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AbstractThe kinetics of oxidation catalysis by TAML activators of peroxides [LFeIII(OH2)]− (TAML = tetraamido macrocyclic ligand) in water can be typically quantified by a mechanism comprised of two key steps: catalyst activation to the reactive state with rate constant kI, followed by substrate oxidation with rate constant kII. Usually, kI ≪ kII and the overall catalytic activity is limited by the first step. The second-order rate constant kI can be enhanced by changing structural features in the TAML macrocycle that make the iron site more electrophilic. Chemical interventions beyond changes at the catalyst itself should also be able to change kI. In examining potentially useful interventions, the effect of chloride on kI was explored and an intriguing fact was found. For the NewTAML catalyst, [FeIII{4-NO2C6H3-1,2-(NCOCMe2NSO2)2CHMe}(OH2)]−, increasing chloride concentration reduces the rate constant kI when the pH is below the pKa of the catalyst ([LFeIII(OH2)]− ⇄ [LFeIII(OH)]2− + H+), but increases kI when the pH > pKa. Mechanisms of the observed deceleration/acceleration effects are discussed. A linear dependence between KCl and pKa for iron(III) TAMLs is established: logKCl = 16 ± 2 – (1.6 ± 0.2) × pKa. [ABSTRACT FROM AUTHOR]

The preparation, characterization, and evaluation of a cobalt(III) complex with 13-membered tetraamide macrocyclic ligand (TAML) is described. This is a square-planar (X-ray) S = 1 paramagnetic (1H NMR) compound, which becomes an S = 0 diamagnetic octahedral species in excess d5-pyridine. Its one-electron oxidation at an electrode is fully reversible with the lowest E½ value (0.66 V vs SCE) among all investigated CoIII TAML complexes. The oxidation results in a neutral blue species which is consistent with a CoIII/radical-cation ligand. The ease of oxidation is likely due to the two benzene rings incorporated in the ligand structure (whereas there is just one in many other CoIII TAMLs). The oxidized neutral species are unexpectedly EPR silent, presumably due to the π-stacking aggregation. However, they display eight-line hyperfine patterns in the presence of excess of 4-tert-butylpyridine or 4-tert-butyl isonitrile. The EPR spectra are more consistent with the CoIII/radical-cation ligand formulation rather than with a CoIV complex. Attempts to synthesize a similar vanadium complex under the same conditions as for cobalt using [VVO(OCHMe2)3] were not successful. TAML-free decavanadate was isolated instead. [ABSTRACT FROM AUTHOR]

Iron derivatives have emerged as valuable catalysts for a variety of transformations, as well as for biological and photophysical applications, and iminophosphorane can be considered an ideal ligand scaffold for modulating electronic and steric parameters in transition metal complexes. In this report, we aimed to synthesize dichloride and dibromide iron(II) complexes supported by symmetric bis(iminophosphorane)pyridine ligands, starting from readily available ferrous halides. The ease of synthesis of this class of ligands served to access several derivatives with distinct electronic and steric properties imparted by the phosphine moiety. The ligands and the resulting iron(II) complexes were characterized by 31P and 1H NMR spectroscopy and DART or ESI mass spectrometry. While none of these iron(II) complexes could be characterized by single-crystal X-ray diffraction, suitable crystals of a µ-O bridged dinuclear iron complex bearing an iminophosphorane ligand were obtained, confirming a κ3 binding motif. The bis(iminophosphorane)pyridine ligands in the obtained iron(II) complexes are labile, as demonstrated by their facile substitution by terpyridine. Cyclic voltammetry studies revealed that the oxidation of bis(iminophosphorane)pyridine iron(II) complexes to iron(III) species is quasi-reversible, suggesting the strong thermodynamic stabilization of the iron(III) center imparted by the σ-donating iminophosphorane ligands. [ABSTRACT FROM AUTHOR]

TAML activators of peroxides are iron(III) complexes. The ligation by four deprotonated amide nitrogens in macrocyclic motifs is the signature of TAMLs where the macrocyclic structures vary considerably. TAML activators are exceptional functional replicas of the peroxidases and cytochrome P450 oxidizing enzymes. In water, they catalyze peroxide oxidation of a broad spectrum of compounds, many of which are micropollutants, compounds that produce undesired effects at low concentrations as with the enzymes, peroxide is typically activated with near-quantitative efficiency. In nonaqueous solvents such as organic nitriles, the prototype TAML activator gave the structurally authenticated reactive iron(V)oxo units (FeVO), wherein the iron atom is two oxidation equivalents above the FeIII resting state. The iron(V) state can be achieved through the intermediacy of iron(IV) species, which are usually μ-oxo-bridged dimers (FeIVFeIV), and this allows for the reactivity of this potent reactive intermediate to be studied in stoichiometric processes. The present review is primarily focused at the mechanistic features of the oxidation by FeVO of hydrocarbons including cyclohexane. The main topic is preceded by a description of mechanisms of oxidation of thioanisoles by FeVO, because the associated studies provide valuable insight into the ability of FeVO to oxidize organic molecules. The review is opened by a summary of the interconversions between FeIII, FeIVFeIV, and FeVO species, since this information is crucial for interpreting the kinetic data. The highest reactivity in both reaction classes described belongs to FeVO. The resting state FeIII is unreactive oxidatively. Intermediate reactivity is typically found for FeIVFeIV; therefore, kinetic features for these species in interchange and oxidation processes are also reviewed. Examples of using TAML activators for C-H bond cleavage applied to fine organic synthesis conclude the review. [ABSTRACT FROM AUTHOR]

[Fe(NCN)2]PF6 ( 1·PF6) [NCHN = 1,3-di(pyridin-2-yl)benzene] was readily obtained by a transmetalation reaction between [Fe3(CO)12] and Hg(NCN)Cl followed by a metathesis reaction with KPF6. X-ray diffraction, electron paramagnetic resonance spectroscopy, and cyclic voltammetry studies confirmed the proposed structure. Cytotoxic assays in human colon cancer (HCT-15), lung cancer (SKLU), and gastric cancer (AGS, KATOIII) cells were performed, and the IC50 data obtained for all cell lines showed that 1·PF6 has a much higher activity than cisplatin. [ABSTRACT FROM AUTHOR]

TAML complexis oxidized by H2O2ortBuOOH in water at pH < 10 into the corresponding iron(IV) μ-oxo-bridged dimer2, which oxidizes readily ring-substituted thioanisolesp-XC6H4SMe (X=H, MeO, Me, Cl, CN) into the corresponding sulfoxides with regeneration of1. The oxidation studied under pseudo-first-order conditions using the stopped-flow technique by monitoring the fading of the 420-nm band of2follows hyperbolic kinetics according to the rate lawkobs = ab[p-XC6H4SMe]/(1 + b[p-XC6H4SMe]) at pH 8 and 25 °C. Parametersa,b, andaball decrease for electron-poorer thioanisoles and the Hammett valueρ ~ 1 has been found forab, which can be associated with the second-order rate constants for oxidation of thioanisoles by2. The kinetics of oxidation ofp-NO2C6H4SMe by H2O2catalyzed by1has been studied under steady-state conditions. Covering the concentration of1in a 100-fold range has revealed that though first-order kinetics in1is observed at low catalyst concentrations (below 10−6 M), there is a significant negative deviation from linearity at [1] > 10−6 M. The latter was rationalized by the equilibrium between the monomeric and dimeric FeIVspecies 2 M ⇌ M–M (Kd), both being able to oxidizep-NO2C6H4SMe with rate constantskmandkdwhich were found to be (13 ± 1) × 104and (0.32 ± 0.01) × 104 M−1 s−1, respectively. The difference in the rate constants is the key for resolving the dilemma of faster catalysisversusslower single-turnover reactivity of TAML activators in water. [ABSTRACT FROM AUTHOR]

The ferric TAML catalysts [Fe{C6H2-1,2-(NCOCMe2NCO)2CMe2} (OH2)]- (1) with counterions Na+ (a) and PPh4+ (b) function similar to horseradish peroxidase in the mediated electron transfer relays, which constitute a basis for amperometric biosensors. The mediators are mono- and bis-cyclometalated Ru and Os compounds of the type of [M(C∼N)x(N∼N)3- x]m+ with x = 1 and 2 (N∼N = 2,2′-bipyridine, -C∼N = 2-phenylpyridinato). Cyclic voltammograms of the Ru and Os compounds are not affected by 1a though cathodic currents increase drastically in the presence of hydrogen peroxide. The reduction potentials of [M(C∼N)x(N∼N)3-x]m+ complexes vary with both the nature of metal (Ru or Os) and the number of cyclometalated ligands x (1 or 2) and therefore the potential of working electrode can be set in the range of from -0.1 to +0.6 V versus the normal hydrogen electrode (NHE). A prototype of a biosensor for H2O2 is described, in which the 1b catalyst and [Os(C∼N) 2(N∼N)]+ mediator were coimmobilized on the surface of the glassy carbon electrode using a polymeric coating. [ABSTRACT FROM AUTHOR]

Oxidative degradation of pinacyanol chloride (PNC) dye by H2O2, as catalyzed by the 1 FeIII-TAML activator (TAML = tetraamidomacrocyclic ligand), occurs rapidly in water, goes to completion, and exhibits noticeably complex kinetics at pH 11. The reaction achieves a carbon mineralization of 51%. The detected products are acetate, formate, oxalate, maleate, 2-nitrobenzoate, nitrite, and nitrate. The catalytic reaction is a first-order process in 1 and the reaction rate has a Michaelis dependence in hydrogen peroxide (H2O2). The reaction rate increases sharply with increasing PNC concentration, reaches a maximal value, and then declines as the PNC concentration is further increased. The initial rate (v) versus [PNC] profile has been quantified in terms of the equation: v = (c1[PNC] + c2[PNC]2)/(c3 + c4[PNC] + [PNC]2) which accounts for the maximum and further rate decline. Kinetic analysis at a more acidic pH (9 vs. 11) revealed that there is no initial rate increase and only the hyperbolic retardation by PNC is observed, in accord with the rate law v = (b1 + b2[PNC])/(b3 + [PNC]). The kinetic data has been rationalized using the adopted mechanism of catalysis by FeIII-TAML activators, which involves the reaction between 1 and H2O2 to form reactive, oxidized TAML (kI, k-I) followed by its reaction with the dye (kII). The minimalistic addition to the scheme to account for the PNC case is the assumption that 1 may rapidly and reversibly associate with PNC (K), and the associated complex reacts also with H2O2 (kID, k-ID) to form also the oxidized TAML. Spectral evidence for this association is presented. The optimization of PNC structure by density functional theory rules out coordination of PNC to 1 via the formation of a Fe-N bond. The kinetic data indicate that the rate constant kII exceeds 1 × 105 (mol L-1)-1 s-1 at pH 11 and 25°C. [ABSTRACT FROM AUTHOR]

Abstract: Yellow cyclometalatated ruthenium (II) complexes [Ru(o-X-2-py)(MeCN)4]PF6 (1, X=C6H4 (a) or 4-MeC6H3 (b)) react readily with 1,10-phenanthroline (LL) in MeCN to give brownish-red species cis-[Ru(o-X-2-py)(LL)(MeCN)2]PF6 in high yields. The same reaction of the same complexes under the same conditions with 2,2′-bipyridine results in a significant color change from yellow to brownish-orange suggesting a formation of new species. Surprisingly, X-ray structural studies of these two complexes showed that they are structurally indistinguishable from the starting complexes 1. Referred to as complexes 4a,b, the new compounds are slightly more stable in the air though their spectral characteristics in solution are similar to 1a,b. The diffuse reflectance spectroscopy is so far the only technique that indicated differences between 1 and 4. [Copyright &y& Elsevier]

Redox potentials of photosensitive cyclometalated RuII derivatives of 2-phenylpyridine or 2-(4-tolyl)pyridine are controllably decreased by up to 0.8 V within several minutes. This is achieved by irradiation of the ruthena(II)cycles cis-[Ru(o-X-2-py)(LL)(MeCN)2]PF6(2, X = C6H4 (a) or 4-MeC6H3 (b), LL = 1,10-phenanthroline or 2,2′-bipyridine). The cis geometry of the MeCN ligands has been confirmed by the X-ray structural studies. The σ-bound sp² carbon of the metalated ring is trans to LL nitrogen. Complexes 2 are made from [Ru(σ-X-2-py)(MeCN)4]PF6 (1) and LL. This “trivial” ligand substitution is unusual because 1a reacts readily with phen in MeCN as solvent to give cis-[Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 (2c) in a 83% yield, but bpy does not afford the bpy-containing 2 under the same conditions. cis-[Ru(o-C6H4-2-py)(bpy)(MeCN)2]PF6 (2e) has been prepared in CH2CI2 (74%). Studies of complexes 2c,e by cyclic voltammetry in MeOH in the dark reveal RuII/III quasy-reversible redox features at 573 and 578 mV (vs Ag/AgCI), respectively. A minute irradiation 2c and 2e converts them into new species with redox potentials of -230 and 270 mV, respectively. An exceptional potential drop for 2c is accounted for in terms of a photosubstitution of both MeCN ligands by methanol. ESR, ¹H NMR, and UV—vis data indicate that the primary product of photolysis of 2c is an octahedral monomeric low-spin (S = ½) RuIII species, presumably cis-[RuIII(o-C6H4-2-py)(phen)(MeOH)2]2+. The primary photoproduct of bpy complex 2e is cis-[RuII(o-C6H4-2-py)(bpy)(MeCN)-(MeON)]+, and this accounts for a lower decrease in the redox potential. Irradiation of 2c in the presence of added chloride affords [(phen)(o-C6H4-2-py)CIRuIIIORuIVCI(o-C6H4-2-py)(phen)]PF6, a first μ-oxo-bridged mixed valent dimer with a cyclometalated unit. The structure of the dimer has been established by X-ray crystallography. [ABSTRACT FROM AUTHOR]

Intact photosensitive cyclometalated RuII derivatives of 2-phenylpyridine or N,N-dimethylbenzylamine cis-[Ru-(C∼N)(LL)X2]PF6[C∼N =o-C6H4-py or o-C6H4CH2NMe2;LL= 1,10-phenanththroline (phen), 2,2'-bipyridine (bpy), or 4,4'-Me2-2,2'-bipyridine (Me2bpy); X = MeCN or pyridine (py)] are efficient mediators of glucose oxidase (GO) from Aspergillus niger and horseradish peroxidase (HRP). Their redox potentials in an aqueous buffer are in the range 0.15-0.35 V versus SCE, and the rate constants for the oxidation GO(red) (where red indicates reduced) by the electrochemically generated RuIII species equal (1.7-2.5) × 106 M-1 at pH 7 and 25 °C. The redox potentials of all complexes decrease cathodically by 0.4-0.6 V upon irradiation by visible light because of the photoinduced solvolysis of acetonitrile or py ligands. These in situ generated species display an even better mediating performance with HRP, although their behavior toward GO is different. The loading of a ruthenium unit into the protein interior brings about large catalytic currents in a self-assembled system GO-Ru-D-glucose. The estimated rate constant for intramolecular electron transfer from FADH2 of the active site at RuIII, kintra, equals 4.4 × 10³ s-1. This suggests that the distance between the redox partners is around 19 Å. The value of 21 Å was obtained through the docking analysis of a possible closest-to-FAD localization of a Ru-containing fragment derived from the irradiated complex cis-[Ru(o-C6H4-py)-(phen)(MeCN)2]PF6. The operational stability of the GO-Ru assemblies depends on the nature of complex used, the highest being observed for cis-[Ru(o-C6H4-py)Me2-bpy)(MeCN)2]PF6 (2). UV-vis studies of interaction of 2 with GO revealed photomechanical oscillations in the system GO-Ru-D-glucose. When irradiated complex 2 is mixed with GO and D-glucose, the absorbance at 510 nm increases because of the enzymatic reduction of RuIII to RuII. The absorbance drops rapidly and then increases as in the first cycle after shaking the reaction solution. Many cycles are possible, and the rate of absorbance increase does not depend on a cycle number. A plausible mechanism of the oscillations is presented. [ABSTRACT FROM AUTHOR]

The cycloruthenation of 2-phenylimidazole (phim) by [Ru(η6-C6H6)(μ-Cl)Cl]2 in acetonitrile in the presence of NaOH has been carried out. The unstable intermediate [Ru(phim)(MeCN)4]PF6 formed has been converted into the complexes [Ru(phim)(4,4′-Me2bpy)(MeCN)2]PF6 (2) and [Ru(phim)(LL)2]PF6 (3, LL=phen (a), bpy, 4,4′-Me2bpy), which were characterized by the mass-spectrometry, 1H-NMR spectroscopy, UV–vis spectrophotometry, and cyclic voltammetry. The RuII/III redox potentials of complexes 3 equal 130–250 mV (vs. Ag–AgCl) at pH 7 (0.01 M phosphate). Such potential range is favorable for fast exchange of electrons with the active sites of redox enzymes. In fact, the second-order rate constant for the oxidation of reduced glucose oxidase (GO) from Aspergillus niger by the electrochemically generated RuIII derivative of complex 3a equals (8.1×106 M−1 s−1). The second-order rate constant for the oxidation of 3a by the Compound II of horseradish peroxidase is 9.3×107 M−1 s−1. Complexes 3 were used as mediators for the fabrication of enzyme electrodes by simple co-adsorbing with GO or horseradish peroxidase on graphite electrodes. These electrodes were tested in flow-injection systems and showed linear responses in the range of d-glucose and H2O2 concentrations 0.1–30 mM and 1–200 μM, respectively. The new mediators reported herein seem promising for the construction of amperometric biosensors based on GO, horseradish peroxidase, and similar enzymes. [Copyright &y& Elsevier]

Examines the structural mechanistic aspects of orthoplatination of acetophenone and benzaldehyde oximes. Reaction of acetophenone oxime with sulfoxide complex 2a in methanol solvent; Formation of the unreactive dichlorobis(N-oxime)platinum(II) cation accounts for the rate retardation; Intra- and intermolecular hydrogen bond networks in complex 3b.

Examines the synthesis and bio-application of cyclometalated ruthenium(II) complexes for fast mediated electron transfer with peroxidase and glucose oxidase (GO). Determination of innovative use of cycloruthenated; Analysis of the structure of cation; Reduction of flavin adenine dinucleotide of GO.

AbstractRuthenium(II) and iron(II) POCOP pincer complexes have readily been obtained from ligands derived from the 1,3- and 1,7-dihydroxynaphtalene isomers. The two ruthenium(II) isomers displayed remarkable catalytic activity for the Friedländer annulation, and the reaction was tolerant to a wide array of electron-withdrawing and -donating substituted ketones. The catalytic reactions produced selectively the quinoline derivatives in conversions up to 99% at low catalysts loadings with turnover numbers close to 1000. The iron catalysts also exhibited a notable catalytic activity, albeit lower than their ruthenium counterparts. These results mark a significant advancement in developing catalytic reactions with ruthenium and iron POCOP pincer derivatives. [ABSTRACT FROM AUTHOR]

Demonstrates the synthesis, characterization and mechanism of action of eta1-I21 organometallic `pincer' complexes of platinum. Models for the initial stages of oxidative addition; Structural characterization of the platinum complexes by single-crystal X-ray diffraction methods; Role of the metal-bound halide anion as the point of initial attack of I2.

Studies the biodegradation of soluble redox polymers. Apparatus; Reagents; Preparation of ferrocene-modified amylose; Synthesis of soluble (0.017Ferrocene)amylose; Electrochemical properties of (0.017Ferrocene)amylose; Quantitative treatment of cyclic voltammograms; Applications.

Reports on a photochemical reaction that stabilized the thermodynamically unstable ligand cis-azobenzene. Location of platinum centers; Elongation of the Pt-N bonds; Visualizing a photochemical trans to cis isomerization of azobenzene; Effect of a ligand's configuration on its ability to bind metal centers.

Reactions of cyclometalated compounds are numerous. This account is focused on one of such reactions, the exchange of cyclometalated ligands, a reaction between a cyclometalated compound and an incoming ligand that replaces a previously cyclometalated ligand to form a new metalacycle: + H-C*~Z ⇄ + H-C~Y. Originally discovered for PdII complexes with Y/Z = N, P, S, the exchange appeared to be a mechanistically challenging, simple, and convenient routine for the synthesis of cyclopalladated complexes. Over four decades it was expanded to cyclometalated derivatives of platinum, ruthenium, manganese, rhodium, and iridium. The exchange, which is also questionably referred to as transcyclometalation, offers attractive synthetic possibilities and assists in disclosing key mechanistic pathways associated with the C–H bond activation by transition metal complexes and C–M bond cleavage. Both synthetic and mechanistic aspects of the exchange are reviewed and discussed. [ABSTRACT FROM AUTHOR]

Describes the synthesis of low-potential cyclometalated osmium(II) mediators of glucose oxidase. Transmetalation; Second-order rate constant; Redox potentials; Molecular structure.

Studies the mechanism of H+-induced demetalation as a design strategy for robust iron (III) peroxide-activating catalysts. Properties of enzymes that activate dioxygen or hydrogen peroxide; Function of polychlorophenol mineralization.

The main features of iron-tetra-amido macrocyclic ligand complex (a sub-branch of TAML) catalysis of peroxide oxidations are rationalized by a twostep mechanism: FeIII + H2O2 → Active catalyst (Ac) (Ki), and Ac + Substrate (S) → FeIII + Product (kII). TAML activators also undergo inactivation under catalytic conditions: Ac → Inactive catalyst (ki). The recently developed relationship, In (S0/S∡) = (kII/ki)[FeIII]tot, where S0 and S∡ are [S] at time t = 0 and ∡, respectively, gives access to ki under any conditions. Analysis of the rate constants ki; kII) and ki at the environmentally significant pH of 7 for a broad series of TAML activators has revealed a 6 orders of magnitude reactivity differential in both fcu and Iq and 3 orders differential in kII Linear free energy relationships linking kII with ki and kI reveal that the reactivity toward substrates is related to the instability of the active TAML intermediates and suggest that the reactivity in all three processes derives from a common electronic origin. The reactivities of TAML activators and the horseradish peroxidase enzyme are critically compared. [ABSTRACT FROM AUTHOR]

Ferric tetraamido macrocyclic ligand (TAML)-based catalysts [Fe└┌{C6H4-1,2-(NCOCMe2NCO)2CR2}(OH2)]PPh4 [1; R = Me (a), Et (b)] are oxidized by m-chloroperoxybenzoic acid at −40 °C in acetonitrile containing trace water in two steps to form Fe(V)oxo complexes (2a,b). These uniquely authenticated FeV(O) species comproportionate with the FeIII starting materials 1a,b to give μ-oxo-(FeIV)2 dimers. The comproportionation of 1a-2a is faster and that of 1b-2b is slower than the oxidation by 2a,b of sulfides (p-XC6H4SMe) to sulfoxides, highlighting a remarkable steric control of the dynamics. Sulfide oxidation follows saturation kinetics in [p-XC6H4SMe] with electron-rich substrates (X = Me, H), but changes to linear kinetics with electron-poor substrates (X = Cl, CN) as the sulfide affinity for iron decreases. As the sulfide becomes less basic, the FeIV/FeIII ratio at the end of reaction for 2b suggests a decreasing contribution of concerted oxygen-atom transfer (FeIV → FeIII) concomitant with increasing electron transfer oxidation (FeVI → FeIV). FeV is more reactive toward PhSMe than FeIV by 4 orders of magnitude, a gap even larger than that known for peroxidase Compounds I and II. The findings reinforce prior work typecasting TAML activators as faithful peroxidase mimics. [ABSTRACT FROM AUTHOR]

The metal-mediated coupling between coordinated EtCN in the ptatinum(II) and platinum(IV) complexes cis- and trans-[PtCl2(EtCN)2], trans-[PtCl4(EtCN)2], a mixture of cis/trans-[PtCl4(EtCN)2] or [Ph3PCH2Ph][PtCln(EtCN)] (n = 3, 5), and dialkyl- and dibenzylhydroxylamines R2NOH (R = Me, Et, CH2Ph, CH2C6H4Cl-p) proceeds smoothly in CH2Cl2 at 20–25 °C and the subsequent workup allowed the isolation of new imino species [PtCln&lcub;NH=C(Et)-ONR2&rcub;2] (n = 2, R = Me, cis-1 and trans-1; Et, cis-2 and trans-2; CH2Ph, cis-3 and trans-3; CH2C6H4Cl-p, cis-4 and trans-4; n = 4, R = Me, trans-9; Et, trans-10; CH2Ph, trans-11; CH2C6H4Cl-p, trans-12) or [Ph3PCH2Ph]-[PtCln&lcub;NH=C(Et)ONR2&rcub;] (n = 3, R = Me, 5; Et, 6; CH2Ph, 7; CH2C6H4Cl-p, 8; n = 5, R = Me, 13; Et, 14; CH2Ph, 15; CH2C6H4Cl-p, 16) in excellent to good (95–80%) isolated yields. The reduction of the Pt(IV) complexes 9–16 with the ylide Ph3P=CHCO2Me allows the synthesis of Pt(II) species 1–8. The compounds 1–16 were characterized by elemental analyses (C, H, N), FAB-MS, IR, ¹H, ¹C&lcub;¹H&rcub;, and 31P&lcub;¹H&rcub; NMR (the latter for the anionic type complexes 5–8 and 13–16) and by X-ray crystallography for the Pt(II) (cis-1, cis-2, and trans-4) and Pt(IV) (18) species. Kinetic studies of addition of R2NOH (R = CH2C6H4Cl-p) to complexes [Ph3PCH2Ph]-[PtIICl3(EtCN)] and [Ph3PCH2Ph][PtIVCl5(EtCN)] by the ¹H NMR technique revealed that both reactions are first order in (p-CIC6H4CH2)2NOH and Pt(II) or Pt(IV) complex, the second-order rate constant k2 being three orders of magnitude larger for the Pt(IV) complex. The reactions are intermolecular in nature as proved by the independence of k2 on the concentrations of added EtC = N and Cl¯. These data and the calculated values of ΔH‡ and ΔS&Dagger are consistent with the mechanism involving the rate-limiting nucleophilic attack of the oxygen of (p-ClC6H4CH2)2NOH at the sp-carbon of the C=N bond followed by a fast proton migration. [ABSTRACT FROM AUTHOR]

The orthopalladation of benzylamine (baH) by Pd(II) acetate in acetonitrile occurs in two time-resolved steps. A first faster step taking place at 25 °C results in the formation of the N-bound complex [Pd(OAc)2(baH)2] and follows a second-order kinetics in the incoming amine according to the rate law kobs=k1[baH]2. The second order in baH arises from the successive substitution of the solvent in [Pd(OAc)2(MeCN)2]. The latter complex transforms slowly into the orthometalated derivative [Pd(ba)(OAc)]2 at 60 °C. The initial rate of this step is inversely proportional to the concentration of baH and the following rate law holds: V0=km Pd(II)t/[baH]. This is accounted for in terms of the mechanism involving a reversible dissociation of one baH ligand from [Pd(OAc)2(baH)2] followed by the electrophilic C&z.sbnd;H bond cleavage of N-bound baH by Pd(II). [Copyright &y& Elsevier]

The synthesis of cyclometalated osmium complexes is usually more complicated than of other transition metals such as Ni, Pd, Pt, Rh, where cyclometalation reactions readily occur via direct activation of C–H bonds. It differs also from their ruthenium analogs. Cyclometalation for osmium usually occurs under more severe conditions, in polar solvents, using specific precursors, stronger acids, or bases. Such requirements expand reaction mechanisms to electrophilic activation, transmetalation, and oxidative addition, often involving C–H bond activations. Osmacycles exhibit specific applications in homogeneous catalysis, photophysics, bioelectrocatalysis and are studied as anticancer agents. This review describes major synthetic pathways to osmacycles and related compounds and discusses their practical applications. [ABSTRACT FROM AUTHOR]

A cyclic voltammetry study of a series of iron(III) TAML activators of peroxides of several generations in acetonitrile as solvent reveals reversible or quasireversible FeIII/IV and FeIV/V anodic transitions, the formal reduction potentials (E°′) for which are observed in the ranges 0.4–1.2 and 1.4–1.6 V, respectively, versus Ag/AgCl. The slope of 0.33 for a linear E°′(IV/V) against E°′(III/IV) plot suggests that the TAML ligand system plays a bigger role in the FeIII/IV transition, whereas the second electron transfer is to a larger extent an iron‐centered phenomenon. The reduction potentials appear to be a convenient tool for analysis of various properties of iron TAML activators in terms of linear free energy relationships (LFERs). The values of E°′(III/IV) and E°′(IV V−1) correlate 1) with the pKa values of the axial aqua ligand of iron(III) TAMLs with slopes of 0.28 and 0.06 V, respectively; 2) with the Stern–Volmer constants KSV for the quenching of fluorescence of propranolol, a micropollutant of broad concern; 3) with the calculated ionization potentials of FeIII and FeIV TAMLs; and 4) with rate constants kI and kII for the oxidation of the resting iron(III) TAML state by H2O2 and reactions of the active forms of TAMLs formed with donors of electrons S, respectively. Interestingly, slopes of log kII versus E°′(III/IV) plots are lower for fast‐to‐oxidize S than for slow‐to‐oxidize S. The log kI versus E°′(III/IV) plot suggests that the manmade TAML catalyst can never be as reactive toward H2O2 as a horseradish peroxidase enzyme. [ABSTRACT FROM AUTHOR]

The bis-sulfonamide TAML activator of peroxides [Fe{4-NO2C6H3-1,2-(NCOCMe2NSO2)2CHMe}]- (2) catalyzes the H2O2 oxidation of microcystin-LR (m-LR), a common surface water contaminant produced by cyanobacteria that is toxic at very low concentrations. The major reaction product is by 16 Da heavier than m-LR, suggesting that the first oxidative step involves addition of oxygen to one of m-LRs three C = C units to form an epoxide. The kinetic data suggest that the m-LR → m + 16 conversion occurs without any kinetically meaningful intermediate with the catalytic rate constant kII of 2.5 × 105 M−1 s−1, which characterizes the interaction of m-LR with the oxidized, active form of the catalyst. The primary m + 16 product undergoes much slower further catalytic oxidation in the aqueous reaction medium. This communication describes a potential utility of TAML/H2O2 catalysis for microcystin detoxification that calls for further research. [ABSTRACT FROM AUTHOR]

Bis‐sulfonamide bis‐amide TAML activator [Fe{4‐NO2C6H3‐1,2‐(NCOCMe2NSO2)2CHMe}]− (2) catalyzes oxidative degradation of the oxidation‐resistant neonicotinoid insecticide, imidacloprid (IMI), by H2O2 at pH 7 and 25 °C, whereas the tetrakis‐amide TAML [Fe{4‐NO2C6H3‐1,2‐(NCOCMe2NCO)2CF2}]− (1), previously regarded as the most catalytically active TAML, is inactive under the same conditions. At ultra‐low concentrations of both imidacloprid and 2, 62 % of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a succeeding aliquot of 2. Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [2]≥[IMI], the reaction kinetics revealed unusually low kinetic order in 2 (0.164±0.006), which is observed alongside the first order in imidacloprid and an ascending hyperbolic dependence in [H2O2]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible noncovalent binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst]≪[substrate] but explains the zero order in the catalyst when [2]>[IMI]. A plausible mechanism of the TAML‐catalyzed oxidations of imidacloprid is briefly discussed. Similar zero‐order catalysis is presented for the oxidation of 3‐methyl‐4‐nitrophenol by H2O2, catalyzed by the TAML analogue of 1 without a NO2‐group in the aromatic ring. [ABSTRACT FROM AUTHOR]

Designing technologies that mitigate the low-dose adverse effects of exposures to large-volume, everyday-everywhere chemicals such as bisphenol A (BPA, 1a) requires an understanding of the scope of the exposures and the nature of the adverse effects. Therefore, we review the literature of, (i) the occurrences of 1a in humans, waters and products and the effectiveness of widely deployed mitigation methods in 1a stewardship and, (ii) the adverse effects of 1a exposures on human cells and fish. Within this broad context, we present and evaluate experimental results on TAML/H2O2 purification of 1a contaminated waters. TAML/H2O2 catalysis readily oxidizes BPA (1a) and the ring-tetramethyl (1b), tetrachloro (1c), and tetrabromo (1d)-substituted derivatives. At pH 8.5, TAML/H2O2 induces controllable, oxidative oligomerisation of 1a (2-, 3-, 4-, and 5-unit species were identified) with precipitation, establishing a green synthetic pathway to these substances for biological safety characterisation and an easy method for near quantitative removal of 1a from water. TAML/H2O2 (24 nM/4 mM) treatment of 1a (10 000 μg L−1) in pH 8.5 (0.01 M, carbonate) lab water effects a ＞99% reduction (to ＜100 μg L−11a) within 30 min. Yeast oestrogen screens (YES) of the pH 8.5, TAML/H2O2 treated, catalase quenched, and filtered oxidation solutions show elimination of 1a oestrogenicity. Zebrafish developmental assays of TAML/H2O2 treated, unfiltered, agitated pH 7, 1a solutions showed no significant incidences of abnormality among any of 22 endpoints―treated samples showed an insignificant increase in mortality. At pH 11, the TAML/H2O2 oxidations of 1a–d are fast with second order rate constants for the substrate oxidation process (kII values) of (0.57–8) × 104 M−1 s−1. The 1a oxidation gives CO and CO2 (∼78%), acetone (∼25%) and formate (∼1%). In striking contrast with pH 8.5 treatment, no oligomers were detected. TAML/H2O2 (150 nM/7.5 mM) treatment of 1a (34 244 μg L−1) in pH 11 (0.01 M, phosphate) lab water effected a ＞99.9% reduction (to ＜23 μg L−11a) within 15 min. The pH dependent behaviour of 1a was examined as a possible origin of the differing outcomes. The 1st and 2nd pKa values of 1a were estimated by fitting the pH dependence of the UV-vis spectra (pKa1 = 9.4 ± 0.3; pKa2 = 10.37 ± 0.07). At pH 8.5, coupling of the radical produced on initial oxidation evidently outcompetes further oxidation. A linear free energy relationship between the logarithm of the pH 11, kII values and the redox potentials of 1a–d as determined by differential pulse voltammetry in CH3CN is consistent with rate-limiting, electron transfer from the dianionic form of 1a at pH 11, followed by a multistep, deep degradation without observation of 4-(prop-1-en-2-yl)phenol 12, a common 1a oxidation product―an improved synthesis of 12 is described. Microtox® analyses of pH 12, TAML/H2O2 treated 1a solutions showed significantly reduced toxicity. The facility and high efficiency by which TAML/H2O2 catalysis eliminates 1a from water, by either mechanism, suggests a new and simple procedure for 1a stewardship. [ABSTRACT FROM AUTHOR]

The unique properties of entirely aliphatic TAML activator [FeIII{(Me2CNCOCMe2NCO)2CMe2}OH2]− (3), namely the increased steric bulk of the ligand and the unmatched resistance to the acid-induced demetalation, enables the generation of high-valent iron derivatives in pure water at any pH. An iron(V)oxo species is readily produced with NaClO at pH values from 2 to 10.6 without any observable intermediate. This is the first reported example of iron(V)oxo formed in pure water. At pH 13, iron(V)oxo is not formed and NaClO oxidizes 3 to an iron(IV)oxo derivative. [ABSTRACT FROM AUTHOR]

Lactate dehydrogenase (LDH) is a redox enzyme often overexpressed in cancer cells allowing their survival in stressful metabolic tumor environment. Ruthenium(II) complexes have been shown to impact on the activity of purified horseradish peroxidase and glucose oxidase but the physiological relevance remains unclear. In this study we investigated how ruthenium complexes impact on the activity of LDH in vitro and in cancer cells and performed a comparative study using polypyridine ruthenium(II) complex [Ru(bpy) 3 ] 2 + ( 1 ) and its structurally related cyclometalated 2-phenylpyridinato counterpart [Ru(phpy)(bpy) 2 ] + ( 2 ) (bpy = 2,2′-bipyridine, phpyH = 2-phenylpyridine). We show that the cytotoxicity in gastric and colon cancer cells induced by 2 is significantly higher compared to 1 . The kinetic inhibition mechanisms on purified LDH and the corresponding inhibition constants K i or i 0.5 values were calculated. Though complexes 1 and 2 are structurally very similar (one Ru−C bond in 2 replaces one Ru−N bond in 1 ), their inhibition modes are different. Cyclometalated complex 2 behaves exclusively as a non-competitive inhibitor of LDH from rabbit muscle (LDH rm) , strongly suggesting that 2 does not interact with LDH in the vicinities of either lactate/pyruvate or NAD + /NADH binding sites. Sites of interaction of 1 and 2 with LDH rm were revealed theoretically through computational molecular docking. Inhibition of LDH activity by 2 was confirmed in cancer cells. Altogether, these results revealed an inhibition of LDH activity by ruthenium complex through a direct interaction structurally tuned by a Ru−C bond. [ABSTRACT FROM AUTHOR]

The oxidation of TAML complex(1) by various oxidants is explored in MeCN with 0.2% water at −40 °C, where the iron(V)oxo complex is stable enough for reliable spectral identification. The iron(V)oxo state is achieved using NaClO even faster than in the case of previously exploredm-chloroperoxybenzoic acid. In contrast, H2O2and organic peroxides (benzoyl peroxide,tert-butylperoxide, andtert-butylhydroperoxide) all convert1into the corresponding diiron(IV)-μ-oxo dimer (2) under the same conditions. The latter does not form when (NH4)2[Ce(NO3)6] is employed and the FeIVproduct obtained does not seem to contain an oxo moiety. In contrast to all other oxidants, the conversion of1bytBuOOH into2is characterized by non-conventional kinetics, and therefore this reaction was explored in some detail. The evidence is presented that this light-, O2-, TEMPO-, and base-dependent reaction is a free radical process under the conditions used. [ABSTRACT FROM AUTHOR]

Iron TAML activators of peroxides are functional catalase-peroxidase mimics. Switching from hydrogen peroxide (H2O2) to dioxygen (O2) as the primary oxidant was achieved by using a system of reverse micelles of Aerosol OT (AOT) in n-octane. Hydrophilic TAML activators are localized in the aqueous microreactors of reverse micelles where water is present in much lower abundance than in bulk water. n-Octane serves as a proximate reservoir supplying O2 to result in partial oxidation of FeIII to FeIV-containing species, mostly the FeIIIFeIV (major) and FeIVFeIV (minor) dimers which coexist with the FeIII TAML monomeric species. The speciation depends on the pH and the degree of hydration w0, viz., the amount of water in the reverse micelles. The previously unknown FeIIIFeIV dimer has been characterized by UV-vis, EPR, and Mössbauer spectroscopies. Reactive electron donors such as NADH, pinacyanol chloride, and hydroquinone undergo the TAML-catalyzed oxidation by O2. The oxidation of NADH, studied in most detail, is much faster at the lowest degree of hydration w0 (in "drier micelles") and is accelerated by light through NADH photochemistry. Dyes that are more resistant to oxidation than pinacyanol chloride (Orange II, Safranine O) are not oxidized in the reverse micellar media. Despite the limitation of low reactivity, the new systems highlight an encouraging step in replacing TAML peroxidase-like chemistry with more attractive dioxygen-activation chemistry. [ABSTRACT FROM AUTHOR]

The catalytic activity of the N-tailed ('biuret') TAML (tetraamido macrocyclic ligand) activators [Fe{4-XC6H3-1,2-( NCOCMe2 NCO)2NR}Cl]2− ( 3; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me ( a); NO2, Me ( b); H, Ph ( c)] in the oxidative bleaching of Orange II dye by H2O2 in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4-XC6H3-1,2-( NCOCMe2 NCO)2CMe2}OH2]− ( 1) and the more aggressive analogue [Fe(Me2C{CON(1,2-C6H3-4-X) NCO}2)OH2]− ( 2). Catalysis by 3 of the reaction between H2O2 and Orange II (S) occurs according to the rate law found generally for TAML activators ( v= kI kII[FeIII][S][H2O2]/( kI[H2O2]+ kII[S]) and the rate constants kI and kII at pH 7 both decrease within the series 3 b> 3 a> 3 c. The pH dependency of kI and kII was investigated for 3 a. As with all TAML activators studied to-date, bell-shaped profiles were found for both rate constants. For kI, the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a. For kII, the broad bell pH profile exhibits a maximum at pH about 10.5. The condition kI≪ kII holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants ki for suicidal inactivation of the active forms of complexes 3 a- c were calculated using the general formula ln([S0]/[S∞])=( kII/ ki)[FeIII]; here [FeIII], [S0], and [S∞] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X-ray characterization of 3 c are also described. [ABSTRACT FROM AUTHOR]

The electronic properties of iron tetraamido macrocyclic ligand (TAML) activators of peroxides can be finely and coarsely tuned by varying the substituents on the 'head' and 'tail' macrocyclic components, respectively. By examining the reactivity of the TAML oxidoiron(V) complex with head-NO2 and tail-F substituents, one is able to compare the impact of significantly reduced macrocyclic tetraamide donor capacity on fundamental processes such as hydrogen-atom abstraction, oxygen-atom transfer, and electron transfer by using prior studies with more electron-rich TAML systems. Herein, we demonstrate that the oxidoiron(V) form 3c can be generated by treatment of [Fe{4-NO2C6H3-1,2-(N2COCMe2N3CO)2CF2( Fe-N2)( Fe-N3)}(OH2)]- ( 1c) with m-chloroperoxybenzoic acid ( mCPBA) in MeCN at -40 °C. The oxidation proceeds through the intermediacy of the μ-oxo[iron(IV)]2 dimer. The overall rate of the FeIII→FeV conversion by mCPBA is slightly faster for 1c than that of its less electron-rich precursor [Fe{C6H4-1,2-(N1COCMe2N2CO)2CMe2( Fe-N1)( Fe-N2)}(OH2)]- ( 1a). Nevertheless, the oxidative reactivity of 3c toward thioanisole and the hydrocarbons ethylbenzene and cyclohexane exceeds that of 3a by 4.3, 2.1, and 2.6 times, respectively. The reactivity of 3c is significantly greater towards ethylbenzene than that of the oxidoiron(V) species 3b derived from [Fe{C6H4-1,2-(N1COCMe2N2CO)2NMe( Fe-N1)( Fe-N2)}(OH2)]- ( 1b). [ABSTRACT FROM AUTHOR]

The results of low-temperature investigations of the oxidations of 9,10-dihydroanthracene, cumene, ethylbenzene, [D10]ethylbenzene, cyclooctane, and cyclohexane by an iron(V)-oxo TAML complex ( 2; see Figure 1) are presented, including product identification and determination of the second-order rate constants k2 in the range 233-243 K and the activation parameters (Δ H≠ and Δ S≠). Statistically normalized k2 values (log k2′) correlate linearly with the CH bond dissociation energies DCH, but Δ H≠ does not. The point for 9,10-dihydroanthracene for the Δ H≠ vs. DCH correlation lies markedly off a common straight line of best fit for all other hydrocarbons, suggesting it proceeds via an alternate mechanism than the rate-limiting CH bond homolysis promoted by 2. Contribution from an electron-transfer pathway may be substantial for 9,10-dihydroanthracene. Low-temperature kinetic measurements with ethylbenzene and [D10]ethylbenzene reveal a kinetic isotope effect of 26, indicating tunneling. The tunnel effect is drastically reduced at 0 °C and above, although it is an important feature of the reactivity of TAML activators at lower temperatures. The diiron(IV) μ-oxo dimer that is often a common component of the reaction medium involving 2 also oxidizes 9,10- dihydroanthracene, although its reactivity is three orders of magnitude lower than that of 2. [ABSTRACT FROM AUTHOR]

The synthesis of 1,2-C6H4(NHCOCMe2NHCO)2-3,3′-(2,2′-bpy) (3), a TAML (tetraamidomacrocyclicligand) incorporating the peripheral 2,2′-bipyridine unit, is described. Its geometry after optimization by density functional theory (DFT) indicated a rather unfavorable conformation of four N–H amide units for forming macrocyclic transition metal complexes. This explains why the iron(III) derivative of3could not be obtained even after deprotonation of the N–H bonds byn-BuLi. Nevertheless, the macrocyclic complex of CoIIIwas synthesized in moderate yield, characterized, and explored by DFT. Our data suggest a strongly distorted square-planar geometry of the macrocyclic complex between CoIIIand3. The dihedral angle between the pyridine rings equals 80° ruling out the possibility of metal chelation by the bipyridine unit. [ABSTRACT FROM PUBLISHER]

Three cyclometalated and one coordination compounds [Os(C–N) x (bpy)3− x ] m (x/m =0/2+ (4); 1/1+ (3); 2/1+ (2); 3/0 (1); −C–N=2-phenylpyridinato, bpy=2,2′-bipyridine) with drastically different reduction potentials have been used for analyzing the second-order rate constants for one-electron, metal-based osmium(II) to osmium(III) oxidation of the complexes by compound I (k 2) and compound II (k 3) of horseradish peroxidase. Previously unknown k 2 and k 3 have been determined by digital simulation of cyclic voltammograms measured in phosphate buffer of pH7.6 and 21±1°C. Osmium(II) species derived from osmium(III) complexes 1 and 2 were generated electrochemically in situ. Under the conditions used the reduction potentials for the OsIII/II feature equal −0.90, −0.095, 0.23 and 0.85V versus NHE (normal hydrogen electrode) for 1–4, respectively. The rate constants k 2 equal ~5×107, 6×108, 2×106 and 1×105 M−1 s−1 and the rate constants k 3 equal ~9×106, 4×107, 1×106 and 1×105 M−1 s−1 for complexes 1–4, respectively. Both rate constants k 2 and k 3 first increase with increasing the reaction driving force on going from 4 to 2 but then both decrease on going to complex 1 though the reaction driving force is the highest in this case. The system described has been explored theoretically using docking Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Iron-TAML activators of peroxides are functional mimics of peroxidase and short-circuited cytochrome P450 enzymes that perform numerous transformations that appear by all measures to date to be fully life cycle compatible with the environment. Here we show how to design the same catalytic chemistry without the direct addition of H2O2, thereby removing the need to transport and store hydrogen peroxide. In this new approach, dioxygen is reduced in situ by d-glucose in the presence of glucose oxidase (GO) from Aspergillus niger. The resulting tandem TAML–GO system exhibits similar catalytic efficiency to the TAML/H2O2 prototype. The tandem system is shown here to efficiently decolorize Orange II and oxidize NADH, both near neutral pH (7.5). Computational simulations of the kinetic data suggest that denaturing of GO by oxidized TAML intermediates does not occur throughout each process. This tandem system brings the advantage of in situ generation of low concentrations of H2O2 during the catalytic cycles. This minimizes both unproductive H2O2 consumption resulting from the catalase-like activity of iron TAMLs and suicidal inactivation. Kinetic data for oxidation of NADH by TAML/H2O2 are also reported. [ABSTRACT FROM AUTHOR]

TAML activators are well-known for their ability to activate hydrogen peroxide to oxidize persistent pollutants in water. The trinitroaromatic explosives, 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrobenzene (TNB), are often encountered together as persistent, toxic pollutants. Here we show that an aggressive TAML activator with peroxides boosts the effectiveness of the known surfactant/base promoted breakdown of TNT and transforms the surfactant induced nondestructive binding of base to TNB into an extensive multistep degradation process. Treatment of basic cationic surfactant solutions of either TNT or TNB with TAML/peroxide (hydrogen peroxide and tert-butylhydroperoxide, TBHP) gave complete pollutant removal for both in <1 h with >75% of the nitrogen and ≥20% of the carbon converted to nitrite/nitrate and formate, respectively. For TNT, the TAML advantage is to advance the process toward mineralization. Basic surfactant solutions of TNB gave the colored solutions typical of known Meisenheimer complexes which did not progress to degradation products over many hours. However with added TAML activator, the color was bleached quickly and the TNB starting compound was degraded extensively toward minerals within an hour. A slower surfactant-free TAML activator/peroxide process also degrades TNT/TNB effectively. Thus, TAML/peroxide amplification effectively advances TNT and TNB water treatment giving reason to explore the environmental applicability of the approach. [ABSTRACT FROM AUTHOR]

A versatile photoactivated catalytic system based ona cyclometalatedruthenium(II) complex, composed of strongly coordinating bidentateand relatively labile ligands, in conjunction with a traditional alkylbromide initiator, has been developed for living/controlled radicalpolymerization. Polymerizations of three typical hydrophobic monomersmethylmethacrylate (MMA), styrene (St), and n-butyl acrylate(BA)proceeded to high conversions under visible light irradiation.The polymerization process was photoresponsive, i.e., took place onlyunder irradiation and immediately stopped when the light was turnedoff. Block copolymers of MMA with St and BA with St, as well as statisticalcopolymer of BA and St, could also be conveniently prepared. 1H NMR and electrochemical studies suggest a mechanism of thecatalytic activation, which involves a photoinduced formation of thesolvento 18-electron species cis-[Ru(o-C6H4-2-py)(phen)(MeCN)(acetone)]+through the intermediacy of the 16-electron five-coordinated complex cis-[Ru(o-C6H4-2-py)(phen)(MeCN)]+which is believed to be a crucial intermediate of the overallATRPprocess. [ABSTRACT FROM AUTHOR]

Stopped-flow kinetic studies of the oxidation of FeIII-TAML catalysts, [⌈F⌈e{1,2-X2C6H2-4,5-(⌉NCOCMe2NCO)2CMe2}(OH2)]- (1), by t-BuOOH and H2O2 in water affording FeIV species has helped to clarify the mechanism of the interaction of 1 with primary oxidants. The data collected for substituted FeIII-TAMLs at pH 6.0-13.8 and 17-45 °C has confirmed that the reaction is first order both in 1 and in peroxides. Bell-shaped pH profiles of the effective second-order rate constants kI have maximum values in the pH range of 10.5-12.5 depending on the nature of 1 and the selected peroxide. The "acidic" part is governed by the deprotonation of the diaqua form of 1 and therefore electron-withdrawing groups move the lower pH limit of the reactivity toward neutral pH, although the rate constants kI do not change much. The dissection of kI into individual intrinsic rate constants k1 ([FeL(OH2)2]- + ROOH), k2 ([FeL(OH2)OH)]2- + ROOH), k3 ([FeL(OH2)2]- + ROO-), and k4 ([FeL(OH2)OH)]2- + ROO-) provides a model for understanding the bell-shaped pH-profiles. Analysis of the pressure and substituent effects on the reaction kinetics suggest that the k2 pathway is (i) more probable than the kinetically indistinguishable k3 pathway, and (ii) presumably mechanistically similar to the induced cleavage of the peroxide O-O bond postulated for cytochrome P450 enzymes. The redox titration of 1 by IrIV and electrochemical data suggest that under basic conditions the reduction potential for the half-reaction [FeIVL(=O)(OH2)]2- + e- + H2O → [FeIIIL(OH)(OH2)]2- + OH- is close to 0.87 V (vs NHE). [ABSTRACT FROM AUTHOR]

We describe the synthesis, characterization, aqueous behavior, and catalytic activity of a new generation of FeIII-TAML (tetraamido macrocycle ligand) activators of peroxides (2), variants of [Fe{(OC)2(o,o′-NC6H4NCO)2CMe2}(OH2)-] (2d), which have been designed to be especially suitable for purifying water of recalcitrant oxidizable pollutants. Activation of H2O2 by 2 (kI) as a function of pH was analyzed via kinetic studies of Orange II bleaching. This was compared with the known behavior of the first generation of FeIII-TAMLs (1). Novel reactivity features impact the potential for oxidant activation for water purification by 2d and its aromatic ring-substituted dinitro (2e) and tetrachloro (2f) derivatives. Thus, the maximum activity for 2e occurs at pH 9, the closest yet to the EPA guidelines for drinking water (6.5-8.5), allowing 2e to rapidly activate H2O2 at pH 7.7. In water, 2e has two axial water ligands with pKa's of 8.4 and 10.0 (25 °C). The former is the lowest for all FeIII-TAMLs developed to date and is key to 2e's exceptional catalytic activity in neutral and slightly basic solutions. Below pH 7, 2d was found to be quite sensitive to demetalation in phosphate buffers. This was overcome by iterative design to give 2e (hydrolysis rate 2d > 100 × 2e). Mechanistic studies highlight 2e's increased stability by establishing that to demetalate 2e at a comparable rate to which H2PO4- demetalates 2d, H3PO4 is required. A critical criterion for green catalysts for water purification is the avoidance of endocrine disruptors, which can impair aquatic life. FeIII-TAMLs do not alter transcription mediated by mammalian thyroid, androgen, or estrogen hormone receptors, suggesting that 2 do not bind to the receptors and reducing concerns that the catalysts might have endocrine disrupting activity. [ABSTRACT FROM AUTHOR]

Abstract: Cyclometalation of benzo[h]quinoline (bzqH) by [RuCl(μ-Cl)(η6-C6H6)]2 in acetonitrile occurs in a similar way to that of 2-phenylpyridine (phpyH) to afford [Ru(bzq)(MeCN)4]PF6 (3) in 52% yield. The properties of 3 containing ‘non-flexible’ benzo[h]quinoline were compared with the corresponding [Ru(phpy)(MeCN)4]PF6 (1) complex with ‘flexible’ 2-phenylpyridine. The [Ru(phpy)(MeCN)4]PF6 complex is known to react in MeCN solvent with ‘non-flexible’ diimine 1,10-phenanthroline to form [Ru(phpy)(phen)(MeCN)2]PF6, being unreactive toward ‘flexible’ 2,2′-bipyridine under the same conditions. In contrast, complex 3 reacts both with phen and bpy in MeCN to form [Ru(bzq)(LL)(MeCN)2]PF6 {LL=bpy (4) and phen (5)}. Similar reaction of 3 in methanol results in the substitution of all four MeCN ligands to form [Ru(bzq)(LL)2]PF6 {LL=bpy (6) and phen (7)}. Photosolvolysis of 4 and 5 in MeOH occurs similarly to afford [Ru(bzq)(LL)(MeCN)(MeOH)]PF6 as a major product. This contrasts with the behavior of [Ru(phpy)(LL)(MeCN)2]PF6, which lose one and two MeCN ligands for LL=bpy and phen, respectively. The results reported demonstrate a profound sensitivity of properties of octahedral compounds to the flexibility of cyclometalated ligand. Analogous to the 2-phenylpyridine counterparts, compounds 4–7 are involved in the electron exchange with reduced active site of glucose oxidase from Aspergillus niger. Structure of complexes 4 and 6 was confirmed by X-ray crystallography. [Copyright &y& Elsevier]

The reactivity of the acido RuII complexes cis-[RuCl2(LL)2], [RuCO3(LL)2], cis-[RuCO3- (bquin)2] (LL = 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen); bquin = 2,2′-biquinoline) and cyclometalated RuII derivatives of 2-phenylpyridine and 4-(2-tolyl)pyridine [Ru(0-C6H4-2-py)(phen)2]PF6 (1), [Ru(0-C6H3-p-R-2-py)(bpy)(MeCN)2]PF6 (2), and [Ru(0-C6H3-p-R-2-py)(phen)(MeCN)2]PF6 (3) (R = H (a), Me (b)) toward laccase from Coriolus hirsutus has been investigated by conventional UV-vis spectroscopy at pH 3-7 and 25 °C. The acido and cyclometalated complexes are readily oxidized into the corresponding RuIII species, but the two types of complexes differ substantially in reactivity and obey different rate laws. The acido complexes are oxidized more slowly and the second-order kinetics, first-order in laccase and RuII, holds with the rate constants around 5 x 104 M-1 s-1 at pH 4.5 and 25 °C. The cyclometalated complexes 1-3 react much faster and the hyperbolic Michaelis-Menten kinetics holds. However, it is not due to formation of an enzyme-substrate complex but rather because of the ping-pong mechanism of catalysis, viz. E(ox) + RuII E(red) → RuII (k1); E(red) + 1/4O2 → E(ox) (k2), with the rate constants k, in the range (2-9) x 107 M-1 s-1 under the same conditions. The huge values of k1 move the enzymatic oxidation toward a kinetic regime when the dioxygen half-reaction becomes the rate-limiting step. Cyclometalated compounds 1-3 can therefore be used for routine estimation of k2, that is, the rate constant for reoxidation for laccases by dioxygen. The mechanism proposed was confirmed by the direct stopped-flow measurements of the k2 rate constant (8.1 x 105 M-1 s-1 at 26 °C) and supported by the theoretical modeling of interaction between the bpy analogue of 1 and Coriolus hirsutes laccase using Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Exceptionally high peroxidase-like and catalase-like activities of iron(lll)-TAML activators of H[sub2]O[sub2] (1: Tetra-Amidato-Macrocyclic-Ligand Fe[supIII]complexes [Fe(1,2-X[sub2]C[sub6]H[sub2]-4,5-(NCOCMe[sub2]NCO)[sub2]CR[sub2])(OH[sub2])][sup-]) are reported from pH 6-12.4 and 25-45 °C. Oxidation of the cyclometalated 2-phenylpyridine organometallic complex, [Ru[supII]o-C[sub6]H[sub4]py)(phen)[sub2]]PF[sub6] (2) or "ruthenium dye", occurs via the equation [Ru[supII]] + 1/2 H[sub2]O[sub2] + H[sup+][supFe[supIII]-TAML] ➛ [Ru[supIII]] + H[sub2]O, following a simple rate law rate = k[supcat][subobs][1][H[sub2]O[sub2]], that is, the rate is independent of the concentration of 2 at all pHs and temperatures studied. The kinetics of the catalase-like activity H[sup+][supFe[supIII]-TAML] ➛ [Ru[supIII]] + H[sub2]O + 1/2 O[sub2]) obeys a similar rate law: rate = K[supcat][subobs][1][H[sub2]O[sub2]]. The rate constants, K[supcat][subobs] and are strongly and similarly pH dependent, with a maximum around pH 10. Both bell-shaped pH profiles are quantitatively accounted for in terms of a common mechanism based on the known speciation of 1 and H[sub2]O[sub2] in this pH range. Complexes 1 exist as axial diaqua species [FeL(H[sub2]O)[sub2][sup-](1[subaqua]) which are deprotonated to afford [FeL(OH)(H[sub2]O)][sup2-] (1[subOH]) at pH 9-10. The pathways 1[subaqua] + H[sub2]O[sub2] (k[sub1]), 1[subOH] + H[sub2]O[sub2] (k[sub2]), and 1[subOH] + HO[sub2][sup-] (k[sub4]) afford one or more oxidized Fe-TAML species that further rapidly oxidize the dye (peroxidase- like activity) or a second H[sub2]O[sub2] molecule (catalase-like activity). This mechanism is supported by the observations that (i) the catalase-like activity of 1 is controllably retarded by addition of reducing agents into solution and (ii) second order kinetics in H[sub2]O[sub2] has been observed when the rate of O[sub2] evolution was monitored in the presence of added reducing agents. The performances of the 1 complexes in catalyzing H[sub2]O[sub2] oxidations are shown to compare favorably with the peroxidases further establishing Fe[subIII]-TAML activators as miniaturized enzyme replicas with the potential to greatly expand the technological utility of hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Abstract: Introduced approximately two decades ago, macrocyclic deprotonated tetraamido (4N) and, nearly a decade earlier, acyclic diamidodialkoxido or diamidophenolato (2N/2O) ligand systems have been used, among other things, for the synthesis of a wide variety of high-valent complexes of iron, manganese, cobalt, vanadium, nickel, chromium, and copper. Structural, magnetic, and catalytic properties of these mononuclear, dinuclear, and polynuclear complexes created by the Collins group are reviewed. The present account continues an overview of complexes of this type published recently and devoted to iron species exclusively [Chanda et al., J. Inorg. Biochem., 100 (2006) 606], which provide the first highly effective small molecule mimics of peroxidase enzymes, called TAML activators. The story of the reviewed first-row complexes does not include the diverse and instructive chemistry discovered for osmium, but like the osmium chemistry, it derives its greatest significance from the fact that key members of the various species mark the steps along the design pathway that led to iron-TAML activators. Consideration is given to recent questioning in the literature of the innocence of a TAML system that was designed to be innocent. The reasons underlying the now 15-year old refocusing of our research program on oxidation catalysis and green chemistry with the associated termination of research into designed molecule-based magnetic materials are explained. Our closing contributions from the mid-1990s to the design of molecule-based magnetic materials are reviewed. Previously reported data are discussed in conjunction with newly obtained information on the complexes using density functional theory. [Copyright &y& Elsevier]

Mild electrophilic C(sp²)-H cyclometalation of 2-phenylpyridine and N,N-dimethylbenzylamine by the chloro-bridged osmium(ll) dimer [OsCI(μ-CI)(η6-C6H6)]2 in acetonitrile affords cyclometalated pseudotetrahedral OsII complexes [Os(C~N)(η6-C6H6)(NCMe)]PF6 (C~N = ο-C6H4py-κC,N (2) and ο-C6H4CH2NMe2-κC,N (5), respectively) in good to excellent yields. The cyclometalation reactions are super sensitive to the nature of an external base. Sodium hydroxide is essential for cyclometalation of 2-phenylpyridine, but NaOH retards metalation of N,N-dimethylben- zylamine, the tertiary amine being self-sufficient as a base. Further reactions of compounds 2 and 5 with 1,10-phenanthroline or 2,2′-bipyridine (N~N) lead to the substitution of the η6-bound benzene to produce octahedral species [Os(C~N)(N~N)(NCMe)2]PF6 or [Os(C~N)(N~N)2]PF6 in MeCN or MeOH as solvent, respectively. The cis configuration of the MeCN ligands in [Os(C~N)(phen)(NCMe)2]PF6 has been confirmed by an X-ray crystallographic study. Electrochemical investigation of the octahedral osma(II)cycles by cyclic voltammetry showed a pseudoreversible MIII/II redox feature at (-50)-(+109) and 190-300 mV versus Ag/AgCI in water and MeCN, respectively. As a possible application of the compounds, a rapid electron exchange between the reduced active site of glucose oxidase enzyme from Aspergillus niger and the electrochemically generated OsIII species has been demonstrated. The corresponding second-order rate constants cover the range (0.7-4.8) × 106 M-1 s-1 at 25 °C and pH 7. [ABSTRACT FROM AUTHOR]