A mononuclear iron(II) complex, [Fe(phen) 3 ]Cl 2 (1) (phen =1,10-phenanthroline), has been synthesized in crystalline phase and characterized using various spectroscopic techniques including single crystal X-ray diffraction. Crystal structure analysis revealed that 1 crystallizes in a monoclinic system with C2/m space group. Complex 1 acts as a functional model for a biomimetic catalyst promoting the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) through radical pathways with a significant turnover number (k cat =3.55 × 10 3 h À1 ) and exhibits catechol dioxygenase activity towards the same 3,5-DTBC substrate at room temperature in oxygen-saturated ethanol medium. The existence of an isobestic point at 610 nm from spectrophotometric data indicates the presence of Fe 3+ À3,5-DTBC adduct favouring an enzyme-substrate binding phenomenon. Upon stoichiometric addition of 3,5-DTBC pretreated with two equivalents of triethylamine to the iron complex, two catecholate-to-iron(III) ligand-to-metal charge transfer bands (575 and 721 nm) are observed and the in situ generated catecholate intermediate reacts with dioxygen (k obs =9.89 × 10 À4 min À1 ) in ethanol medium to afford exclusively intradiol cleavage products along with a small amount of benzoquinone, and a small amount of extradiol cleavage products, which provide substantial evidence for a substrate activation mechanism.

No abstract

An unprecedented solid of coper(II) complexes, [Cu(dpa) 2 NCS] 2 [Cu(dpa) 2 (NCS) 2 ](ClO 4) 2 (1) [dpa = 2,2-dipyridylamine; SCN = thiocyanate], has been synthesized and crystallographically characterized with the aim to study the catecholase activity. The Cu(II) complex mimics the full catalytic cycle of the active site of catechol oxidase enzyme in acetonitrile medium with a turnover number of 4.788 × 10 3 h −1 along with the production of semiquinone radical and hydrogen peroxide. In situ generation of Cu(I) species in the catalytic pathway of catechol oxidation was established by electrochemical study and further confirmed by electron paramagnetic resonance (EPR) spectroscopy.

An oxido-bridged diiron(II)-phenanthroline complex, [Fe 2 O(phen) 2 Cl 2 ] (1) [phen = 1,10-phenanthroline] has been synthesized from an oxido-bridged diiron(III) precursor in presence of sodium azide and structurally characterized by different spectroscopic tools including single crystal X-ray diffraction study.-From X-ray crystal structure of 1, it is revealed that each of the Fe(II) centre is in distorted octahedral geometry with FeN 4 OCl core and the molecule crystallizes in Pnc2 space group. Bond valence sum (BVS) calculation confirms the existence of iron ions in + 2 oxidation state in 1. The diiron(II) complex has been evaluated as model system for the catechol dioxygenase enzyme by using 3,5-di-tert-butylcatechol (DTBC) as the substrate in acetonitrile medium, revealing that 1 efficiently mimics the catalytic cycle of catechol dioxygenase. Upon stoichiometric addition of DTBC pretreated with two equivalents of triethylamine (Et 3 N) to the diiron complex, two catecholate-to-iron(III) LMCT bands (515 nm and 734 nm) are observed. The in situgenerated catecholate adduct from 1in acetonitrile solution react with dioxygen to afford exclusively extradiol cleavage products along with a small amount of benzoquinone, which is also discerned from the appearance and decrease in intensity of the electronic spectral bands around (708 nm; 507 nm) nm. Nucleophilic attack by molecular oxygen on catecholate adduct in solution provides substantial evidence for the regioselective extradiol cleavage products.

No abstract