Preparation,characterization and electrochemistry of an iron-only hydrogenase active site model covalently linked to a ruthenium tris(bipyridine) photosensitizer

An NH₂-functionlized [Fe₂S₂] model complex of the iron-only hydrogenase active site was covalently linked to the tris(bipyridine)ruthenium photosensitizer. The [RuFeFe] trinuclear complex 1 was characterized by MS, IR, UV-vis, ¹H & ¹³C NMR spectra. A quasi-reversible reduction peak at ?1.41 V versus Ag/Ag⁺ for the Fe^IFe^I/Fe^IFe⁰ process is observed in the cyclic voltammogram of 1.     

Synthetic [FeFe]-H2ase models bearing phosphino thioether chelating ligands

Through the oxidation-reduction combination procedure, the neutral tri-substituted {2Fe3S} complex 2 was synthesized by replacing the CO ligand in 1 with phosphine. This substitution leads to the Fe-Fe bonds in 1 and 2 with large Lewis basicity difference, i.e. △pK_a^MeCN~10.     

SPh functionalized bridging-vinyliminium diiron and diruthenium complexes

The SPh functionalized vinyliminium complexes [Fe₂{μ-η¹:η³-C_γ(R′)C_β(SPh)C_αN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] [R = Xyl, R′ = Me, 2a; R = Me, R′ = Me, 2b; R = 4-C₆H₄OMe, R′ = Me, 2c; R = Xyl, R′ = CH₂OH, 2d; R = Me, R′ = CH₂OH, 2e; Xyl = 2,6-Me₂C₆H₃] are generated in high yields by treatment of the corresponding vinyliminium complexes [Fe₂{μ-η¹:η³-C_γ(R′)C_β(H)C_αN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (1a-e) with NaH in the presence of PhSSPh. Likewise, the diruthenium complex [Ru₂{μ-η¹:η³-C_γ(Me)C_β(SPh)C_αN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (2f) was obtained from the corresponding vinyliminium complex [Ru₂{μ-η¹:η³-C_γ(Me)C_β(H)C_αN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (1f). The synthesis of 2c is accompanied by the formation, in comparable amounts, of the aminocarbyne complex [Fe₂{μ-CN(Me)(4-C₆H₄OMe)}(SPh)(μ-CO)(CO)(Cp)₂] (3).The molecular structures of 2d, 2e and 3 have been determined by X-ray diffraction studies.     

Synthesis and DNA cleavage activity of diiron(III) complex bearing pyrene group

As DNA cleavage agent, a new diiron(III) complex (Fe2Lb), in which a DNA-intercalator "(pyrene) is covalently linked to a diferric moiety, has been synthesized and characterized. The DNA-binding property and DNA cleavage activity of the complex have also been investigated.     

Ethynylferrocene insertion into Fe-C bond in bridging aminocarbyne diiron complexes: New triiron vinyliminium complexes

The μ-aminocarbyne complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCMe)(Cp)₂][SO₃CF₃] (R = Me, 1a; Xyl, 1b; Xyl = 2,6-Me₂C₆H₃) react with ethynylferrocene to give the corresponding bridging vinyliminium complexes [Fe₂{μ-η¹:η³-CN(Me)(R)CHC(Fc)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = Me, 2a; R = Xyl, 2b). Insertion of the ethynylferrocene in the metal-carbyne bond is regiospecific, and leads to the formation of only one isomer.Complexes 2a and 2b undergo hydride addition (by NaBH₄) affording the enaminoalkylidene complex [Fe₂{μ-η¹:η³-C(H)(N(Me)₂)CHC(Fc)}(μ-CO)(CO)(Cp)₂] (3a) and the bis-alkylidene [Fe₂{μ-η¹:η²-C(N(Me)(Xyl))CH₂C(Fc)}(μ-CO)(CO)(Cp)₂] (3b), respectively. Upon treatment with NaH, compounds 2a and 2b undergo fragmentation, affording the 1-metalla-2-aminocyclopenta-1,3-dien-5-one complexes [Fe(CO)(Cp){C(N(Me)(R))}CHC(Fc)C(O)}] (R = Me, 4a; R = Xyl, 4b).The molecular structures of 2b, 3b and 4b have been determined by X-ray diffraction studies.     

Unexpected fragmentation of phenyldithiobenzoate, formation and X-ray structure of [μ,η(S,S)-1,2-(dithio)-1,2-(diphenylethylene)] diiron hexacarbonyl complex

The reaction of Fe₂(CO)₉ with phenyldithiobenzoate PhCS₂Ph 1 afforded four colored compounds: [(μ-η³(C,S,S)PhCS₂Ph)]Fe₂(CO)₆2, (μ-S)₂Fe₃(CO)₉3, (μ-SPh)₂Fe₂(CO)₆4 and [μ-η²(S,S)][PhC(S)C(S)Ph]Fe₂(CO)₆5. Complex 5 was characterized by X-ray crystallography. The formation of complexes 4 and 5 was unexpected since it involved a fragmentation of the organic ligand 1 during its reaction with Fe₂(CO)₉. The electrochemical studies of 1, complexes 2 and 3 were undertaken in order to get information about the chemical behaviors of the intermediates generated by electron transfer. The results of cyclic voltammetry studies of 2 and 1 suggested that the reaction of 1 with Fe₂(CO)₉ involved two competitive reactions: (i) a thermal reaction which led to the expected compounds 2 and 3 and (ii) an electron transfer reaction involving a fragmentation of starting ligand 1 led to the unexpected complex 5. The required electrons may be provided by iron during the thermal decay of complexes 2 or 3 or Fe₂(CO)₉.     

SYNTHESIS AND CHARACTERIZATION OF A LINEAR μ-OXO DIIRON(III) COMPOUND AND A COPPER(II) NITRITE COMPLEX CONTAINING,A TRIPODAL POLYBENZIMIDAZOLE LIGAND

Abstract

Iron(III) and copper(II) complexes of the polybenzimidazole ligand, tris((benzimidazol-2-yl)methyl)amine (tmba) have been synthesized and structurally characterized. The mononuclear complex [Cu(tmba)(NO₂)]⁺[CH₃OH][NO^? ₂], 1, has been isolated and characterized by X-ray crystallography. The complex crystallizes in the triclinic space group P1 with two molecules in the unit cell of dimension a = 8.891(5), b = 11.775(6), and c = 13.702(8)Å, and α = 67.76(1), β = 71.79(2) and γ = 88.96(1)°, and volume = 1253.0(12)ų. The structure was refined to a final agreement factor R = 0.0901 using 4134 observed reflections. The complex consists of cationic copper(tmba) complex covalently bonded to a nitrite, and a pair of these cations is dibridged by a pair of nitrite anions. The gap between this dimer is occupied by a methanol molecule. The coordination environment around each copper can be described as trigonal bipyramidal, with the tertiary amine, a benzimidazole nitrogen and an oxygen from the nitrite providing the ligating atoms of the trigonal plane.

The μ-oxo bridged binuclear complex [Fe₂O(tmba)₂Cl₂](H₂O)(EtOH)₂·Cl₂, 2, was also characterized by single crystal X-ray diffraction and magnetic susceptibility. The complex crystallizes in the triclinic space group P1 with one molecule in the unit cell of dimensions, a = 11.5791(7), b = 13.3369(8), and c = 13.7002(9) Å, and α = 103.904(1), β = 108.903(2) and γ = 112.845(1)°, and volume = 1674.1(2) å³. The structure was refined to a final agreement factor R = 0.073 using 5597 observed reflections. The complex is a centrosymmetric dimer, with the two iron(III) atoms bridged by an oxygen atom, with an Fe—O—Fe angle of 180°, and a Fe—Fe distance of 3.61(1)Å. The coordination around each iron(III) is best described as octahedral, with the bridging oxygen trans to one end of the benzimidazole group, and a chlorine atom trans to the tertiary amine nitrogen of the ligand.     

Chemie der Isoblausäure. VIII. Protonierung eines ‚mobilen’︁ Cyanoliganden: cis-[(μ-CNH2)Fe2Cp2(CO)3]X (X = Cl,BF4, PF6, I)

Chemistry of Hydrogen Isocyanide. VIII. Protonation of a ‘Mobile’ Cyano Ligand: cis-[μ-CNH₂)Fe₂Cp₂(CO)₃]X (X = Cl, BF₄, PF₆, I) . Protonation of the terminal cyano ligand in the complex cis-Na[Fe₂(CN)Cp₂(CO)₃] affords the N-diprotonated produkt [Fe₂Cp₂(CO)₃(μ-CNH₂)]⁺ X^? (X = Cl, BF₄, PF₆, I) exclusively; the structure of the chloride has been determined by X-ray analysis.     

Aromatic hydroxylation catalyzed by toluene 4-monooxygenase in organic solvent/aqueous buffer mixtures

Toluene 4-monooxygenase is a four-protein component diiron enzyme complex. The enzyme catalyzes the hydroxylation of toluene to give p-cresol with ∼96% regioselectivity. The performance of the enzyme in two-phase reaction systems consisting of toluene, hexane, or perfluorohexane and an aqueous buffer was tested. In each of the cosolvent systems, containing up to 93% (v/v) of solvent, the enzyme was active and exhibited regioselectivity indistinguishable from the aqueous reaction. Using the perfluorohexane/buffer system, a number of polycyclic aromatic hydrocarbons were oxidized that were not readily oxidized in aqueous buffer. An instability of the hydroxylase component and a substantial uncoupling of NADH utilization and product formation were observed in reactions that were continued for longer than ∼3 min. More stable enzyme complexes will be needed for broad applicability of this hydroxylating system in nonaqueous media.     

Models of the iron-only hydrogenase: Reactions of [Fe2(CO)6(μ-pdt)] with small bite-angle diphosphines yielding bridge and chelate diphosphine complexes [Fe2(CO)4(diphosphine)(μ-pdt)]

Reactions of [Fe₂(CO)₆(μ-pdt)] (1) (pdt = SCH₂CH₂CH₂S) and small bite-angle diphosphines have been studied. A range of products can be formed being dependent upon the nature of the diphosphine and reaction conditions. With bis(diphenylphosphino)methane (dppm), thermolysis in toluene leads to the formation of a mixture of bridge and chelate isomers [Fe₂(CO)₄(μ-dppm)(μ-pdt)] (2) and [Fe₂(CO)₄(κ²-dppm)(μ-pdt)] (3), respectively. Both have been crystallographically characterised, 3 being a rare example of a chelating dppm ligand in a first row binuclear system. At room temperature in MeCN with added Me₃NO · 2H₂O, the monodentate complex [Fe₂(CO)₅(κ¹-dppm)(μ-pdt)] (4) is initially formed. Warming 4 to 100 °C leads the slow conversion to 2, while oxidation (on alumina) gives [Fe₂(CO)₅(κ¹-dppmO)(μ-pdt)] (5). With bis(dicyclohexylphosphino)methane (dcpm), heating in toluene cleanly affords [Fe₂(CO)₄(μ-dcpm)(μ-pdt)] (6). With Me₃NO · 2H₂O in MeCN the reaction is not clean as the phosphine is oxidised but monodentate [Fe₂(CO)₅(κ¹-dcpm)(μ-pdt)] (7) can be seen spectroscopically. With 1,2-bis(diphenylphosphino)benzene (dppb) and cis-1,2-bis(diphenylphosphino)ethene (dppv) the chelate complexes [Fe₂(CO)₄(κ²-dppb)(μ-pdt)] (8) and [Fe₂(CO)₄(κ²-dppv)(μ-pdt)] (9), respectively are the final products under all conditions, although a small amount of [Fe₂(CO)₅(κ²-dppvO)(μ-pdt)] (10) was also isolated. Protonation of 2 with HBF₄ affords a cation with poor stability while with the more basic diiron centre in 6 readily forms the stable bridging-hydride complex [(μ-H)Fe₂(CO)₄(μ-dcpm)(μ-pdt)][BF₄] (11) which has been crystallographically characterised.