Anionic Chelating Ligands Research Articles

A copper complex of an unusual hy-droxy-carboxyl-ate ligand: [Cu(bpy)(C4H4O6)

A copper(II) complex, (2,2'-bi-pyridine-κ2 N,N')[2-hy-droxy-2-(hy-droxy-methyl-κO)propane-dioato-κ2 O 1,O 3]copper(II), [Cu(C4H4O6)(C10H8N2)], containing the unusual anionic chelating ligand 2-(hy-droxy-meth-yl)tartronate, has been synthesized. [Cu(bpy)2(NO3)](NO3) was mixed with ascorbic acid and Dabco (1,4-di-aza-bicyclo-[2.2.2]octa-ne) in DMF (dimethylformamide) solution in the presence of air to produce the title compound. The structure consists of square-pyramidal complexes that are joined by Cu⋯O contacts [2.703 (2) Å] into centrosymmetric dimers. The C4H4O6 2- ligand, which occupies three coordination sites at Cu, has previously been identified as an oxidation product of ascorbate ion.

New Neutral Nickel and Palladium Sandwich Catalysts: Synthesis of Ultra-High Molecular Weight Polyethylene (UHMWPE) via Highly Controlled Polymerization and Mechanistic Studies of Chain Propagation

New neutral nickel and palladium ethylene polymerization catalysts have been prepared that incorporate an anionic (N,O) chelating ligand. Extensive axial shielding is provided by two 3,5-dichloroaryl moieties in a "sandwich" orientation. Such shielding results in an exceptionally slow rate of chain transfer relative to migratory insertion in the nickel catalyst, and thus highly controlled polymerization of ethylene is observed, leading to lightly branched ultra-high molecular weight polyethylene with Mn values up to 4.1 × 106 g/mol. The analogous palladium catalysts provide the means for a detailed mechanistic study of chain propagation in an electronically asymmetric neutral palladium catalyst. Both isomers of the methyl ethylene complex can be generated and observed at low temperatures allowing experimental elucidation of mechanistic details of chain propagation probed in other electronically asymmetric systems only through DFT studies or by examination of model studies. The barrier to migratory insertion in these complexes is ca. 19.2 kcal/mol. Investigation of the equilibration of the methyl ethylene isomers in the presence of excess ethylene showed the isomerization rate is dependent on ethylene concentration. This is the first direct proof that isomerization in these alkyl ethylene intermediates is catalyzed by ethylene. Furthermore, isomer equilibration is much faster than migratory insertion so that the barriers for insertion of individual isomers cannot be determined.

A DFT study of the structure-property relationships of bistetrazole-based high-nitrogen energetic metal complexes.

In this work, six series of new energetic metal complexes were designed. Each complex contained a large, high-energy, high-nitrogen, anionic chelating ligand (either the 5,5'-bistetrazolate anion, the 5,5'-azobistetrazolate anion, or the 5,5'-(hydrazine-1,2-diyl)bis-[1H-tetrazol-1-ide] anion-each of which has a different bridging group), Cu or Ni as the metal atom, and two small complexing agent ligands (NH3 and/or NH2NO2). The molecular and electronic structures, heats of formation, densities, detonation properties, and impact sensitivities of the novel complexes were studied using density functional theory. Furthermore, the effects of varying the large chelating ligand (and thus the bridging group), the small complexing agents, and the metal atom on the structure and properties of the complex were investigated and analyzed in depth. The results show that the particular metal, bridging group, and complexing agents included in the energetic complex influence its structure and properties, but the effects of varying the constituents of the complex are complicated or unclear, and these effects are sometimes intertwined. In addition, the detonation pressures, detonation velocities, and impact sensitivities of the novel complexes ranged from 25.9 to 38.6GPa, from 7.21 to 8.80kms-1, and from 17 to 48cm, respectively. Five of the complexes (B3, C3, D3, E3, and F3) appear to possess comparable performance to the famous and widely used high explosive 1,3,5-trinitro-1,3,5-triazinane, making these new complexes attractive to energetic materials experimentalists.

Variable coordination of tris(2-pyridyl)phosphine and its oxide toward M(hfac)2: a metal-specifiable switching between the formation of mono- and bis-scorpionate complexes.

An unexpected substitution of the anionic chelating ligands at the MII centre by a neutral tripodal ligand has been observed in the reaction of MnII, CoII, NiII and CuII hexafluoroacetylacetonates (hfac) with tris(2-pyridyl)phosphine (Py3P) or its oxide (Py3P = O). The nature of the metal ion in M(hfac)2 and the M/L ratio determine the degree of substitution of hfac-anions (partial vs. total) and therefore, the structure of the complex formed (scorpionate vs. bis-scorpionate ones, respectively). Hence, the reaction of the ligands with [Cu(hfac)2(H2O)2] in an equimolar ratio affords scorpionate [Cu(N,N',N''-Py3P = X)(O,O'-hfac)(O-hfac)], wherein one hfac-ligand chelates metal, while the other hfac acts as an O-monodentate one. Using the two equivalents of Py3P in this reaction leads to [Cu(N,N',N''-Py3P)2](hfac)2, which contains a bis-scorpionate cation [Cu(Py3P)2]2+ and two noncoordinated hfac-anions. [Co(hfac)2(H2O)2] and [Ni(hfac)2(H2O)2], regardless of the M/L molar ratio, react with Py3P = O to give cationic scorpionates [M(N,N',N''-Py3P = O)(O,O'-hfac)(H2O)](hfac), in which one hfac-anion is noncoordinated. In contrast, [Mn(hfac)2(H2O)2], on interaction with Py3P, results in the cationic complex [Mn(N,N',N''-Py3P)2][Mn(hfac)3]2 bearing a bis-scorpionate cation [Mn(Py3P)2]2+ and two [Mn(hfac)3]2- counterions. The synthesized scorpionates have been characterized by X-ray diffractometry, cyclic voltammetry, SQUID magnetometry, FT-IR and UV-Vis techniques.

Derivatization of Bichromic Cyclometalated Ru(II) Complexes with Hydrophobic Substituents

The syntheses and physical properties of cyclometalated Ru(II) complexes containing a triphenylamine (TPA) unit bearing aliphatic groups are reported. Each member of the series consists of an octahedral Ru(II) center coordinated by a tridentate polypyridyl ligand and a tridentate cyclometalating ligand. One of the chelating ligands contains electron-deficient methyl ester groups, while a TPA unit is attached to the central ring of the adjacent chelating ligand through a thiophene bridge. This study builds on our previous work (Inorg. Chem. 2011, 50, 6019-6028; Inorg. Chem. 2011, 50, 5494-5508) by (i) outlining a synthetic protocol for installing aliphatic groups on the TPA substituents, (ii) examining the role that terminal -O-hexyl and -S-hexyl groups situated on the TPA have on the electrochemical properties, and (iii) demonstrating the potential benefit of installing the TPA on the neutral chelating ligand rather than the anionic chelating ligand. The results reported herein provide important synthetic advances for our broader goal of developing bis-tridentate cyclometalated Ru(II) complexes for light-harvesting applications.

New half sandwich-type Ru(ii) coordination compounds characterized by the fac-Ru(dmso-S)3 fragment: influence of the face-capping group on the chemical behavior and in vitro anticancer activity

The Ru(II) complex fac-[RuCl(dmso-S)(3)(dmso-O)(2)][PF(6)] (P2) was found to be an excellent precursor for the facile preparation in high yield of half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)(3)(N)(2)][PF(6)] (e.g. (N)(2) = 1,2-diaminoethane (en, 4), trans-1,2-diaminocyclohexane (dach, 5), or 2 NH(3) (6)). Neutral half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)(3)(N-O)] where N-O is an anionic chelating ligand (e.g. N-O = picolinate (pic, 7)) are best prepared from the universal Ru(II)-dmso precursor cis-[RuCl(2)(dmso)(4)] (P1). These complexes, that were fully characterized in solution and in the solid state, are structurally similar to the anticancer organometallic compounds [Ru(η(6)-arene)(chel)Cl][PF(6)](n) but, in place of a face-capping arene, have the fac-Ru(dmso-S)(3) fragment. In contrast to what observed for the corresponding arene compounds, that rapidly hydrolyze the Cl ligand upon dissolution in water, compounds 4-6 are very stable and inert in aqueous solution. Probably their inertness is the reason why they showed no significant cytotoxicity against the MDA-MB-231 cancer cell line.

Quinoxaline-2-carboxamide as a carrier ligand in two new platinum(ii) compounds: Synthesis, crystal structure, cytotoxic activity and DNA interaction

The search for platinum compounds structurally different from cisplatin has led to two new platinum(II) compounds containing quinoxaline-2-carboxamide as a carrier ligand, i.e. cis-[Pt(qnxca)(MeCN)Cl2] (1) and the [Pt(qnxca-H)(dmso)Cl] (2). Both compounds have been synthesized and characterized using different spectroscopic methods. In addition, single-crystal structures have been determined by X-Ray diffraction for both compounds. In each case a square planar Pt(II) is present; in (1) the qnxca is monodentate and neutral, whereas in (2) the ligand has lost a hydrogen, to form the anionic chelating ligand abbreviated as qnxca-H. The biological activity of both compounds has been investigated in a panel of seven human tumour cells, displaying poor cytotoxic activity, compared to cisplatin. The interaction of the new compounds with 1 or 2 equiv. of 9-ethylguanine has been studied using (1)H NMR, (195)Pt NMR and ESI-MS spectroscopy, finding poor reactivity of 1 towards the model base, forming only the monosubstituted adduct. Surprisingly, compound 2, which is more sterically crowded, interacts more efficiently with the 9-EtG, forming a bifunctional adduct with two 9-EtG with substitution of the dmso and the chloride ligand. Unwinding studies of pUC19 plasmid DNA by compound 1 show similar unwinding properties to cisplatin.

Design, Synthesis, and Catalysis of Bio-inspired Immobilized Metallocomplex Catalyst

Novel immobilized metallocomplex catalyst based on bio-inspired concept has been developed. The allyl functional group in the anionic chelating ligand reacts with thiols to give the linker for immobilization. The immobilization of the chelating ligand onto amorphous silica supports results in the isolated metal-binding sites giving the coordinatively unsaturated metal center. The biomimetic iron complex-immobilized silica exhibits the catalysis for olefin epoxidation with aqueous H2O2 at ambient temperature.

Synthesis and first X-ray structures of cobalt(II) and cobalt(III) complexes bearing 2,4-dioxo-alkanoic acid dialkylamide ligands

The aerobic oxidation of 5-hydroxy pentenes to trans-tetrahydrofurans (THFs), the Mukaiyama oxidation, has in recent years emerged as a powerful tool in synthetic chemistry. In this report we describe the first crystal structures of 2,4-dioxo-alkanoic acid dialkylamide complexes for both Co(II) and Co(III) salts. The Co(II) structures show an unprecedented arrangement of atoms, with a central Co(II)(H2O)6 flanked by two Co(II) atoms each coordinated with three anionic chelating ligands. The dimeric Co(III) structures show two anionic chelating ligands and bridging hydroxyl groups.Key words: aerobic oxidation, trans-tetrahydrofuran (THF), cobalt, X-ray crystallography, oxidation, coordination.

Synthesis of a Hetero-bimetallic Complex with an Inorganic Cyclic Framework Using a Bis(iminophosphorane)iron Complex as a Chelating Ligand

Abstract An iron–rhodium bimetallic complex bearing a six-membered metallacycle was synthesized from a lithium bis(iminophosphorane)iron complex, which served as an anionic chelating ligand carrying a bis(iminophosphorano)methanide-like inorganic framework. The metallacycle complex takes a peculiar boat shape, in which the two metal centers are in close proximity and the carbonyl ligand on the iron atom overhangs the rhodium atom, giving a considerably low-frequency IR absorption and assuming a slightly bent structure.

Water‐elutability of nucleic acids from metal‐chelate affinity adsorbents: enhancement by control of surface charge density

Immobilized metal affinity chromatography (IMAC) is widely used for purification of proteins, especially "hexahistidine-tagged" recombinant proteins. We previously demonstrated the application of IMAC to selective capture of nucleic acids, including RNA, selectively-denatured genomic DNA, and PCR primers through interactions with purine bases exposed in single-stranded regions. We also found that the binding affinity of nucleic acids for IMAC adsorbents can be increased several-fold by addition of 20 volume% of neutral additives such as ethanol or DMSO. In the present work, it is demonstrated that bound nucleic acids can be effectively eluted with water instead of the usual imidazole-containing competitive eluants, when the surface density of negative charges is enhanced by operation at alkaline pH, or by deliberate metal-underloading of the anionic chelating ligands. With enhanced negative surface charge density, nucleic acid adsorption can be made strongly dependent on the presence of adsorption-promoting additives and/or repulsion-shielding salts, and removal of these induces elution. Complete water-elutability is demonstrated for baker's yeast RNA bound to 10% Cu(II)- underloaded IDA Chelating Sepharose in a binding buffer of 20 mM HEPES, 240 mM NaCl, pH 7. Water elutability will significantly enhance the utility of IMAC in nucleic acid separations.

Directed Supramolecular Assembly of Infinite 1-D M(II)-Containing Chains (M = Cu, Co, Ni) Using Structurally Bifunctional Ligands

The directed assembly of six different M(II) complexes (M = Cu, Co, and Ni) into infinite chains has been achieved by combining anionic chelating ligands (for controlling the coordination geometry) with bifunctional ligands containing a metal-coordinating pyridyl moiety and a self-complementary hydrogen-bonding moiety. Six crystal structures are presented, and in each case, the chelating acac ligand occupies the four equatorial coordination sites leaving room for the bifunctional ligand to coordinate in the axial positions. The supramolecular chemistry, which organizes the coordination complexes into the desired infinite 1-D chains, is driven by a combination of N-H...N and N-H...O hydrogen bonds.

Synthesis and coordinating ability of an anionic cobaltabisdicarbollide ligand geometrically analogous to BINAP.

The anionic chelating ligand [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- has been synthesized from [3,3'-Co(1,2-C2B9H11)2]- in very good yield in a one-pot process with an easy work-up procedure. The coordinating ability of this ligand has been studied with Group 11 metal ions (Ag, Au) and with transition-metal ions (Pd, Rh). The two dicarbollide halves of the [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- ligand can swing about one axis in a manner analogous to the constituent parts of BINAP and ferrocenyl phosphine derivatives. All these ligands function as hinges, with the most important property in relation to the coordination requirements of the metal being the PP distance. [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]-, BINAP, ferrocenyl phosphine derivatives, and other hinge ligands present a range of different PP separations, and consequently different coordination spheres and dispositions around metal cations. To account for these differences, the equation Dphi2 = D02 + 4 R2cos2(90-phi/2) has been developed. It relates the PP distance (Dphi) in a complex with the minimum PP distance (D0) that is characteristic of the hinge-type ligand.

Nucleophilic additions to pseudohalides in the coordination sphere of transition metal ions and coligand isomerism

Coordinated pyrazoles exhibit a nucleophilic addition to the cyanate ligand inside the transition metal coordination sphere and new chelate complexes are formed; the new anionic ligand of the carbamoylpyrazolate type can be released. The conditions for such an addition were studied and established by selecting various central atoms and different N-donor heterocyclic ligands. Some non-linear pseudohalides, namely N(CN) 2 −, C(CN) 3 − and ONC(CN) 2 −, are also capable of such reactions but the addition proceeds under different conditions due to different electronic and steric requirements. A new type of isomerism—coligand isomerism—has been discovered: one isomer is the usual complex of the [MX 2(pzt) 2] type (pzt, pyrazole-type ligand) whereas in the second isomer [M(pzt·X) 2] a new anionic chelating ligand formed by nucleophilic addition is present. Another type of nucleophilic addition, reaction of methanol with the N(CN) 2 − specifically in the coordination sphere of Cu II leads to the formation of a six-membered metallacycle. Nucleophilic addition of methanol to the ONC(CN) 2 − anion in the transition metal coordination sphere results in formation of a five-membered metallacycle. All nucleophilic additions studied have a common feature in a coordinative activation of the carbon β-site of the pseudohalides changing its hybridization and providing an unsaturated valency for a nucleophilic attack.

Studies on Pt–S bonds. Competition of chelating methylsulfanyl- or methylsulfinyl-acetate, -benzoate and -phenolate for PtII(H2NCH2CH2NH2)

A. Pasini and M. Moroni, J. Chem. Soc., Dalton Trans., 1997, 1093 DOI: 10.1039/A605475G

Inorganic Ring Systems Containing Lanthanide Elements

Abstract Lanthanide complexes containing fourmembered N-C-N-Ln, N-S-N-Ln and N-P-N-Ln rings have been synthesized by treatment of lanthanide halides with bulky anionic chelating ligands. Similar ring systems containing four different elements (N-Si-0- Ln) have been obtained by reacting anhydrous lanthanide trichlorides with Li[Me2Si(OtBu)(NtBu)]. A twelve-membered inorganic ring is formed during the reaction of Cp∗2Sm(THF)2 with [Cp∗Fe(CO)2]2.

Synthesis and Reactivity of “Bismuthinidene” Compounds and the Formation of Bi1 Chelate Complexes

Treatment of [Cp′Mn(CO)2THF] (Cp′C5H4Me) with BiCl3 at 20°C affords the “bismuthinidene” species [Cp′‐ (CO)2Mn]2BiCl (1b) and very small amounts of the “star‐type” compound [Cp′(CO)2Mn]3Bi2 (2). Higher yields of both compounds are obtained from the reaction of BiCl3 with [Na] [Cp′(CO)2MnSi(C6H5)3‐]. The molecular structure of 1b has been determined by an X‐ray diffraction study, which shows that the bismuth atom, having a trigonal‐planar coordination geometry, is bonded to two manganese atoms and one chlorine atom. There are weak interactions between the molecules of 1b in the solid state thus forming infinite spiral chains of “inidene” complexes. Compound 1b reacts with NaI to afford the iodine‐substituted species [Cp′(CO)2Mn]2BiI (3). Displacement of the chloride substituent from 1b by anionic chelating ligands AB− is also possible; 1b reacts with tropolonate, 8‐oxoquinolate, or 8‐mercaptoquinolate to form the bismuth(I) chelate compounds [CP′(CO)2Mn]Bi − AB (5a–c). The molecular structure of 5b has been determined by X‐ray crystallography which shows the bismuth atom in a pseudo trigonalbipyramidal geometry with the nitrogen atom lying above the plane defined by the two manganese and the oxygen atoms in an apical position. The molecular structure of 5c has also been determined, and although the numerical values are not very accurate, the coordination geometry of the bismuth atom is seen to be intermediate between pseudo trigonalbipyramidal and distorted tetrahedral. Abstraction of a chloride ligand from 1b by Me3SiOSO2CF3 affords the cationic cumulene‐type complex [Cp′(CO)2MnBiMn(CO)2Cp][CF3SO3] (6a). Dichloromethane solutions of 6a are not stable at room temperature but may be treated with 2,−2′‐bipyridine (bpy) to afford the stable adduct [{CP′(CO)2Mn}2Bi(bpy)][CF3SO3](7). The molecular structure of 7 has been determined by X‐ray analysis, and – similarly to 5c, although the numerical values are not very accurate – the overall geometry has been determined unequivocally. The bismuth atom is shown to have a distorted tetrahedral geometry, thus being ligated by two manganese atoms and the two nitrogen atoms of the bpy ligands.

Fluorinated barrelene-ruthenium(II) complexes with anionic chelating ligands

Reaction of ruthenium(III) chloride with the barrelene diolefins (tetrafluoro-benzobarrelene (TFB) or (trimethyltetrafluorobenzobarrelene) (Me 3 TFB) leads to the formation of the polymeric complexes [RuCl 2(barrelene)] n . These compounds react with anionic chelating ligands with formation of new hexacoordinated neutral complexes of the general formulae [Rh(chelate) 2(barrelene)], where chelate = acetylacetonate, tropolonate, salicylal-dehydate and 8-oxyquinolinate. The IR and 1H NMR spectra of the complexes are given and discussed.

Crystal and molecular structures of three transition metal complexes incorporating the anionic tridentate chelating ligands [Me2Ga(N2C5H7)OCH2CH2SR]− where R = Et or Ph

X-ray crystallographic studies of three transition metal complexes incorporating the novel anionic tridentate chelating ligand [Me2Ga(N2C5H7)OCH2CH2SR]− (R = Et or Ph) show that the ligand is facially coordinated in each case. Crystals of [dimethyl(3,5-dimethyl-1-pyrazolyl) (2-thioethoxyethoxy)gallato(N(2), O,S)]nitrosylnickel(I) are monoclinic, a = 8.8313(4), b = 7.2402(2), c = 26.539(1) Å, β = 94.390(3)°, Z = 4, space group P21/c, R = 0.040 and Rw = 0.050 for 2489 reflections. The Ni atom is in a distorted tetrahedral environment with bond angles about Ni ranging from 87.90(7) to 127.9(1)°. The nitrosyl coordination is slightly non-linear with Ni—N—O = 170.1(4)°. Important bond lengths (corrected for libration) are: Ni—S, 2.326(1), Ni—O, 2.019(2), Ni—N(pyrazolyl), 1.980(3), Ni—N(O), 1.633(3) and N—O, 1.156(4) Å. Crystals of [dimethyl(3,5-dimethyl-1-pyrazolyl) (2-thiophenoxyethoxy)gallato(N(2),O,S)]tricarbonylmanganese(I) are triclinic, a = 9.4911(5), b = 10.4323(6), c = 11.7618(7) Å, α = 86.17(1), β = 69.547(5), γ = 81.402(4)°, Z = 2, space group [Formula: see text]R = 0.029 and Rw = 0.035 for 2496 reflections. The Mn atom is coordinated to the fac-tridentate gallate ligand and to three carbonyl ligands resulting in a slightly distorted octahedral geometry. Important corrected bond lengths are: Mn—S, 2.397(1), Mn—O, 2.055(2), Mn—N, 2.082(3), and Mn—C, 1.794(4), 1.807(4), and 1.807(4) Å. Crystals of [dimethyl(3,5-dimethyl-1-pyrazolyl) (2-thioethoxyethoxy)gallato(N(2),O,S)](η3-cycloheptatrienyl)dicarbonylmolybdenum are monoclinic, a = 17.030(3), b = 19.097(2), c = 15.908(3) Å, β = 115.99(1)°, Z = 8, space group P21/n R =0.036 and Rw = 0.043 for 4477 reflections. The two crystallographically independent molecules differ primarily in the orientation of the S-ethyl moiety and each contains an η3-C7H7 ligand which occupies one coordination site of a distorted octahedron as a %-donating ligand. Important corrected bond distances are: Mo—S, 2.527(2) and 2.541(2), Mo—O, 2.241(5) and 2.237(4), Mo—N, 2.277(5) and 2.254(5), Mo—C(O), 1.940(7)–1.960(7), and Mo—C(C7H7), 2.198(6)−2.391(7) Å.

Preparation and characterization of tetrakis (β-ketophosphonato) thorium(IV) complexes

Tetrakis (β-ketosphonato) thorium(IV) complexes have been prepared using a liquid—liquid extraction method. They have been well characterized by i.r., Raman, 1H, 13C and 31P NMR spectroscopies. β-ketophosphonates act as anionic chelating ligands and are coordinated by the PO and CO oxygen atoms. An asymmetric repartition of the negative charge on the chelate ring is observed. A stabilities order of the studied β-ketophosphonato-thorium complexes has been established.