Hypervalent, low-coordinate phosphorus(III) centers in complexes of the phosphadiazonium cation with chelate ligands

Trifluoromethylsulfonyloxy-(2,4,6-tri-tert-butylphenylimino)phosphine, Mes*NPOTf (Mes = 2,4,6-tri-tert-butylphenyl, OTf = trifluoromethanesulfonate, triflate) reacts quantitatively with the multifunctional ligands 2,2'-bipyridine (2,2'-BIPY), N,N,N',N'-tetramethylethylenediamine (TMEDA), 1,2-bis(diethylphosphino)ethane (DEPE), 1,2-bis(diphenylphosphino)ethane (DIPHOS), and N,N,N',N' ',N' '-pentamethyldiethylenetriamine (PMDETA) to give the Lewis acid-base complexes [Mes*NP(2,2'-BIPY)][OTf], [Mes*NP(TMEDA)][OTf], [Mes*NP(DIPHOS)][OTf], [Mes*NP(DEPE)][OTf], and [Mes*NP(PMDETA)][OTf], respectively. Single-crystal X-ray diffraction studies indicate that the closest contact of the ligand donor atoms occurs at phosphorus in all cases, affecting significant displacement of the OTf anion. The resulting cations [Mes*NP(L)]+ are best described as complexes of a neutral chelating ligand on a phosphadiazonium Lewis acceptor, and highlight the potential for electron-rich centers to behave as Lewis acids despite the presence of a lone pair of electrons at the acceptor site. More importantly, the new complexes represent rare examples of systems containing hypervalent, low-coordinate phosphorus(III) centers.     

Role of electronic structure of ruthenium polypyridyl dyes in the photoconversion efficiency of dye‐sensitized solar cells: Semiempirical investigation

ZINDO/S calculations on cis‐Ru(4,4′‐dicarboxy‐2,2′‐bipyridine)₂(X)₂ and cis‐Ru(5,5′‐dicarboxy‐2,2′‐bipyridine)₂(X)₂ complexes where X = Cl^?, CN^?, and NCS^? reveal that the highest occupied molecular orbital (HOMO) of these complexes has a large amplitude on both the nonchromophoric ligand X and the central ruthenium atom. The lowest‐energy metal to ligand charge transfer (MLCT) transition in these complexes involves electron transfer from ruthenium as well as the halide/pseudohalide ligand to the polypyridyl ligand. The contribution of the halide/pseudohalide ligand(X) to the HOMO affects the total amount of charge transferred to the polypyridyl ligand and hence the photoconversion efficiency. The virtual orbitals involved in the second MLCT transition in 4,4′‐dicarboxy‐2,2′‐bipyridine complexes have higher electron density on the ? COOH group compared to the lowest unoccupied molecular orbital and hence a stronger electronic coupling with the TiO₂ surface and higher injection efficiency at shorter wavelengths. In comparison, the virtual orbitals involved in the second MLCT transition in 5,5′‐dicarboxy‐2,2′‐bipyridine complexes have lesser electron density on the ? COOH group, leading to a weaker electronic coupling with the TiO₂ surface and therefore lower efficiency for electron injection at shorter wavelengths for these complexes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Polyelectrolyte-templated synthesis of bimetallic nanoparticles

Bimetallic nanoparticles (NPs) are known to exhibit enhanced optical and catalytic properties that can be optimized by tailoring NP composition, size, and morphology. Galvanic deposition of a second metal onto a primary metal NP template is a versatile method for fabricating bimetallic NPs using a scalable, solution-based synthesis. We demonstrate that the galvanic displacement reaction pathway can be controlled through appropriate surface modification of the NP template. To synthesize bimetallic Au-Ag NPs, we used colloidal Ag NPs modified by layer-by-layer (LBL) assembled polyelectrolyte layers to template the reduction of HAuCl(4). NPs terminated with positively and negatively charged polyelectrolytes yield highly contrasting morphologies and Au surface concentrations. We propose that these charged surface layers control galvanic charge transfer by controlling nucleation and diffusion at the deposition front. This surface-directed synthetic strategy can be advantageously used to tailor both overall NP morphology and Au surface concentrations.     

The syntheses and electrochemical studies of a ferrocene substituted diiminopyridine ligand and its p, s, se, and te complexes

A new reversible, redox active diiminopyridine ligand (1Fc) containing pendant ferrocene functionalities was isolated and fully characterized. The reaction of 1Fc with chalcogen pseudohalides of sulfur, selenium, and tellurium yielded the respective N,N',N″-chelated chalcogen dications. Phosphorus chemistry proceeded in a related manner but, in this case, by the direct addition of 1Fc with PI(3) to yield the N,N',N″-chelated P(I) cation. These species represent the first synthesized main group complexes involving a redox active diiminopyridine ligand containing pendant ferrocenes. Electrochemical studies of the free ligand shows a reversible two-electron process. The chelated phosphorus cation, however, displayed three events, the first being a quasi-reversible two-electron process, involving the oxidation at the P(I) center, resulting in a P(III) cation. The subsequent reversible one- and two-electron processes arise from the ligand framework and pendant ferrocenes, respectively.     

两个手性Salen型过渡金属配合物的合成、波谱与结构

本文报道了2个手性Salen型过渡金属配合物[(N,N′-bis(3-t-butyl-5-methylsalicylidene)-1S,2S-cyclohexanediamine-N,N′,O,O′) nickel(Ⅱ)] (1)和[(N,N′-bis(3-t-butyl-5-methylsalicylidene)-1S,2S-cyclohexanediamine-N,N′,O,O′) copper(Ⅱ)] (2)的合成、波谱与结构表征。它们由(1S,2S)-环己烷-1,2-二胺和3-叔丁基-5-甲基-2-羟基苯甲醛发生席夫碱缩合反应制得的配体分别与Cu(Ⅱ)和Ni(Ⅱ)盐反应而得到。产品经过红外光谱、元素分析、电喷雾质谱、紫外和圆二色光谱等方法表征,并测定其晶体结构。结果表明配合物1和2中的中心金属离子Cu(Ⅱ)和Ni(Ⅱ)均为四配位平面正方形配位构型,而且在其晶体堆积中观察到一种通过芳环之间弱π-π相互作用形成的二聚结构。     

Synthesis of CdS, ZnS and Ag2S nanoparticles stabilized by sodium bis(2-ethylhexyl)sulfosuccinate and polyoxyethylenesorbitan monooleate in aqueous medium

The effect of synthesis conditions (molar ratio between precursors, concentration of surfactants, synthesis temperature) on the size of CdS, ZnS and Ag₂S nanoparticles (NPs) stabilized by sodium bis(2-ethylhexyl)succinate and polyoxyethylenesorbitan monooleate was studied. It was established that stabilization by polyoxyethylenesorbitan results in formation of smaller NPs (～8 nm) as compared to that in the presence of sodium bis(2-ethylhexyl)sulfosuccinate (14–60 nm), which is due to the difference between the adsorption rates of these surfactants onto the surface of synthesized NPs. The resulting aqueous dispersions of CdS, ZnS and Ag₂S NPs exhibit long-term stability to sedimentation. The nanoparticle size increases insignificantly with temperature increasing to 65–70°C and rises abruptly at higher temperatures. The increase in the ratio between concentrations of precursors (sulfide and metal ions) also results in an increase in NP size, allowing one to synthesize nanoparticles of prescribed sizes. The optical properties of the resulting nanoparticles were studied. The positions of the exciton peaks and the luminescence intensity peaks of the dispersions of synthesized CdS and ZnS NPs were determined.     

Reactions of diiminopyridine ligands with chalcogen halides

The reactions of the chalcogen halides (Ch = S, Se, Te) with a series of diiminopyridine (DIMPY) ligands were explored. It was determined through these studies that varying both the substitution on the α-carbon and the chalcogen halide reagent afforded different products. If methyl groups were present on the α-carbon, reactivity was observed through the eneamine tautomer to yield N,N',C-bound neutral chalcogen complexes. In the cases where H and C(6)H(5) groups were in the same position, N,N',N″-chelated chalcogen cations or dications were produced. Many of the reactions resulted in complex mixtures postulated to occur by the release of halogen decomposing the product or, for reactions with the CH(3) substituted ligand, uncontrollable reactivity with the eneamine tautomer. This is the first report of reactions of sulfur and selenium halides with the ubiquitous diiminopyridine ligands and only the second example for a tellurium halide.     

Direct Assembly of Metal-Phenolic Network Nanoparticles for Biomedical Applications

Coordination assembly offers a versatile means to developing advanced materials for various applications. However, current strategies for assembling metal-organic networks into nanoparticles (NPs) often face challenges such as the use of toxic organic solvents, cytotoxicity because of synthetic organic ligands, and complex synthesis procedures. Herein, we directly assemble metal-organic networks into NPs using metal ions and polyphenols (i.e., metal-phenolic networks (MPNs)) in aqueous solutions without templating or seeding agents. We demonstrate the role of buffers (e.g., phosphate buffer) in governing NP formation and the engineering of the NP physicochemical properties (e.g., tunable sizes from 50 to 270 nm) by altering the assembly conditions. A library of MPN NPs is prepared using natural polyphenols and various metal ions. Diverse functional cargos, including anticancer drugs and proteins with different molecular weights and isoelectric points, are readily loaded within the NPs for various applications (e.g., biocatalysis, therapeutic delivery) by direct mixing, without surface modification, owing to the strong affinity of polyphenols to various guest molecules. This study provides insights into the assembly mechanism of metal-organic complexes into NPs and offers a simple strategy to engineer nanosized materials with desired properties for diverse biotechnological applications.     

The First One‐Pot Synthesis of Metal–Organic Frameworks Functionalised with Two Transition‐Metal Complexes

The synthesis of a metal–organic framework (UiO‐67) functionalised simultaneously with two different transition metal complexes (Ir and Pd or Rh) through a one‐pot procedure is reported for the first time. This has been achieved by an iterative modification of the synthesis parameters combined with characterisation of the resulting materials using different techniques, including X‐ray absorption spectroscopy (XAS). The method also allows the first synthesis of UiO‐67 with a very wide range of loadings (from 4 to 43 mol %) of an iridium complex ([IrCp*(bpydc)(Cl)Cl]^2?; bpydc=2,2′‐bipyridine‐5,5′‐dicarboxylate, Cp*=pentamethylcyclopentadienyl) through a pre‐functionalisation methodology.     

Synthesis of Pd@graphene oxide framework nanocatalyst with enhanced activity in Heck-Mizoroki cross-coupling reaction

A new method was developed for producing a catalyst involving a Pd nanoparticle (NP) embedded in a graphene oxide framework (Pd@GOF) with ordered macro- and mesoporous structures. First, 5,5′-diamino-2,2′-bipyridine was selected as cross-linking for covalent modification of GO nanosheets to prepare a three-dimensional (3D) framework with interlayer spaces in which well-dispersed and ultra-small Pd NPs in situ grew and embedded the framework. The synthesized nanopores 3D Pd@GOF can act as nanoreactors to help the reaction substrates thoroughly come into contact with the surface of Pd NPs, thereby exhibiting high activity toward the Heck reaction, rarely reported concerning Pd NPs supported on one-side functionalized graphene. The Pd@GOF catalyst can be used 10 times without any significant loss in the catalytic activity, confirming the long-term stability of this catalyst. Therefore, the covalently assembled GOF was proposed as a universal platform for hosting noble metal NPs to construct the desired metal@GOF nanocatalyst with improved activity and stability that can be used in a broad range of practical applications.     

The Use of Electrospray Mass Spectrometry to Determine Speciation in a Dynamic Combinatorial Library for Anion Recognition

The composition of a dynamic mixture of similar 2,2′‐bipyridine complexes of iron(II) bearing either an amide (5‐benzylamido‐2,2′‐bipyridine and 5‐(2‐methoxyethane)amido‐2,2′‐bipyridine) or an ester (2,2′‐bipyridine‐5‐carboxylic acid benzylester and 2,2′‐bipyridine‐5‐carboxylic acid 2‐methoxyethane ester) side chain have been evaluated by electrospray mass spectroscopy in acetonitrile. The time taken for the complexes to come to equilibrium appears to be dependent on the counteranion, with chloride causing a rapid redistribution of two preformed heteroleptic complexes (of the order of 1 hour), whereas the time it takes in the presence of tetrafluoroborate salts is in excess of 24 h. Similarly the final distribution of products is dependent on the anion present, with the presence of chloride, and to a lesser extent bromide, preferring three amide‐functionalized ligands, and a slight preference for an appended benzyl over a methoxyethyl group. Furthermore, for the first time, this study shows that the distribution of a dynamic library of metal complexes monitored by ESI‐MS can adapt following the introduction of a different anion, in this case tetrabutylammonium chloride to give the most favoured heteroleptic complex despite the increasing ionic strength of the solution.     

Synthesis and photophysical properties of novel amphiphilic ruthenium (II) complexes containing 4,4′‐dialkylaminomethyl‐2,2′‐bipyridyl ligands

The synthesis of a number of new 2,2′‐bipyridine ligands functionalized with bulky amino side groups is reported. Three homoleptic polypyridyl ruthenium (II) complexes, [Ru(L)₃]²⁺ 2(PF₆^?), where L is 4,4′‐dioctylaminomethyl‐2,2′‐bipyridine (Ru4a), 4,4′‐didodecylaminomethyl‐2,2′‐bipyridine (Ru4b) and 4,4′‐dioctadodecylaminomethyl‐2,2′‐bipyridine (Ru4c), have been synthesized. These compounds were characterized and their photophysical properties examined. The electronic spectra of three complexes show pyridyl π → π* transitions in the UV region and metal‐to‐ligand charge transfer bands in the visible region. Copyright © 2005 John Wiley & Sons, Ltd.     

Bifunctional RuII‐Complex‐Catalysed Tandem C−C Bond Formation: Efficient and Atom Economical Strategy for the Utilisation of Alcohols as Alkylating Agents

Catalytic activities of a series of functional bipyridine‐based Ru^II complexes in β‐alkylation of secondary alcohols using primary alcohols were investigated. Bifunctional Ru^II complex ( 3 a ) bearing 6,6’‐dihydroxy‐2,2’‐bipyridine (6DHBP) ligand exhibited the highest catalytic activity for this reaction. Using significantly lower catalyst loading (0.1 mol %) dehydrogenative carbon?carbon bond formation between numerous aromatic, aliphatic and heteroatom substituted alcohols were achieved with high selectivity. Notably, for the synthesis of β‐alkylated secondary alcohols this protocol is a rare one‐pot strategy using a metal–ligand cooperative Ru^II system. Remarkably, complex 3 a demonstrated the highest reactivity compared to all the reported transition metal complexes in this reaction.     

The first nitro-substituted heteroscorpionate ligand

The new dihydridobis(3-nitro-1,2,4-triazolyl)borate ligand, [H2B(tzNO2)2]-, has been synthesized in dimethylacetamide solution, using 3-nitro-1,2,4-triazole and KBH4 through careful temperature control, and characterized as its potassium salt. The zinc(II) and cadmium(II) complexes, {M[H2B(tzNO2)2]Cl(H2O)2}, have been prepared by metathesis of [H2B(tzNO2)2]K with ZnCl2 and CdCl2, respectively. The complexes likely contain a metal core in which the ligand is coordinated to the metal ions in the K2-N,N' or K4-N,N',O,O' fashion. A single-crystal structural characterization is reported for the potassium dihydrobis(3-nitro-1,2,4-triazolyl)borate. The potassium salt is polymeric and shows several K...N and K...O interactions.     

Synthesis, Characterization, Spectroscopic and Electrochemical Properties of New Mono- and Binuclear Copper（Ⅰ） Complexes with Substituted 2,2′-Bipyridine

The mono- and binuclear Cu(Ⅰ) complexes with substituted 2,2′-bipyridine and iodide ligands, [CuL2]BF4(L=4-methoxycarbonyl-6-(4-methylphenyl)-2,2′-bipyridine (a), 6-(4-hydroxymethylphenyl)-2,2′-bipyridine (b) and 6-(4-methoxylphenyl)-2,2′-bipyridine (c)) and [Cu2(μ-I)2L2] were prepared, and the crystal structures of the complexes were obtained from signal-crystal X-ray diffractional analysis. The spectroscopic properties of the complexes in dichloromethane are dominated by low energy MLCT bands from 360 to 650 nrn. The electrochemical studies of mononuclear complexes reveal that the complexes have stable copper(Ⅰ) state.     

Ligand displacement reactions of dimer and trimer pyridyl ligand/transition metal complexes

Ligand exchange reactions of pyridyl ligand/transition metal complexes are examined in a quadrupole ion trap mass spectrometer to evaluate the ability of multidentate ligands to displace other pyridyl ligands in complexes where the charge is highly delocalized and there is a great degree of ligand repulsions. Partially or fully coordinated transition metal ions in dimer or trimer species involving small mono- or bidentate pyridyl ligands undergo ligand displacement reactions with larger bi- and tridentate pyridyl ligands. Larger ligands with greater chelation abilities, such as 1,10-phenanthroline and 2,2′:6,2″-terpyridine, are often able to simultaneously displace two nonchelating ligands from a partially coordinated metal ion. However, the analogous reactions involving displacement of bidentate chelating ligands from more fully coordinated transition metal ion complexes are nearly quenched. In other cases, mixed-ligand dimer and trimer complexes are observed, indicating step-wise displacement of the initially complexed ligands.     

Gas‐phase geometries and energies of bis(2,2′‐bipyridine) interacting either with Cu(I) or Ag(I): Computational study

With a polarized double‐zeta basis set, we carried out MP2 and density functional theory geometry optimization of bis(2,2′‐bipyridine) interacting either with Cu(I) or Ag(I). The computed gas‐phase geometries of both Cu and Ag complexes present tetrahedral distortions around the ions. However, geometry optimization on Cu or Ag ions complexing with ammonia molecules yield perfect tetrahedral coordination and interaction energies comparable to those of the bis(2,2′‐bipyridine) complexes. Solid‐state laboratory studies on complexes of the same metal ions with substituted bis(2,2′‐bipyridine) revealed tetrahedral distortions around the ions, even stronger than those computed in the gas phase. From our analysis of the potential interaction energies we conclude that the origin of the larger distortions in the solid state result from stacking interactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 395–404, 2003     

A general route to prepare one- and three-dimensional carbon nanotube/metal nanoparticle composite nanostructures

Adsorption of polyethyleneimine (PEI)-metal ion complexes onto the surfaces of carbon nanotubes (CNTs) and subsequent reduction of the metal ion leads to the fabrication of one-dimensional CNT/metal nanoparticle (CNT/M NP) heterogeneous nanostructures. Alternating adsorption of PEI-metal ion complexes and CNTs on substrates results in the formation of multilayered CNT films. After exposing the films to NaBH4, three-dimensional CNT composite films embedded with metal nanoparticles (NPs) are obtained. UV-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy are used to characterize the film assembly. The resulting (CNT/M NP)n films inherit the properties from both the metal NPs and CNTs that exhibit unique performance in surface-enhanced Raman scattering (SERS) and electrocatalytic activities to the reduction of O2; as a result, they are more attractive compared to (CNT/polyelectrolyte)n and (NP/polyelectrolyte)n films because of their multifunctionality.     

From heterobimetallic transition metal complexes to linear coordination polymers based on cis‐ and trans‐L2Pt(CCPh)2

The reaction of cis‐(2,2′‐bipyridine) Pt(CCPh)₂ cis‐(4,4′‐dimethyl‐2,2′‐bipyridine) Pt‐(CCPh)₂ and trans‐(Ph₃P)₂Pt(CCPh)₂ towards different group 11 transition‐metal salts [M′X] (M′ = Cu, Ag; X = inorganic ligand) to give heterobimetallic or linear oligomeric and polymeric transition metal complexes is described. Different coordination modes for M′, PhCC, PPh₃, and X were found in these species. The structural aspects as well as the preference for one coordination mode over another is discussed. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:521–533, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10097