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.

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The reaction of iron(III) perchlorate nonahydrate with the tripodal tetradentate ligand tris[(2‐pyridyl)methyl]amine (tpa) or bis[(2‐pyridyl)methyl][(1‐methylimidazol‐2‐yl)methyl]amine (bpia) and 1, 2‐benzenedithiolate (dtc) yields the iron(III) coordination compounds [Fe(tpa)(dtc)]ClO4·0.25 MeOH (1) and [Fe(bpia)(dtc)]ClO4 (2), respectively. These are the first iron(III) complexes with tripodal ligands and dtc, resulting in a N4S2 coordination environment. The new compounds were isolated and characterized by single crystal X‐ray crystallography as well as spectroscopic methods. Compound 1 crystallizes in the monoclinic space group P21/c (No. 14) with a = 29.636(6), b = 12.502(3), c = 14.390(3)Å, β = 102.19(3)°, V = 5211(2)Å3, Z = 8. Compound 2 crystallizes in the orthorhombic space group P212121 (No. 19) with a = 8.881(2), b = 16.155(3), c = 17.895(4)Å, V = 2567.4(9)Å3, Z = 4. Furthermore the new compound [Fe(tpa)(tcc)](ClO4)·0.25 H2O (3) (where tcc = tetrachlorocatecholate dianion) is presented and compared to the dithiolato complexes. 3 crystallizes in the monoclinic space group P21/c (No. 14) with a = 8.982(1)Å, b = 34.329(6)Å, c = 8.648(1)Å, β = 94.22(1)°, V = 2659.3(6)Å3, Z = 4.