18261-07-9Relevant articles and documents
Intradiol Oxygenation of 3,5-Di-t-butylcatechol Catalyzed by Iron(III) Salts
Funabiki, Takuzo,Konishi, Toru,Kobayashi, Shogo,Mizoguchi, Akira,Takano, Mikio,Yoshida, Satohiro
, p. 719 - 722 (1987)
3,5-Di-t-butylcatechol is oxygenated by Fe(III) salts without addition of ligands in THF/water, DMF, or DMF/aqueous borate buffer to give intradiol cleavage products.Intermediate formation of semiquinonatoiron(II) and catecholatoiron(III) complexes is indicated by electronic, Moessbauer, ESR spectroscopy.
Biomimetic iron(iii) complexes of N3O and N3O 2 donor ligands: Protonation of coordinated ethanolate donor enhances dioxygenase activity
Sundaravel, Karuppasamy,Sankaralingam, Muniyandi,Suresh, Eringathodi,Palaniandavar, Mallayan
, p. 8444 - 8458 (2011)
A series of iron(iii) complexes 1-4 of the tripodal tetradentate ligands N,N-bis(pyrid-2-ylmethyl)-N-(2-hydroxyethyl)amine H(L1), N,N-bis(pyrid-2- ylmethyl)-N-(2-hydroxy- propyl)amine H(L2), N,N-bis(pyrid-2-ylmethyl)-N- ethoxyethanolamine H(L3), and N-((pyrid-2-ylmethyl)(1-methylimidazol-2-ylmethyl) )-N-(2-hydroxyethyl)amine H(L4), have been isolated, characterized and studied as functional models for intradiol-cleaving catechol dioxygenases. In the X-ray crystal structure of [Fe(L1)Cl2] 1, the tertiary amine nitrogen and two pyridine nitrogen atoms of H(L1) are coordinated meridionally to iron(iii) and the deprotonated ethanolate oxygen is coordinated axially. In contrast, [Fe(HL3)Cl3] 3 contains the tertiary amine nitrogen and two pyridine nitrogen atoms coordinated facially to iron(iii) with the ligand ethoxyethanol moiety remaining uncoordinated. The X-ray structure of the bis(μ-alkoxo) dimer [{Fe(L5)Cl}2](ClO4)25, where HL is the tetradentate N3O donor ligand N,N-bis(1-methylimidazol-2-ylmethyl)-N- (2-hydroxyethyl)amine H(L5), contains the ethanolate oxygen donors coordinated to iron(iii). Interestingly, the [Fe(HL)(DBC)]+ and [Fe(HL3)(HDBC)X] adducts, generated by adding ～1 equivalent of piperidine to solutions containing equimolar quantities of iron(iii) complexes 1-5 and H2DBC (3,5-di-tert-butylcatechol), display two DBC2- → iron(iii) LMCT bands (λmax: 1, 577, 905; 2, 575,915; 3, 586, 920; 4, 563, 870; 5, 557, 856 nm; Δλmax, 299-340 nm); however, the bands are blue-shifted (λmax: 1, 443, 700; 2, 425, 702; 3, 424, 684; 4, 431, 687; 5, 434, 685 nm; Δλmax, 251-277 nm) on adding 1 more equivalent of piperidine to form the adducts [Fe(L)(DBC)] and [Fe(HL3)(HDBC)X]. Electronic spectral and pH-metric titration studies in methanol disclose that the ligand in [Fe(HL)(DBC)]+ is protonated. The [Fe(L)(DBC)] adducts of iron(iii) complexes of bis(pyridyl)-based ligands (1,2) afford higher amounts of intradiol-cleavage products, whereas those of mono/bis(imidazole)-based ligands (4,5) yield mainly the auto-oxidation product benzoquinone. It is remarkable that the adducts [Fe(HL)(DBC)] +/[Fe(HL3)(DBC)X] exhibit higher rates of oxygenation affording larger amounts of intradiol-cleavage products and lower amounts of benzoquinone. The Royal Society of Chemistry 2011.
Iron(iii) complexes of tripodal tetradentate 4N ligands as functional models for catechol dioxygenases: The electronic vs. steric effect on extradiol cleavage
Balamurugan, Mani,Vadivelu, Prabha,Palaniandavar, Mallayan
, p. 14653 - 14668 (2014)
A few mononuclear iron(iii) complexes of the type [Fe(L)Cl2]Cl 1-6, where L is a tetradentate tripodal 4N ligand such as N,N-dimethyl-N′,N′-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L1), N,N-diethyl-N′,N′-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L2), N,N-dimethyl-N′,N′-bis-(6-methylpyrid-2-ylmethyl)ethane-1,2-diamine (L3), N,N-dimethyl-N′-(pyrid-2-ylmethyl)-N′-(1-methyl-1H-imidazol-2-ylmethyl)ethane-1,2-diamine (L4), N,N-dimethyl-N′,N′-bis(1-methyl-1H-imidazol-2-ylmethyl)ethane-1,2-diamine (L5) and N,N-dimethyl-N′,N′-bis(quinolin-2-ylmethyl)ethane-1,2-diamine (L6), have been isolated and characterized by CHN analysis, UV-Visible spectroscopy and electrochemical methods. The complex cation [Fe(HL1)Cl3]+1a possesses a distorted octahedral geometry in which iron is coordinated by the monoprotonated 4N ligand in a tridentate fashion and the remaining three sites of the octahedron are occupied by chloride ions. The DFT optimized octahedral geometries of 1, 5 and 6 contain iron(iii) with a high-spin (S = 5/2) ground state. The catecholate adducts [Fe(L)(DBC)]+, where H2DBC is 3,5-di-tert-butylcatechol, of all the complexes have been generated in situ in acetonitrile solution and their spectral and redox properties and dioxygenase activities have been studied. The DFT optimized geometries of the catecholate adducts [Fe(L1)(DBC)]+, [Fe(L5)(DBC)]+ and [Fe(L6)(DBC)]+ have also been generated to illustrate the ability of the complexes to cleave H2DBC in the presence of molecular oxygen to afford varying amounts of intra- (I) and extradiol (E) cleavage products. The extradiol to intradiol product selectivity (E/I, 0.1-2.0) depends upon the asymmetry in bidentate coordination of catecholate, as determined by the stereoelectronic properties of the ligand donor functionalities. While the higher E/I value obtained for [Fe(L6)(DBC)]+ is on account of the steric hindrance of the quinolyl moiety to coordination the lower value observed for [Fe(L4)(DBC)]+ and [Fe(L6)(DBC)]+ is on account of the electron-releasing effect of the N-methylimidazolyl moiety. Based on the data obtained it is proposed that the detachment of the -NMe2 group from the coordination sphere in the semiquinone intermediate is followed for dioxygen binding and activation to yield the extradiol cleavage product. This journal is
INTRA- AND EXTRADIOL OXYGENATIONS OF 3,5-DI-TERT-BUTYLCATECHOL CATALYZED BY BIPYRIDINEPYRIDINEIRON(III) COMPLEX
Funabiki, Takuzo,Mizoguchi, Akira,Sugimoto, Tsunemi,Yoshida, Satohiro
, p. 917 - 920 (1983)
Iron(III) complex coordinated by 2,2'-bipyridine and pyridine catalyzes oxygenation of 3,5-di-t-butylcatechol with molecular oxygen to give intra- and extradiol fission products as well as oxidation to give 3,5-di-t-butyl-1,2-benzoquinone.Structures and reactivities of the products have indicated that the oxygenation proceeds by the Hamilton process rather than the dioxetane process.
Biomimetic iron(iii) complexes of facially and meridionally coordinating tridentate 3N ligands: Tuning of regioselective extradiol dioxygenase activity in organized assemblies
Sankaralingam, Muniyandi,Saravanan, Natarajan,Anitha, Natarajan,Suresh, Eringathodi,Palaniandavar, Mallayan
, p. 6828 - 6841 (2014)
Four mononuclear iron(iii) complexes of the type [Fe(L)Cl3] 1-4, where L is a tridentate 3N ligand such as (2-pyridin-2-ylethyl)(pyridin-2- ylmethyl)amine (L1), (methyl)(2-pyridin-2-ylethyl)(pyridin-2-ylmethyl)amine (L2), bis(pyridin-2-ylethyl)amine (L3), and (1-methyl-1H-imidazol-2-ylmethyl) (pyridin-2-ylethyl)amine (L4), have been isolated and studied as functional models for catechol dioxygenase enzymes. In [Fe(L2)Cl3] 2, the ligand L2 is coordinated facially to iron(iii) whereas in [Fe(L1)Cl3] 1 and [Fe(L4)Cl3] 4 the ligands L1 and L4 are coordinated meridionally. In DCM, CH3CN and aqueous SDS, CTAB and TX-100 micellar media, the positions of both the low and high energy catecholate-to-iron(iii) LMCT bands (465-530, 690-860 nm) observed for the 3,4-di-tert-butylcatecholate (DBC 2-) adducts of the iron(iii) complexes vary in the order 2 > 1 > 3 > 4, which reflects the influence of the stereoelectronic factors, mode of coordination and the chelate ring size formed by the tridentate ligands. Spectral and electrochemical studies disclose the formation and location of the cationic adducts as solvated [Fe(L)(DBC)(H2O)]+ species mostly in the aqueous micellar pseudophases of SDS and TX-100 and in the aqueous phase of CTAB micellar solution. The [Fe(L)(DBC)Cl] adducts of 1, 3 and 4, generated in situ, afford major amounts of intradiol cleavage products (17.0-70.0%) and smaller amounts of extradiol (1.2-4.2%) products with varying extradiol to intradiol cleavage product selectivity (E/I: 1, 0.08:1; 3, 0.02:1; 4, 0.3:1). On the other hand, interestingly, the adduct [Fe(L2)(DBC)Cl] of 2 generated in DCM yields a major amount of extradiol (54.0%) and a lower amount (18.3%) of the intradiol cleavage products (E/I, 3:1). Remarkably, in aqueous SDS micellar media, it shows exclusive extradiol cleavage products (79.4%) while all the other complexes show very low selectivity (E/I: 1, 0.03:1; 2, 79.4:0, 3, 0.06:1, 4, 0.06:1), suggesting the suitability of SDS medium for 2 to elicit exclusive extradiol cleavage. The TX-100 micellar medium also provides a suitable hydrophobic environment for 2 to elicit extradiol cleavage. However, in CTAB micellar medium, 2 shows cleavage selectivity lower than others. Also, the rate of dioxygenation is higher in SDS micellar medium than in DCM, and is dependent upon the chelate ring size. This journal is the Partner Organisations 2014.
A novel pentadentate redox-active ligand and its iron(III) complexes: Electronic structures and O2 reactivity
Metzinger, Ramona,Demeshko, Serhiy,Limberg, Christian
, p. 4721 - 4735 (2014/05/06)
A novel redox-active ligand, H4Ph2SLAP (1) which was designed to be potentially pentadentate with an O,N,S,N,O donor set is described. Treatment of 1 with two equivalents of potassium hydride gave access to octametallic precursor complex [H2Ph2SL APK2(thf)]4 (2), which reacted with FeCl 3 to yield iron(III) complex [H2Ph2SL APFeCl] (3). Employing Fe[N(SiMe3)2] 3 for a direct reaction with 1 led to ligand rearrangement through C-S bond cleavage and thiolate formation, finally yielding [HLAPFe] (5). Upon exposure to O2, 3 and 5 are oxidized through formal hydrogen-atom abstraction from the ligand NH units to form [ Ph2SLSQFeCl] (4) and [LSQFe] (6) featuring two or one coordinated iminosemiquinone moieties, respectively. Moessbauer measurements demonstrated that the iron centers remain in their +III oxidation states. Compounds 3 and 5 were tested with respect to their potential as models for the catechol dioxygenase. Thus, they were treated with 3,5-di-tert-butyl- catechol, triethylamine and O2. It turned out that the iron-catecholate complexes react with O2 in dichloromethane at ambient conditions through C-C bond cleavage mainly forming extradiol cleavage products. Intradiol products are only side products and quinone formation becomes negligible. This observation has been rationalized by a dissociation of two donor functions upon coordination of the catecholate. A radical convention: A novel pentadentate O,N,S,N,O ligand system, LH4, which is redox active, has been developed, so that its iron(III) complex (H2LFeCl) reacts with O2. H atoms are abstracted from the NH units present so that the ligand is converted into a diradical, featuring two iminosemiquinonato moieties that clamp a high-spin iron(III) center. The complex proved capable of mimicking catechol dioxygenase reactivity, and mediates extradiol cleavage with remarkable selectivity.
