Syntheses, structures, luminescence and electrochemistry of benzene- and biphenyl-centered bis- and tris-1,3,2-diazaboroles and -1,3,2-diazaborolidines

Reaction of 1,4-bis(dibromoboryl)benzene (1a) with 2 equiv. of the diazabutadiene tBuN=CH-CH=NtBu and subsequent reduction of the obtained bis(1,3,2-diazaborolium)salt 2a with sodium amalgam afforded the 1,4-bis(1,3,2-diazaborolyl)benzene 3a. Similarly, 1,3-bis(dibromoboryl)benzene (1b), 1,3,5-tris(dibromoboryl)benzene (1c) and 4,4'-bis(dibromoboryl)biphenyl (1d) were converted into compounds 3b, 3c and 3d which contain two or three diazaborolyl substituents at the arene core. Treatment of precursors 1a,b,d with two equiv. or with three equiv. of N,N'-di-tert-butylethane-1,2-diamine in the presence of an excess of NEt3 gave rise to the diazaborolidine derivatives 4a-4d. Reaction of 1,3-bis(diiodoboryl)benzene with two equivalents of N,N'-dimethylethane-1,2-diamine in the presence of NEt3 furnished the corresponding 1,3-bis(diazaborolidinyl)benzene 4e. The novel compounds were characterized by elemental analyses and spectroscopy (1H, 13C, 11B NMR, MS). The molecular structures of 3c, 4a and 4e were eludicated by X-ray-diffraction analyses. In addition to this, the oxidative cyclovoltammograms and blue emission spectra of these novel compounds were discussed. Here, the electronic communication between boron heterocycles on the different spacer-units and the luminescence of the oligo-diazaborolylarenes were of interest.     

Polykis(pyrazol-1-yl)benzenes: preparation, structure, and complexation with copper and palladium

A series of polykis(pyrazol-1-yl)benzenes, potential chelating ligands for transition metals, have been prepared by nucleophilic substitution of fluorine in 1,2-difluoro-, 1,2,3,4-tetrafluoro-, 1,2,4,5-tetrafluoro-, and hexafluorobenzenes. The observed substitution pattern indicated formation of early TS, making activation by fluorines ortho- to the site of nucleophilic attack dominant. Complexation of the synthesized ligands with copper(II) and palladium(II) was analyzed by ESI mass spectrometry. X-ray structures were determined for palladium(II) complex with 1,2-bis(pyrazol-1-yl)benzene and copper(II) complex with 1,4-difluoro-2,3-bis(pyrazol-1-yl)benzene, revealing an unusual seven-membered chelate cycle formation.     

New electroluminescent materials based on chelate zinc complexes

Three new chelate zinc complexes with azomethine groups characterized by luminescence in the visible spectral region were synthesized: bis(N-(2-oxybenzylidene)cyclohexylamine)zinc, bis(N-(2-oxybenzylidene)-4-tert-butylaniline)zinc, and N,N′-bis(oxybenzylidene)-1,2-phenylenediaminezinc. Their spectral properties were studied. Based on these complexes, we prepared electroluminescence devices giving an intense emission in the blue, green, and red spectral regions.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2056–2059, October, 2004.     

Synthesis of benzo-1,3-ditellurole and its precursors

Poly(o-phenyleneditelluride) 6 has been prepared by the reduction of 1,2-bis(trichlorotelluro)benzene obtained by treatment of 1,2-bis(trimethylsilyl)benzene with TeCl₂. The reduction of 6 with NaBH₄ in ethanol solution affords sodium benzene-1,2-ditellurolate, which, upon treatment with methylene bromide, forms benzo-1,3-ditellurole in 40–47% yield. Benzo-1, 3-ditellurole has also been synthesized in 18–20% yeild by the reaction of 1,2-bis(trimethylslyl)benzene with bis(trichlorotelluro)methane, with subsequent reduction of the product, 1,1,3,3-tetrachlorobenzo-1,3-ditellurole.     

Synthesis of indan-based unusual alpha-amino acid derivatives under phase-transfer catalysis conditions

Conformationally constrained cyclic alpha-amino acid derivatives were synthesized under solid-liquid phase-transfer catalysis conditions. This methodology involves the bis-alkylation of ethyl isocyanoacetate with various alpha,alpha'-dibromo-o-xylene derivatives [alpha,alpha'-dibromo-o-xylene 5, 2,3-bis(bromomethyl)-1, 4-dimethoxybenzene 6, 1,2-bis(bromomethyl)-4,5-dibromobenzene 7, 2, 3-bis(bromomethyl)naphthalene 8, 1,8-bis(bromomethyl)-naphthalene 9, 6,7-bis(bromomethyl)-2,2-dimethyl-1H-phenalene-1,3(2H)-dione 10, 2, 3-bis(bromomethyl)-1,4-anthraquinone 11, 6, 7-bis(bromomethyl)quinoxaline 12, 3,4-bis(bromomethyl)furan 13, 1,2, 4,5-tetrakis(bromomethyl)benzene 28, and hexakis(bromomethyl)benzene 30] using potassium carbonate as a base and tetrabutylammonium hydrogensulfate as a phase-transfer catalyst to give corresponding isonitrile derivatives, which upon hydrolysis with HCl in ethanol gave amino esters. Using this method electron-deficient as well as electron-rich and halogen-substituted indan-based alpha-amino acids were prepared. The preparation of bis-indan as well as tris-indan alpha-amino esters is also described.     

Regiospecific metalation of oligobromobenzenes

The metalation of selected oligobromobenzenes with lithium diisopropylamide (LDA) was investigated. 1,3-Dibromo-substituted benzenes were metalated without special precautions since the resultant 2,6-dibromophenyllithium intermediates are relatively stable under reaction conditions: corresponding benzaldehydes were obtained in good or moderate yields after subsequent quench with N,N-dimethylformamide (DMF). Aryllithium compounds derived from 1,4- and 1,2-dibromobenzene are much less stable, but they could be trapped by the in situ use of chlorotrimethylsilane. The one-pot metalation/disilylation of 1,4-dibromo- and 1,2-dibromobenzene afforded 1,4-dibromo-2,5-bis(trimethylsilyl)benzene and 2,3-dibromo-1,4-bis(trimethylsilyl)benzene, respectively.     

Thermal C1-C5 diradical cyclization of enediynes

Computational studies at the BLYP/6-31G(d) level (supplemented by BCCD(T)/cc-pVDZ calculations) suggest that in aryl-substituted 1,2-diethynylbenzenes, steric effects disfavor the thermal C1-C6 diradical cyclization reaction (Bergman) and electronic effects favor the regiovariant C1-C5 cyclization to the extent that the C1-C5 process should become an important reaction pathway in the thermolyses of such compounds. Experimentally, thermolyses of 1,2-bis(2,4,6-trichlorophenylethynyl)benzene, a particularly favorable case, yields only products derived from C1-C5 cyclization [specifically, 1-(2,4,6-trichlorobenzylidene)-2-(2,4,6-trichlorophenyl)-1H-indene and its hydrogenation product 3-(2,4,6-trichlorobenzyl)-2-(2,4,6-trichlorophenyl)-1H-indene], and even for the parent hydrocarbon 1,2-bis(phenylethynyl)benzene, the formation of C1-C5 cyclization products is competitive with the major Bergman reaction. Although some C1-C5 cyclization products are probably formed by transfer hydrogenation from 1,4-cyclohexadiene (commonly included in such reactions), thermolyses in the absence of 1,4-CHD as well as deuterium labeling studies confirm the existence of direct C1-C5 diradical cyclizations for diaryl-substituted enediynes.     

Blue luminescent 2-(2'-pyridyl)benzimidazole derivative ligands and their orange luminescent mononuclear and polynuclear organoplatinum(II) complexes

Five new 2-(2'-pyridyl)benzimidazole derivative ligands, 1,4-bis[2-(2'-pyridyl)benzimidazolyl]benzene (1,4-bmb), 4,4'-bis[2-(2'-pyridyl)benzimidazolyl]biphenyl (bmbp), 1-bromo-4-[2-(2'-pyridyl)benzimidazolyl]benzene (Brmb), 1,3-bis[2-(2'-pyridyl)benzimidazolyl]benzene (1,3-bmb), and 1,3,5-tris[2-(2'-pyridyl)benzimidazolyl]benzene (tmb), have been synthesized by Ullmann condensation methods. The corresponding mononuclear and polynuclear PtII complexes, Pt2(1,4-bmb)Ph4 (1), Pt2(bmbp)Ph4 (2), Pt(Brmb)Ph2 (3), Pt2(1,3-bmb)Ph4 (4), and Pt3(tmb)Ph6 (5), have been obtained by the reaction of the appropriate ligand with [PtPh2(SMe2)]n. The structures of the free ligands 1,4-bmb, bmbp, and tmb, as well as the complexes 1-3, were determined by single-crystal X-ray diffraction. All ligands display fluorescent emissions in the purple/blue region of the spectrum at ambient temperature and phosphorescent emissions in the blue/green region at 77 K, which are attributable to ligand-centered pi --> pi* transition. No ligand-based emission was observed for the PtII complexes 1-5. All PtII complexes display orange/red emissions at 77 K in a frozen solution or in the solid state, attributable to metal-to-ligand charge transfers (MLCT). Variable-temperature 1H NMR experiments establish that complexes 1, 4, and 5 exist in isomeric forms in solution at ambient temperature due to the hindered rotation of the square PtC2N2 planes in the complexes.     

Synthesis of 1, 2-bis(b-amino-o-carboranyl)ethane and 1,4-bis(b-amino-o-carboranyl)benzene

Conclusions 1,2-Bis(B-amino-o-carboranyl)ethane and 1,4-bis(B-amino-o-carboranyl)benzene were synthesized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1669–1670, July, 1976.     

Dielectric spectroscopy of polyazomethine with vinylene moieties in the main chain

We have explored the dielectric properties of polyazomethine with vinylene moieties in the main chain (PAZ-PV). The dialdehyde 2,5-bis(hexyloxy)-1,4-bis[(2,5-bis(hexyloxy)-4-formyl-phenylenevinylene]benzene was polymerised in solid-state with the diamine poly(1,4-butanediol)bis(4-aminobenzoate). The polymer obtained exhibited liquid crystal properties. The molecular dynamics and phase transitions including the liquid crystal phase of PAZ-PV were investigated by dielectric spectroscopy. The dielectric constant decreases with a decrease in the temperature, except in the nematic phase region, where a slight increase was observed. The temperatures of the phase transitions were well seen and were compared with differential scanning calorimetry (DSC) and polarised optical microscopy experiments. All values determined from dielectric data were a few degrees higher than those obtained in previous measurements (DSC).     

Über den mechanismus der licht-induzierten eliminierung des biphenyl-systems aus cis-bis(phenyl)platin(II)-verbindungen

We report the light-induced reductive elimination of the biphenyl system from compounds of the types bis(phenyl)[η²-1,2-bis(diphenylphosphano)ethan]platinum(II), bis(phenyl)[η²-cis-1,2-bis(diphenylphosphano)ethene]platinum(II) and bis(phenyl)[η²-1,2-bis(diphenylphosphano)benzene]platinum(II) with substituents in the platinum-bound phenyl rings. The elimination proceeds via a concerted reaction mechanism without any observable free radical involvement.     

Phenothiazine cruciforms: synthesis and metallochromic properties

We report the synthesis and characterization of five novel phenothiazine-containing cruciforms (5-9). The targets were prepared by a NaH-promoted Horner reaction of tetraethyl(2,5-diiodo-1,4-phenylene)bis(methylene)diphosphonate with 10-hexyl-10H-phenothiazine-3-carbaldehyde. The formed intermediary 3,3'-(1E,1'E)-2,2'-(2,5-diiodo-1,4-phenylene)bis(ethene-2,1-diyl)bis(10-hexyl-10H-phenothiazine) was reacted with several different aromatic alkynes (1-tert-butyl-4-ethynylbenzene, N,N-dibutyl-4-ethynylaniline, 1-ethynyl-3-(trifluoromethyl)benzene, and 1-ethynyl-3,5-bis(trifluoromethyl)benzene) to give the corresponding cruciform fluororphores (XF). The XFs were fully characterized by NMR and IR spectroscopy and then exposed to trifluoroacetic acid as well as to several metal triflates. The XFs show dramatic shifts in emission and to a lesser extent in absorption when exposed to magnesium triflate or zinc triflate. In the case of magnesium triflate, a blue shift in emission was observed; in contrast, addition of zinc triflate results in either quenching or a red-shifted emission. Due to the electronic situation, these XFs display spatially separated frontier molecular orbitals, allowing the HOMO or the LUMO of the XFs to be addressed independently by addition of zinc or magnesium ions. Phenothiazine XFs may have potential in array-type sensory applications for metal cations.     

Reactions of 1,4-bis(tetrazole)benzenes: formation of long chain alkyl halides

The reactions of 1,4-bis[2-(tributylstannyl)tetrazol-5-yl]benzene with α,ω-dibromoalkanes were carried out in order to synthesise pendant alkyl halide derivatives of the parent bis-tetrazole. This led to the formation of several alkyl halide derivatives, substituted variously at N1 or N2 on the tetrazole ring. The crystal structures of 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (2-N,2-N′), 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (1-N,2-N′) and 1,4-bis[(2-(8-bromooctyl)tetrazol-5-yl)]benzene (2-N,2-N′) are reported. Further discussion involves the structure of 1,4-bis[2-(6-bromohexyl)-2H-tetrazol-5-yl]benzene (2-N,2-N′) previously reported.     

Phosphorylation of 1,4-bis(hydroxymethyl)benzene with trivalent phosphorus derivatives

Phosphorylation of 1,4-bis(hydroxymethyl)benzene with complete phosphorous acid amides and phenyl phosphorodichloridite is studied. Some phosphorus-containing linear systems, the phosphamacrocycle precursors, are synthesized. The possibility of synthesis of phosphamacrocyclic systems based on 1,4-bis(hydroxymethyl)benzene is considered; it was shown that this compound does not tend to form macrocycles.     

Synthesis of ditopic ligands containing bis(1<Emphasis Type="Italic">H</Emphasis>-pyrazol-1-yl)-methane fragments

New approaches have been proposed for the synthesis of compounds containing two bis(1H-pyrazol-1-yl)methane fragments. Nucleophilic replacement of the halogen atoms in appropriate tetrabromo derivatives by pyrazoles in the superbasic system KOH-DMSO gave ditopic chelating ligands: 1,1,2,2-tetrakis(1H-pyrazol-1-yl)ethane, 1,4-bis[bis(1H-pyrazol-1-yl)methyl]benzene, and 1,4-bis[bis(3,5-dimethyl-1H-pyrazol-1-yl)methyl]benzene. 1,4-Bis[bis(1H-pyrazol-1-yl)methyl]benzene was also synthesized by reaction of 1H-pyrazole with terephthalaldehyde in the presence of thionyl chloride. 1,1,2,2-Tetrakis(1H-pyrazol-1-yl)ethane was converted into the corresponding tetraiodo and tetranitro derivatives.     

Novel fluorophores: efficient synthesis and photophysical study

[structure: see text] We have synthesized novel fluorophores by using Sonogashira reactions of 1,4-bis(dibromovinyl)benzene and 2,5-bis(dibromovinyl)thiophene with various aromatic bromides. The emission maxima of these fluorophores vary from the indigo blue to the reddish-orange region, depending on the structures of aromatic nuclei and peripheral moieties.     

Synthesis of novel cyclohexanediol-derived chiral phosphite ligands and their application in the Cu-catalyzed conjugate addition of organozinc to cyclic enones

A series of novel chiral diphosphite ligands have been synthesized from (1R,2R)-trans-1,2-cyclohexanediol, (1S,2S)-trans-1,2-cyclohexanediol, racemic trans-1,2-cyclohexanediol and chlorophosphoric acid diary ester, and were successfully employed in the Cu-catalyzed asymmetric 1,4-conjugate addition of diethylzinc to cyclohexenone with up to 99% ee. It was found that ligand 1,2-bis[(R)-1,1'-binaphthyl-2,2'-diyl]phosphitecyclohexanediol 6a derived from racemic diol skeleton can show similar catalytic performance compared with ligand (1R,2R)-bis[(R)-1,1'-binaphthyl-2,2'-diyl]phosphitecyclohexanediol 6a' derived from enantiopure startingmaterial. A significant dependence of stereoselectivity on the type of enone and the ring size of the cyclic enone was observed. Moreover, the configuration of the products was mainly determined by the configuration of the binaphthyl moieties of diphosphite ligands in the 1,4-addition of cyclic enones.     

Synthesis and characterisation of tetra-tetrazole macrocycles

The syntheses of tetra-tetrazole macrocycles, containing two bis-tetrazole units linked by a variety of alkyl-chain lengths from four to eight carbons, are described. The crystal structures of three of these derivatives are reported, and the molecular conformation in the solid state is compared to that of the previously reported tetra-tetrazole macrocycle and to other bis- and tris(tetrazole)benzene structures. The macrocycle conformation is influenced by the length of the alkyl-chain linker, the relative orientation of the tetrazole rings on the benzene ring and by intermolecular interactions. In the macrocycles based on 1,2-bis(tetrazole)benzene, the adjacent tetrazole rings on the benzene ring are prevented from becoming co-planar on intramolecular (steric) grounds. In the 1,3- and 1,4-bis(tetrazole)benzene derivatives, there is no such impediment, and a co-planar arrangement is observed where intra- and/or intermolecular stacking interactions exist. Deviations from co-planarity are associated with optimisation of intermolecular interactions between the tetrazole rings and adjacent alkyl chains. In the macrocycle based on 1,4-bis(tetrazole)benzene with four-carbon linkers, an intramolecular stacking interaction exists, which precludes the presence of any cavity. In the macrocycle based on 1,3-bis(tetrazole)benzene with six-carbon linkers, a cavity of 10.8×9.4 Å is observed for each molecule in the solid state, although the packing of adjacent molecules is such that there are no extended channels running through the crystal.     

Synthesis and Conformational Properties of Bis（calix [4] arene）

The bis(calix [4] arene)3 was synthesized in moderate yield by the reaction of p-tert-butylcalix [4] arene (1) with 1,4-bis(chloromethyl) benzene (2). The conformation of all alkylated product 4 was investigated by the variable-temperature ^1H-NMR.     

New viologen analogs: 1,4-bis[2-(pyridin-4-yl)ethenyl]benzene quaternary salts

Alkylation of 1,4-bis[2-(pyridin-4-yl)ethenyl]benzene with alkyl p-toluenesulfonates and dimethyl sulfate gave new viologen analogs, 1-alkyl-4-(2-{4-[2-(1-alkylpyridinium-4-yl)ethenyl]phenyl}ethenyl)-pyridinium bis(p-toluenesulfonates) and sulfate. Their derivatives with tetrafluoroborate and tetraphenylborate ions were also obtained. Spectral properties of the synthesized compounds were examined, and their structure was determined by X-ray analysis.