Search

Palladium complexes of polycatenar 2,5-diphenylpyridine ligands were prepared in a two-stage reaction from (NH4)2[PdCl4]; their liquid crystal and emission properties are reported and discussed. For tetracatenar and hexacatenar derivatives, neither the ligand nor their complexes were liquid crystalline. The tricatenar ligand only showed a SmC phase identified by a Schlieren texture. Palladation of the tricatenar and dicatenar ligands led to complexes showing a SmA phase, with a range that depended on the ligand. The identity of the mesophases was supported by small angle X-ray scattering (SAXS). All ligands and complexes exhibited luminescence properties with the emission lifetimes of the complexes suggesting the absence of phosphorescence.

Herein, we report on a new series of mesomorphic compounds synthesised by directional functionalisation of 2,5-di(4-dodecoxyphen-1-yl-c-cyclopentene-pyridine) on the c-cyclopentene moiety. The first functionalisation of the starting compound gave rise to a racemic product modified with a hydroxyl group on the fused cyclopentene ring. Further oxidation of this alcohol to a prochiral ketone and subsequent enantioselective reduction back to the alcohol afforded a new chiral alcohol. Further, the hydroxyl group of the chiral alcohol could be substituted by fluorine in a SN2 reaction, leading to a chiral compound with enantiomeric excess (ee) of 66% and chiral nematic liquid-crystalline (LC) phase.

Rational design of selective and sensitive 'off-on' fluorescent probes for Zn(II) cations exploiting both PET and ICT mechanisms of sensing is illustrated by the synthesis and application of 5-aryl-2,20-bipyridines modified with a dipicolylaminomethyl fragment. The aryl substituent provides tuning of the properties. © 2012 Elsevier Ltd. All rights reserved.

The 'triazine' methodology for the synthesis of functionalized pyridine ligands proved to be a convenient method for the preparation of a luminescent Pt(II) complex. The key ligand can be assembled easily starting from readily accessible reagents. Further cycloplatination and post-functionalization led to the ready-to-go luminescent 'tag' 2 for peptide labeling. © 2012 Elsevier Ltd. All rights reserved.

The synthesis of pyridine and bipyridine derivatives of m-carborane via aza Diels–Alder reaction of 1,2,4-triazines with 9-allyl m-carborane and their structural characterization and photophysical properties are described. The products 3- and 4-(m-carborane-9-ylmethyl)-2,2′-bipyridines form Zn(II) complexes on reaction with ZnCl2, which increases significantly their fluorescence intensity.

Meanwhile 5-aryl-6-cyano-2,2′-bipyridines are very stable towards various nucleophiles, addition copper(II) chloride to the reactional mixture facilitates nucleophilic addition to the cyano group dramatically. The cyanobipyridines react easily with water, methanol, ethanolamine in the presence of CuCl2 yielding well-crystallized complexes containing carboxylates, carboximidates or carboxamidines as ligands. 5-Cyano-1,2,4-triazines are more active in the reactions due to higher electron-withdrawing properties of this heterocycle. Due to the same reason acetylene moiety of 5-ethynyl-3-pyridyl-1,2,4-triazine adds water quite easily but in the presence of copper chloride as well.

The new N,N,O-ligand 6-phenyl-3-(2-pyridyl)-5-(trifluoroacetylmethylidene)-4,5-dihydro-1,2,4-triazine (L) was synthesized, and its complex with CuII was prepared. The structure of the complex was established by X-ray diffraction. Magnetic measurements and ESR studies were carried out. Ab initio calculations of the electronic structure, exchange interactions, and the effective magnetic moment were performed. The intrastack polarization effect between the π states of 1,2,4-triazine and the d states of copper was revealed and numerically validated.

An efficient strategy for the synthesis of functionalized 2,2′-bipyridines is reported. The strategy is based on readily available 3-pyridyl-1,2,4-triazine 4-oxides and uses a reaction sequence of nucleophilic substitution of hydrogen and aza Diels–Alder reaction.

5-Acylmethyl-3-(2-pyridyl)-1,2,4-triazines are easily prepared from accessible 3-(2-pyridyl)-1,2,4-triazine 4-oxides by reaction of the latter with acetophenone or trifluoroacetone in the presence of NaH. The compounds obtained behaved as efficient ligands in reaction with CuCl2 furnishing dimeric neutral complexes with Cu(II) whose structure was investigated by means of X-ray diffraction analysis.

A series of three Pt(II) complexes with a doubly cyclometalating terdentate ligand L1, L1H2 = 3,6-bis(p-anizolyl)-2-carboranyl-pyridine, and diethyl sulfide (1), triphenylphosphine (2), and t-butylisonitrile (3) as ancillary ligands were synthesized. X-ray diffraction studies of 1 and 2 show a coordination of the L1 ligand in a C-N-C mode in which the bulky and rigid o-carborane fragment is cyclometalated via a C atom. Importantly, no close intermolecular Pt-Pt contacts occur with this ligand type. The new Pt(II) pincer complexes display very high luminescence quantum yields at decay times of several tens of μs even in solution under ambient conditions. On the basis of the low-temperature (T = 1.3 K) emission decay behavior, the emission is assigned to a ligand centered triplet excited state (3)LC with small (1,3)MLCT admixtures. Because the phosphorescence is effectively quenched by molecular oxygen, optical sensors operating in a wide range of oxygen pressure can be developed. Owing to the very high luminescence quantum yields, the new materials might also become attractive as emitter materials for diverse optoelectronic applications.

This review covers the work published in the calendar year 2013. Novel reaction chemistry and new ring synthetic methods for 1,2,3-triazines, 1,2,4-triazines, 1,3,5-triazines, and tetrazines are reviewed.

Addition of hydroxylamine at the 3 position of 6-aryl-5-amino-1,2,4-triazine-4-oxides initiates the amidine rearrangement resulting in 6-aryl-5-hydroxylamine-1,2,4-triazines, as confirmed by an experiment with 15 N-labeling.

The N-oxides of azines 1a–g react with lithium and/or potassium acetylides to give the corresponding ethynylazines 2a–g. Reaction with lithium acetylide requires subsequent acylation of the intermediate anionic adduct for rearomatization whereas in the case of potassium acetylide, auto-aromatization takes place.

Pyrimidine 1-oxides with cyanamide afforded 2-ureidopyrimidines as the result of the nucleophilic substitution of hydrogen, whereas the formation of similar 2-trichloroacetylaminopyrimidines occurs as dipolar 1,3-cycloaddition of the same oxides to trichloroacetonitrile under much more drastic conditions and in lower yields.

The review covers work published in the calendar year 2010. Novel reaction chemistry and new ring synthetic methods for 1,2,3-triazines, 1,2,4-triazines, 1,3,5-triazines, tetrazines, and purines are reviewed.

International audience; The ‘triazine’ methodology for the synthesis of functionalized bipyridine ligands proved to be a convenient method for the preparation of luminescent Eu(III) complexes. The approach allows flexible construction of chromophore and coordination sphere with control of photophysical properties. Europium(III) complexes [Eu1]–[Eu5] prepared in this way exhibit intense long-life metal-centered luminescence in aqueous media. The aromatic substituent in the position 5 of bipyridine has a significant influence on luminescence parameters and is used to introduce functionality for bioconjugation. The complexes [Eu4] and [Eu5] bearing primary amine groups are ready-to-go luminescent ‘tags’ for peptide labeling.

It was shown that cyanamide can successfully be used in reactions of nucleophilic substitution of hydrogen with 1,2,4-triazin-4-oxides in the presence of a base to give 5-cyanoimino-1,2,4-triazines. It was found by13C NMR spectroscopy that these compounds and their alkylation products at the cyclic nitrogen atom exist in the form of 5-cyanoimino-2,5-dihydro-1,2,4-triazines.

The SNHreactions of the lithio derivatives of 1,2- or 1,7-dicarba-closo-dodecaboranes with 1,2,4-triazine 4-oxides represent a versatile synthetic approach to carboranes bearing heteroaromatic substituents.

Addition of the Grignard reagents to 1,2,4-triazine 4-oxides followed by aromatization ofthe intermediate σ H -adducts by dehydrogenation or dehydration was used for synthesis of 5-alkyl- or 5-aryl-substituted 1,2,4-triazines and their 4-oxides.

Pyrimidine 1-oxides with cyanamide afforded 2-ureidopyrimidines as the result of the nucleophilic substitution of hydrogen, whereas the formation of similar 2-trichloroacetylaminopyrimidines occurs as dipolar 1,3-cycloaddition of the same oxides to trichloroacetonitrile under much more drastic conditions and in lower yields.

1,2,4-Triazine 4-oxides react with stable carbanions to form 5-substituted 1,2,4-triazines as the products of deoxygenation nucleophilic substitution of hydrogen.

Addition of hydroxylamine at the 3 position of 6-aryl-5-amino-1,2,4-triazine-4-oxides initiates the amidine rearrangement resulting in 6-aryl-5-hydroxylamine-1,2,4-triazines, as confirmed by an experiment with 15 N-labeling.

Novel B,N,N-cyclometallated Pt(II) complexes of 2,2'-bipyridin-6-yl carboranes exhibit absorption and emission similar to relative Pt(II) complexes of aromatic C,N,N-ligands: the same transitions but lower intensities. DFT calculations suggest the former emits from the (3)MLCT state while for the latter the mixed (3)ICT-MLCT transitions should be considered.

1,2,4-Triazine 4-oxides react with stable carbanions to form 5-substituted 1,2,4-triazines as the products of deoxygenation nucleophilic substitution of hydrogen.

A stable optical discharge in xenon was initiated by a cw CO2 laser beam which evaporated a surface impurity film from a solid target. Some characteristics of this discharge were investigated and it was found that its maintenance resulted in screening of the target from the incident radiation.