Triazacyclononane Ligand Research Articles

Influence of Divalent Cations in the Protein Crystallization Process Assisted by Lanthanide-Based Additives.

The use of lanthanide complexes as powerful auxiliaries for biocrystallography prompted us to systematically analyze the influence of the commercial crystallization kit composition on the efficiency of two lanthanide additives: [Eu(DPA)3]3- and Tb-Xo4. This study reveals that the tris(dipicolinate) complex presents a lower chemical stability and a strong tendency toward false positives, which are detrimental for its use in a high-throughput robotized crystallization platform. In particular, the crystal structures of (Mg(H2O)6)3[Eu(DPA)3]2·7H2O (1), {(Ca(H2O)4)3[Eu(DPA)3]2}n·10nH2O (2), and {Cu(DPA)(H2O)2}n (3), resulting from spontaneous crystallization in the presence of a divalent alkaline-earth cation and transmetalation, are reported. On the other hand, Tb-Xo4 is perfectly soluble in the crystallization media, stable in the presence of alkaline-earth dications, and slowly decomposes (within days) by transmetalation with transition metals. The original structure of [Tb4L4(H2O)4]Cl4·15H2O (4) is also described, where L represents a bis(pinacolato)triazacyclononane ligand. This paper also highlights a potential synergy of interactions between Tb-Xo4 and components of the crystallization mixtures, leading to the formation of complex adducts like {AdkA/Tb-Xo4/Mg2+/glycerol} in the protein binding sites. The observation of such multicomponent adducts illustrated the complexity and versatility of the supramolecular chemistry occurring at the surface of the proteins.

Synthesis of an unsymmetrical N-functionalized triazacyclononane ligand and its Cu(II) complex

The unsymmetrical 1,4-bis(2-aminophenyl)-7-(pyridin-2-ylmethyl)-1,4,7-triazacyclononane ligand (L3) has been prepared and characterized by NMR spectroscopy. The L3 ligand is based on the triazamacrocycle ring bearing one flexible 2-pyridylmethyl linked to the macrocycle group via the methyl group, and two rigid 2-aminophenyl pendant donor groups linked to the macrocycle via the aromatic carbon atoms. Reaction of this ligand with Cu(ClO4)2·6H2O afforded the corresponding complex [Cu(L3)](ClO4)2·H2O (4) which was structurally characterized both in solid state and in solution. The crystal structure of 4 consists of a discrete monomeric [Cu(L3)]2+ in which the Cu(II) ion is six coordinated with three nitrogen atoms of the macrocycle ring, two of the aminophenyle and one of the pyridine appended functions. The triazacyclonane macrocycle ring is facially coordinated and the N-donor atoms of the three pendant groups (two aniline and one pyridine groups), are disposed in the same side of the basal macrocyclic ring, leading to a distorted and elongated CuN4N2 octahedron. UV–Vis spectroscopy of complex 4 in acetonitrile displays a d–d transition band at λ=673nm. The voltammetric studies show that the [Cu(L3)]2+ cation can be reduced quasi-reversibly and oxidized irreversibly, both process being monoelectronic.

Computational study of the spin-state energies and UV-Visspectra of bis(1,4,7-triazacyclononane) complexes of some first-row transition metal cations

We report here computed spin-state energies and UV-Vis spectra for several transition metal complexes with a triazacyclononane ligand. Our results show that the spin ground-state is correctly obtained with either OPBE or SSB-D, except for the high-spin ground-state of the Co(ii) complex that was properly described only by SSB-D. The UV-Vis spectra from TD-DFT reproduce in general rather well the experimental spectra, but in cases of the Cr(III) and Co(II) complexes it clearly failed. Better results for the UV-Vis spectra have been obtained by using Ligand Field DFT.

Structure, resolution and chiroptical analysis of stable lanthanide complexes of a pyridylphenylphosphinate triazacyclononane ligand

Lanthanide complexes of a pyridylphenylphosphinate ligand based on triazacyclononane form an isostructural series. The C(3)-symmetric Δ and Λ complexes of Eu and Tb are strongly emissive and can be resolved by chiral HPLC; the absolute configuration of each complex has been assigned using CD and CPL measurements.

A new diamantane functionalized tris(aryloxide) ligand system for small molecule activation chemistry at reactive uranium complexes

The diamantane functionalized triazacyclononane ligand ( Dia ArOH) 3 tacn (L 3 ) has been synthesized and the reactivity of its U(III) metallated product [(( Dia ArO) 3 tacn)U] (1) has been explored. Complex 1 promotes dichloromethane and azidotrimethylsilane activation to generate U(IV) complex [(( Dia ArO) 3 tacn)U(Cl)] (2) and U(V) complex [(( Dia ArO) 3 tacn)U(NTMS)] (3), respectively. Spectroscopic investigations of complexes 1, 2, and 3 will be discussed, along with molecular structures where possible.

New Iron(II) Complexes for Atom‐Transfer Radical Polymerization: The Ligand Design for Triazacyclononane Results in High Reactivity and Catalyst Performance

AbstractMononuclear cordinatively unsaturated iron(II) complexes having a triazacyclononane ligand were developed as highly efficient and environmentally friendly catalysts for the atom‐transfer radical polymerization (ATRP). These iron catalysts showed high performance in the well‐controlled ATRP of styrene, methacrylates, and acrylates. The high reactivity of these catalysts led to well‐controlled polymerization and block copolymerization even with lower catalyst concentrations.

Resin-supported catalytic dendrimers as multivalent artificial metallonucleases

Tentagel resin was functionalized with dendrons containing 4 and 8 triazacyclononane ligands able to complex the Zn II metal ion. The supported dendritic metallo-complexes showed enzyme-like behaviour in the cleavage of HPNPP, a model substrate for RNA. The obtained Michaelis–Menten parameters were in excellent agreement with those obtained for the identical catalysts in solution. Diffusion studies have revealed the upper limit for the rate constants that can be assessed under these conditions.

Carbon Dioxide Activation with Sterically Pressured Mid- and High-Valent Uranium Complexes

Sterically pressured mid- to high-valent uranium complexes with an aryloxide substituted triazacyclononane ligand scaffold, [(((R)ArO)3tacn)(3-)], were studied for carbon dioxide activation and transformation chemistry. The high valent uranium(V) imido species [(((R)ArO)3tacn)U(NR)] (R = (t)Bu, R' = 2,4,6-trimethylphenyl (2-(t)Bu); R = Ad, R' = 2,4,6-trimethylphenyl (2-Ad); R = (t)Bu, R' = phenyl (3-(t)Bu)) were synthesized and spectroscopically characterized. X-ray crystallography of the tert-butyl mesityl imido derivative, 2-(t)Bu , reveals coordination of a bent imido fragment with a relatively long U-N bond distance of 2.05 A. The mesityl imido complexes reacted with carbon dioxide, readily extruding free isocyanate to produce uranium(V) terminal oxo species, [(((R)ArO)3tacn)U(O)] (R = (t)Bu (4-(t)Bu), Ad (4-Ad)), presumably through multiple bond metathesis via a uranium(V) carbimate intermediate. Using the smaller phenyl imido fragment in 3-(t) Bu slowed isocyanate loss, allowing the uranium(V) carbimate intermediate to undergo a second metathesis reaction, ultimately producing the diphenyl ureate derivative, [(((tBu)ArO)3tacn)U(NPh2)CO] (5-(t)Bu). Single crystal X-ray diffraction studies were carried out on both uranium(V) terminal oxo complexes and revealed short U-O bonds (1.85 A) indicative of a formal UO triple bond. The electronic structure of the oxo U(V) complexes was investigated by electronic absorption and EPR spectroscopies as well as SQUID magnetization and DFT studies, which indicated that their electronic properties are highly unusual. To obtain insight into the reactivity of CO2 with U-N bonds, the reaction of the uranium(IV) amide species, [(((R)ArO)3tacn)U(NHMes)] (R = (t)Bu (6-(t)Bu), Ad (6-Ad) with carbon dioxide was investigated. These reactions produced the uranium(IV) carbamate complexes, [(((R)ArO)3tacn)U(CO2NHMes)] (R = (t)Bu (7-(t)Bu), Ad (7-Ad)), resulting from insertion of carbon dioxide into U-N(amide) bonds. The molecular structures of the synthesized uranium carbamate complexes highlight the different reactivities due to the steric pressure introduced by the alkyl derivatized tris(aryloxide) triazacyclononane ligand. The sterically open tert-butyl derivative creates a monodentate eta(1)-O bound carbamate species, while the sterically more bulky adamantyl-substituted compound forces a bidentate kappa(2)-O,O coordination mode of the carbamate ligand.

Preparation of Monodispersed Nanoparticles by Electrostatic Assembly of Keggin‐Type Polyoxometalates and 1,4,7‐Triazacyclononane‐Based Transition‐Metal Complexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Preparation of Monodispersed Nanoparticles by Electrostatic Assembly of Keggin-Type Polyoxometalates and 1,4,7-Triazacyclononane-Based Transition-Metal Complexes

Complexation of Keggin-type polyoxometalates (POMs), [α-PW12O40]3- (PW), [α-SiW12O40]4- (SiW), and [γ-SiV2W10O38(OH)2]4- (SiVWH) with cationic transition-metal complexes having a triazacyclononane ligand, [M(tacn)2]n+ (M−tacn; M = CoIII and NiII; tacn = 1,4,7-triazacyclononane), yields fine particles of inorganic−organic composites. The strong electrostatic interaction between the highly negatively charged POMs and the +2- or +3-charged [M(tacn)2]n+ as well as the hydrophobicity of [M(tacn)2]n+ results in the formation of the water-insoluble binary composites. The crystal structure of the 1:1 (=the molar ratio of POM to M−tacn) composite [Co(tacn)2][α-PW12O40]·2H2O (1·H2O) shows the close packing of PW and Co−tacn in the crystal lattice. The guest sorption properties of the corresponding anhydrous compound 1 show that the amounts of hydrophobic molecules sorbed are comparable to that of water. The reaction of SiVWH with Co−tacn yields fine particles of [Co(tacn)2]2[γ-SiV2W10O40]·6H2O (2·H2O), and the mola...

Synthesis, Molecular Structure, and Catalytic Potential of the Tetrairon Complex [Fe4(N3O2-L)4(μ-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.

Dinuclear Manganese Complexes Containing Chiral 1,4,7-Triazacyclononane-Derived Ligands and Their Catalytic Potential for the Oxidation of Olefins, Alkanes, and Alcohols

Five new 1,4,7-triazacyclononane-derived compounds, sodium 3-(4,7-dimethyl-1,4,7-triazacyclononan-1-yl)propionate (Na[LMe2R']) as well as the enantiopure derivatives (S)-1-(2-methylbutyl)-4,7-dimethyl-1,4,7-triazacyclononane (S-LMe2R''), SS-trans-2,5,8-trimethyl-2,5,8-triazabicyclo[7.4.01,9]tridecane (SS-LBMe3), (S)-1-(2-hydroxypropyl)-4,7-dimethyl-1,4,7-triazacyclononane (S-LMe2R), and (R)-1-(2-hydroxypropyl)-4,7-dimethyl-1,4,7-triazacyclononane (R-LMe2R), have been synthesized. Reaction of manganese dichloride with the chiral macrocycles S-LMe2R and R-LMe2R in aqueous ethanol gives, upon oxidation with hydrogen peroxide, the brown dinuclear Mn(III)-Mn(IV) complexes which are enantiomers, [Mn2(S-LMe2R)2(mu-O)2]3+ (S,S-1) and [Mn2(R-LMe2R)2(mu-O)2]3+ (R,R-1). The single-crystal X-ray structure analyses of [S,S-1][PF6]3.0.5(CH3)2CO and [R,R-1][PF6]3.0.5(CH3)2CO show both enantiomers to contain Mn(III) and Mn(IV) centers, each of which being coordinated to three nitrogen atoms of a triazacyclononane ligand and each of which being bridged by two oxo and by two chiral hydroxypropyl pendent arms of the macrocycle. The enantiomeric complexes S,S-1 and R,R-1 were found to catalyze the oxidation of olefins, alkanes, and alcohols with hydrogen peroxide. In the epoxidation of indene the enantiomeric excess values attain 13%. The bond selectivities of the oxidation of linear and branched alkanes suggest the crucial step in this process to be the attack of a sterically hindered high-valent manganese-oxo species on the C-H bond.

Synthesis and reactivity of uranium(iv) amide complexes supported by a triamidotriazacyclononane ligand

Reaction of [U{(SiMe2NPh)3-tacn}Cl] with LiNEt2 or LiNPh2 affords the corresponding amide compounds, [U{(SiMe2NPh)3-tacn}(NR2)] (R = Et (1), R = Ph (2)). The complexes have been fully characterized by spectroscopic methods and the solid-state structure of 1 was determined by single-crystal X-ray diffraction analysis. The six nitrogen atoms of the tris(dimethylsilylanilide)triazacyclononane ligand are in a trigonal prismatic configuration with the nitrogen atom of the diethylamide ligand capping one of the trigonal faces of the trigonal prism. Crystallization of 2 from CH3CN solution gave crystals of the six-membered heterocycle [U{(SiMe2NPh)3-tacn}{kappa2-(HNC(Me))2CC[triple bond]N}] (3). The reactivity of the amides was investigated. Both compounds undergo acid-base reactions with protic substrates such as HOC6H2-2,4,6-Me3, 3,5-Me2pzH (pz = pyrazolyl) and HSC5H4N to give the corresponding [U{(SiMe2NPh)3-tacn}X] (X = OC6H2-2,4,6-Me3 (4), 3,5-Me2pzH (5), kappa2-SC5H4N (6)) complexes. The solid-state structures of and were determined by single-crystal X-ray diffraction and revealed that the compounds are eight-coordinate with dodecahedral geometry.

An unsolvated lithium trihydroaluminate and the correponding trialkynylaluminates supported by an anionic triazacyclononane ligand

Reaction of the anionic tacn ligand ((tacn)H = 1,4-diisopropyl-1,4,7-triazacyclononane) with LiAlH4 in THF afforded a dimeric, unsolvated lithium trihydroaluminate, which upon treatment with terminal acetylenes HCCR (R = Ph, SiMe3) yielded the corresponding monomeric trialkynylaluminates in which one acetylide ligand bridges the Li and Al atom at the Cα atom while the two terminal acetylide ligands are coordinated to the Al atom.

Reactivity of a tantalum-lithium alkylidene supported by an anionic triazacyclononane ligand.

Reactivity of a tantalum-lithium alkylidene supported by an anionic triazacyclononane ligand.

Alkyl and Alkylidene Tantalum−Lithium Complexes Supported by an Anionic Triazacyclononane Ligand

A new iPr2-tacn--supported alkyl tantalum species, (Me3SiCH2)2(RN)Ta(μ-CH2SiMe3)(μ-η1:η3-iPr2-tacn)Li (R = 2,6-iPr2C6H3; 2), was synthesized and found to undergo α-H abstraction under gentle heating to form the alkylidene (Me3SiCH2)(RN)Ta(μ-CHSiMe3)(μ-η1:η3-iPr2-tacn)Li (3). The syntheses and crystal structures of 2 and 3 and their precursor ((iPr2-tacn)TaCl2(NR) (1)) are described, as well as kinetic data for the first-order thermolysis reaction producing 3.

Titanium tert-butyl- and trimethylsilyl-imido complexes with monopendant arm triazacyclononane ligands.

Neutral and cationic titanium imido complexes (R = t-Bu or SiMe3) with a triazacyclononane ligand bearing a monopendant arm have been synthesized. The structures of [Ti(NSiMe3)(L1)Cl] and [Ti(NBut)(L2)Cl]Cl are reported where HL1 = 1-(2-hydroxy-3,5-di-tert-butylbenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane and L2 = 1-(2-pyridylmethyl)-4,7-diisopropyl-1,4,7-triazacyclononane.

Neutral and cationic organometallic aluminium and indium complexes of mono-pendant arm triazacyclononane ligands

Organometallic monomeric and dimeric, neutral and cationic, κ2- and κ4-coordinated mono-pendant arm triazacyclononane complexes of aluminium and indium have been prepared, along with three new mono-pendant arm triazacyclononane ligand precursors HL4, HL5 and HL6 (HL4 = 1-(2-hydroxy-2-methylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane; HL5 = 1-(2-hydroxy-2-methylethyl)-4,7-dimethyl-1,4,7-triazacyclononane; HL6 = 1-(2-hydroxy-2,2-diphenylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane). Reaction of HL4 or HL5 with AlMe3 or AlMe3·py gives the μ-alkoxide bridged dimeric complexes [Al2(κ2-L4)2Me4] and [Al2(κ2-L5)2Me4]. Reaction of HL4 with two equivalents of AlMe3 gives the monomeric compound [Al(κ2-L4·AlMe3)Me2] which can also be prepared by treating [Al2(κ2-L4)2Me4] with two equivalents of AlMe3. Reaction of HL2 with AlMe3·py gives [Al(κ2-L2)Me2], whereas AlMe3 reacts with one or two equivalents of HL1 to give exclusively [Al(κ2-L1)2Me] which contains two κ2-L1 ligands (HL1 = 1-(2-hydroxy-3,5-dimethylbenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane; L2 = 1-(3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane). Reaction of AlMe3 with HL6 gives low yields of the monomeric derivative [Al(κ2-L6)Me2]. The κ2-coordination mode of the triazacyclononane ligands in all these compounds is unique in the chemisty of these ligands. The crystal structures of four of them are discussed. Methyl group abstraction from [Al(κ2-L4·AlMe3)Me2] or [Al(κ2-L2)Me2] using B(C6F5)3 gives the κ4-coordinated cationic derivatives [Al(κ4-L2)Me][MeB(C6F5)3] and [Al(κ4-L4·AlMe3)Me][MeB(C6F5)3], and the latter undergoes reaction with pyridine or MeCN to form [Al(κ4-L4)Me][MeB(C6F5)3]. The cationic centres in the last three compounds are unreactive to unsaturated substrates and aprotic Lewis bases. Reaction of In(CH2Ph)3 with HL1 or HL2 affords the four-coordinate complexes [In(κ2-L1)(CH2Ph)2] and [In(κ2-L2)(CH2Ph)2] in which the L1,2 ligand is κ2 bound to In. With the sterically less demanding HL3 [1-(3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-dimethyl-1,4,7-triazacyclononane], however, the six-coordinate complex [In(κ4-L3)(CH2Ph)2] is formed. The compound [In(κ2-L2)(CH2Ph)2] reacts with B(C6F5)3 to form [In(κ4-L2)(CH2Ph)][(PhCH2)B(C6F5)3]. p

A new route to (N)n-donor functionalised phosphines; novel homo- and hetero-nuclear complexes of a phosphino-substituted triazacyclononane ligand

A phosphino-substituted triazacyclononane ligand, OPtacn, has been prepared by a new, potentially versatile route, the complexes [CuI(OPtacn)][PF6], [PtIICl2{H(OPtacn)}2][PF6]2 and [PtIICl2{(OPtacn)[CuII(OAc)]}2][PF6]2 made, and the crystal structure of [CuI(OPtacn)][PF6] determined.

Nitrogen versus oxygen co-ordination of carboxamide-functionalized triazacyclononane ligands in transition metal ion complexes

Mononuclear complexes of zinc(II), copper(II), nickel(II), cobalt(II), iron(II), manganese(II), chromium(III), vanadium(III) and vanadyl(IV) with the ligands 1,4,7-tris(carbamoylmethyl)-1,4,7-triazacyclonanone (L) and its N-methyl derivative C6H12N3(CH2CONHMe)3 (MeL) have been prepared and structurally, magnetochemically and spectroscopically characterized. The ligands on complexation provide, in general, the MN3O3 moiety, i.e. they co-ordinate through the carboxamide oxygens with the exception of chromium(III). Chromium(III) forms complexes not only with the carboxamide oxygens, but also with the deprotonated amide nitrogen, thus yielding both CrN3O3 and CrN4O2 chromophores, respectively, which have been confirmed by crystal structures. The crystal structure of the VO2+ complex reveals a typical six-co-ordinate geometry with one amide dangling free, while that of the vanadium(III) compound shows seven-co-ordinate pentagonal bipyramidal geometry with the amide co-ordinated to the metal via its carbonyl oxygen atoms together with a chloride ion. The pendant carboxamide groups hydrolyse slowly to the corresponding carboxylic acid groups. The ligands L and MeL provide weak ligand fields and, relative to the trimethyl substituted cyclic amine [9]aneN3, i.e. 1,4,7-trimethyl-1,4,7-triazacyclononane, are more effective in stabilizing the metal centers in the oxidation state II.