Iron-macrocycle complex

Alatorre Ordaz, A., Manriquez Rocha, J., Acevedo Aguilar, F.J., Gutierrez Granados, S. and Bedioui, F. (2000) Electrocatalysis of the reduction of organic halide derivatives at modified electrodes coated by cobalt and iron macrocyclic complex-based films Application to the electrochemical determination of pollutants. Analusis 28, 238-244. 

Similarly, Li et al. [190] investigated the interaction between dioxygen and various iron macrocyclic complexes (Fig. 11.8) by means of first-principle calculations. Their results indicated that the macrocyclic ligands without aromaticity were better electron-donor ligands, facilitating the backbonding from iron to O2... 

Electrocatalytic ORR carries out in three pathways the 1-electron transfer pathway, producing superoxide ion the 2-electron transfer pathway, producing hydrogen peroxide and the 4-electron transfer pathway, producing water. In a non-aqueous aprotic solvent system, a room-temperature ionic liquid system, and on specific transition-metal, macrocyclic-compounds-coated graphite electrodes in alkaline solutions, 1-electron reduction can be observed. Carbon materials, quinone and derivatives, mono-nuclear cobalt macrocyclic compounds, and some chalcogenides can only catalyze 2-electron ORR. Noble metal, noble metal alloy materials, iron-macrocyclic complexes, di-nuclear cobalt macrocyclic complexes, some chalcogenides, and transition-metal carbide-promoted Pt catalysts can catalyze 4-electron reduction. 

Fig. 5 Volcano plot for oxidation of hydrazine in 0.1 mol NaOH on graphite modified electrode with several iron macrocyclic complexes. Data taken from Ref. [56]...

From 2,6-diacetylpyridine dioxime, ferric chloride hydrate, and phenylboronic acid as starting materials the macrocyclic dinuclear iron(ll) complexes 133 can be prepared (Fig. 36). 

Compounds 139 are tris(oximehydrazone) derivatives with an iron(ll) ion in the center of the cavity [230]. Compound 140 (Fig. 38) has been known for 30 years [231, 232] and was prepared from a tris(2-aldoximo-6-pyridyl)phos-phine that is capped by a BF unit to encapsulate cobalt(ll), zinc(ll), nickel(ll), and iron(II). All four macrocyclic complexes were characterized later by a comparative X-ray crystallographic study [233-236]. 

Woo et al. [54] prepared new chiral tetraaza macrocyclic hgands (48 in Scheme 23) and their corresponding iron(II) complexes and tested them, as well as chiral iron(II) porphyrin complexes such as Fe (D4 -TpAP) 49, in asymmetric cyclopropanation of styrene. 

To mimic the square-pyramidal coordination of iron bleomycin, a series of iron (Il)complexes with pyridine-containing macrocycles 4 was synthesized and used for the epoxidation of alkenes with H2O2 (Scheme 4) [35]. These macrocycles bear an aminopropyl pendant arm and in presence of poorly coordinating acids like triflic acid a reversible dissociation of the arm is possible and the catalytic active species is formed. These complexes perform well in alkene epoxidations (66-89% yield with 90-98% selectivity in 5 min at room temperature). Furthermore, recyclable terpyridines 5 lead to highly active Fe -complexes, which show good to excellent results (up to 96% yield) for the epoxidation with oxone at room temperature (Scheme 4) [36]. 

In addition, iron(II) complexes of tetraaza macrocyclic ligands 17-20 were encapsulated within the nanopores of zeolite-Y and were used as catalysts for the oxidation of styrene with molecular oxygen under mild conditions (Scheme 9) [57]. 

Selected other metal ion systems. There have been a number of investigations of the reduction of iron macrocyclic ligand complexes. In one such study, the Fe(n) complex [FeL(CH3CN)2]2+ [where L = (292)] was shown to exhibit three reduction waves in acetonitrile (Rakowski Busch, 1973). Controlled-potential electrolysis at the first reduction plateau (—1.2 V) led to isolation of [FeL]+ for which the esr spectrum is typical of a low-spin Fe(i) system. The quasi-reversible Fe(i)/Fe(n) couple occurs at —0.69 V versus Ag/AgN03. 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

Tetraza-macrocycles of the right ring size are expected to give very high inplane ligand field strengths. Fe(II) complexes based on such ligands are therefore expected to be either low-spin or spin-crossover. Busch and his coworkers [17] have synthesized six coordinate iron(II) complexes [Fe (tet-a)X2], where tet-a is one of the isomers of hexamethyl cyclam, a 14-membered tetraza-macrocycle (8). 

The phthalocyanine [1-4] system is structurally derived from the aza-[18]-annulene series, a macrocyclic hetero system comprising 18 conjugated n-electrons. Two well known derivatives of this parent structure, which is commonly referred to as porphine, are the iron(III)complex of hemoglobin and the magnesium complex of chlorophyll. Both satisfy the Htickel and Sondheimer (4n + 2)- electron rule and thus form planar aromatic systems. 

A review of the stabilities and catalytic properties of binuclear metal complexes of large-ring N,0 macrocycles concentrates on the iron(II) and iron(III) complexes of (184) and (185). ... 

Several macrocyclic polycatechols, with up to six catechol units incorporated into the ring, have been designed for possible treatment for iron overload and were prepared using high dilution techniques. They form stable iron(III) complexes the complex with the three-catechol ring as ligand has log K= ii.l... 

Electric fleld gradient, 22 214-218 Electroabsorption spectroscopy, 41 279 class II mixed-valence complexes, 41 289, 291, 294-297 [j(jl-pyz)]=+, 41 294, 296 Electrocatalytic reduction, nickel(n) macro-cyclic complexes, 44 119-121 Electrochemical interconversions, heteronuclear gold cluster compounds, 39 338-339 Electrochemical oxidation, of iron triazenide complexes, 30 21 Electrochemical properties fullerene adducts, 44 19-21, 33-34 nickeljll) macrocyclic complexes, 44 112-113... 

Curtis-type macrocyclic complexes are sufficiently stable to undergo a variety of oxidation and reduction processes to yield a range of complexes containing from zero to four imine linkages (Scheme 10).40 66 84 85 96 The oxidative dehydrogenation process is metal-ion dependent, as illustrated by the alternative ligand structure developed from the iron(II) complex (equation 14) 97 9S... 

The nickel(II) ions can be removed from the above range of macrocyclic complexes and the resulting free ligands can then be converted into iron(II) complexes, 130 which have been shown to exhibit reversible oxygen binding.131,132 Similar characteristics have been observed for iron(II) complexes such as (60), which contain bridging from methyl carbon atoms rather than nitrogen atoms.132 Synthetic information has not been disclosed, but several routes are possible. 

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