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 iron(III) complexes [Fe(2)(HPTB)(mu-OH)(NO(3))(2)](NO(3))(2).CH(3)OH.2H(2)O (1), [Fe(2)(HPTB)(mu-OCH(3))(NO(3))(2)](NO(3))(2).4.5CH(3)OH (2), [Fe(2)(HPTB)(mu-OH)(OBz)(2)](ClO(4))(2).4.5H(2)O (3), [Fe(2)(N-EtOH-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3CH(3)OH.1.5H(2)O (4), [Fe(2)(5,6-Me(2)-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3.5CH(3)OH.C(2)H(5)OC(2)H(5).0.5H(2)O (5), and [Fe(4)(HPTB)(2)(mu-F)(2)(OH)(4)](ClO(4))(4).CH(3)CN.C(2)H(5)OC(2)H(5).H(2)O (6) were synthesized (HPTB = N,N,N',N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, N-EtOH-HPTB = N,N,N',N'-tetrakis(N' '-(2-hydroxoethyl)-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, 5,6-Me(2)-HPTB = N,N,N',N'-tetrakis(5,6-dimethyl-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane). The molecular structures of 2-6 were established by single-crystal X-ray crystallography. Iron(II) complexes with ligands similar to the dinucleating ligands described herein have been used previously as model compounds for the dioxygen uptake at the active sites of non-heme iron enzymes. The same metastable (mu-peroxo)diiron(III) adducts were observed during these studies. They can be prepared by adding hydrogen peroxide to the iron(III) compounds 1-6. Using stopped-flow techniques these reactions were kinetically investigated in different solvents and a mechanism was postulated.

A highly selective method for the determination of hydrogen peroxide is presented. In a flow injection analysis (FIA) instrument, the analyte is brought into contact with a dinuclear heptadentate iron(III) complex. The formation of the peroxide adduct is quantified using electrospray tandem mass spectrometry (ESI-MS/MS). Selected reaction monitoring (SRM) based on the transition from the triply charged peroxide adduct with m/z = 251.2 to the triply charged fragment ion of m/z = 240.5 is performed. The limit of detection for hydrogen peroxide is 10(-7) mol dm(-3), limit of quantification is 3 x 10(-7) mol dm(-3), and a linear range of 2.5 decades starting at the limit of quantification is observed.

M onodentate, Semicarbazone, Thiosem icarbazone, But-2-yne, Tungsten(II) Reaction of [W I(C O )(N C M e)(dppm )(772 -M eC2M e)][BF4] {dppm = Ph2 P(C H 2 )PPh2} with an equim olar quantity of L {L = R R 'C N N H C O N H 2 (R = R ' = Me; R = H, R ' = Ph)} or L {L = R R 'C N N H C S N H 2 (R = R ' = Me, Et; R = Me, R ' = E t, Pr", Bu', Ph; R = H, R ' = Ph)} gives the m onodentately coordinated sem icarbazone or thiosem icarbazone products [W I(CO)L(dppm)(?7 2 -M eC2M e)][BF4] (1 -9 ) . 13C N M R spectroscopy suggests that the but-2 -yne ligand is donating four electrons to the tungsten in [W I(CO){H(Ph)CNN H CSN H 2 }(dppm)(?7 2 -M eC2M e)][BF4].