Chelate ring size variations and their effects on coordination act chemistry and catechol dioxygenase reactivity of iron(III) complexes

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 Delta H-double dagger = 23 +/- 1 U mol(-1) and Delta S-double dagger = -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(111), dichloro-((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N'',N')-iron(111) and (tetrachlorocatecholato-O,O')((2(2-pyridyl) ethyl) bis((2-pyridyl) methyl)amine-N,N', N'', N') -iron (I 11) are reported.