The systematic influence of tripodal ligands on the catechol cleaving activity of iron(III) containing model compounds for catechol 1,2-dioxygenases †

Abstract

A series of mononuclear iron() complexes as functional and structural model compounds for intradiol cleaving catechol dioxygenases were synthesized. For all model compounds the iron() cores are in a distorted octahedral environment derived from tripodal tetradentate N 4 -donor ligands and a catechol. Model complexes for enzymesubstrate adducts were characterized by spectroscopic and electrochemical methods, and in four cases by singlecrystal X-ray crystallography. The systematic variation of one ligand arm in the structurally characterized complexes yields a different steric shielding of the iron() center, significantly influencing the bonding of the catechol substrate and the subsequent reaction with dioxygen. The spectroscopic features and catechol cleaving activities of in situ generated complexes with the above ligands were probed. All complexes are highly reactive towards intradiol cleavage of various catechols in the presence of air. The catechol 1,2-dioxygenase reaction depends on the redox potential of both the iron() complex and the catechol derivative as well as the steric demand of the tripodal ligand. Some complexes show high catalytic activities with yields up to 84% with respect to aerial cleavage of catechols.

Synthesis, properties, and catecholase-like activity of the [1,4-di(6′-methyl-2′-pyridyl)aminophthalazine]dimanganese(II) complex, Mn2(6′Me2PAP)2Cl4

“…By adding non-oxidizable catechol such as tetrachlorocatechol (Cl 4 CatH 2 ) into the reaction mixture during the oxidation of 3,5-DTBCH 2 the reaction was stopped, supporting the inhibition effect of the Cl 4 CatH 2 , which can be explained by the catechol coordination [28,29]. As shown in Figure 6, in the series 3,5-DTBCH 2 , 4-t-butylcatechol (4-TBCatH 2 ), 4-methoxycatechol (4-MeOCatH 2 ), 4-methylcatechol (4-MeCatH 2 ) and catechol (CatH 2 ) the redox potentials increase due to the decreasing electron donating potential of the catechol substituents and the resulting decrease in Lewis basicity of the catechols [30]. With a higher electron donating character (lower redox potential) of the substrate, the charge donation from the coordinated catechol to the metal centers is increased in the dimetal-catechol intermediate, thereby making the substrate more prone to oxidation by O 2 [14].…”

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)

“…[4,46] Furthermore, several other systems with tripodal N 4 donor ligands showed considerable catechol dioxygenase activity. [47,48] Complexes with enzyme-analogous N 2 O 2 donor sets represent good structural and spectroscopic model compounds, however, they are poor functional models so far.…”

Effect of Deprotonation of a Benzimidazolyl Ligand on the Redox Potential and the Structures of Mononuclear Ruthenium(II) Complexes

“…The starting complex [Ru(bbpaH)(dmso)Cl](PF 6 ) 2 was prepared by the reaction of Ru(dmso) 4 Cl 2 [25] and the bbpaH ligand [26] according to the literature procedure for the preparation of the analogous complex [Ru(tpa)(dmso)-Cl](PF 6 ) [tpa = tris(2-pyridylmethyl)amine]. [27] The subsequent reaction of [Ru(bbpaH)(dmso)Cl](PF 6 + were determined at -80°C by X-ray diffraction analyses.…”