Transition Metal Derivatives Research Articles

Synthesis and molecular structures of metal complexes (M = Al, Mn, Fe or Co) supported by sterically encumbered salicylaldiminate ligands

Complexes of sterically bulky salicylaldiminate ligands, [OC6H2tBu2C(H)NAr∗]– (Ar∗ = C6H2-2,6-(CHPh2)2-4-X, X = F or OCH3), with Al(III), Mn(II), Fe(II) or Co(II) were synthesized through salt metathesis reactions in good to excellent yields. The compounds were characterized by 1H NMR, IR, UV–Vis spectroscopy and X-ray crystallography. The molecular structures of the aluminum complexes show that the ligands are bidentate and can bind in either 1:1 or 1:2 ratio, with a tetrahedral or trigonal bipyramidal coordination geometry, respectively. In contrast, all the prepared transition metal derivatives contain two ligand sets per metal center, with most compounds featuring a tetrahedral coordination environment. One of the iron complexes (4a) adopts a rare four-coordinate seesaw geometry, possibly because of the strong intramolecular steric repulsion between the two salicylaldiminate ligands. Detailed structural parameters of a series of cobalt bis(salicylaldiminate) complexes were compared, which revealed that the benzhydryl-containing Ar∗ group imposes less steric bulk when compared to the commonly used 2,6-diisopropylphenyl group.

Coordination of bis(azol-1-yl)methane-based bisphosphines towards RuII, RhI, PdII and PtII: synthesis, structural and catalytic studies.

The coordination chemistry of bisphosphine ligands assembled on the five-membered heterocyclic platform of bis(azol-1-yl)methane viz.: bis(2-diphenylphosphinoimidazol-1-yl)methane (1), bis(5-diphenylphosphinopyrazol-1-yl)methane (2) and bis(5-diphenylphosphino-1,2,4-triazol-1-yl)methane (3) with RuII, RhI, PdII and PtII is described. The bisphosphines 1-3 react with elemental selenium to give the corresponding bis-selenoyl derivatives 4-6. The reactions of 1-3 with transition metal derivatives produce complexes with different coordination modes. Bisphosphine 1 showed a preference for the κ2-P,P mode of coordination, whereas bisphosphines 2 and 3, besides the κ2-P,P mode also showed a head-to-tail κ2-P,N coordination mode resulting in the formation of binuclear complexes [Rh2(COD)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,N}][BF4]2 (14), [Rh2(COD)2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,N}][BF4]2 (15), [Pd2(η3-C3H5)2{(CH2(1,2-C3H2N2PPh2)2)-κ2P,N}][BF4]2 (21) and [Pd2(η3-C3H5)2{(CH2(1,2,4-C2HN3PPh2)2)-κ2P,N}][BF4]2 (22). Several of these complexes have also been structurally characterized. The in situ generated RhI complex of bisphosphine 1 showed moderate to good selectivity in the hydroformylation of various styrene derivatives.

One-step electroreductively deposited iron-cobalt composite films as efficient bifunctional electrocatalysts for overall water splitting

Due to the large overpotentials on both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) during the process of water splitting, the large-scale production of hydrogen is limited. Therefore, it is crucial to find earth-abundant, low-cost and efficient bifunctional catalysts for such process. In this paper, we report one-step electroreductive deposition of Fe-Co composite films on carbon fiber papers (CFPs) in a solution containing Fe(III) and Co(II) ions without and with N2 bubbling, and the prepared composite films show highly efficient electrocatalytic performances and good durabilities for both OER and HER in 1.0M KOH. To reach a current density of 10mAcm−2, the overpotentials are only 283mV for OER and −163mV for HER with small Tafel slopes of 34 and 51mVdec−1, respectively. Moreover, the Fe-Co composite films can be used as bifunctional catalysts for water splitting with the current density of 10mAcm−2 at 1.68V, which is comparable with most of the Ni-based films reported. This proves that the Ni-free derivatives of 3d transition metals can also show high catalytic performance.

Two Triazole-Based Phosphine Ligands Prepared via Temperature-Mediated Li/H Exchange: Cu(I) and Au(I) Complexes and Structural Studies.

The kinetically favored triazole-based phosphine 1-(2-(diphenylphosphino)phenyl)-4-phenyl-1H-1,2,3-triazole (2, L1) and its thermodynamically preferred isomer, 5-(diphenylphosphino)-1,4-diphenyl-1H-1,2,3-triazole (3, L2), were obtained by the temperature-controlled lithiation of 2-bromotriazole followed by the reaction with chlorodiphenylphosphine. The structures of phosphines 2 and 3 were determined by X-ray diffraction. Upon reaction with late transition-metal derivatives (Cu(I), Ag(I), and Au(I)), phosphines 2 and 3 form complexes with monodentate (Cu(I), Ag(I), and Au(I); κ(1)-P), chelate (Cu(I); κ(2)-P,N), bridged bidentate (Cu(I); μ(2)-P,N), and tridentate (Cu(I); μ(2),κ(2)-P,N,N) modes of coordination. Reactions with copper(I) halides produced mono-, di-, and tetranuclear complexes, whereas the reaction of 2 with [Cu(NCCH3)4]BF4 yielded the binuclear complex [Cu2(CH3CN)2{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(H)}-μ-(κ-P,κ-N),κ-N}2](BF4)2 (10) with the ligand acting as a six-electron donor involving phosphorus and two triazole nitrogen atoms. The copper complexes of 2 and 3 containing rhomboid Cu2X2 units, [(Cu)2(μ-X)2{o-Ph2P(C6H4){1,2,3-N3C(Ph)C(H)}-κ-P}2] (4, X = Cl; 5, X = Br), on treatment with 1,10-phenanthroline and 2,2'-bipyridine gave mixed-ligand complexes of the type [(CuX)(N∩N-κ(2)-N,N){o-Ph2P(C6H4){1,2,3-N3C(Ph)C(H)}-κ-P}] (N∩N = 1,10-phen and 2,2'-bipy; X = Cl, Br, and I).

Synthesis, Pyrolytic, and Antibacterial Study of 3-[(E)-(2-phenylhydrazinylidene)methyl]pyridine(PHMP) and Its Transition Metal Complexes

Phenyl hydrazine and pyridine-3-carbaldehyde were coupled to form a new Schiff base 3-[(E)-(2-phenylhydrazinylidene)methyl]pyridine(PHMP), followed by the formation of its transition metal derivatives (i.e., Co(II), Cu(II), and Zn(II) complexes). All of them were characterized by physical and spectral methods such as 1H-NMR, IR, elemental analysis, UV-Vis spectra, and conductance studies. Thermal study was carried out with TG/DTA method to understand the degradation pattern of the newly synthesized ligand and its complexes. Antibacterial study was carried out with both the gram-positive (Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermis, Streptococcus pneumonia) and gram-negative bacteria (Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli). The complexes showed medium activity as compared to the standard imipenem.

ChemInform Abstract: Cyclodiphosphazanes in Metal Organic Frameworks

AbstractReview: 27 refs.

Cyclodiphosphazanes in metal organic frameworks

GRAPHICAL ABSTRACT

Topoisomerase I inhibition and DNA cleavage by zinc, copper, and nickel derivatives of 2-[2-bromoethyliminomethyl]-4-[ethoxymethyl]phenol complexes exhibiting anti-proliferation and anti-metastasis activity

Three transition metal derivatives (Zn, Cu, and Ni) of 2-[2-bromoethyliminomethyl]-4-[ethoxymethyl]phenol (L) were synthesized by the reaction of the metal salts with the Schiff base ligand in one pot. In the crystal structure of [Zn(L)Br], the Schiff base ligand binds to the metal center through its phenolate oxygen and imine nitrogen, and adopts a distorted tetrahedral geometry. These compounds were found to inhibit topoisomerase I (topo I) activity, induce DNA cleavage and show DNA binding activity. Moreover, these compounds were found to be cytotoxic towards several cancer cell lines (A2780, MCF-7, HT29, HepG2, A549, PC3, LNCaP) and prevent metastasis of PC3. Collectively, Cu(II) complex 2 shows superior activity relative to its Zn(II) and Ni(II) analogs.

Further studies of the Enhanced Structural Carborane Effect: tricarbonylruthenium and related derivatives of benzocarborane, dihydrobenzocarborane and biphenylcarborane.

Detailed comparison of the molecular structures of [1,2-μ-(C4H4)-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (1) and [1,2-μ-(C4H6)-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (2) reveals evidence for an Enhanced Structural Carborane Effect in 1 arising from the involvement of the cage pπ orbitals in the exopolyhedral ring to some degree. A minor co-product in the synthesis of 2 is [η-{1,2-μ-(C4H6)}-3,3-(CO)2-3,1,2-closo-RuC2B9H9] (3). Compounds 2 and 3 are readily interconverted, since heating 2 to reflux in THF or reaction with Me3NO affords 3 which readily reacts with CO to regenerate 2. The η-ene bonding in 3 is also displaced by PMe3, P(OMe)3 and t-BuNC to yield [1,2-μ-(C4H6)-3,3-(CO)2-3-PMe3-3,1,2-closo-RuC2B9H9] (4), [1,2-μ-(C4H6)-3,3-(CO)2-3-P(OMe)3-3,1,2-closo-RuC2B9H9] (5) and [1,2-μ-(C4H6)-3,3-(CO)2-3-t-BuNC-3,1,2-closo-RuC2B9H9] (6), respectively. Structural studies of 4-6, focussing on the Exopolyhedral Ligand Orientation of the {Ru(CO)2L} fragment relative to the C2B3 carborane face, are discussed in terms of the structural trans effects of PMe3, P(OMe)3 and t-BuNC relative to that of CO. An improved synthesis of [1,2-μ-(C6H4)2-1,2-closo-C2B10H10], "biphenylcarborane", is reported following which the first transition-metal derivatives of this species, [1,2-μ-(C6H4)2-3-Cp-3,1,2-closo-CoC2B9H9] (7) and [1,2-μ-(C6H4)2-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (8), are prepared. Comparisons of the structures of 7 and 8 with the corresponding benzocarborane derivatives [1,2-μ-(C4H4)-3-Cp-3,1,2-closo-CoC2B9H9] and 1, respectively, suggest that Clar's rule for aromaticity can be applied to polycyclic aromatic hydrocarbons fused onto carborane cages.

Synthesis of Schiff base 24-membered trivalent transition metal derivatives with their anti-inflammation and antimicrobial evaluation

The paper presents the synthesis of macrocyclic complexes [{M(C52H36N12O4)X}X2] of Cr(III), Mn(III) and Fe(III) with Schiff base ligand (C52H36N12O4) obtained through the condensation of 1,4-dicarbonyl phenyl dihydrazide with 1,2-di(1H-indol-1-yl)ethane-1,2-dione. The newly formed Schiff base and its complexes have been characterized with the help of elemental analysis, condensation measurements, magnetic measurements and their structure configuration have been determined by various spectroscopic (electronic, IR, 1H NMR, 13C NMR, GCMS) techniques. The electronic spectra of the complexes indicate a five coordinate square pyramidal geometry of the center metal ion. These metal complexes and ligand were tested for their anti-inflammation and antimicrobial inhibiting potential and compared with standard drugs Phenyl butazone (anti-inflammation), Imipenem (antibacterial) and Miconazole (antifungal).

Bis(methylborole) sandwich compounds of the first row transition metals

Bis(borole)nickel derivatives (η5-C4H4BR)2Ni, isoelectronic with the corresponding ferrocenes (η5-C5H4R)2Fe, have been synthesized and characterized structurally by X-ray crystallography as sandwich compounds with parallel borole rings. The geometries, energetics, and preferred spin states of the complete series of bis(methylborole)metal sandwich compounds (C4H4BCH3)2M of the first row transition metals (M=Ti to Ni) have now been investigated by density functional theory. The late transition metal derivatives (η5-C4H4BCH3)2M energetically prefer metallocene-like sandwich structures having parallel pentahapto borole rings with singlet, doublet, triplet, quartet, and quintet spin states for M=Ni, Co, Fe, Mn, and Cr, respectively. However, the early transition metal (η5-C4H4BCH3)2M derivatives energetically prefer bent sandwich structures having ∼30° dihedral angles between the pentahapto borole rings with singlet, doublet, and triplet spin states for M=Ti, V, and Cr, respectively. For (η5-C4H4BCH3)2Cr the closeness in energy (within ∼1kcal/mol) of the parallel quintet and bent triplet structures suggests interesting magnetic properties. The titanium and vanadium derivatives are predicted to form marginally stable [(C4H4BCH3)2M]2 dimers (M=Ti, V) with the two halves linked by a metal–metal bond as well as two bridging borole carbon atoms through agostic hydrogen atoms.

ChemInform Abstract: Advances in the Organometallic Chemistry of Carbon Nanomaterials

AbstractReview: 106 refs.

Advances in the Organometallic Chemistry of Carbon Nanomaterials

Carbon nanomaterials demonstrate remarkable electrical, thermal, and mechanical properties that allow for a number of very important and exciting potential applications. In this review, we present an overview of the major advances in the organometallic chemistry of carbon nanotubes and graphene over the past decade. The review is focused only on carbon nanocomposites with metal–carbon bonds. We review and discuss various organometallic functionalization approaches and their role in the modification of carbon nanotubes and graphene nanomaterials. Particular attention is paid to reactions of carbon nanotubes with organolithium compounds and to organometallic η6 transition metal complexes with carbon nanotubes and graphene. We also consider the main applications of organometallic reactions of carbon nanomaterials for the preparation of polymer-grafted carbon nanotubes and the corresponding reinforced polymer composites and review the potential applications of transition metal derivatives of carbon nanomaterials in nanoelectronics, fabrication of high-mobility organometallic transistor devices, memory components, spintronics, and catalysis. Finally, we give a future outlook for the further development and applications of carbon nanomaterials containing metal–carbon bonds.

Complexes {Cp*(Dppe)FeC≡CC2R[Co2L2(CO)4]} n+ (R = H, Si(CH3)3; n = 0, 1, 2; L2 = (CO)2, Dppm): Synthesis, redox properties, and electronic characteristics

New neutral and cationic complexes containing the mononuclear organoiron Cp*(Dppe)Fe and cluster Co2C2 fragments have been synthesized. It was shown that the redox reactions substantially extend possibilities for the synthesis of the cationic complexes, and the transition metal derivatives with the unoccupied electron shell represent an interesting and promising direction of studies. It has been confirmed by spectroscopy in the near-IR range a substantial intramolecular electron interaction between the cobalt and iron atoms in the cationic complexes. The obtained estimates for the interaction energy suggest that these compounds can be perspective as molecular devices.

First-Row Transition Metals in Binuclear Cyclopentadienylmetal Derivatives of Tetramethyleneethane: η3,η3 versus η4,η4 Ligand–Metal Bonding Related to Spin State and Metal–Metal Bonds

The tetramethyleneethane (TME) ligand is found in the η3,η3 complex trans-(η3,η3-TME)Ni2Cp2 and the η4,η4 complex trans-(η4,η4-TME)Co2Cp2, which have both been synthesized and structurally characterized by X-ray crystallography. The structures of the complete series of (TME)M2Cp2 derivatives of the first-row transition metals from Ti to Ni have now been investigated by density functional theory. The experimentally known nickel and cobalt complexes are found to have closed-shell electronic ground states. The lowest energy structure for the iron complex is the triplet spin state trans-(η4,η4-TME)Fe2Cp2 structure with geometry similar to that of the lowest energy cobalt structure. All of the low-energy (TME)M2Cp2 structures for manganese and the first-row transition metals to the left of manganese (Cr, V, and Ti) exhibit cis-(η4,η4-TME)M2Cp2 stereochemistry, thereby providing the possibility for direct metal–metal interactions. Vanadium is the only first-row transition metal to the left of cobalt where the lowest energy (TME)M2Cp2 structure is a singlet spin state, suggesting limited applicability of the 18-electron rule in these systems. The frontier molecular orbitals of these cis-(η4,η4-TME)M2Cp2 systems have been examined in order to provide insight regarding metal–metal bonding. Thus, low-energy cis-(η4,η4-TME)Mn2Cp2 structures are found in both quintet and triplet spin states with formal Mn═Mn double bonds. The lowest energy cis-(η4,η4-TME)Cr2Cp2 and cis-(η4,η4-TME)Ti2Cp2 structures have triplet spin states with a formal Cr≡Cr triple bond and a formal Ti═Ti double bond, respectively. The lowest energy cis-(η4,η4-TME)V2Cp2 structure is a singlet structure with a formal V≡V triple bond.

Zinc, copper and nickel derivatives of 2-[2-bromoethyliminomethyl]phenol as topoisomerase inhibitors exhibiting anti-proliferative and anti-metastatic properties

Transition metal (Zn, Cu and Ni) derivatives of (2-[2-bromoethyliminomethyl]phenol), were found to inhibit topoisomerase I activity, induce DNA cleavage and bind to calf thymus DNA. The compounds are also cytotoxic and anti-invasive against PC3.

Enhanced removal of aqueous BPA model compounds using Metalloligs

A model compound, 4-(t-butyl)phenol, was used as a substitute for BPA (bisphenol acetone or Bisphenol A) a material used for the production of a large volume of common plastics. Unfortunately, BPA is suspected to have estrogenic properties, and there is a suspicion that even small amounts can have a deleterious effect against humans, especially female infants. The model compound has some similarities to BPA, but lacks some of the serious properties of BPA dust. Since other workers have demonstrated the capability of removing BPA from plastics by extraction with saline or alcohol, we studied whether Octolig, a polyethylenediimine supported on silica gel, or transition metal derivatives of Octolig could be used to remove concentrations for model compounds from aqueous solution. Octolig gave modest results 20%, the manganese (II) and iron (III) derivatives gave poor results, Cuprilig was an improvement over those two Metalloligs, but the cobalt(II) derivative was able to remove up to 56% of the model compound. Two methods were studied, batch and column chromatography. Under the conditions used in this study, the batch method was superior.

A new type of sandwich compound: homoleptic bis(trimethylenemethane) complexes of the first row transition metals

The metal carbonyl complexes [η4-(CH2)3C]Fe(CO)3 and [η4-(CH2)3C]Cr(CO)4 have been synthesized containing the umbrella-shaped trimethylenemethane ligand. The prospect of using this ligand in the metal sandwich complexes [(CH2)3C]2M (M = Ti, V, Cr, Mn, Fe, Co, Ni) has now been investigated by density functional theory. The lowest energy structures of such complexes have the metal atom sandwiched between two tetrahapto trimethylenemethane ligands. Singlet spin state structures are strongly preferred for the titanium and nickel derivatives and doublet spin state structures for the vanadium and cobalt derivatives. Similarly, the triplet spin state is preferred for the iron derivative by more than 11 kcal mol−1. The preferred spin states for the chromium and manganese derivatives depend on the functional used for the structure optimization. Thus the B3LYP and B3LYP* methods predict the higher spin states, namely triplet for chromium and quartet for manganese. However, the BP86 method predicts the lower spin states of singlet for chromium and doublet for manganese. The higher spin state structures for the late transition metal derivatives, namely quintet [(CH2)3C]2Fe, quartet [(CH2)3C]2Co, and triplet [(CH2)3C]2Ni, have trihapto rather than tetrahapto trimethylenemethane ligands. The frontier molecular orbitals in the singlet [(CH2)3C]2M derivatives (M = Ti, Ni) suggest strong metal–ligand σ and π bonding but insignificant metal–ligand δ bonding.

Organo-Ru supported sandwich-type tungstoarsenates: synthesis, structure and catalytic properties

Five organo-Ru supported sandwich-type 17-tungsto-2-arsenates [{B-α-AsW9O33(OH)}{B-β-AsW8O30(OH)}{M4(OH)2(H2O)2}{(RuC6H6)3}]6− (M = NiII, 1; ZnII, 2; CuII, 3; MnII, 4; CoII, 5) have been synthesized by reacting the salts of the corresponding transitional metals with [(RuC6H6)AsW9O34]7− in sodium acetate solutions at pH 6.0. The synthetic method is different from the previously reported transition metal-derivatives. We instead used the organo-Ru functional lacunary species [(RuC6H6)AsW9O34]7− as the starting material. The salts of 1–5 were characterized by powder XRD, IR spectroscopy and elemental analysis. The structures of 1 and 2 have been solved by single-crystal XRD, comprising a rhomblike (M4O16) group sandwiched between two different lacunary Keggin moieties, [B-α-AsW9O34]9− and [B-β-AsW8O31]9−, leading to the asymmetric sandwich-type frameworks, to which three (RuC6H6) units are grafted via Ru–O–W, Ru–O–M and Ru–O–M(W) bonds. Most importantly, the salts of 1–5 show high catalytic activities towards the oxidation of n-hexadecane with air without any additives and solvents. Comparing with the catalytic activities of the corresponding transition metals salts of [As2W18M4(H2O)2O68]10− (M = NiII, 6; ZnII, 7; CuII, 8; MnII, 9; CoII, 10) and their precursors [AsW9O34]9− (11) and [(RuC6H6)AsW9O34]7− (12), the synergistic effect of Ru and transition metal ions in the compounds leads to the enhanced catalytic properties.

Spectroscopic studies and biological activity of some transition metal complexes of unusual Schiff base

Unusual Schiff base ligand, 4-ethanimidoyl-6-[(1E)-N-(2-hydroxy-4-methylphenyl)ethanimidoyl]benzene-1,3-diol, L, was synthesized via catalytic process involving the interaction of some metal ions with a macrocyclic Schiff base (MSB). The transition metal derivatives [ML(H2O)4](NO3)3, M=Cr(III) and Fe(III), [NiL(H2O)4](NO3)2, [ML(H2O)2](NO3)2, M=Zn(II) and Cd(II), [Cl2Pd(μ-Cl)2PdL], [PtL(Cl)2] and [PtL(Cl)4] were also synthesized from the corresponding metal species with L. The Schiff bases and complexes were characterized by elemental analysis, mass spectrometry, IR and 1H NMR spectroscopy. The crystal structure of L was determined by X-ray analysis. The spectroscopic studies revealed a variety of structure arrangements for the complexes. The biological activities of L and metal complexes against the Escherchia coli as Gram-negative bacteria and Staphylococcus aureus as Gram-positive bacteria, and the two fungus Aspergillus flavus and Candida albicans were screened. The cytotoxicity of [PtL(Cl)2] complex, a cis-platin analogous, was checked as an antitumor agent on two breast cancer cell lines (MCF7 and T47D) and human liver carcinoma cell line (HepG2).