TFAcatalyzed condensation of equimolar amounts of triphenylbenzaldehyde and pyrrole indichloromethane was also achieved in up to10-15%yield.A one-pot, direct synthesis of A3-type unsymmetrical porphyrin (4a) was achieved viaconventional TFA catalyzed condensation of pyrrole and para-dimethylaminobenzaldehyde indichloromethane. It was found highly specific for para-dimethylaminobenzaldehyde givingA3-type unsymmetrical porphyrin. This is the first report of one-pot access to an electron-richunsymmetrical porphyrin, which is a useful precursor for post-functionalizations.Seven A3-and trans-A2B manganese(III) corroles (1-7-Mn) based on meso-substitutionwith pentafluorophenyl,4-bromophenyl,2,6-dibromophenyl,2,6-dibromo-4-fluorophenyl,phenyl, and4-cyanophenyl were synthesized. β-pyrrole-brominated manganese(III) corroles(1a-7a-Mn) were also prepared to investigate the effects of β-bromination. All manganese(III)corroles were well characterized by UV-vis, MS, electron-paramagnetic resonance (EPR)spectroscopy and cyclic voltammetry. The characteristics Soret and Q-bands in (1-7-Mn)were red shifted upon β-bromination in (1a-7a-Mn). In cyclic voltammetry, a positive shift ofoxidation potential from (1-7-Mn) to (1a-7a-Mn) was observed. EPR spectra indicated+3 oxidation states in all investigated manganese(III) corroles.(oxo)manganese(V) corroles1-7-Mn(oxo) and1a-7a-Mn(oxo) were prepared byreaction of corresponding manganese(III) complexes with iodosylbenzene (PhIO) andcharacterized by UV-vis spectra and ESI/HRMS. The most notable UV-Vis differences werethe appearance of MnV≡O peak at350-360nm in1-7-Mn(oxo) and at about380nm in1a-7a-Mn(oxo) and the appearance of a broad band near500nm. DFT calculations indicateda significant decrease in the HOMO-LUMO energy gaps in all β-pyrrole-brominated(oxo)manganese(V) corroles1a-7a-Mn(oxo) than1-7-Mn(oxo), in accordance with theobserved red-shifted UV-vis spectra upon β-bromination.The stability of (oxo)manganese(V) corroles1-7-Mn(oxo) and1a-7a-Mn(oxo) wereinvestigated by their UV-vis spectroscopy. The self-decay rate constants in toluene were in thefollowing order:1-Mn(oxo)>2-Mn(oxo)>7-Mn(oxo)>4-Mn(oxo)>3-Mn(oxo)>6-Mn(oxo)≈5-Mn(oxo), i.e., electron-poor (oxo)manganese(V) corroles decayed faster thanelectron-rich corroles, and sterically protected (oxo)manganese(V) corroles were more stablethan less sterically protected corroles. Similar self-decay order was observed for1a-7a-Mn(oxo). The pseudo-first-order rate constants for the oxygen atom transfer from(oxo)manganese(V) corroles to styrene was found to be the following:1-Mn(oxo)>2-Mn(oxo)>7-Mn(oxo)>4-Mn(oxo)>3-Mn(oxo)>6-Mn(oxo)≈5-Mn(oxo). The samereactivity order was observed for their β-brominated analogues1a-7a-Mn(oxo), but theirreactivity was remarkably higher than β-nonbrominated counterparts. This order suggestsdirect oxygen atom transfer from (oxo)manganese(V) corroles to styrene in all these cases.The observed difference in the reactivity is correlated with the electronic and steric features ofcorrole macrocycle.