Bis Pyridyl Ligands Research Articles

Superchiral Pd3 L6 Coordination Complex and Its Reversible Structural Conversion into Pd3 L3 Cl6 Metallocycles.

Large, non-symmetrical, inherently chiral bispyridyl ligand L derived from natural ursodeoxycholic bile acid was used for square-planar coordination of tetravalent Pd(II) , yielding the cationic single enantiomer of superchiral coordination complex 1 Pd3 L6 containing 60 well-defined chiral centers in its flower-like structure. Complex 1 can readily be transformed by addition of chloride into a smaller enantiomerically pure cyclic trimer 2 Pd3 L3 Cl6 containing 30 chiral centers. This transformation is reversible and can be restored by the addition of silver cations. Furthermore, a mixture of two constitutional isomers of trimer, 2 and 2', and dimer, 3 and 3', can be obtained directly from L by its coordination to trans- or cis-N-pyridyl-coordinating Pd(II) . These intriguing, water-resistant, stable supramolecular assemblies have been thoroughly described by (1) H DOSY NMR, mass spectrometry, circular dichroism, molecular modelling, and drift tube ion-mobility mass spectrometry.

Rational Design of a Face‐Centred Square‐Cuboid Coordination Cage

The simple synthetic conversion of a 90°-angled bis-pyridyl ligand into a tripodal tris-pyridyl ligand leads to the formal transformation of a cubic (a=b=c) into a square-cuboid (a=b≠c) coordination cage. Mathematical considerations associated with the ligand design, together with X-ray structure results, NMR spectroscopic and mass spectrometric characterization and molecular modeling of both coordination cages are presented and discussed.

Influential Role of Geometrical Disparity of Linker and Metal Ionic Radii in Elucidating the Structural Diversity of Coordination Polymers Based on Angular Dicarboxylate and Bis-pyridyl Ligands

As a continuation of our recent investigations on coordination polymer/metal–organic framework containing compounds, herein, four new coordination polymers, namely, {Co2(ADA)2(px2ampy)}n (1), {Cd(ADA)(px2ampy)0.5}n (2), {Co2(IPTA)2(px2ampy)}n (3), {Mn(IPTA)(px3ampy)}n (4) have been synthesized, based on the flexible dicarboxylate ligand H2ADA and rigid dicarboxylate ligand H2IPTA along with long flexible bis-pyridyl linkers as coligand (where H2ADA = 1,3-adamantanediacetic acid; H2IPTA = isopthalic acid; px2ampy = 1,4-bis(2-pyridylaminomethyl)benzene; px3ampy = 1,4-bis(3-pyridylaminomethyl)benzene). Compounds 1–4 have been characterized by routine elemental analysis, IR spectroscopy, and thermogravimetric (TG) analysis and unambiguously by single crystal X-ray diffraction analysis. The solid-state luminescent property of compound 2 has been additionally characterized. Compound 1 is a two-dimensional (2D) framework, constructed by the connectivity of Co2 paddle-wheels as secondary building units (SBUs) and...

Towards the installation of transition metal ions on donor ligand decorated tin sulfide clusters

Decoration of tetrelchalcogenide T-E clusters with chelating donor ligands was achieved to capture transition metal ions on their surfaces. We demonstrate that by covalent linking of bispyridyl ligands to an Sn-S complex, [ZnX](+) units can be trapped and incorporated into the cluster framework. Intermediates that were identified using spectroscopy and/or X-ray diffraction gave insight into the formation processes.

Solvent-Driven Structural Diversities in ZnII Coordination Polymers and Complexes Derived from Bis-pyridyl Ligands Equipped with a Hydrogen-Bond-Capable Urea Backbone

A new series ZnII metal–organic compounds [both coordination complexes (CCs) and coordination polymers (CPs)] derived from bis-pyridyl ligands equipped with hydrogen-bonding functionality such as urea have been synthesized and characterized by single crystal X-ray crystallography. Out of the six compounds reported herein, [{Zn(μ-3bpmu)Cl2}] (CP1), [{Zn(μ-3bpmu)Cl2}·benzene] (CP2), [{Zn(μ-3bpmu)Cl2}·p-xylene] (CP3), and [{Zn(μ-4bpmu)Cl2}·p-xylene] (CP4) are coordination polymers, whereas [{Zn2(μ-3bpu)2Cl4}·p-xylene] (CC1) and [{Zn2(μ-3bpu)2Cl4}·benzene] (CC2) are coordination complexes. The solvent of crystallization has profound effect on the supramolecular architecture of the resultant coordination compounds; while crystallization in the presence of aromatic solvents resulted in guest occluded crystals (CP2–CP4, CC1, and CC2), crystallization using only polar solvents produced crystals devoid of guests. Aromatic solvents appear to have induced the formation of metallamacrocycle in CC1 and CC2.

Coordination polymers: what has been achieved in going from innocent 4,4′-bipyridine to bis-pyridyl ligands having a non-innocent backbone?

The last two decades have witnessed the research activities in the area of coordination polymers (CPs), which are structurally diverse and functionally intriguing materials. In this endeavor, the most exploited ligand has been a structurally rigid N-donor compound having an innocent backbone (incapable of forming hydrogen bond) namely 4,4'-bipyridine. Much has been achieved by exploiting this wonder ligand in the area of CPs. However, the positional isomers such as 3,3'-bipyridine or 4,3'-bipyridine (which understandably induce diverse ligating topology as compared to their more symmetrical 4,4' counterpart) were not exploited in much detail presumably because of the difficulty in their synthetic accessibility. To get access to such N-donor ditopic ligands having diverse ligating topology, much efforts have been focused in the last decade or so to design such positional isomers of 4,4'-bipyridine having a non-innocent backbone (capable of forming hydrogen bond). The principal focus of such studies is to decipher the effect of diverse ligating topology and the non-innocent backbone of the ligands on the overall supramolecular structures and functions of the resultant CPs. This tutorial review aims at highlighting some of the developments of such structurally diverse and functionally intriguing CPs derived from N-donor ditopic ligands having a non-innocent backbone.

Metal–organic coordination polymers based on dicarboxylate and a flexible bispyridyl ligand: Synthesis, structures, and photoluminescence

Three new transition metal–organic coordination polymers [Zn(bpp)(C 4H 4O 4)]·1.2H 2O 1, [Cd(bpp) 2(H 2O) 2](C 4O 4)·8H 2O 2 and [Cd(bpp) 2(C 4O 4)]·H 2O 3 have been synthesized from the reaction of d 10 block metal, dicarboxylic acid with 1,3-bis(4-pyridyl)-propane (bpp). Structural analysis reveal that the Zn atoms in 1 are bridged by the succinate anions to generate helical chains, which are interlinked by bpp ligands to a 3D framework with Sra (4 2 · 6 3 · 8) topology. The CdN 4O 2 octahedras in 2 are bridged by a pair of bpp ligands to form 1D repeated rhomboid chains, which are assembled into 2D layer via the hydrogen bonds. The six-coordinated Cd 2+ ions in 3 are bridged by the acetylenedicarboxylato ligand to form 1D zigzag chains, which are interconnected by bpp ligands to construct 3D metal–organic framework with a (4 8 · 6 7) topology. The fluorescent spectra of 1– 3 indicate intraligand fluorescence emission upon irradiation.

The Use of a Bis(phenylpyrazolyl)pyridyl Ligand to Prepare [Mn4] and [Mn10] Cage Complexes

Many branches in molecular magnetism live on the production of novel transition-metal (TM) coordination clusters. This has been the source of high-spin molecules, most single-molecule magnets (SMMs), or the possible future qubits for quantum computing. Without doubt, the great advances made in these areas have benefited, for the most part, from the preparation of molecules through so-called “serendipitous self-assembly”. Even though the designed preparation of clusters with predetermined structures and properties is highly desirable, it continues to be a huge synthetic challenge. Therefore, there is no reason to think that the “nonpredictable” approach will cease to be instrumental in the near future. For this, synthetic coordination chemists will keep providing original methods of preparation of polynuclear TM complexes. Typically, these are produced from reactions involving one or more small ligands with donor atoms capable of bridging metals, normally exhibiting several potential coordination modes. By contrast, the synthesis of large multidentate ligands with numerous donor atoms is far less common in this context. We have recently prepared a new ligand with two aligned hydroxyphenylpyrazolyl units separated by a pyridine group (2,6-bis[5-(2-hydroxyphenyl)pyrazol-3-yl]pyridine, H4L, Scheme 1). [10] Hydroxyphenylpyrazolyl derivatives or related pyrazolinoles have proven to be excellent ligands for the assembly of TM clusters with novel structures. The build up of more than one such moiety on the same molecule promises to be an open door to a variety of unprecedented architectures. Ligand H4L is well suited, for example, to stimulate the aggregation of a sequence of five closely spaced metals within a cluster (Scheme 2B). We report herein very promis-

Bis(pyridyl)siloxane–Pd(II) complex catalyzed oxidation of alcohol to aldehyde: Effect of ligand tethering on catalytic activity and deactivation behavior

A series of oligomeric methylsiloxane compounds functionalized with pyridyl groups was synthesized and used as ligands in the aerobic Pd(OAc) 2-catalyzed oxidation of benzyl alcohol to benzaldehyde at 353 K. The effect of tethering two pyridine ligands at the terminal positions of linear siloxanes of varying length was systematically investigated, as was the effect of the attachment point of the pyridine ring ( meta or para). It was found that meta-substituted pyridylsiloxanes were generally more effective in protecting the catalyst against Pd agglomeration. For this purpose, the optimal meta-pyridylsiloxane ligands had 4–6 silicon atoms or 10 silicon atoms for para-pyridylsiloxane ligands. The metal–ligand binding properties were used to interpret the catalytic behavior, and the ability of the catalyst stability correlated with ability of the bis-pyridyl ligand to form a mononuclear cyclic complex with Pd.

Influence of the metal centers of 2,6‐bis(imino)pyridyl transition metal complexes on ethylene polymerization/ oligomerization catalytic activities

AbstractMuch work on bis(imino)pyridyl complexes with Fe(II) and Co(II) as ethylene polymerization catalysts has been reported in terms of designing new analogous ligands, while little work has been dedicated to the study of the effect of the metal center on catalyst performance. A series of bis(imino)pyridyl‐MCl2 (M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II)) transition metal complexes were synthesized, for which single crystals of the Co(II) and Cu(II) complexes were obtained. The crystal structures indicated that these complexes had similar coordination geometries. Being applied to ethylene polymerization at 25 °C and employing 500 equiv. of methylaluminoxane as co‐catalyst, the complexes with Fe(II), Co(II) and Ni(II) centers showed, respectively, catalytic activities of 1.25 × 106 g (mol Fe)−1 h−1 Pa for ethylene polymerization, and 3.98 × 105 g (mol Co)−1 h−1 Pa and 5.13 × 103 g (mol Ni)−1 h−1 Pa for ethylene oligomerization. In contrast, the complexes with Cu(II) and Zn(II) centers were inactive. Crystal structure data showed that the coordination interactions provided a comparatively reliable quantification of the selectivity of the bis(imino)pyridyl ligand for the studied metal ions, which was in reasonable agreement with the Irving–Williams list. Moreover, for the Ni(II) and Cu(II) complexes, the strong coordination bonds and small N(imino)MN(imino) angles were unfavorable for several steps in the mechanism, such as ethylene coordination to the metal center, ethylene migratory insertion and olefin chain growth. All of these will reduce the speed of the overall reaction, indicating a decrease of catalytic efficiency in a given period. The poor activity of the Zn(II) complex for ethylene polymerization may be related to the reduction process by the alkylating agent. Copyright © 2010 Society of Chemical Industry

Dimensionality Trends in Metal−Organic Frameworks Containing Perfluorinated or Nonfluorinated Benzenedicarboxylates

A new family of hybrid inorganic−organic materials has been synthesized using a combination of flexible bis-pyridyl ligands in conjunction with a perfluorinated or nonfluorinated benzenedicarboxylate ligand. A significant difference between the carboxylate torsion angles of the fluorinated and nonfluorinated ligands leads to the formation of markedly different structures for the two groups of materials. No isostructural phases were found, and the use of perfluorinated ligands tends to increase the dimensionality of the resulting frameworks.

An Unsymmetrical Iron(II) Bis(imino)pyridyl Catalyst for Ethylene Polymerization: Effect of a Bulky Ortho Substituent on the Thermostability and Molecular Weight of Polyethylene

Three new iron(II) 2,6-bis(imino)pyridyl complexes bearing bulky and unsymmetrical substituted aniline groups, [2-(CH(CH3)(C6H5))-4-R1-6-R2-C6H2N═C(CH3)]2C5H3NFeCl2 (1, R1 = H, R2 = methyl; 2, R1 = methyl, R2 = methyl; 3, R1 = H, R2 = methoxy), were synthesized. The unsymmetrical bis(imino)pyridyl ligand L2 contains three isomers that can be detected by 1H NMR and 13C NMR spectroscopy. However, the corresponding complex 2 exhibits only one isomer in solution. X-ray diffraction of 2 confirms that the iron complex adopts a Cs configuration. These complexes activated by methylaluminoxane (MAO) have high catalytic activities for ethylene polymerization and produce linear polyethylenes with bimodal or broad molecular weight distribution. The steric and electronic effects of the ortho substituents on the aniline moiety distinctly affect the molecular weight of the obtained polyethylene. In comparison with 1 and 3, having a single ortho substituent on the aryl rings, and the typical complex 4, containing o-diiso...

Template synthesis of precisely monodisperse silica nanoparticles within self-assembled organometallic spheres

One of the key challenges in materials science is to control the size and shape of inorganic nanoparticles with a high degree of precision, as these parameters have a significant influence on the nanoparticles' properties and potential applications. Here, we describe the preparation of highly monodisperse silica nanoparticles smaller than 5 nm in diameter by using self-assembled, hollow, spherical compounds as 'endo-templates'. These coordination complexes with pendant sugar groups lining their interiors-assembled from 12 metal ions and 24 bis-pyridyl ligands containing glucose substituents-acted as structurally well-defined templates for the sol-gel condensation of alkoxysilanes. The polydispersities of the silica nanoparticles made with this method approached unity, with M(w)/M(n) < 1.01. The component ligands are modified easily, which enables an accurate expansion of the coordination complex and the subsequent control of the monodisperse silica nanoparticles that span molecular weights of 5,000 to 31,000 Da (corresponding to 2-4 nm in diameter). This method could be applicable to the preparation of other inorganic nanoparticles.

Cobalt(II) and nickel(II) complexes bearing mono(imino)pyridyl and bis(imino)pyridyl ligands: preparation, structure and ethylene polymerization/oligomerization behaviors

AbstractBACKGROUND: Ethylene oligomerization is the major industrial process to produce linear α‐olefins. Recently much work has been devoted to late transition metal catalysts used in this process, especially those with 2,6‐bis(imino)pyridyl dihalide ligands. Considering that most work has focused on simple modification to the substituents in imino‐aryl rings based on the symmetric bis(imino)pyridyl framework, here we expand this work to the asymmetric mono(imino)pyridyl ligands.RESULTS: The preparation, structure and ethylene polymerization/oligomerization behavior of series of mono(imino) pyridyl–MCl2 and bis(imino)pyridyl–MXn complexes are presented. The systematic studies were focused on the relationship between the catalytic behavior of these complexes for ethylene polymerization/oligomerization and reaction conditions, ligand structures, metal centers and counter‐anions. The influence of the coordination environment on catalyst behavior is also discussed.CONCLUSION: For mono(imino)pyridyl–Co(II) and Ni(II) catalysts bearing the Cl− counter‐anion, good activities ranging from 0.513 × 105 to 1.58 × 105 g polyethylene (mol metal)−1 h−1 atm−1 are afforded, and the most active catalysts are those with methyl in both ortho‐ and para‐positions of the imine N‐aryl ring. For bis(imino)pyridyl–Co(II) and Ni(II) catalysts bearing the SO42− and NO3− counter‐anions, the low activities for ethylene oligomerization are in sharp contrast to those of their chloride analogues. Copyright © 2009 Society of Chemical Industry

Synthesis, Characterization, and Photoinduced Electron Transfer Processes of Orthogonal Ruthenium Phthalocyanine−Fullerene Assemblies

The convergent synthesis, electrochemical characterization, and photophysical studies of phthalocyanine-fullerene hybrids 3-5 bearing an orthogonal geometry (Chart ) are reported. These donor-acceptor arrays have been assembled through metal coordination of linear fullerene mono- and bispyridyl ligands to ruthenium(II) phthalocyanines. The hybrid [Ru(CO)(C(60)Py)Pc] (3) and the triad [Ru(2)(CO)(2)(C(60)Py(2))Pc(2)] (5) were prepared by treatment of the phthalocyanine 6 with the mono- and hexakis-substituted C(60)-pyridyl ligands 1 and 2, respectively. The triad [Ru(C(60)Py)(2)Pc] (4) was prepared in a similar manner from the monosubstituted C(60)-pyridyl ligand 1 and the phthalocyanine precursor 7. The simplicity of this versatile synthetic approach allows to determine the influence of the donor and acceptor ratio in the radical ion pair state lifetime. The chemical, electrochemical, and photophysical characterization of the phthalocyanine-fullerene hybrids 3-5 was conducted using (1)H and (13)C NMR, UV/vis, and IR spectroscopies, as well as mass spectrometry, cyclic voltammetry, femtosecond transient absorption studies, and nanosecond laser flash photolysis experiments. Arrays 3-5 exhibit electronic coupling between the two electroactive components in the ground state, which is modulated by the axial CO and 4-pyridylfulleropyrrolidine ligands. With respect to the excited state, we have demonstrated that RuPc/C(60) electron donor-acceptor hybrids are a versatile platform to fine-tune the outcome and dynamics of charge transfer processes. The use of ruthenium(II) phthalocyanines instead of the corresponding zinc(II) complexes allows the suppression of energy wasting and unwanted charge recombination, affording radical ion pair state lifetimes on the order of hundreds of nanoseconds for the C(60)-monoadduct-based complexes 3 and 4. For the hexakis-substituted C(60) unit 2, the reduction potential is shifted cathodically, thus raising the radical ion pair state energy. However, the location of the RuPc triplet excited state is not high enough, and still offers a rapid deactivation of the radical ion pair state.

2,6-Bis(imidazol-2-ylidene)pyridine Complexes of Lanthanoïdes: A Theoretical Study of the Bonding Situation and Selective Complexation

The coordination of a bis(NHC)pyridyl (NHC = N-heterocyclic carbene) ligand to d0 fragments of group 3, lanthanide, and actinide series (M = Sc, Y, La, Sm, Lu, U, and Am) has been theoretically investigated at the DFT level. The influence of the π-donation ability of the co-ligand has been emphasized by comparing the trichloro, trisamido fragments and bare ions. The coordination of the tridentate CNC ligand is dominated by the ligand→metal σ-donations, but unprecedented Nam→Ccarb “back-bonding” was evidenced in the trisamido complexes of La, Sm, and Am. The ability of the bis(NHC)pyridine ligand B for lanthanide/actinide differentiation has been examined, substantiating the critical influence of the electronic properties of the co-ligand and carbene moieties.

Fe(acac)n and Co(acac)n bearing different bis(imino)pyridine ligands for ethylene polymerization and oligomerization

AbstractA series of iron and cobalt complexes ligated with different bis(imino)pyridyl ligands were synthesized and used in ethylene polymerization. The reaction temperature and Al/Fe ratio had a great influence on the activities and properties of the polymer in the iron system when methylaluminoxane was used as the cocatalyst. Bimodal polyethylene, unimodal polyethylene, and oligomers were achieved with ethylene polymerization according to the structures of the ligands and polymerization conditions. The cobalt systems showed low activities when bis(imino)pyridyl was used as the ligand in comparison with the iron system catalysts. Ethylene oligomerization was conducted, and the main products were 1‐butylene and 1‐hexene. A fast deactivation process was observed from the curve of the polymerization kinetics. The polymerization mechanism was examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Syntheses and studies of flexible amide ligands: a toolkit for studying metallo-supramolecular assemblies for anion binding

The syntheses of seven flexible bidentate bis-pyridyl diamide and four monodentate pyridyl amide ligands containing central amide units are described. The bis-pyridyl ligands were prepared in one step from commercially available compounds in moderate to good yield. These compounds all possess external metal coordinating pyridyl groups and internal amide functionalities, with the potential to bind anions. Crystal structures of six of the bis-pyridyl diamide ligands are described. The four compounds with xylene cores N, N′-[1,3-phenylenebis(methylene)]bis-3-pyridinecarboxamide 1, N, N′-[1,3-phenylenebis(methylene)]bis-4-pyridinecarboxamide 2, N, N′-[1,4-phenylenebis(methylene)]bis-3-pyridinecarboxamide 3 and N, N′-[1,4-phenylenebis(methylene)]bis-4-pyridinecarboxamide 4 crystallize with extensive amide N–H⋯O C hydrogen bonding between the diamide compounds, giving rise to two and three dimensional hydrogen bonded networks. N, N′-Bis(3-pyridylmethyl)benzene-1,3-dicarboxamide 5, the only compound with the amide groups directly attached to a central benzene core, was not able to be crystallised. N, N′-2,6-Bis(3-pyridylmethyl)pyridine dicarboxamide 6 and N, N′-2,6-bis(4-pyridylmethyl)pyridine dicarboxamide 7 have a mismatch of hydrogen bond donor and acceptor regions preventing ready involvement of the amide NH groups in network formation. For comparison we also prepared compounds N, N′-2′-propyl-6-(3-pyridylmethyl)pyridine dicarboxamide 10 and N, N′-2′-propyl-6-(4-pyridylmethyl)pyridine dicarboxamide 11 with two amide groups but only the one external donor pyridyl moiety, and compounds N-6-[(3-pyridylmethylamino)carbonyl]-2-pyridinecarboxylic acid methyl ester 8 and N-6-[(4-pyridylmethylamino)carbonyl]-2-pyridinecarboxylic acid methyl ester 9, which have only the one amide.

Solvent-Induced Structural Changes in Complexes of 1,2-Bis(3-(3-pyridyl)pyrazolyl)ethane

A series of complexes have been obtained using the flexible ditopic ligand 1,2-bis(3-(3-pyridyl)pyrazolyl)ethane (LEt) with M(SCN)2 (M = Co, Fe) and ZnCl2. The ligand is observed to exist in a variety of conformations with rotations around the ethane spacer and around the pyridyl/pyrazole bond. The bridging length of the ligand (i.e., distance between pyridyl nitrogen atoms) varies by 3.5 Å depending on its geometry. Three different cobalt(ii) complexes of the general form [Co(LEt)2(SCN)2]·Solv (where Solv is a variable number/type of non-coordinated solvent) have been structurally characterized and form a series of solvent dependant supramolecular isomers. When Solv = 2MeCN a (4,4)-sheet is formed (1), however, when Solv = H2O an alternate ‘collapsed’ (4,4)-sheet is observed (2). Changing the solvent to two molecules of N,N-dimethylformamide (DMF) leads to a radical change in structure with a one-dimensional (1D) polymer formed (3) that contains two bridging ligands between adjacent metal atoms (i.e., maintaining the same metal/ligand ratio as in the (4,4)-sheet structures). A monomeric thiocyanate complex [Fe(LEt)2(SCN)2(H2O)2] (4) is reported in which the bispyridyl ligands are terminal and partake in an extended hydrogen-bonded network. A 1D polymer [Zn(LEt)Cl2] (5) is also presented. The structures of the metal complexes are contrasted with that of the free ligand.

Metal–organic frameworks based on the pyridine-2,3-dicarboxylate and a flexible bispyridyl ligand: syntheses, structures, and photoluminescence

Three new metal–organic coordination polymers, [Cu(2,3-pydc)(bpp)]·2.5H2O (1), [Zn(2,3-pydc)(bpp)]·2.5H2O (2) and [Cd(2,3-pydc)(bpp)(H2O)]·3H2O (3) (2,3-pydcH2 = pyridine-2,3-dicarboxylic acid, bpp = 1,3-bis(4-pyridyl)propane), have been synthesized at room temperature. All complexes have metal ions serving as 4-connected nodes but represent two quite different structural motifs. Complexes 1 and 2 are isomorphous, both of which feature 2D → 3D parallel interpenetration. Each two-dimensional (2D) layer with (4, 4) topology is interlocked by two nearest neighbours, one above and one below, thus leading to an unusual 3D motif. Complex 3 has a non-interpenetrating 3D CdSO4 framework with cavities occupied by uncoordinated water molecules. The compounds have been characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis and X-ray crystallography. The photoluminescent studies of 2 and 3 show that both complexes exhibit intense fluorescent emissions at room temperature.