共价双金属配合物在分子导线方面的研究进展

共价双金属配合物因其结构的优越性,在分子器件特别是分子导线的研究方面有广阔的应用前景。分子内电子耦合作用的研究是揭示这类配合物构成的分子导线性能的关键之一。本文介绍了共价双金属配合物的分子内电子耦合作用及此类配合物的结构特点,总结了近年来共价双金属配合物在分子导线领域的研究进展,并对共价双金属配合物的发展前景进行了展望。     

Bimetallic anilido-aldimine Al or Zn complexes for efficient ring-opening polymerization of epsilon-caprolactone

Four bimetallic Al or Zn complexes supported by anilido-aldimine ligands (o-C6H4(NHAr)-CH=N)2CH2CH2 (Ar = 2,6-Me2C6H3,L1H2; Ar = 2,6-iPr2C6H3, L2H2) have been synthesized and characterized. Treatment of L1H2 or L2H2 with two equiv. of AlMe3 gives bimetallic complex L1(AlMe2)2 1 or L2 (AlMe2)2 2, respectively. Reaction of L1H2 or L2H2 with two equiv. of ZnEt2 leads to bimetallic complex L1(ZnEt)2 3 or L2(ZnEt)2 4, respectively. All of the complexes 1-4 are efficient catalysts for ring-opening polymerization of epsilon-caprolactone (CL) in the presence of benzyl alcohol and catalyze the polymerization of CL in living fashion yielding polymers with a narrow polydispersity index. The activity of bimetallic Zn complexes 3 and 4 is higher than bimetallic Al complexes 1 and 2.     

Synthesis of Tetradentate Schiff Base Derivatives of Transition Bimetallic Complexes as Antimicrobial Agents

A series of Co(II), Cu(II), Mn(II) and Zn(II) bimetallic complexes have been synthesized with the schiff base ligand 2‐(bis‐2‐hydroxyl phenylidene) diimine (L) derived from the condensation of hydrazine and salicylaldehyde. The synthesized ligand and bimetallic complexes were characterized by different spectroscopic techniques. The characterization of ligand was carried out by FT‐IR, H¹NMR, C¹³NMR and MS while the bimetallic complexes were characterized by FT‐IR and X‐ray crystallographic techniques. The complexes and ligand were employed in vitro for antifungal and antibacterial activities using disc diffusion method. Different fungal strains such as Alternaria Alternate, Aspergillus Flavus and Aspergillus Niger were used to check antifungal activities of bimetallic complexes and ligand. Similarly, the bacterial strains used were Staphylococcus Aureus, Bacillus Subbtilis and Escheria Coli. The biological studies showed that the ligand exhibited lower value of antifungal and antibacterial activities than bimetallic complexes.     

Inter- and intramolecular phosphonium salt cocatalysis in cyclic carbonate synthesis catalysed by a bimetallic aluminium(salen) complex

Quaternary phosphonium salts can be used as cocatalysts for the conversion of epoxides and carbon dioxide into cyclic carbonates catalysed by bimetallic aluminium(salen) complexes at ambient temperature and one atmosphere pressure. The phosphonium groups could also be attached onto the salen ligands of the bimetallic aluminium(salen) complex to form one-component catalysts, and in this case the catalytic activity was heavily influenced by the solubility of the catalyst in the epoxide substrate. The results are consistent with a previously proposed catalytic cycle for cyclic carbonate synthesis catalysed by bimetallic aluminium(salen) complexes.     

Combinatorial synthesis of bimetallic complexes with three halogeno bridges

Methods for the synthesis of bimetallic complexes in which two different metal fragments are connected by three chloro or bromo bridges are reported. The reactions are general, fast, and give rise to structurally defined products in quantitative yields. Therefore, they are ideally suited for generating a library of homo- and heterobimetallic complexes in a combinatorial fashion. This is of special interest for applications in homogeneous catalysis. Selected members of this library were synthesized and comprehensively characterized; single-crystal X-ray analyses were performed for 15 new bimetallic compounds.     

Spectroscopic and electrochemical studies of hetero-bimetallic copper complexes with Schiff's base ligand

Using Schiff's base ligand, several Cu(II) based bimetallic complexes such as Cu-Cu, Cu-Co, Cu-Ni, Cu-Zn, Cu-Mn have been prepared in a stepwise procedure. The structures of these complexes and the ligand have been proposed on the basis of FAB mass, elemental analysis, UV-vis, IR, electron paramagnetic resonance (EPR) and CV studies. EPR parameters, obtained through complete simulation, suggest that the formation of bimetallic complexes forces the Cu(II) centre to increase the flexibility in comparison with the monometallic Cu(II) complex. However, the nature of the second metal ion in the bimetallic complex effects the distortion around the first metal ion. The reduction of the complexes from Cu(II) to Cu(I) involves a large geometrical change and is found to be irreversible. A large positive shift is seen in the cathodic process, which can be ascribed to increased distortion due to bimetallic coordination. These complexes have potential usage in DNA studies.     

线型共轭Cx桥联双金属有机化合物

分子电子器件是近年来的一个热门课题。线型共轭Cx桥联双金属有机化合物是分子导线、分子开关等分子电子器件的模型化合物之一。本文介绍了线型共轭Cx桥联双金属有机化合物的结构、合成及光电性质。     

Cu-catalyzed synthesis of symmetric group 6 (Fischer) bis-carbene complexes

The efficient copper oxidative homocoupling (CuCl/TMEDA/O2) of alkynyl Fischer carbene complexes yields bis-carbene complexes having pi-tethers. The bimetallic complexes are exceptional templates to prepare diverse organic symmetric structures connected by pi-extended fragments.     

Enantioselective hydrocyanation of aldehydes catalyzed by [Li{Ru(phgly)2(binap)}]X (X = Cl, Br)

Novel bimetallic complexes [Li{Ru[(S)-phgly](2)[(S)-binap]}]X (X = Cl, Br) are readily synthesized by mixing Ru[(S)-phgly](2)[(S)-binap] and LiX. A single-crystal X-ray analysis reveals the structure. These bimetallic complexes efficiently catalyze asymmetric hydrocyanation of aldehydes with a substrate-to-catalyst molar ratio of 500-2000 at -78 to -60 °C. A range of aromatic, heteroaromatic, and α,β-unsaturated aldehydes as well as a tert-alkyl aldehyde is converted to the cyanohydrins in high enantiomeric excess (up to 99%).     

Nanoscopic structure and function of polymer‐protected metal clusters

Colloidal dispersion of polymer‐protected metal clusters were prepared by heat treatment of macromolecule‐metal complexes, composed of water‐soluble polymer and noble metal ions. The mixtures of two kinds of noble metal ions can provide polymer‐protected bimetallic nanoclusters with a core/shell structure by the same procedure. In contrast, bimetallic clusters with the inverted core/shell structure are difficult to be prepared by the similar procedure. A sacrificial hydrogen strategy has been successfully proposed for the preparation of the inverted ones. When copper or nickel ions were used as one of the elements to prepare bimetallic clusters, rather random alloy structured nanoparticles were produced. The catalytic activity of these bimetallic clusters is, in general, higher than that of the corresponding monometallic ones.     

Distal metal effects in cobalt porphyrins related to CcO

Cobalt(II) porphyrins were studied to determine the influence of distal site metalation and superstructure upon dioxygen reactivity in active site models of cytochrome c oxidase (CcO). Monometallic, Co(II)(P) complexes when ligated by an axial imidazole react with dioxygen to form reversible Co-superoxide adducts, which were characterized by EPR and resonance Raman (RR). Unexpectedly, certain Co porphyrins with Cu(I) metalated imidazole pickets do not form mu-peroxo Co(III)/Cu(II) products even though the calculated intermetallic distance suggests this is possible. Instead, cobalt-porphyrin-superoxide complexes are obtained with the distal copper remaining as Cu(I). Moreover, distal metals (Cu(I) or Zn(II)) greatly enhance the stability of the dioxygen adduct, such that Co superoxides of bimetallic complexes demonstrate minimal reversibility. The "trapping" of dioxygen by a second metal is attributed to structural and electrostatic changes within the distal pocket upon metalation. EPR evidence suggests that the terminal oxygen in these bimetallic Co-superoxide systems is H-bonded to the NH of an imidazole picket amide linker, which may contribute to enthalpic stabilization of the dioxygen adduct. Stabilization of the dioxygen adduct in these bimetallic systems suggests one possible role for the distal copper in the Fe/Cu bimetallic active site of terminal oxidases, which form a heme-superoxide/copper(I) adduct upon oxygenation.     

Facile Preparation of Homo‐ and Hetero‐Dimetallic Complexes with a 4‐Phosphino‐Substituted NHC Ligand. Toward the Design of Multifunctional Catalysts

A series of bimetallic complexes have been synthesized that are supported by a 4‐phosphino‐substituted NHC ligand. The use of this stable ligand reduces the number of synthetic steps and allows for a wide range of metal combinations to be introduced into the complexes.     

Synthesis of thiometallate complexes and catalytic hydration of acetonitrile

The bimetallic complexes [M(bipy)nS2M′X2], where M=FeII, RuII, NiII or CoII; bipy=2,2′-bipyridine; n=1 or 2; M′=MoVI or WVI and X=O or S, were synthesized using tetrathiometallates and dithiometallates as bidentate ligands. The characterization of the new bimetallic complexes was carried out by standard techniques. The complexes were tested as catalysts in acetonitrile hydrolysis. The reaction products are acetamide and acetic acid, formed by hydrolysis of acetamide. The most active catalysts in the acetonitrile hydrolysis are [Fe(bipy)2S2MoS2], [Ru(bipy)2S2MoS2] and [Co(bipy)2S2WS2], whereas the lowest activity is shown by the nickel complexes. However, the latter exhibit the highest selectivity in acetamide formation. ZINDO semi-empirical calculations were performed in order to explain some of the properties of the complexes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Metal-Metal Cooperation in Dinucleating Complexes Involving Late Transition Metals Directed towards Organic Catalysis

Cooperatively bimetallic organic catalysis,coupling actions of two metal centers in a catalytic organic transformation via co-activation of a single molecule or synergistic activation of two molecules,has witnessed rapid development in the last decades.     

Bimetallic reactivity. On the use of oxadiazoles as binucleating ligands

Two (1,3,4)-oxadiazole ligands have been prepared. In one case the oxadiazole ring is flanked by two o-aniline groups, and in the other case it is an extension of the first where the amines are condensed with 2-picolyl groups. A monometallic copper(II) complex of the former has been prepared, and its crystal structure was determined. A number of bimetallic copper(II), cobalt(II), and nickel(II) complexes of the di-deprotonated latter ligand were prepared and isolated. The crystal structure of the cobalt(II) complex bearing two acetate bridges is reported. The work demonstrates that the seldom-employed oxadiazole ring can be used effectively for generating bimetallic complexes.     

Sensitized luminescence from lanthanides in d–f bimetallic complexes

This article reviews progress in the research of transition metal–lanthanide (d–f) bimetallic complexes. Through efficient energy transfer, sensitized luminescence of lanthanide ions from the visible range (Eu^III) to the near-infrared region (Nd^III, Yb^III, Er^III and Pr^III) is obtained in these bimetallic assembles. The d-block in d–f bimetallic complexes mainly contributes to the improvement of lanthanide emission efficiency and the extension of the excitation window for the lanthanide complexes. Examples are catalogued by various transition metals, such as Ru^II, Os^II (Fe^II), Pt^II (Au^I), Pd^II, Re^I, Cr^III, Co^III, Zn^II and Ir^III. The relevant synthetic procedures, crystal structures and photophysical properties of these d–f complexes are briefly described. Additionally, the molecular properties responsible for the performance of certain d–f systems, such as energy levels, nuclear distances and coordination environments, will be discussed.     

Bimetallic cluster complexes: synthesis, structures and applications to catalysis

A brief history of the seminal discoveries in the field of bimetallic cluster complexes with their structures is presented. A review of some recent studies of palladium and platinum-ruthenium cluster complexes is concluded with a discussion of applications of these complexes in the area of homogeneous hydrogenation catalysis of alkynes.     

Metallomacrocycles incorporating a hemilabile Tröger's base derived ligand

Tr?ger's base, a chiral molecule with a rigid 90 degrees backbone, has been incorporated into a novel hemilabile phosphinoalkyl thioether ligand. Using the Weak Link Approach, this ligand has been reacted with Cu(CH3CN)4PF6 and [Rh(COE)2Cl]x (COE = cyclooctene) to form metallomacrocycles. Upon reaction of the ligand with Cu(I), which prefers a tetrahedral coordination geometry, a bimetallic macrocycle was formed. Alternatively, owing to the steric restrictions imposed by the 90 degrees backbone of the ligand and the square-planar geometry of Rh(I), when the ligand was reacted with [Rh(COE)2Cl]x, the formation of bimetallic closed macrocycles was not observed, and instead a mixture of tri- and tetrametallic closed macrocycles is formed. Introducing pyridine to the Cu(I) complex causes the weak thioether-Cu bonds to break, generating a large bimetallic open macrocycle. Upon reaction of the mixture of Rh(I) metallomacrocycles with CO and Cl-, the cyclic structure of these complexes becomes flexible enough that the dimeric bimetallic macrocycle forms, along with tri- and tetrameric open complexes. The mixture of differently sized Rh(I) macrocyclic complexes has been analyzed using gel permeation chromatography, and the tetramer has been characterized by a single-crystal X-ray diffraction study. These are the first examples of metallomacrocycles containing a Tr?ger's base derivative.     

Binuclear rhenium(I) complexes for the photocatalytic reduction of CO2

Binuclear rhenium(I) complexes with 1,2-bis(4,4'-methyl-[2,2']bipyridyl)-ethane and 1,2-bis(4,4'-methyl-[2,2']bipyridyl)-dodecane as bridging ligands and their mononuclear analogues have been synthesized and characterized by their spectroscopic and electrochemical properties. First reduction potentials and luminescence properties as well as the reductive quenching of the emissive state with TEOA were not affected by the alkyl linker. By means of a detailed comparison of the photocatalytic CO(2) reductions of the monometallic and the bimetallic complexes a great beneficial effect on the activity depending on the proximity of the centres was found. In high dilution the overall kinetics in the CO(2) photoreduction of mononuclear complexes are clearly monometallic. If the proximity of the centres is adjusted according to the lifetime of the OER (one electron reduced species) the photocatalytic activity is greatly improved showing a clear bimetallic mechanism. In the binuclear rhenium complexes, both the facile generation of a free coordination site and binuclear interactions for effective two electron transfer can be realized.     

Bimetallic Carbonyl Complexes Based on Iridium and Rhodium: Useful Tools for Hydrodefluorination Reactions

A set of bimetallic complexes based on iridium and rhodium with bis(diphenylphosphino)methane, bis(di-iso-propylphosphino)methane, diphenyl-2-pyridylphosphine and 2-(di-iso-propylphosphino)imidazole bridging ligands was prepared. The complexes were characterized by NMR and IR spectroscopy and studied quantum-chemically using DFT methods. The bimetallic systems succeeded in catalytic hydrodefluorination reactions of lower fluorinated aryl fluorides using molecular hydrogen and sodium tert-butoxide as a base. Effects of (i) ligand variation, (ii) mono- vs bimetallic nuclearity, and (iii) Ir vs Rh metal identity were studied and rationalized en route to achieve an effective hydrodefluorination.