Synthesis of a new C60-substituted tris(2,2′-bipyridine)ruthenium(II) complex

A new tris(2,2′-bipyridine)ruthenium(II) complex substituted with two fullerene subunits has been prepared starting from a fullerene carboxylic acid derivative and a 2,2′-bipyridine ligand bearing two alcohol functions.     

Synthesis and characterizations of 3,3′-bis(diphenylphosphinoamine)-2,2′-bipyridine and 3,3′-bis(diphenylphosphinite)-2,2′-bipyridine and their chalcogenides

New bis(phosphinoamine) and bis(phosphinite) derivatives of 2,2′-bipyridine were prepared through a single step reaction of 3,3′-diamino-2,2′-bipyridine or 3,3′-dihydroxy-2,2′-bipyridine with diphenylchlorophosphine, respectively. Their P = E chalcogenides (E = O, S, Se) were also prepared. All the new compounds were characterized by elemental analysis, IR and NMR spectroscopies. The molecular structure of 3,3′-bis(diphenylthiophosphinite)-2,2′-bipyridine was elucidated by single-crystal X-ray crystallography.     

Ultra-high pressure synthesis of a tetrathiafulvalene-diquat cyclophane

Quaternization of a tetrathiafulvalene (TTF)/2,2′-bipyridine cyclophane under 10 kbar of pressure yields a TTF-diquat donor-acceptor cyclophane revealing distinct charge-transfer interactions.     

Palladium-catalyzed oxidation of cyclohexanones to conjugated enones using molecular oxygen

Oxidation of cyclohexanones into conjugated enones with molecular oxygen as oxidant was achieved by palladium catalysts. A catalyst system consists of 1 mol % Pd(OCOCF₃)₂ and 5,5′-dimethyl-2,2′-bipyridine accomplished maximum 84% yield for the oxidation of cyclohexanone and 51-78% yields for 4-substituted-cyclohexanones.     

InCl3 mediated one-pot synthesis of indol-3-yl pyridine and 2,2′-bipyridine derivatives through multi-component reaction

A simple protocol for the efficient preparation of 2-(1H-Indol-3-yl)-6-methoxy-4-aryl pyridine-3,5-dicarbonitrile and 6-methoxy-4-aryl-2,2′-bipyridine-5-carbonitrile derivatives has been achieved through one-pot multi-component reaction under reflux condition. Particularly valuable features of this method include high yields of products in short reaction time and broad substrate scope. It is an efficient and promising synthetic strategy to build indol-3-yl pyridine and 2,2′-bipyridine skeletons.     

Dendritic BINOL ligands for asymmetric catalysis: effect of the linking positions and generations of the dendritic wedges on catalyst properties

Three types of new chiral BINOL ligands (2, 3 and 4) bearing dendritic wedges have been synthesized through coupling reaction between 3-hydroxymethyl-2,2′-bis(methoxymethyl)-1,1′-binaphthol (7), 6,6′-dihydroxymethyl-2,2′-bis(methoxymethyl)-1,1′-binaphthol (12), 6-hydroxymethyl-2,2′-bis(methoxymethyl)-1,1′-binaphthol (15) and Fréchet-type polyether dendritic benzyl bromide, followed by deprotection of methoxymethyl groups by ⁱPrOH/HCl, respectively. These new ligands obtained were assessed in enantioselective Lewis acid-catalyzed addition of diethylzinc to benzaldehyde. Compared to the enantioselectivity observed with dendrimer 1 bearing the dendritic wedges at 3,3′-positions of the binaphthyl backbone, higher enantioselectivity for all these ligands was observed. Difference in the effect of linking positions and generations on enantioselectivity and/or activity for all three kinds of dendritic ligand-derived catalysts was observed. Among these dendritic ligands, (R)-3/Ti(IV) catalyst with the dendritic wedges at 6,6′-positions of BINOL gave the highest enantioselectivity (up to 87% ee).     

A facile S-transalkylation of 2,2′-bipyridine alkyl sulfides—a new tool for the synthesis of annulated biheterocycles

A simple and efficient synthesis of annulated 2,2′-bipyridinium salts with attached dihydrothiazole or dihydro-1,3-thiazine rings has been developed through tandem S-transalkylation/intramolecular ring closure of 2,2′-bipyridine alkyl sulfides. The structures were confirmed by X-ray crystallographic analysis.     

The first approach to optically active 2,2′-bipyridine alkyl sulfoxides

The synthesis of 6,6′-bis(alkylsulfanyl)-2,2′-bipyridines and their asymmetric oxidation to non-racemic 2,2′-bipyridine alkyl sulfoxides using either (+)-(8,8-dichlorocamphorylsulfonyl)oxaziridine or a modified Sharpless reagent is reported.     

The intercalation reaction of 2,2′-bipyridine with layered compound MnPS3

The intercalation process of 2,2′-bipyridine into layered MnPS₃ is studied with powder X-ray powder diffraction (XRD) technology as the monitoring tool. From the XRD results, it is found that the absence or presence of acid greatly influences the existing form and the arranged orientation of the guest. Two series of the reactions are carried out. In Series A, only MnPS₃ and 2,2′-bipyridine are present. While in Series B, a variety of acetic acid is added. During the intercalation of Series A, there coexist four phases: the 00l phase (with lattice spacing of 6.47 Å) is pristine MnPS₃; the 00l′ phase (with lattice spacing of 9.81 Å), indicating the parallel orientation of the 2,2′-bipyridine molecular ring to the layer; the 00l″ phase (with lattice spacing of 12.20 Å), indicating the perpendicular orientation of the 2,2′-bipyridine molecular ring to the layer of the host, which is only an intermediate phase for the formation of the 00l′′′ phase; the 00l′′′ phase (with the lattice spacing of 15.33 Å), indicating the existence of the complex cation [Mn(bipy)₃]²⁺ coming from the in situ coordination of the inserted guest with intralayered Mn²⁺ ions between the interlayer space of host. As the intercalation proceeds, the 00l, 00l′ and 00l″ phases finally disappear, and 00l′′′ phase is intensified and a complete intercalate is obtained. In Series B, due to the presence of the acid, the formation of the complex cation [Mn(bipy)₃]²⁺ is inhibited, and the amount of the acid in the intercalation plays a key role in the formation of the guest. With the increase of the acid, the protonated bipyridine becomes the main existing form of the guest, which is arranged in the perpendicular orientation of molecular ring to the layer. From the experimental evidences, the possible intercalation mechanisms are proposed and the novel intercalation phenomenon of in situ coordination of the inserted 2,2′-bipyridine with Mn²⁺ of the host is elucidated.     

6,6′-Dimethyl-2,2′-bipyridine-4-ester: A pivotal synthon for building tethered bipyridine ligands

We describe an efficient and scalable synthesis of 4-carbomethoxy-6,6′-dimethyl-2,2′-bipyridine starting from easily available substituted 2-halopyridines and based on the application of modified Negishi cross-coupling conditions. This compound is a versatile starting material for the synthesis of 4-functionalized 2,2′-bipyridines bearing halide, alcohol, amine, and other functionalities, suitable for conjugation to biological material (2a-c, 3a-g). The utility of this compound in the construction of more complex architectures was further demonstrated by the synthesis of two bifunctional lanthanide chelators; an open chain ligand based on one 2,2′-bipyridine unit and a cryptand based on three 2,2′-bipyridine units [N₂(bpy)₃COOMe]. In the field of luminophoric biolabels, the photophysical properties of the corresponding Eu(III) cryptate are reported.     

Copper-catalyzed direct thiolation of benzoxazole with diaryl disulfides and aryl thiols

The cross-coupling reaction of benzoxazole with aryl thiols using the CuI/2,2′-bipyridine complex as a catalyst in DMF at 80 °C under oxygen produced the corresponding aryl thioethers in moderate to good yields. The coupling reaction with diaryl disulfide also occurred under similar oxidative conditions.     

Convenient synthesis of tridentate 2,6-di(pyrazol-1-yl)-4-carboxypyridine and tetradentate 6,6′-di(pyrazol-1-yl)-4,4′-dicarboxy-2,2′-bipyridine ligands

Citrazinic acid is used as a convenient starting material for both tridentate 2,6-di(pyrazol-1-yl)-pyridine and tetradentate 6,6′-di(pyrazol-1-yl)-2,2′-bipyridine ligands containing carboxylic groups useful for further anchoring of sensitizer on TiO₂ for dye-sensitized solar cells (DSCs). Using 2,6-dichloro-4-carboxypyridine, the synthesis of the terdentate ligands was improved compared to previously used 2,6-dibromo-4-carboxypyridine or 2,6-dichloro-4-ethylcarboxylate pyridine. Controlling the reaction conditions, it is possible to efficiently obtain the monosubstituted 2-chloro-6-pyrazol-1-yl-4-carboxypyridine, a key intermediate for the preparation of tetradentate 6,6′-di(pyrazol-1-yl)-4,4′-dicarboxy-2,2′-bipyridine ligand.     

Ring opening reactions of pyromellitic dianhydride for the synthesis of first row transition metal dicarboxylate complexes

The ring opening reaction of pyromellitic dianhydride by methanol is an effective method to prepare first row transition metal dicarboxylate complexes. The reactions of different first row transition metal salts with pyromellitic dianhydride in the presence of nitrogen donating bidentate ligands such as 1,10-phenanthroline and 2,2′-bipyridine gives different compositions depending on the ligand and the metal salts used. For example, the reaction of nickel(II) acetate with pyromellitic dianhydride in the presence of 1,10-phenanthroline results in the formation of a carboxylato bridged nickel(II) metallacycle through the ring opening reaction of pyromellitic dianhydride (PAH) at the 1 and 3-positions, whereas a mononuclear tetra-aqua 2,2′-bipyridine nickel(II) complex is formed in a similar reaction of nickel(II) acetate through ring opening at the 1,4-position of PAH. Mononuclear cobalt(II) dicarboxylate complexes are formed from the ring opening reaction of pyromellitic dianhydride in methanol in the presence of the nitrogen donor ligands 1,10-phenanthroline or 2,2′-bipyridine. Copper(II) chloride on reaction with PAH and 2,2′-bipyridine gives a mononuclear complex via ring opening at the 1 and 4-positions; having chlorides inside and outside the coordination sphere. Whereas, the reaction of copper(II)acetate gives dinuclear copper complexes having a monodentate carboxylato bridge arising from the carboxylato groups at the 1 and 4-positions on the aromatic ring. The crystal structures of all the complexes have been determined.     

Functional dyes: bipyridines and bipyrimidine based boradiazaindacene

The synthesis of molecules bearing pyridine, 2,2^′-bipyridine or 2,2^′-bipyrimidine donor units appended with one or two highly luminescent indacene fragments was undertaken by using two distinct pathways. The first used direct condensation of krytopyrrole with the corresponding aldehydes. The second, and more universal is based on a Pd cross-coupling reaction between an iodo functionalized BODIPY and the corresponding stable ethynyl derivatives. All compounds are strongly luminescent in solution with quantum yields as high as 70%. Interlocking of two 6,6^′-BODIPY substituted bipyridines around a single copper(I) center is observed by proton NMR and cyclic voltammetry. These synthetic routes have made a variety of functionalized dyes available for studies of their optical properties in the presence of incoming cations, of their coordination chemistry and as light emitting solid state materials.     

Practical synthesis of pinacolborane for one-pot synthesis of unsymmetrical biaryls via aromatic C-H borylation-cross-coupling sequence

A method for practical preparation of pinacolborane from borane-diethylaniline and pinacol was newly developed. Aromatic C-H borylation of arenes with pinacolborane or bis(pinacolato)diboron catalyzed by 1/2[Ir(OMe)(COD)]₂-(4,4′-di-tert-butyl-2,2′-bipyridine) at 25 °C in hexane to give arylboronic esters was directly followed by cross-coupling with aromatic bromides at 60 °C in the presence of PdCl₂(dppf) (3.0 mol %) and K₃PO₄ in DMF. This one-pot, two-step procedure provided a variety of unsymmetrical biaryls in high yields.     

Photoluminescent and electrochemiluminescent dual-signaling probe for bio-thiols based on a ruthenium(II) complex

Photoluminescence (PL) and electrochemiluminescence (ECL) detection techniques are highly sensitive and widely used methods for clinical diagnostics and analytical biotechnology. In this work, a unique ruthenium(II) complex, [Ru(bpy)₂(DNBSO-bpy)](PF₆)₂ (bpy: 2,2′-bipyridine; DNBSO-bpy: 2,4-dinitrobenzenesulfonate of 4-(4-hydroxyphenyl)-2,2′-bipyridine), has been designed and synthesized as a highly sensitive and selective PL and ECL dual-signaling probe for the recognition and detection of bio-thiols in aqueous media. As a thiol-responsive probe, the complex can specifically and rapidly react with bio-thiols in aqueous solutions to yield a bipyridine-Ru(II) complex derivative, [Ru(bpy)₂(HP-bpy)]²⁺ (HP-bpy: 4-(4-hydroxyphenyl)-2,2′-bipyridine), accompanied by the remarkable PL and ECL enhancements. The complex was used as a probe for the PL and ECL detections of cysteine (Cys) and glutathione (GSH) in aqueous solutions. The dose-dependent PL and ECL enhancements showed good linear relationships against the Cys/GSH concentrations with the detection limits at nano-molar concentration level. Moreover, the complex-loaded HeLa cells were prepared for PL imaging of the endogenous intracellular thiols. The results demonstrated the practical utility of the complex as a cell-membrane permeable probe for PL imaging detection of bio-thiols in living cells.     

S-Transalkylation/ring closing metathesis as a route to azathiamacrocycles incorporating 2,2′-bipyridine subunits

A new route to cyclophanes 6a,b incorporating 2,2′-bipyridine subunits has been elaborated using as the key steps (1) S-transalkylation of 6,6′-bis(methylsulfanyl)-2,2′-bipyridines 2a,b with ethyl bromoacetate resulting in the formation of 6,6′-bis[(ethoxycarbonyl)methylsulfanyl]-2,2′-bipyridines 3a,b and (2) ring-closing metathesis of the corresponding alkenyl ethers 5a,b.     

Synthesis and electrochemical properties of dendrimers containing meta-terphenyl peripheral groups and a 4,4′-bipyridinium core

Fréchet-type poly(arylether) dendrons carrying m-terphenyl peripheral groups were synthesized up to second generation by convergent methodology. Simple quarternisation of 4,4′-bipyridine with the dendritic bromides afforded the corresponding dendrimers containing a 4,4′-bipyridine core. The electrochemical parameters were obtained for all the dendrimers and the half-wave potentials of both the first and second redox processes shift to less-negative values as the dendrimer generation increases.     

Two new supramolecular assemblies based on Keggin-type polyoxometalates through AgO and ππ stacking interactions

Two new supramolecular assemblies based on Keggin-type polyoxometalates, [Ag₃(4,4′-bipy)₂(2,2′-bipy)₂][Ag(2,2′-bipy)₂][{Ag(2,2′-bipy)}HSiW₁₁VO₄₀] (1) and [Ag₃(4,4′-bipy)₂(2,2′-bipy)₂][Ag(2,2′-bipy)₂][{Ag(2,2′-bipy)}PW₁₁VO₄₀] (2) (4,4′-bipy = 4,4′-bipyridine, 2,2′-bipy = 2,2′-bipyridine), have been synthesized under the hydrothermal conditions and structurally characterized by IR, XPS, TG and single-crystal X-ray diffraction. Compound 1 has a 2D layer network structure via weak Ag^...O interactions. Compound 2 is isostructural with compound 1. In addition, the fluorescence of compound 1 is reported.     

Effect of 5-Me substituent(s) on the catalytic activity of palladium(II) 2,2-bipyridine complexes in CO/4-tert-butylstyrene copolymerization

The coordination of two 5-substituted-2,2^′-bipyridines L (L¹=5-methyl-2,2^′-bipyridine, L²=5,5^′-dimethyl-2,2^′-bipyridine) to palladium was studied. The neutral complexes [Pd(L)Cl₂] and [Pd(L)(Me)Cl], and the cationic complexes obtained after chlorine abstraction [Pd(L)₂][BAr^′₄]₂ and [Pd(L)(Me)(NCMe)][BAr^′₄] (Ar^′=3,5-(CF₃)₂-C₆H₃), respectively, were isolated and characterized by NMR and FAB mass spectroscopy. The complex [Pd(L²)(L³)][BAr^′₄]₂ (L³=2,2^′-bipyridine) bearing different ligands, was prepared for comparison purposes. The activity of the monocationic and dicationic complexes as catalytic precursors in the CO/4-tert-butylstyrene copolymerization was compared with that of related well-known catalysts containing the unsubstituted 2,2^′-bipyridine as nitrogen ligand, to evaluate the influence of the substituents in 5- and 5,5^′-position. The presence of one or two substituents on the nitrogen ligand has a positive effect on productivity using both types of precursors. No influence was observed on the polymer properties in terms of molecular weight and tacticity. Analysis of the reactivity of the methyl-palladium complexes towards carbon monoxide shows further differences depending on the nitrogen ligand.