Chelate Ring Size Variations and Their Effects on Coordination Chemistry and Catechol Dioxygenase Reactivity of Iron(III) Complexes

Abstract

The catechol dioxygenase reactivity of iron(III) complexes using tripodal ligands was investigated. Increasing, as well as decreasing, chelate ring sizes in the highly active complex [Fe(tmpa)(dbc)]B(C6H5)4 (tmpa = tris[(2-pyridyl)methyl]amine; dbc = 3,5-di-tert-butylcatecholate dianion), using related ligands, 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 DeltaH++ = 23 +/- 1 kJ mol(-1) and DeltaS++ = -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), (mu-oxo)-bis(bromo)(bis((2-pyridyl)methyl)-2-pyridylamine-N,N',N' ',N''')-diiron(III), dichloro-((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N' ',N''')-iron(III) and (tetrachlorocatecholato-O,O')((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N' ',N''')-iron(III) are reported.

Iron(III) Complexes with the Ligand N′,N′‐Bis[(2‐pyridyl)methyl]ethylenediamine (uns‐penp) and Its Amide Derivative N‐Acetyl‐N′,N′‐bis[(2‐pyridyl)methyl]ethylenediamine (acetyl‐uns‐penp)

“…[57] Stopped-flow kinetic investigations revealed again that the rate of the reaction of the iron tmpa system is faster under these conditions, however, at least the iron-uns-penp complex was only slower by a factor of 20. No further detailed kinetic studies were performed on this system because of the fact that the rate could not be increased and that no reactive intermediates could be detected spectroscopically.…”

“…[57] The substrate-binding process in the reaction cycle of the catechol cleavage involves protonation of two ligands at the active site, Tyr447 and a hydroxide. [58,59] These two proton acceptors dissociate from the metal ion and thereby enable the proton donor molecule, the catechol, to coordinate in its dianionic form (see Scheme 2).…”

Tripodal Tetraamine Ligands Containing Three Pyridine Units: The other Polypyridyl Ligands

“…It can also act as a bridging ligand in a number of coordination polymers 19. The ligand L2 ( x = y = 1, z = 0) appears to be the simplest tripyridyl tripodal ligand which can act as a tetradentate ligand; it coordinates through all four nitrogen atoms in the oxo‐bridged dimer [(L2)BrFeOFeBr(L2)] 2+ 20…”

Spin Crossover in a Family of Iron(II) Complexes with Hexadentate ligands: Ligand Strain as a Factor Determining the Transition Temperature

“…For example, significant chelate-ring-size effects have been found in the copper-dioxygen chemistry, [14,15] catechol dioxygenase reactivity of ironA C H T U N G T R E N N U N G (III) compounds, [16] electrochemical properties of manganeseA C H T U N G T R E N N U N G (III) and (IV) complexes, [17] spectroscopic properties of nickel(II) [18] and cobaltA C H T U N G T R E N N U N G (III) compounds. [19][20][21] Some attempts to consider the effect of chelate cycles size on the spin state of iron(II) have been done in the literature.…”