Segmented multitopic ligands constructed from bipyrimidine, phenanthroline, and terpyridine modules

Starting from bromo-substituted 2,2′-bipyrimidine or 1,10-phenanthroline building blocks, the preparation in a first step of ethynyl grafted molecules allows the production in a second step of multitopic ligands by cross-coupling with difunctionalised chelating molecules. Various combinations allow the interconnection of bipyrimidine to terpyridine, pyrene, or phenanthroline fragments. When two alkyne functions are present, a simple protocol gives a large variety of linear or bent ligands with an increasing number of nitrogen atoms. It was also possible to construct a linear complex capped at the periphery by ruthenium(II) centers and retaining an uncomplexed phenanthroline fragment in its core.     

Synthesis,structure, and luminescence of rhenium(I) complexes with substituted bipyridines

Two new rhenium(I) complexes chelated by a substituted 2,2′-bipyridine with general formula Re(CO)₃LCl, where L?=?6?-(2″-methoxyphenyl)-2,2′-bipyridine (L₁ ) and 6?-(4″-diphenylaminophenyl)-2,2′-bipyridine (L₂ ), are synthesized and characterized by IR, NMR, and elemental analysis. Structure of 1 was determined by single-crystal X-ray crystallography, revealing that rhenium is six-coordinate octahedral. The electrochemical, photophysical, and thermal properties of the two rhenium(I) complexes were investigated. Electroluminescent devices were fabricated by doping 1 in polymer blend host of poly(vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole using simple solution spin-coating technique. The device exhibits a maximum current efficiency of 2.97?cd?A^?1 and peak brightness in excess of 2390?cd?m^?2.     

Cation sensors based on terpyridine-functionalized boradiazaindacene

A new class of highly luminescent dyes is reported. The characteristic feature of these compounds is that a terpyridine fragment is closely appended to a boradiazaindacene moiety in such a way that cation binding to the vacant terpyridine causes strong perturbations of the photophysical properties of the boradiazaindacene unit. In particular, these sensors are especially applicable to the fluorescence detection of trace quantities of zinc(II) ions in solution. The mechanism of the cation-induced quenching process has been investigated by a combination of electrochemistry, UV/Vis absorption, emission, and NMR spectroscopy. Highly luminescent arrays can be formed by doping transparent polymers with low concentrations of these new dyes. In such materials, the change in photophysical properties upon cation binding is so marked that "cation writing" becomes feasible under routine conditions.     

Pyrrole‐2‐carbaldehyde Thiosemicarbazonates of Nickel(II) and Palladium(II): Synthesis,Structure, and Spectroscopy

Complexes of pyrrole‐2‐carbaldehyde thiosemicarbazones, [(C₄H₄N⁴)(H)C²=N³–N²(H)–C¹(=S)–N¹HR; R = Ph, H₂L¹; Me, H₂L²; H, H₂L³] with nickel(II) and palladium(II) are described. The reaction of nickel(II) acetate with H₂L¹ in methanol in 1:1 molar ratio yielded a complex of composition, [Ni(κ²‐N³,S‐HL¹)₂] ( 1 ). Likewise reaction of NiCl₂ with H₂L² in 1:1 molar ratio in acetonitrile in the presence of triethylamine base followed by the addition of pyridine did not yield the anticipated [Ni(κ³‐N⁴,N³,S‐L²)(py)] complex, moreover a bis‐square‐planar complex, [Ni(κ²‐N³,S‐HL²)₂] ( 2 ) was formed. However, in the presence of bipyridine (bipy), it yielded the addition product, [Ni(κ²‐N³,S‐HL²)₂(κ²‐N, N‐bipy)] ( 3 ). Reaction of PdCl₂(κ²‐P, P–PPh₂–CH₂–PPh₂) with H₂L³ in toluene in the presence of triethylamine has yielded a complex of stoichiometry, [Pd(κ³‐N⁴,N³,S–L³)(κ¹‐P–PPh₂–CH₂–P(O)Ph₂] ( 4 ). The ligands (HL¹)^– and (HL²)^– are chelating to Ni^II metal atom as anions binding through N³,S‐donor atoms with pendant pyrrole groups, and (L³)^2– is chelating to the Pd^II metal atom as dianion through N⁴,N³,S‐donor atoms (pyrrole is N⁴‐bonded). Fourth site in 4 is bonded to one P‐donor atom of PPh₂–CH₂–P(O)Ph₂, whose pendant –PPh₂ group involves auto oxidation to –P(O)PPh₂ during reaction. These complexes were characterized using analytical data, IR, NMR (¹H, ³¹P) spectroscopy and X‐ray crystallography. Complexes 1 , 2 , and 4 have square‐planar arrangement, whereas complex 3 is octahedral.     

Palladium(II)-catalyzed addition of arylboronic acid to nitriles

The addition of arylboronic acid to nitriles catalyzed by palladium(II) species in the presence of bipyridine as the ligand was developed. The use of bipyridine is crucial for changing the properties of arylpalladium species from more electrophilic to more nucleophilic making the reaction possible.     

π-Stacked ortho-Palladated Bipyridine Complexes Exhibiting Unusual Liquid Crystalline Behavior

A columnar structure with lamellar morphology in the liquid crystalline state is displayed by the palladium complex salt 1 , which is synthesized from nonmesogenic ligands.     

A convenient method of producing thiophene linked bipyridine oligomers

A series of soluble polybipyridine ligands comprising one to five bipyridine modules sandwiched between rigid carbon-carbon triple bonds substituted by 3,4-dibutylthiophene repeating units was synthesized. Two different protocols have been explored with the idea to use a divergent/convergent approach starting from bisymmetrically and symmetrically substituted bipyridine modules. At each stage of the iteration two bipy/thiophene modules are connected. The use of triethylsilylacetylene and 2-methylbut-3-yn-2-ol insures an easy entry to pivotal building blocks, which could be selectively deprotected from the TES or 2-hydroxyprop-2-yl sites. All cross-coupling reactions are promoted with palladium(0) tetrakistriphenylphosphine under mild conditions.     

A versatile protocol for the preparation of substituted 1- and 2-naphthyl piperazines from aminonaphthols

Aminonaphthols are easily transformed into a variety of 1- and 2-naphthyl piperazines using a sequence of diazotization, iodide substitution and Pd(0) catalyzed coupling reactions.     

Design, synthesis and redox properties of a fluorene platform linking two different Bodipy dyes

Several new fluorophores have been prepared by grafting boradiazaindacene (red absorbing) and/or styrylboradiazaindacene (blue absorbing) units as terminal energy acceptors onto a fluorene-derived platform. In one case, an amino-bis(bipyridine) pocket has been attached to enable strong binding of transition metal ions. The stepwise syntheses were largely based on Pd-catalysed cross-coupling reactions. The electrochemistry of the dyes has been analysed by reference to the properties of the various synthetic intermediates, protonation of the tertiary amine site present in the bis(bipyridine) species enabling processes involving this centre to be distinguished from those associated with the boradiazaindacene (Bodipy) unit.     

Palladium catalyzed transformations of monoterpenes: stereoselective deuteriation and oxidative dimerization of camphene

Camphene undergoes a highly regio and stereoselective palladium catalyzed deuteriation in deuteriated acetic acid solutions of Pd(OAc)₂. NMR reveals that an outward oriented vinylic hydrogen is selectively exchanged for ²H, resulting in 90% camphene-d₁ (ca. 100% stereoselectivity) and 10% camphene-d₂ at 75% conversion of camphene (6 h, 25 °C). Neither π-allyl nor π-olefin palladium complexes are formed in detectable concentrations during the reaction, whereas palladium hydride (singlet at −6.86 ppm) and palladium deuteride (singlet at −6.78 ppm) intermediates have been detected by ¹H and ²H NMR, respectively. At higher temperature, oxidative coupling of camphene readily occurs giving the (E,E)-diene, i.e., bis(3,3-dimethyl-2-norbornylidene)ethane, which formally originates by abstracting the outward oriented vinylic hydrogens and coupling the resulting fragments of two camphene molecules. The reaction is catalytic at palladium in the Pd(OAc)₂-LiNO₃(cat)-O₂ and Pd(OAc)₂-benzoquinone systems. Similar mechanisms for the deuteriation and oxidative coupling of camphene are proposed, which involve the formation of σ-vinyl palladium hydride intermediates. No deuteriation neither oxidative coupling of limonene, myrcene and β-pinene were observed under the same conditions.     

Ferrocenyl-palladium complexes in cross-coupling reactions: a comparative study

Ferrocenecarboxaldehyde hydrazones were converted into palladium complexes on treatment with sodium tetrachloropalladate. The substitution pattern of the ferrocenylhydrazones was found to have a marked influence on the mode the palladium was attached to the organic moiety. The catalytic activity of the new palladium complexes in cross-coupling reactions was examined in detail, and it was compared with conventional catalyst systems.     

Heterogenous catalytic method for the synthesis of biquinolines and bipyridines

A method has been developed for the synthesis of 2,2′- and 3,3′-biquinolines and of 4,4′-bipyridine based on the coupling of 2- and 3-bromoquinoline or 4-bromopyridine using a Pd/C-hydrazine-KOH catalytic system. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1839–1840, December, 2008.     

Regioselective synthesis of substituted pyrrolopyridines based on Pd(II)-mediated cross coupling and base induced heteroannulation

Novel pyrrolopyridines have been synthesized by an efficient, regioselective and catalytic method from commercially available and inexpensive 3-aminopyridine or 2-aminopyridine.     

Chiral molecular squares based on angular bipyridines: self-assembly, characterization, and photophysical properties

Chiral molecular squares 1-12 based on [M(dppe)](2+) metallocorners (M = Pd or Pt, and dppe = bis(diphenylphosphino)ethane) and new angular bipyridine bridging ligands derived from the 1,1'-binaphthyl framework were readily assembled and characterized by a variety of techniques including infrared, UV-vis, circular dichroism (CD), and NMR spectroscopy, and ESI mass spectrometry. All these chiral metallocycles are highly luminescent in solution at room temperature with quantum efficiency of 0.06-0.63. Interestingly, when equal molar enantiopure molecular squares of opposite handedness were mixed in solution, a new meso dimeric metallocycle with C(2) symmetry formed. This result indicates the lability of the M-pyridyl bonds in these metallocycles, which may hinder their applications in many enantioselective processes.     

Novel DNA Binding Agents: Hydrazone‐based Helical Trinuclear Ag Complexes

Using the hydrazone linker and the self‐assembly, functionalized Ag complexes with a helical structure showed a 2.96 Å distance between metal‐metal bonds, well‐aligned aromatic rings, and the strong affinity toward DNA.     

Catalytic activity of Pd(II) and Pd(II)/DAB-R systems for the Heck arylation of olefins

Palladium-catalyzed reactions of aryl bromides with various olefins involving Pd(II)/diazabutadiene (DAB-R) systems have been investigated. The scope of a coupling process using Pd(II) sources and an α-diimine as ligand in the presence of Cs₂CO₃ as base was tested using various substrates. The Pd(OAc)₂/DAB-Cy (1, DAB-Cy=1,4-dicyclohexyl-diazabutadiene) system presents the highest activity with respect to electron-neutral and electron-deficient aryl bromides in coupling with electron rich olefins. The synthesis and X-ray characterization of a Pd(II)-diazabutadiene ligand is reported. Extensive optimization experiments showed that another Pd(II) source, Pd(acac)₂ (acac=acetylacetonate), proved to activate aryl bromides at high temperatures, low catalyst loadings when the appropriate concentration of ⁿBu₄NBr additive was employed. The effect of the DAB-Cy ligand is important at very low catalyst loadings and high temperatures. Pd(acac)₂ and Pd(acac)₂/DAB-Cy precatalysts were very effective for the arylation of various olefins with aryl bromides with respect to reaction rate, catalyst loadings, and functional group tolerance.     

Di-t-butyl(ferrocenylmethyl)phosphine: air-stability, structural characterization, coordination chemistry, and application to palladium-catalyzed cross-coupling reactions

Di-t-butyl(ferrocenylmethyl)phosphine (1) has been isolated and structurally characterized. This ligand was found to be reasonably air stable as a solid and it has been shown to possess electron donating ability similar to that of tri-i-propylphosphine. A palladium catalyst bearing this ligand performed room temperature Suzuki-Miyaura coupling reactions with aryl bromides. Modest Heck coupling reactivity with aryl bromides was also observed at 100 °C. Complexation of 1 with Pd₂(dba)₃ led to formation of (1)₂Pd⁰. Addition of 4-bromoanisole to solutions containing both 1 and Pd₂(dba)₃ led to formation of an oxidative addition product when 1:Pd ratios were ?1. With a 2:1 ratio of 1:Pd, monophosphine complex formation and oxidative addition were significantly inhibited.     

The construction of two lanthanide coordination polymers based on 5-hydroxyisophthalate and bipyridine

Two lanthanide coordination polymers, [Tm₂·(5-IPA)₄·(2,2′-Hbipy)₂]·3H₂O (1, 5-H₂IPA?=?5-hydroxyisophthalic acid, 2,2′-bipy?=?2,2′-bipyridine) and [Er·(5-HIPA)₃·(4,4′-bipy)₃·(H₂O)₂]·3H₂O (2, 4,4′-bipy?=?4,4′-bipyridine), have formed by hydrothermal synthesis. Complex 1 exhibits a 2-D coordination network containing parallelepiped-shaped voids occupied by guest 2′2-bipy molecules. Complex 2 possesses a 1-D linear chain structure. The 1-D chains are linked by 4,4′-bipy molecules to form a 3-D supramolecular framework. IR spectroscopy, elemental analysis, and thermogravimetric analysis were also investigated.     

Addition of lithioimidazoles to isocyanates followed by Pd-coupling: access to 4-substituted imidazole-2,5-dicarboxamides

Facile access to 4-substituted N-butyl 2,5-dicarboxamides is achieved via direct lithiation of N-butyl imidazole and subsequent quenching with isocyanates followed by Pd-catalyzed coupling reactions.