To provide a better understanding of the reactions of iron and copper proteins with dioxygen, the corresponding reactions of small molecule model complexes with dioxygen were analysed using spectroscopic and kinetic methods. Special attention focused upon the binding and activation of dioxygen by iron proteins such as hemerythrin (Hr) and protocatechuat-3,4-dioxygenase (3,4-PCD) and by copper proteins like hemocyanin (Hc) and tyrosinase.
Iron complexes of the ligand tmpa (tmpa = tris[(2-pyridyl)methyl]amine, also known as tpa in literature) were synthesised and modifications of the tmpa ligand were made. Increasing as well as decreasing chelate ring sizes in the highly active complex [Fe(tmpa)(dbc)]B(C6H5)4 (dbc = 3,5-di-tert-butylcatecholate dianion), only resulted in decreased reactivity of the investigated compounds. A detailed low-temperature stopped-flow investigation of the reaction of dioxygen with [Fe(tmpa)(dbc)]B(C6H5)4 was performed and activation parameters of Delta H# = 23 +- 1 kJ mol-1 and Delta S# = -199 +- 4 J mol-1 K-1 were obtained. Crystal structures of bromo-(tetrachlorocatecholato-O,O')(bis((2-pyridyl)methyl)-2-pyridylamine-N,N',N'')-iron(III) (2), (mu-oxo)-bis(bromo)(bis((2-pyridyl)methyl)-2-pyridylamine-N,N',N'',N''')-diiron(III) (3), dichloro-((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N'',N''')-iron(III) (4) and (tetrabromocatecholato-O,O')((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N'',N''')-iron(III) (5) are reported (Chapter 2).
Besides altering the chelate ring size the influence of the donor atoms of the ligand on catechol dioxygenase reactivity was investigated. Two derivatives of the tmpa ligand (uns-penp and acetyl-uns-penp) were synthesised, where one aromatic nitrogen donor was replaced by an aliphatic nitrogen donor. The iron(III) complexes of the tripodal ligands N',N'-bis[(2-pyridyl)methyl]ethylenediamine (uns-penp), [Fe(uns-penp)Cl2]ClO4 x CH3CN, [{Fe(uns-penp)Cl}2O](ClO4)2 x 2CH3CN and the amide derivative N-Acetyl-N',N'-bis[(2-pyridyl)methyl]ethylenediamine (acetyl-uns-penp), [Fe2(acetyl-uns-penp)2O](ClO4)2 x H2O, [Fe(acetyl-uns-penp)(tcc)Br] x (C2H5)2O and [{Fe(acetyl-uns-penp)(tcc)}2O] x (C2H5)2O x CH3OH were synthesised and characterised. Catechol dioxygenase reactivity of in situ prepared complex solutions only showed slower reactions in comparison with the iron tmpa system (Chapter 3).
Corresponding ligand system variations in the small molecule model complexes of copper proteins were made and analysed with respect to dioxygen reactivity. Intramolecular ligand hydroxylation was observed during the reactions of dioxygen with the dicopper(I) complexes of the ligands L3 (L3 = alpha,alpha'-bis[(2-pyridylethyl)amino]-m-xylene) and L5 (L5 = alpha,alpha'-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)-amino]-m-xylene). The dinuclear copper(I) complex [Cu2L5](ClO4)2 and the dicopper(II) complex [Cu2(L3-O)(OH)(ClO4)]ClO4 were characterised by single-crystal X-ray structure analysis. Furthermore, phenolate-bridged complexes were synthesised with the ligand L4-OH and Me-L5-OH (structurally characterised: [Cu2(L4-O)Cl3] with L4 = alpha,alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene and [Cu2(Me-L5-O)(mu-X)](ClO4)2 x nH2O with Me-L5-OH = 2,6-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-4-methylphenol and X = C3H3N2- (prz), MeCO2- and N3-). Temperature-dependent magnetic studies revealed the antiferromagnetic coupling of the copper ions of these complexes (Chapter 4).
The reactions of dioxygen with copper(I) complexes of the tridentate ligands 1,1,4,7,7-pentamethyldiethylethylenetriamine (Me5dien), 1,1,4,7,7-pentaethyldiethylethylenetriamine (Et5dien), N-methyl-[bis(2-pyridyl)methyl]amine (Me-bpa) and N-methyl-[(2-pyridyl)ethyl(2-pyridyl)methyl]amine (MeL) have been investigated using low-temperature stopped-flow techniques. The formation of a bis(mu-oxo) copper complex as a reactive intermediate could only be detected spectroscopically at low temperatures for [Cu(Me5dien)(CH3CN)]ClO4 and allowed a quantitative kinetic analysis to be performed. Crystal structures of the copper(II) complexes [(Me-bpa)Cu(Cl)2], [{(Me-bpa)Cu(Cl)(ClO4)}2], [{(MeL)Cu(Cl)(ClO4)}2] and [(MeL)Cu(NCS)2] are reported. (Chapter 5)
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