Dinuclear copper complexes with cyanamide derivatives as bridging ligands

Three mixed-valence copper complexes [{Cu(phen)₂}₂(μ-L)](PF₆)₂ (where phen = 1,10-phenanthroline, L = 1,4-dicyanamidobenzene (dicyd)), 1,4-dicyanamido-2,5-dimethylbenzene (Me₂dicyd) and 1,4-dicyanamido-2,5-dichlorobenzene (Cl₂dicyd), and one dinuclear Cu(II) complex [{Cu(phen)₂}₂(μ-apc)](PF₆)₃ (where apc = monoanion of 4-azo(phenylcyanamido)benzene) have been prepared and characterized by elemental analysis, IR and electronic absorption spectroscopies and cyclic voltammetry. [{Cu(phen)₂}₂(μ-apc)](PF₆)₃ · 2CH₃COCH₃ crystallized in the triclinic system and both five-coordinate Cu(II) ions in the dinuclear unit are linked through a bridging 4-azo(phenylcyanamido)benzene (apc) ligand. The cyanamide group (NCN) of the bridging ligand is coordinated to Cu(II) ions through the cyano-nitrogen and amido-nitrogen. The bond length between Cu(1) and cyano-nitrogen is slightly larger than that formed by Cu(2) and amido-nitrogen. The angular structural index parameters, τ, for Cu(1) and Cu(2) are 0.9 and 0.5, respectively. The copper(II) atoms display a different geometry with a N₅ chromophore group. The intra Cu?Cu separation is 5.156(1) Å. All of the dicyd dinuclear copper complexes show radical anion absorption.     

New rhodium---ruthenium heterobimetallic complexes with bridging bi- or tri-dentate phosphine ligands

The mononuclear chelated complex [RuCl(Cp)(η²-dppa)] has been synthesised and reacted with [Rh₂Cl₂(CO)₄] to form the heterobimetallic complex [(Cp)Ru(μ-CO)₂{(μ-Ph₂PN(H)PPh₂}RhCl₂]. Complexes of [RuCl(Cp){(PPh₂)₂CHCH₂PPh₂}] have been reacted with [Rh₂Cl₂(CO)₄] or [RhCl(CO)₂(p-toluidene)]. Characterisation of these new ruthenium complexes was carried out using ³¹P-NMR, FAB mass spectroscopy, elemental analysis and IR spectrophotometry.     

Synthesis, characterization and electrochemistry of diruthenium complexes linked by aryl acetylide bridges

The reactions between Ru₂(ap)₄Cl and the appropriate lithiated aryl acetylene resulted in the complexes Ru₂(ap)₄(CC4-C₆H₄CCX) with X as SiMe₃ (1), H (2) and Ru₂(ap)₄ (3), 1,3-[Ru₂(ap)₄(CC)]₂(C₆H₄) (4), 1,3-[{Ru₂(ap)₄(CC)}₂]C₆H₃5-CCH (5) and 1-[Ru₂(ap)₄(CC)]C₆H₃3,5-(CCH)₂ (6), where ap is 2-anilinopyridinate. The spectroscopic and electrochemical properties of the new complexes have been assessed. Complexes 3, 4 and 6 display two-electron oxidation and reductions, implying the absence of any significant electronic interaction between the two Ru₂(ap)₄ units in these complexes.     

Structural varieties in double salts of silver acetylide containing ancillary anions and terminal ligands

New double salts Ag₂C₂·6AgO₂CCHF₂ (1), [HPyCH₂OH][Ag₉(C₂)(CF₃CO₂)₉(HPyCH₂OH)(H₂O)]·0.5H₂O (PyCH₂OH=4-(hydroxymethyl)pyridine) (2), Ag₂C₂·5CF₃SO₃Ag·2MeCN·2H₂O (3) and Ag₂C₂·8CF₃SO₃Ag·2EtCN·3H₂O (4) have been synthesized by dissolving Ag₂C₂ in an aqueous solution of the corresponding silver salt followed by the addition of an ancillary ligand. Complex 1 has a three-dimensional structure in which unprecedented basket-like silver cages are inter-connected by difluoroacetate ligands. In 2, centrosymmetric (C₂)₂@Ag₁₄ double cages with each half taking the shape of a triangulated dodecahedron are linked through additional silver atoms to generate an infinite chain, and unsupported silver(I)–silver(I) interactions exist between neighboring chains. Of the two independent 4-(hydroxymethyl)pyridinium ions in 2, one acts in the O-ligating mode, which is observed for the first time, while the other merely serves to provide charge balance and space-filling. Both 3 and 4 are layer-type structures in which the basic building unit is a distorted monocapped octahedron and monocapped trigonal prism, respectively.     

Trinuclear copper(I) acetylide complexes bearing carbonyl moiety: Synthesis, characterization, and photophysical properties

A series of trinuclear copper(I) acetylide complexes with carbonyl moiety, [Cu₃(μ-dppm)₃(μ₃-η¹-CCC(O)R)₂](ClO₄) (R = H (1), CH₃ (2), OCH₃ (3), NH₂ (4), NEt₂ (5)) (dppm = bis(diphenylphosphino)methane), have been synthesized and characterized. The crystal structures of [Cu₃(μ-dppm)₃(μ₃-η¹-CCC(O)CH₃)₂](ClO₄) (2) and [Cu₃(μ-dppm)₃(μ₃-η¹-CCC(O)NH₂)₂](ClO₄) (4) were determined by X-ray diffraction. The photophysical properties of complexes 1−5 have been studied. Complexes 1−5 show luminescence both in the solid state and in acetonitrile solution at 298 K, and their emission energies are in the order: 5 > 4 > 3 > 2 > 1. Density function theory (DFT) calculations at the hybrid Perdew, Burke, and Ernzerhof functional (PBE1PBE) level were performed on model complex 1 to elucidate the emission origin of complexes 1−5.     

Synthesis and characterization of platinum diimine bis(acetylide) complexes containing easily derivatizable aryl acetylide ligands

New Pt(II) diimine bis(acetylide) complexes where the diimine is a substituted bipyridine or phenanthroline and the arylacetylide is 4-ethynylbenzaldehyde have been prepared in good to excellent yields. Spectroscopic characterization supports a square planar coordination geometry with cis-alkynyl ligands, and the crystal structure of one of the complexes, Pt(phen)(Ctbd1;CC(6)H(4)CHO)(2) (1), confirms the assignment. The new diimine bis(acetylide) complexes exhibit an absorption band ca. 400 nm that corresponds to a Pt(d) --> pi diimine charge transfer transition and are brightly emissive in fluid solution, with excited state lifetimes in the range 100-800 ns. Correlation of diimine substituent with lambda(max) for the 400 nm absorption band gives strong support to the MLCT assignment. Complex 1 undergoes electron transfer quenching, showing good Stern-Volmer behavior with a variety of oxidative and reductive quenchers. Quenching studies conducted with DNA nucleosides (A, T, C, G) were also investigated. Silyl-protected adenosine and guanosine were found to quench the luminescence of 1 better than similarly protected cytidine or thymidine. Since the former are the more easily oxidized bases, the results suggest that the Pt(II) diimine bis(acetylide) complexes are more powerful photooxidants than photoreductants with regard to electron transfer to DNA bases.     

Dinuclear copper complexes of pyridylphenylphosphine ligands: Characterization of a mixed-valence Cu/Cu dimer

Homo bi-copper complexes [Cu₂{PhP(2-py)₂}₂(NO₃)₃] (1) and [Cu₂{P(2-py)₃}₂Cl₂] (2), were synthesized from the reaction of Cu(NO₃)₂·3H₂O and CuCl₂·2H₂O with their corresponding 2-pyridylphosphine ligands. Compound 1 has a mixed valence Cu(I)-Cu(II) core with electron acceptor phosphine atoms and two NO₃⁻ anions coordinated in a monodentate fashion to Cu(I), giving it a distorted tetrahedral geometry. The environment of Cu(II) in 1 is composed of four nitrogen atoms from pyridyl and another NO₃⁻ anion in a square pyramidal geometry. This complex shows luminescence and a low energy absorption band at 969 nm corresponding to intermetallic electron transfer between the copper centers. Complex 2 was prepared from the treatment of copper(II) chloride with tris(2-pyridyl)phosphine, producing a binuclear copper complex which possesses a crystallographic inversion center. The copper geometry in this complex is distorted tetrahedral with coordination of one Cl⁻, two nitrogens from one bridging tris(2-pyridyl)phosphine ligand and one P atom from the other bridging tris(2-pyridyl)phosphine ligand, in a similar way observed in related complexes. The products have been characterized by spectroscopic methods and also by the single-crystal X-ray diffraction method.     

Syntheses and crystal structures of butterfly M2Te2 complexes of molybdenum and tungsten with functionalized cyclopentadienyl ligands

Reactions of singly-bonded dinuclear complexes [(η⁵-CH₃O₂CC₅H₄)₂M₂(CO)₆] (I, M?=?Mo; II, M?=?W) with the diarenylditelluride [4-CH₃C₆H₄Te]₂ in refluxing toluene for 4–6?h afforded dinuclear complexes 1 and 2 trans/ae-[(η⁵-RC₅H₄)₂M₂(CO)₄(μ-ArTe)₂] (Ar?=?4-CH₃C₆H₄Te). Complexes 1 and 2 were also synthesized by reactions of triply-bonded dinuclear complexes [(η⁵-CH₃O₂CC₅H₄)₂M₂(CO)₄] (III, M?=?Mo; IV, M?=?W) with [4-CH₃C₆H₄Te]₂ in refluxing toluene for 1?h. Both complexes have been characterized by elemental analysis, ¹H NMR, ¹³C NMR and IR spectroscopy and X-ray diffraction. Preliminary low-temperature NMR experiments on complexes 1 and 2 have revealed that in solution each complex goes through a rapid inversion of the butterfly four-membered ring M₂Te₂.     

Two new dinuclear complexes with dipicolinate and bridging 2-aminopyrazine ligands: preparation,structural, spectroscopic,and thermal characterizations

Treatment of an aqueous solution of dipicolinic acid (dipicH₂) and 2-aminopyrazine (apyz) with Cu(NO₃)₂?·?3H₂O or ZnCl₂ (in molar ratio 1?:?1?:?1) led to formation of dinuclear complexes, [M₂(H₂O)₄(dipic)₂(µ-apyz)] (M?=?Cu (1) and Zn (2)). Both complexes were characterized by elemental analyses, IR, and UV-Vis spectroscopy. Their molecular and crystal structures were determined by X-ray crystal structure analysis and their thermal stabilities were confirmed by TGA/DTA methods. Complex 1 crystallizes in the triclinic P-1 space group, while 2 crystallizes in the monoclinic P2₁/c space group. The dinuclear complexes are analogous and composed of two metal ions bridged by 2-aminopyrazine. Each M(II) is coordinated by one nitrogen atom and two oxygen atoms of tridentate dipicolinate, one heterocyclic nitrogen of 2-aminopyrazine, and two coordinated water molecules. The resulting geometry for the MN₂O₄ coordination environment can be described as distorted octahedral. Extensive hydrogen-bonding interactions involving all water ligands, dipicolinate oxygen atoms, and amino groups further stabilize the complex units by linking them to form 3-D networks for 1 and 2.     

Investigations into bis(triphenylphosphine)copper(I) complexes with cyclic derivatives of methylpyruvate thiosemicarbazones

The syntheses of four compounds, obtained by the reaction of methylpyruvate thiosemicarbazone (Hmpt) and its methyl (Me-Hmpt) and allyl (Allyl-Hmpt) derivatives with bis(triphenylphosphine)copper(I) acetate, are reported. The compounds [Cu(PPh₃)₂(pt_c)(Hpt_c)]·H₂O (1), [Cu(PPh₃)₂(Me-pt_c)] (2), [Cu₂(PPh₃)₂μ-S(Me-pt)μ-S(Me-pt_c)]·H₂O (3) and [Cu(PPh₃)₂(Allyl-pt_c)] (4) [H₂pt = pyruvic acid thiosemicarbazone and Hpt_c = cyclized pyruvic acid thiosemicarbazone, Me = methyl and Allyl are radical substituents on the amino nitrogen] were characterized by elemental analysis, IR, ¹H NMR, and by X-ray crystallography. Compound 3 was also studied by EPR because of the presence in the compound of two copper atoms in two different oxidation states. During the complexation reaction, the thiosemicarbazone ligands tend to undergo a cyclization reaction that leads to the formation of a six-member heterocyclic ring. All four compounds present the [Cu(PPh₃)₂]⁺ fragment and constant but different coordination situations. Compound 1 contains two cyclic ligand molecules, one protonated and the other deprotonated, bound as monodentate through the sulfur. Compounds 2 and 4 present a single deprotonated cyclic SN bidentate ligand molecule, while compound 3 contains copper(I) and copper(II), and two ligand molecules, one of which is linear and behaves as SNO tridentate and the other is cyclic and behaves as bridging μSN.     

Syntheses and crystal structures of Dimolybdenum complexes containing P2 and functionalized Cyclopentadienyl ligands

The dimolybdenum complex [(η⁵-RC₅H₄)₂Mo₂(CO)₆] (1, R = CH₃CO; II, R = CH₃O₂C) reacts with an equimolar amount of white phosphorus P₄ to yield the corresponding dimolybdenum complex containing the P₂ ligand [(η⁵-RC₅H₄)₂Mo₂(CO)₄(μ,η²-P₂)] (1, R = CH₃CO; 2, R = CH₃O₂C) in moderate yield. The two new compounds have been characterized by elemental analyses, ¹H?NMR, ¹³C?NMR, ³¹ P?NMR and IR spectroscopies and their crystal structures have been determined by X-ray diffraction methods.     

Triazoles as complexing agents: Synthesis and structural studies of some bivalent metal ion complexes with Bi- and tridentate ligands

Summary Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of 4-amino-5-mercapto-3-trifluoromethyl-s-triazole (AMTT) and 5-mercapto-4-salicylideneamino-3-trifluoromethyl-s-triazole (MSTT) have been synthesized and characterized on the basis of elemental analyses, magnetic measurements, infrared and electronic spectral data. The ligandsAMTT andMSTT were characterized by elemental analyses, infrared and¹H NMR spectral studies.AMTT, involving N and S as donor atoms, andMSTT, involving N, O and S as donor atoms, act as bi- and tridentate ligands, respectively. The geometry of the complexes has been assigned on the basis of magnetic and electronic spectral data. EPR parameters for copper (II) complexes have been calculated. Thermal stabilities of the complexes are also reported. Due to insolubility in water and common organic solvents and infusibility at higher temperatures, all the complexes are thought to be polymeric in nature.

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Triazole als Komplexierungs-Agentien: Synthese und Strukturuntersuchungen an einigen bivalenten Metallionenkomplexen mit zwei- und dreizähnigen Liganden

Zusammenfassung Es wurden Co(II)-, Ni(II)-, Cu(II)-, Zn(II)- und Cd(II)-Komplexe von 4-Amino-5-mercapto-3-trifluormethyl-s-triazol (AMTT) und 5-Mercapto-4-salizylidenamino-3-trifluormethyl-s-triazol (MSTT) hergestellt und mittels Elementaranalyse, magnetischen Messungen, Infrarot- und Elektronenspektroskopie charakterisiert. Die LigandenAMTT undMSTT wurden elementaranalytisch und spektroskopisch (IR und¹H-NMR) charakterisiert.AMT wirkt über die N-und S-Donoratome als zweizähniger Ligand,MSTT über N, O und S als dreizähniger Ligand. Die Geometrie der Komplexe wurde auf der Basis von magnetischen und elektronenspektroskopischen Daten zugeordnet. Für die Cu(II)-Komplexe wurden die EPR-Parameter berechnet. Die thermischen Stabilitäten der Komplexe wurde ebenfalls untersucht. Wegen ihrer Unlöslichkeit in Wasser und gängigen organischen Lösungsmitteln und der Unschmelzbarkeit bei höheren Temperaturen wird eine polymere Natur der Komplexe angenommen.

     

Macrocyclic gold(I) complexes and [2]catenanes containing carbonyl functionalized diacetylide ligands

The carbonyl derivatized bis(alkyne) O=C(4-C₆H₄OCH₂CCH)₂ was converted into the imine derivatives RN=C(4-C₆H₄OCH₂CCH)₂ [R=OH, NHC(O)NH₂, NHC₆H₃-2,4-(NO₂)₂] and into the 4-bromomethyl-1,3-dioxolane derivative BrCH₂C₂H₃O₂C(4-C₆H₄OCH₂CCH)₂. The alkyne units in these compounds react with [AuCl(SMe₂)] in the presence of base to form the corresponding digold(I) diacetylide complexes, that exist as insoluble oligomers or polymers. They reacted with the diphosphines Ph₂PZPPh₂ [Z=CC, trans-HC=CH and (CH₂)_n, n=3–5] to give macrocyclic gold(I) complexes of the type [Au₂(μ-LL)(μ-PP)], where LL is the diacetylide and PP the diphosphine ligand. The ability of these macrocyclic complexes to self-assemble to [2]catenanes has been studied. The ketone and imine derivatives do not form [2]catenanes because the orientation of the aryl groups is unfavorable, but the 1,3-dioxolane derivatives may catenate if the ring size is optimum.     

Photochromic and redox properties of bisterpyridine ruthenium complexes based on dimethyldihydropyrene units as bridging ligands

We report herein the synthesis and characterization of four new bisterpyridine dinuclear ruthenium complexes containing the dimethyldihydropyrene (DHP) photochrome as bridging ligand. A synthetic strategy has been developed based on a Suzuki coupling reaction to synthesize these novel terpyridine-DHPs. The reactivity of these different ligands and dinuclear ruthenium complexes with light was examined by (1)H NMR and monitoring the changes in their absorption spectra upon irradiation at controlled wavelengths. The free ligands and their corresponding ruthenium complexes all displayed photochromic properties with highly efficient conversion between the closed stable isomers (DHP) and their open forms (CPD). The properties of the compounds in their closed and open forms were investigated by cyclic voltammetry, spectroscopy, and luminescence measurements.     

Synthesis and thermal behavior of dimethyl scandium complexes featuring anilido-phosphinimine ancillary ligands

A family of N,N donor ligands [1-(NHAr)-2-(PR₂NAr′)C₆H₄] (1a-d; Ar = 2,6-ⁱPr₂-C₆H₃, R = Me, Ph, Ar′ = 2,4,6-Me₃-C₆H₂, 2-ⁱPr-C₆H₄, 2,6-ⁱPr₂-C₆H₃) has been prepared and fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. Lithiation of the N-H unit and subsequent salt metathesis protocols with ScCl₃THF₃ provides an avenue to organometallic scandium complexes. The resultant base-free monomeric dichlorides LScCl₂, 3a-d, have been fully characterized by NMR spectroscopy as well as X-ray crystallography (3a,c,d). Alkylation of the dichlorides using LiMe results in clean formation of dialkyl complexes LScMe₂4a-c. Thermolysis of these materials under argon and hydrogen leads to decomposition products as a result of C-H activation of the ligand. Analysis of these results provides a qualitative assessment of the metalative resistance of each ligand framework.     

Synthesis and structure of metal complexes containing zwitterionic N-hydroxyimidazole ligands

Cu(II) and Zn(II) complexes of N-hydroxyimidazoles were synthesised by reacting simple metal perchlorate salts with the imidazole ligand in alcohol and formulated with a metal:ligand ratio of 1:2. The X-ray crystal structures of five complexes (four Cu(II) and one Zn(II)) were obtained and each showed the two trans, N-hydroxyimidazole ligands forming six-membered, chelate rings with the metal. Both of the NO chelating, neutral N-hydroxyimidazole ligands are in the zwitterion form, with the uncoordinated imidazole imine N atom being protonated and the oxime O atom deprotonated. In the solid state the complexes form hydrogen-bonded supramolecular structures.     

Organometallic complexes for nonlinear optics: Part 32: Synthesis, optical spectroscopy and theoretical studies of some osmium alkynyl complexes

The complexes trans-[Os(CCPh)Cl(dppe)₂] (1), trans-[Os(4-CCC₆H₄CCPh)Cl(dppe)₂] (2), and 1,3,5-{trans-[OsCl(dppe)₂(4-CCC₆H₄CC)]}₃C₆H₃ (3) have been prepared. Cyclic voltammetric studies reveal a quasi-reversible oxidation process for each complex at 0.36–0.39 V (with respect to the ferrocene/ferrocenium couple at 0.56 V), assigned to the Os^II/III couple. In situ oxidation of 1–3 using an optically transparent thin-layer electrochemical (OTTLE) cell affords the UV–Vis–NIR spectra of the corresponding cationic complexes 1⁺–3⁺; a low-energy band is observed in the near-IR region (11 000–14 000 cm⁻¹) in each case, in contrast to the neutral complexes 1–3 which are optically transparent below 20 000 cm⁻¹. Density functional theory calculations on the model compounds trans-[Os(CCPh)Cl(PH₃)₄] and trans-[Os(4-CCC₆H₄CCPh)Cl(PH₃)₄] have been used to rationalize the observed optical spectra and suggest that the low-energy bands in the spectra of the cationic complexes can be assigned to transitions involving orbitals delocalized over the metal, chloro and alkynyl ligands. These intense bands have potential utility in switching nonlinear optical response, of interest in optical technology.     

New approaches to enantioselective fluorination: Cinchona alkaloids combinations and chiral ligands/metal complexes

The selective construction of carbon-fluorine bonds is of great interest to medicinal chemists because the replacement of a hydrogen or an oxygen atom with a fluorine atom in biologically active molecules can confer the molecules with improved physicochemical properties and biological activities. Since the first discovery of enantioselective fluorination using N-fluorocamphorsultam, our synthetic interest had been focused on the development of chiral N-fluorosulfonamide derivatives capable of enantioselective fluorination. However, these initial efforts revealed several limitations in both chemical yields and enantioselectivities of the fluorinated products. We present here the background of our personal story of the enantioselective fluorination reaction and some successful applications of the methods to the design and synthesis of biologically active products. Two novel approaches using cinchona alkaloid/Selectfluor^® combinations and chiral ligands/metal complexes have been pursued, respectively. In addition, the recent advances in this area by other groups are also described briefly.     

Polynuclear metal complexes of ligands containing phenolic units

The coordination properties of a selected series of acyclic and macrocyclic ligands containing one or more phenolic groups are explored. The formation of polynuclear metal complexes was only considered highlighting the key role played by the phenoxide oxygen atom in binding two metal centres in a bridge disposition. This arrangement allows two metal ions to stay close each other and consequently these dinuclear centres are able to mimic many biological sites, especially those where the two metals can cooperate to form an active centre. Catalytic properties of these polynuclear complexes, when studied, have been reported. Also some of the numerous heterodinuclear metal complexes that have been synthesized are here reviewed, included several crystal structures.     

Synthesis of novel platinum-silver and platinum-copper complexes with bridging alkynyl ligands

The study of the reactivity of [Pt₂M₄(CCR)₈] (M=Ag or cu; R=Ph or ^tBu) towards different neutral and anionic ligands is reported. This study reveals that reactions of the phenylacetylide derivatives [Pt₂M₄(CCPh)₈] with anionic, X⁻ (X=Cl or Br) or neutral donors (CN^tBu or py) in a molar ratio 1:4 (m/donor ratio 1:1) yield the trinuclear anionic (NBu₄)₂[{Pt(CCPh)₄ (MX)₂] (M=Ag or Cu, X =Cl or Br) or neutral [{Pt(CCPh0₄=sAGL)₂] (L=CN^tBu or py) complexes, respectively. The crystal structure of (NBu₄)₂[{Pt(CCPh)₄}(CuBr)₂](4) shows that the anion is formed by a dianionic Pt(CCPh)₄ fragment and two neutral CuBr units joined through bridging alkynyl ligands. All the alkynyl groups are σ bonded to Pt and η²-coordinated to a Cu atom which have an approximately trigonal-planar geometry. By contrast, similar reactions with [Pt₂M₄(CC^tBu)₈] (molar ratio M/donor 1:1) afford hexanuclear dianionic (NBu₄)₂[Pt₂M₄(CC^tBu)₈X₂] or neutral [Pt₂Ag₄(CC^tBu0₈Py₂]. Only by treatment with a large exces of Br ⁻ (molar ratio M/Br⁻ 1:2) are the trinuclear complexes (NBu₄)₂[{Pt(CC^tBu₄ (MBr)₂] (M=Ag, Cu) obtained. Attempted preparations of analogous complexes with phosphines (L′=PPh₃ or PEt₃) by reactions of [Pt₂M₄(CCR₈] with L′ leads to displacement of alkynyl ligands from platinum and formation of neutral mononuclear complexes [trans-Pt(CCR)₂L′₂].