Spectroscopic investigation of the charge-transfer interactions between 1,4,7-trimethyl-1,4,7-triazacyclononane and the acceptors iodine, TCNE, TCNQ and chloranil

The interaction of the interesting polynitrogen cyclic base 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) with the sigma-acceptor iodine and pi-acceptors tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetrachloro-p-benzoquinone (chloranil) have been studied spectrophotometrically and cyclic voltametrically in chloroform at 20 degrees C. Based on the obtained data, the formed charge-transfer complexes were formulated as [(TMTACN)I](+).I(3)(-), [(TMTACN)(TCNE)(5)], [(TMTACN)(TCNQ)(3)] and [(TMTACN)(chloranil)(3)] where the stoichiometry of the reactions, donor:acceptor molar ratios, were shown to equal 1:2 for iodine complex, 1:3 for chloranil and TCNQ complexes and 1:5 for TCNE complex.     

Synthesis, spectroscopic and thermal investigations of solid charge-transfer complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane and the acceptors iodine, TCNE, TCNQ and chloranil

The solid charge-transfer complexes formed in the reaction of the electron donor 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) with the acceptors iodine, tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) have been isolated. These were characterized through electronic and infrared spectra as well as thermal and elemental analysis. The results show that the formed solid CT-complexes have the formulas [(TMTACN)I]I3, [(TMTACN)(TCNE)5] and [(TMTACN)(TCNQ)3] in full agreement with the known reaction stoichiometries in solution. The chloranil CT-solid complex cannot be isolated in pure form.     

Highly efficient oxidation of alcohols by the system "hydrogen peroxide-[lmn(o)3mnl](pf6)2 (l = 1,4,7-trimethyl-1,4,7-triazacyclononane)-oxalic acid"

Summary The dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (1, L = 1,4,7-trimethyl-1,4,7-triazacyclononane) catalyzes the extremely efficient oxidation of alcohols with hydrogen peroxide at room temperature. Oxalic acid is an obligatory co-catalyst. The oxidation of isopropanol, for example, yields acetone with turnover numbers up to 40000 after 5-10 h in the absence of a solvent. 2-Cyanoethanol was oxidized by this system with somewhat lower efficiency (conversion 70%). The catalytically active cation from salt 1 was obtained in an insoluble form containing a heteropoly anion [Mn₂O₃(TMTACN)₂]₂[SiW₁₂O₄₀]. Oxidation of 2-cyanoethanol using this heterogenized catalyst and oxalic acid gave the oxo-products with the 54% total yield.     

Oxidations by the system ‘hydrogen peroxide-[Mn2L2O3][PF6]2 (L=1,4,7-trimethyl-1,4,7-triazacyclononane)-carboxylic acid’. Part 10: Co-catalytic effect of different carboxylic acids in the oxidation of cyclohexane, cyclohexanol, and acetone

Hydrogen peroxide oxidation of cyclohexane in acetonitrile solution catalyzed by the dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (L=1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN) at 25 °C in the presence of a carboxylic acid affords cyclohexyl hydroperoxide as well as cyclohexanone and cyclohexanol. A kinetic study of the reactions with participation of three acids (acetic acid, oxalic acid, and pyrazine-2,3-dicarboxylic acid, 2,3-PDCA) led to the following general scheme. In the first stage, the catalyst precursor forms an adduct. The equilibrium constants K₁ calculated for acetic acid, oxalic acid, and 2,3-PDCA were 127±8, (7±2)×10⁴, and 1250±50 M⁻¹, respectively. The same kinetic scheme was applied for the cyclohexanol oxidation catalyzed by the complex in the presence of oxalic acid. The oxidation of cyclohexane in water solution using oxalic acid as a co-catalyst gave cyclohexanol and cyclohexanone, which were rapidly transformed into a mixture of over-oxidation products. In the oxidation of cyclohexanol to cyclohexanone, varying the concentrations of the reactants and the reaction time we were able to find optimal conditions and to obtain the cyclohexanone in 94% yield based on the starting cyclohexanol. Oxidation of acetone to acetic acid by the system containing oxalic acid was also studied.     

Alkene cis-dihydroxylation by [(Me3tacn)(CF3CO2)RuVI O2)]ClO4(Me(3)tacn = 1,4,7-Trimethyl-1,4,7-triazacyclononane): structural characterization of [3 + 2] cycloadducts and kinetic studies

cis-Dioxoruthenium(VI) complex [(Me(3)tacn)(CF(3)CO(2))Ru(VI)O(2)]ClO(4) (1, Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) reacted with alkenes in aqueous tert-butyl alcohol to afford cis-1,2-diols in excellent yields under ambient conditions. When the reactions of 1 with alkenes were conducted in acetonitrile, oxidative C=C cleavage reaction prevailed giving carbonyl products in >90% yields without any cis-diol formation. The alkene cis-dihydroxylation and C=C cleavage reactions proceed via the formation of a [3 + 2] cycloadduct between 1 and alkenes, analogous to the related reactions with alkynes [Che et al. J. Am. Chem. Soc. 2000, 122, 11380]. With cyclooctene and trans-beta-methylstyrene as substrates, the Ru(III) cycloadducts (4a) and (4b) [formula; see text] were isolated and structurally characterized by X-ray crystal analyses. The kinetics of the reactions of 1 with a series of p-substituted styrenes has been studied in acetonitrile by stopped-flow spectrophotometry. The second-order rate constants varied by 14-fold despite an overall span of 1.3 V for the one-electron oxidation potentials of alkenes. Secondary kinetic isotope effect (KIE) was observed for the oxidation of beta-d(2)-styrene (k(H)/k(D) = 0.83 +/- 0.04) and alpha-deuteriostyrene (k(H)/k(D) = 0.96 +/- 0.03), which, together with the stereoselectivity of cis-alkene oxidation by 1, is in favor of a concerted mechanism.     

Hydrocarbon oxygenation with Oxone catalyzed by complex [Mn2L2O3]2+ (L=1,4,7-trimethyl-1,4,7-triazacyclononane) and oxalic acid

Oxone (peroxysulphate) very efficiently oxidizes benzene to p-quinone (TON 1140) and alkanes to the corresponding alcohols and ketones (aldehydes) in aqueous acetonitrile 50 °C if catalytic amounts of complex [Mn₂L₂O₃]²⁺ (L=1,4,7-trimethyl-1,4,7-triazacyclononane) and oxalic acid are present in the solution. In contrast to the similar reaction with H₂O₂, the alkane oxidation with Oxone does not afford the corresponding alkyl hydroperoxides. Phenol was quantitatively oxidized to a mixture of p-quinone and pyrocatechol (9:1 ratio). Cyclohexanol gave cyclohexanone (TON 400). The proposed mechanism includes the formation of an oxidizing species containing the Mn(V)O fragment. A kinetic study demonstrated that an adduct of [Mn₂L₂O₃]²⁺ and oxalic acid is formed in the initial stage. This adduct reacts with Oxone to generate the oxidizing species.     

Zur Koordinationschemie von cis-Trioxowolfram(VI)-Komplexen. Die Kristallstrukturen von LWO3 · 3 H2O, [L′WO2(OH)]Br, [LWO2Br]Br, [L2W2O5](S2O6) · 4 H2O und [LWO2(μ-O)WO(O2)2(OH2)] (L = 1,4,7-Triazacyclononan; L′ = 1,4,7-Trimethyl-1,4,7-triazacyclononan)

Coordination-chemistry of cis-Trioxotungsten(VI) Complexes. Crystal Structures of LWO₃ · 3 H₂O, [L′WO₂(OH)]Br, [LWO₂Br]Br, [L₂W₂O₅](S₂O₆) · 4 H₂O and [LWO₂(μ-O)WO(O₂)₂(OH₂)] (L = 1,4,7-Triazacyclonane; L′ = 1,4,7-Trimethyl-1,4,7-triazacyclononane) The cyclic triamines 1,4,7-triazacyclononane (L; C₆H₁₅N₃) and 1,4,7-trimethyl-1,4,7-triazacyclononane (L′; C₉H₂₁N₃) react in aqueous solution with WO₃ affording LWO₃ · 3 H₂O, 1 , and L′WO₃ · 3 H₂O, respectively, which yield [L′WO₂(OH)]Br, 2 , and [LWO₂Br]Br, 3 , in concentrated HBr solutions. In aqueous CH₃SO₃H solution 1 dimerizes. The iodide and dithionate 4 salts of [L₂W₂O₅]²⁺ have been isolated. In 35% H₂O₂ complex 1 yields the neutral species [LWO₂(μ-O)WO(O₂)₂(H₂O)] 5 . The crystal structures of 1 – 5 have been determined by X-ray analysis. Crystal data: 1 : P2₁/c; a = 7.729(2), b = 14.887(3), c = 10.774(2) Å, β = 90.77(2)°, Z = 4; 2 : Cc; 8.910(3), b = 12.220(6), c = 13.279(6) Å, β = 101.31(3)°, Z = 4; 3 : Cmc2₁, a = 8.857(5), b = 12.062(7), c = 11.218(7) Å, Z = 4; 4 : Cc, a = 17.601(7), b = 12.906(7), c = 14.107(8) Å, β = 124.08(4)°, Z = 4; 5 : P2₁2₁2₁; a = 8.452(4), b = 11.301(6), c = 13.750(6) Å, Z = 4.     

A unique rate-accelerating effect of certain amino acids in the H2O2 oxidation of alkanes catalyzed by a dinuclear manganese complex containing 1,4,7-trimethyl-1,4,7-triazacyclononane

Certain amino acids used in small amounts (10 catalyst equiv) strongly accelerate the H₂O₂ oxidation of cyclohexane catalyzed by a dinuclear manganese(IV) complex with 1,4,7-trimethyl-1,4,7-triazacyclononane. The efficiency of the co-catalyst dramatically depends on the nature and structure of the acid. Pyrazine-2,3-dicarboxylic acid (2,3-PDCA) has been found to be the most efficient co-catalyst whereas picolinic acid is almost inactive in this oxidation. The highest rate has been attained when 2,3-PDCA was used in combination with trifluoroacetic acid.     

Oxidations by the system “hydrogen peroxide-[Mn2L2O3][PF6]2 (L = 1,4,7-trimethyl-1,4,7-triazacyclononane)-oxalic acid”. Part 6. Oxidation of methane and other alkanes and olefins in water

Oxidation of alkanes with hydrogen peroxide in water solution at 10-50 °C is efficiently catalyzed by the cationic dinuclear manganese (IV) derivative [Mn₂L₂O₃]²⁺ (1, with L = 1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN) in the form of the hexafluorophosphate salt ([1][PF₆]₂) if oxalic acid is present as a co-catalyst. Methane gives methanol and formaldehyde (turnover numbers, TONs, were 7 and 2, respectively, after reduction of the reaction mixture with ascorbic acid) whereas cyclohexane was oxidized with TONs up to 160 affording cyclohexyl hydroperoxide, cyclohexanone and cyclohexanol (the ketone was the main product, although at room temperature almost pure alkyl hydroperoxide was formed). In contrast to the oxidation in acetonitrile, the reaction with linear n-alkanes in water exhibits an unusual distribution of oxygenates. For example, in the oxidation of n-heptane the normalized reactivity of the methylene group in position 4 of the chain is 3-7 times higher than that of the CH₂ group in position 2. Dec-1-ene is epoxidized by hydrogen peroxide in water (a biphasic system) catalyzed by [1][PF₆]₂ and oxalic acid in the presence of a small amount of acetonitrile with TONs up to 1000 (no epoxidation has been detected in the absence of MeCN).     

Polynuclear complexes of the pendent-arm ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane

The ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane (H(3)L) has been synthesized and its coordination properties toward Cu(II), Ni(II), Co(II), and Mn(II) in the presence of air have been investigated. Copper(II) yields a mononuclear complex, [Cu(H(2)L)](ClO(4)) (1), cobalt(II) and manganese(II) ions yield mixed-valence Co(III)(2)Co(II) (2a) and Mn(II)(2)Mn(III) (4) complexes, whereas nickel(II) produces a tetranuclear [Ni(4)(HL)(3)](2+) (3) complex. The complexes have been structurally, magnetochemically, and spectroscopically characterized. Complex 3, a planar trigonal-shaped tetranuclear Ni(II) species, exhibits irregular spin-ladder. Variable-temperature (2-290 K) magnetic susceptibility analysis of 3 demonstrates antiferromagnetic exchange interactions (J = -13.4 cm(-1)) between the neighboring Ni(II) ions, which lead to the ground-state S(t) = 2.0 owing to the topology of the spin-carriers in 3. A bulk ferromaganetic interaction (J = +2 cm(-1)) is prevailing between the neighboring high-spin Mn(II) and high-spin Mn(III) ions leading to a ground state of S(t) = 7.0 for 4. The large ground-state spin value of S(t) = 7.0 has been confirmed by magnetization measurements at applied magnetic fields of 1, 4 and 7 T. A bridging monomethyl carbonato ligand formation occurs through an efficient CO(2) uptake from air in methanolic solutions containing a base in the case of complex 4.     

Reactions of (di)manganese carbonyl ions with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN) in the gas phase

The gas-phase reactions of a series of (di)manganese carbonyl positive ions with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me(3)TACN) have been examined with the aid of Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The monomanganese carbonyl ions, [Mn(CO)(n)](+) (n = 2-5), react predominantly by ligand exchange and to a minor extent by electron transfer with the formation of the radical cation of Me(3)TACN. For the [Mn(CO)(n)](+) (n = 2-4) ions, the ligand exchange results in the exclusive formation of a [Mn(Me(3)TACN)](+) complex, whereas small amounts of [Mn(CO)(Me(3)TACN)](+) ions are also generated in the reactions of the [Mn(CO)(5)](+) ion. The [Mn(2)(CO)(n)](+) ions (n = 2, 4 and 5) react also by competing electron transfer and ligand exchange. The reaction of the [Mn(2)(CO)(2)](+) and [Mn(2)(CO)(4)](+) ions is associated with cleavage of the Mn--Mn bond as evidenced by the pronounced formation of [Mn(Me(3)TACN)](+) ions. For [Mn(2)(CO)(5)](+), the ligand exchange leads mainly to the formation of [Mn(2)(CO)(n)(Me(3)TACN)](+) (n = 1-3) ions. These primary product ions react subsequently by the incorporation of a second Me(3)TACN molecule to afford [Mn(2)(CO)(Me(3)TACN)(2)](+) and [Mn(2)(CO)(2)(Me(3)TACN)(2)](+) ions. Both of these latter species incorporate an oxygen molecule with formation of ions with the assigned composition of [Mn(2)(O(2))(CO)(Me(3)TACN)(2)](+) and [Mn(2)(O(2))(CO)(2)(Me(3)TACN)(2)](+).     

The reversible and stereoselective N- to C-bonded rearrangement of tris(2-pyridylmethyl)-1,4,7-triazacyclononanecobalt(III)

The hexaaminecobalt(III) complex [Co(tmptacn)]3+ (tmptacn = 1,4,7-tris(2'-pyridylmethyl)-1,4,7-triazacyclononane) undergoes a novel base-catalyzed N- to C-bonded rearrangement in which a tacn nitrogen is displaced by the alpha-carbon which deprotonates and binds to the metal ion as a carbanion. The X-ray structure establishes the configuration for the regio- and stereoselectively (100%) formed product. The reaction involves both ring expansions and ring contraction. The carbanion is part of a strained four-membered ring. The kinetics are reported for the N- to C-rearrangement, shown to be retentive for the optically resolved (+)-[Co(tmptacn)]3+ reactant, and also the kinetics for a competitive and somewhat faster base-catalyzed racemization reaction of this complex. The reaction is completely but very slowly reversed in acid, also with retention, and in D2O/D+ there is 1:1 D-incorporation into the two sets of inequivalent tacn carbons. Extensive 1D and 2D NMR studies establish mechanistic details, and alternative mechanisms are proposed for the forward and reverse reactions. In neutral solution, there is a competitive oxidation reaction for the reverse C- to N-bonded process, involving the regio- and stereoselective (100%) incorporation of an alpha-OH substituent into the tacn ring.     

Template synthesis of 1,4,7-triphosphacyclononanes

Iron(II) templates based on a [(eta(5)-Cp(R))Fe]+ core have been employed for the successful synthesis of 1,4,7-triphosphacyclononane derivatives (9-aneP3R'3) from a range of appropriately functionalized coordinated diphosphines and monophosphines. 1,2-Diphosphinoethane (1,2-dpe) or (2-phosphinoethyl)phenylphosphine (Phdpe) undergo a base-catalyzed Michael-type addition to trivinylphosphine, divinyl(benzyl)phosphine, or divinyl(phenyl)phosphine in [(eta(5)-Cp(R))Fe(diphosphine)(monophosphine)]+ complexes (2a-j) to give [(eta(5)-Cp(R))Fe(9aneP3R'3)]+ derivatives (4a-j) containing coordinated triphosphacyclononanes bearing one (with Phdpe) or two (with 1,2-dpe) secondary phosphine donors. The rates of macrocyclization show a dependence on the nature of the substituent(s) R on the cyclopentadienyl ligand with increased rates being observed along the series R = H5 < (Me3Si)H4 < 1,3-(Me3Si)2H3 approximately = Me5. For coupling reactions with trivinylphosphine, a pendant vinyl function remains in the macrocyclic product (4a-g) which is readily hydrogenated to the corresponding ethyl derivatives (5a-g). Further functionalization of coordinated secondary phosphines in the initially formed macrocycles (5a-g) is achieved by proton abstraction followed by addition of the appropriate alkyl halide electrophile and gives rise to tritertiary-triphospha-cyclononanes (7a-g, 7l, 7m). All new complexes have been fully characterized by spectroscopic and analytical methods in addition to the structural determination by single-crystal X-ray techniques of [{eta(5)-(Me3Si)2C5H3)Fe(9-aneP3H2C2H3)]PF6, 4c, and [(eta(5)-Me3SiC5H4)Fe(9-aneP3Et3)]BF4, 7b. 1,4,7-Triethyl-1,4,7-triphosphacyclononane is released from its metal template (7a, 7b) by treatment with either H2O2 or Br2/H2O to give the trioxide 9-aneP3(O)3Et3 (8). Attempts to recover the trivalent phosphorus species, 1,4,7-triethyl-1,4,7-triphosphacyclononane, from the trioxide by reduction proved unsuccessful.     

Binuclear copper(II) complexes of xylyl-bridged bis(1,4,7-triazacyclononane) ligands

Copper(II) complexes of three bis(tacn) ligands, [Cu(2)(T(2)-o-X)Cl(4)] (1), [Cu(2)(T(2)-m-X)(H(2)O)(4)](ClO(4))(4).H(2)O.NaClO(4) (2), and [Cu(2)(T(2)-p-X)Cl(4)] (3), were prepared by reacting a Cu(II) salt and L.6HCl (2:1 ratio) in neutral aqueous solution [T(2)-o-X = 1,2-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene; T(2)-m-X = 1,3-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene; T(2)-p-X = 1,4-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene]. Crystals of [Cu(2)(T(2)-m-X)(NPP)(mu-OH)](ClO(4)).H(2)O (4) formed at pH = 7.4 in a solution containing 2 and disodium 4-nitrophenyl phosphate (Na(2)NPP). The binuclear complexes [Cu(2)(T(2)-o-XAc(2))(H(2)O)(2)](ClO(4))(2).4H(2)O (5) and [Cu(2)(T(2)-m-XAc(2))(H(2)O)(2)](ClO(4))(2).4H(2)O (6) were obtained on addition of Cu(ClO(4))(2).6H(2)O to aqueous solutions of the bis(tetradentate) ligands T(2)-o-XAc(2) (1,2-bis((4-(carboxymethyl)-1,4,7-triazacyclonon-1-yl)methyl)benzene and T(2)-m-XAc(2) (1,3-bis((4-(carboxymethyl)-1,4,7-triazacyclonon-1-yl)methyl)benzene), respectively. In the binuclear complex, 3, three N donors from one macrocycle and two chlorides occupy the distorted square pyramidal Cu(II) coordination sphere. The complex features a long Cu...Cu separation (11.81 A) and intermolecular interactions that give rise to weak intermolecular antiferromagnetic coupling between Cu(II) centers. Complex 4 contains binuclear cations with a single hydroxo and p-nitrophenyl phosphate bridging two Cu(II) centers (Cu...Cu = 3.565(2) A). Magnetic susceptibility studies indicated the presence of strong antiferromagnetic interactions between the metal centers (J = -275 cm(-1)). Measurements of the rate of BNPP (bis(p-nitrophenyl) phosphate) hydrolysis by a number of these metal complexes revealed the greatest rate of cleavage for [Cu(2)(T(2)-o-X)(OH(2))(4)](4+) (k = 5 x 10(-6) s(-1) at pH = 7.4 and T = 50 degrees C). Notably, the mononuclear [Cu(Me(3)tacn)(OH(2))(2)](2+) complex induces a much faster rate of cleavage (k = 6 x 10(-5) s(-1) under the same conditions).     

Azo dye oxidation with hydrogen peroxide catalysed by manganese 1,4,7-triazacyclononane complexes in aqueous solution

A kinetic and mechanistic study is reported of the oxidation of a number of azonaphthol dyes with hydrogen peroxide in aqueous solution, catalysed by some mono and dinuclear manganese(IV) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN). The results of UV-Vis investigations, augmented by EPR and ESI-MS studies, are described for a series of experiments in which concentrations, pH and ionic strength have been varied. The reactions are characterised by an induction period followed by a relatively rapid oxidation. For the dinuclear manganese complex 2, these are consistent with an initial perhydrolysis of the manganese complex involving both the dye anion and HO2-, to give mononuclear manganese species and the operation of a catalytic cycle incorporating MnIIIL(OH)3, O = MnVL(OH)2 and MnIVL(OH)3 (L = Me3TACN) (cf. the reactions of peroxidase enzymes). ESI-MS results provide evidence for the formation and reaction (with the dye) of MnIVL(OH)3. With the mononuclear manganese complex MnIVL(OMe)3, there is a short lag-phase attributed to perhydrolysis by HO2- followed by the same catalytic cycle.     

Synthesis, molecular structure, and catalytic potential of the tetrairon complex [Fe4(N3O2-L)4(mu-O)2]4+ (L = 1-carboxymethyl-4,7-dimethyl-1,4,7-triazacyclononane)

The reaction of iron sulfate with 1-carboxymethyl-4,7-dimethyl-1,4,7-triazacyclononane (L) and hydrogen peroxide in aqueous ethanol gives a brown dinuclear complex considered to be [Fe2(N3O-L)2(mu-O)(mu-OOCCH3)] + (1), which converts upon standing in acetonitrile solution into the green tetranuclear complex [Fe4(N3O2-L)4(mu-O)2]4+ (2). A single-crystal X-ray structure analysis of [2][PF6]4.5MeCN reveals 2 to contain four iron(III) centers, each of which is coordinated to three nitrogen atoms of a triazacyclononane ligand and is bridged by one oxo and two carboxylato bridges, a structural feature known from the active center of methane monooxygenase. Accordingly, complex 2 was found to catalyze the oxidative functionalization of methane with hydrogen peroxide in aqueous solution to give methanol, methyl hydroperoxide, and formic acid; the total turnover numbers attain 24 catalytic cycles within 4 h. To gain more insight into the catalytic process, the catalytic potential of 2 was also studied for the oxidation of higher alkanes, cycloalkanes, and isopropanol in acetonitrile, as well as in aqueous solution. The bond selectivities of the oxidation of linear and branched alkanes suggest a ferroxy radical pathway.     

[(R)-2-Methyl-1,4,7-triazacyclononane] [1,1,1-tris(aminomethyl)ethane]-cobalt(III) and some Mono[(R)-2-methyl-1,4,7-triazacyclononane]-cobalt(III) Complexes

Summary [(R)-2-Methyl-1,4,7-triazacyclononane][1,1,1-tris(aminomethyl)ethane]cobalt(III) has been prepared and separated into two isomers which show weak Cotton effects in the¹A₁¹T₁ region (d-electron transition) compared with that of bis[(R)-2-methyl-1,4,7-triazacyclononane]cobalt(III). The effect is comparable to that of tetraammine[(R)-1,2-diamino propane]cobalt(III). The circular dichroism spectra of the mono complex change markedly upon addition of sodium sulphate. The chelate rings are more flexible in the mono than in the bis complex. Some other related mono[(R)-2-methyl 1,4,7-triazacyclononane]cobalt(III) and [(R)-2-methyl-1,4,7 triazacyclononane][1,1,1-tris(aminomethyl)ethaneI nickel (II) complexes have also been prepared and characterized.     

Copper(II) and nickel(II) complexes of the pendant arm ligand benzimidazole-2-yl-methyl-functionalized 1,4,7-triazacyclononane

Two novel complexes [ML]·(ClO₄)₂·EtOH·xH₂O M = Cu^II, x = 3; M = Ni^II, x = 2; L = 1-R-4,7-bis(benzimidazole-2-yl-methyl)-1,4,7-triazacyclononane, [R = 1-(benzimidazole-2-yl-methyl)benzimidazole-2-yl-methy], were prepared by a one-pot method using the 1,4,7-triazacyclononane ligand (tacn) and 2-chloromethylbenzimidazole as starting materials. The ES-MS and u.v. spectra of the complexes indicate that they are very stable thermodynamically and kinetically in aqueous solution. The crystal structure of the Cu^II complex shows that the Cu^II centre is octahedrally coordinated by six nitrogen atoms of three benzimidazoles and tacn.     

A silica gel-supported ruthenium complex of 1,4,7-trimethyl-1,4,7-triazacyclononane as recyclable catalyst for chemoselective oxidation of alcohols and alkenes by tert-butyl hydroperoxide

A silica gel-immobilized [(Me(3)tacn)Ru(III)(CF(3)COO)(2)(H(2)O)]CF(3)CO(2) complex (1-SiO(2), Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) was prepared by simple impregnation, and the catalyst was characterized by powdered X-ray diffraction, nitrogen adsorption/desorption, Raman, and diffuse reflectance UV-vis spectroscopies. The supported Ru catalyst can effect facile oxidation of alcohols by tert-butyl hydroperoxide (TBHP). Primary and secondary benzyl, allylic, and propargylic alcohols were transformed to their corresponding aldehydes and ketones in excellent yields; no oxidation of the C=C and Ctbd1;C bonds was observed for the allylic and propargylic alcohol oxidations. Likewise alkene epoxidation by TBHP can be achieved by 1-SiO(2); cycloalkenes such as norbornene and cyclooctene were oxidized to their exo-epoxides exclusively in excellent yields (>95%). The 1-SiO(2) catalyst can be recycled and reused for consecutive alcohol and alkene oxidations without significant loss of catalytic activity and selectivity; over 9000 turnovers have been attained for the oxidation of 1-phenyl-1-propanol to 1-phenyl-1-propanone. 4-Substituted phenols were oxidized by the "1 + TBHP" protocol to give exclusively ruthenium-catecholate complexes, which were characterized by UV-vis and ESI-MS spectroscopies. No (tert-butyldioxy)cyclohexadienone and other radical coupling/overoxidation products were produced using the "1 + TBHP" protocol. The formation of ruthenium-catecholate is proposed to proceed via ortho-hydroxylation of phenol.     

Electronic structure of oxidized complexes derived from cis-[Ru(II)(bpy)2(H2O)2]2+ and its photoisomerization mechanism

The geometry and electronic structure of cis-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) and its higher oxidation state species up formally to Ru(VI) have been studied by means of UV-vis, EPR, XAS, and DFT and CASSCF/CASPT2 calculations. DFT calculations of the molecular structures of these species show that, as the oxidation state increases, the Ru-O bond distance decreases, indicating increased degrees of Ru-O multiple bonding. In addition, the O-Ru-O valence bond angle increases as the oxidation state increases. EPR spectroscopy and quantum chemical calculations indicate that low-spin configurations are favored for all oxidation states. Thus, cis-[Ru(IV)(bpy)(2)(OH)(2)](2+) (d(4)) has a singlet ground state and is EPR-silent at low temperatures, while cis-[Ru(V)(bpy)(2)(O)(OH)](2+) (d(3)) has a doublet ground state. XAS spectroscopy of higher oxidation state species and DFT calculations further illuminate the electronic structures of these complexes, particularly with respect to the covalent character of the O-Ru-O fragment. In addition, the photochemical isomerization of cis-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) to its trans-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) isomer has been fully characterized through quantum chemical calculations. The excited-state process is predicted to involve decoordination of one aqua ligand, which leads to a coordinatively unsaturated complex that undergoes structural rearrangement followed by recoordination of water to yield the trans isomer.