The stereoselective synthesis of (E)-octafluoro-1,3,5-hexatriene and (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene

(E)-(1,2-Difluoro-1,2-ethenediyl)bis[tributylstannane], 3, readily undergoes a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction with iodotrifluoroethene to yield (E)-octafluoro-1,3,5-hexatriene, 4, in high isomeric purity. (1Z,3E,5Z)-(1,2,3,4,5,6-Hexafluoro-1,3,5-hexenetriyl)bis[tributylstannane], 7, was sequentially prepared from (1Z,3E,5Z)-(1,2,3,4,5,6-hexafluoro-1,3,5-hexenetriyl)bis[triethylsilane], 5, which was prepared via a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction of 3 with (E)-1,2-difluoro-1-iodo-2-triethylsilylethene, 6. Pd(PPh₃)₄/CuI cross-coupling of 7 with iodotrifluoroethene gave (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene, 8.     

Preparation, crystal structure, and spectroscopic, chemical, and electrochemical properties of (2E,4E)-4-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1,3-butadiene compared with those of (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene

Wittig reaction of 3-[4-(dimethylamino)phenyl]propanal (5) with (3-guaiazulenylmethyl)triphenylphosphonium bromide (4) in ethanol containing NaOEt at 25 °C for 24 h under argon gives the title (2E,4E)-1,3-butadiene derivative 6E in 19% isolated yield. Spectroscopic properties, crystal structure, and electrochemical behavior of the obtained new extended π-electron system 6E, compared with those of the previously reported (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene (12), are documented. Furthermore, reaction of 6E with 1,1,2,2-tetracyanoethylene (TCNE) in benzene at 25 °C for 24 h under argon affords a new Diels-Alder adduct 8 in 59% isolated yield. Along with spectroscopic properties of the [π4+π2] cycloaddition product 8, the crystal structure, possessing a cis-3,6-substituted 1,1,2,2-tetracyano-4-cyclohexene unit, is shown. Moreover, reaction of 6E with (E)-1,2-dicyanoethylene (DCNE) under the same reaction conditions as the above gives no product; however, this reaction in p-xylene at reflux temperature (138 °C) for four days under argon affords a new Diels-Alder adduct 9 in 54% isolated yield. Although reaction of 6E with DCNE in toluene at reflux temperature (110 °C) for four days under argon provides 9 very slightly, reaction of 6E with dimethyl acetylenedicarboxylate (DMAD) in toluene at reflux temperature for two days under argon yields a new Diels-Alder adduct 10, in 58% isolated yield, which upon oxidation with MnO₂ in CH₂Cl₂ at 25 °C for 1 h gives 11, converting a (CH₃)₂N-4″ into CH₃NH-4″ group, in 37% isolated yield. The crystal structure of 11 supports the molecular structure 10 possessing a partial structure cis-3,6-substituted 1,2-dimethoxycarbonyl-1,4-cyclohexadiene. The title basic studies on the above are reported in detail.     

Pd(0) or Pd(II)-catalyzed ring-opening reactions of benzylidene- and alkylidenecyclopropyl ketones and aldehydes

Pd(0) catalyzed reactions of methylenecyclopropyl carbonyl compounds afforded a convenient method for the synthesis of conjugate (E,E)-1,3-diene derivatives 2 in good to excellent yields. Moreover, we also found that Pd(II)-catalyzed reactions of methylenecyclopropyl carbonyl compounds with water gave 1,5-diketones in good to high yields via a carbene-palladium intermediate. The plausible reaction mechanisms have also been provided on the basis of control and ¹⁸O-labeling experiments.     

Synthesis, structural, spectroscopic and reactivity properties of a new N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine ligand and its Cu(II) and Pd(II) complexes

A new N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine (1) complexes with Cu(II) (2) and Pd(II) (3) have been synthesized and characterized by X-ray crystallography, UV-Vis, IR, ¹H NMR and EPR spectroscopic techniques. The X-ray crystal structure of complex 2 reveals tetrahedrally distorted square-planar coordination geometry around Cu(II). The UV/Vis and EPR results indicate that the solid state geometry of 2 remains unchanged in solutions. Chemical oxidation of 3 with Ce(IV) in CHCl₃ generates relatively stable Pd(II)-phenoxyl radical complex (g = 2.0073). The results related with the chemical oxidation of 2 and 3 as well as the catalytic activity of 3 in the hydrogenation of PhNO₂ are presented.     

Reactions of (E)-1,2-di(3-guaiazulenyl)ethylene and 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene with tetracyanoethylene (TCNE) in benzene: comparative studies on the products and their spectroscopic properties

Reactions of the title ethylene derivatives, (E)-1,2-di(3-guaiazulenyl)ethylene (1) and 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (2), with a 2 M amount of TCNE in benzene at 25 °C for 24 h under argon give new cycloaddition compounds, 1,1,2,2,11,11,12,12-octacyano-3-(3-guaiazulenyl)-8-isopropyl-5,10-dimethyl-1,2,3,6,9,10a-hexahydro-6,9-ethanobenz[a]azulene (3) from 1 and 1,1,2,2,11,11,12,12-octacyano-8-isopropyl-3,3-bis(4-methoxyphenyl)-5,10-dimethyl-1,2,3,6,9,10a-hexahydro-6,9-ethanobenz[a]-azulene (4) from 2, respectively, in 66 and 87% isolated yields. Comparative studies on the above reactions as well as the spectroscopic properties of the unique products 3 and 4, possessing interesting molecular structures, are reported and, further, a plausible reaction pathway for the formation of these products is described.     

Syntheses and structures of iron carbonyl complexes derived from N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine and N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine

The reaction of N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine (1) with Fe₂(CO)₉ in refluxing acetonitrile yielded di-(μ₃-thia)nonacarbonyltriiron (2), μ-[N-(5-methyl-2-thienylmethyl)-η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido]hexacarbonyldiiron (3), and N-(5-methyl-2-thienylmethylidene)amine (4). If the reaction was carried out at 45 °C, di-μ-[N-(5-methyl-2-thienylmethylidene)-η¹(N);η¹(S)-2-thiolethylamino]-μ-carbonyl-tetracarbonyldiiron (5) and trace amount of 4 were obtained. Stirring 5 in refluxing acetonitrile led to the thermal decomposition of 5, and ligand 1 was recovered quantitatively. However, in the presence of excess amount of Fe₂(CO)₉ in refluxing acetonitrile, complex 5 was converted into 2-4. On the other hand, the reaction of N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine (6) with Fe₂(CO)₉ in refluxing acetonitrile produced 2, μ-[N-(6-methyl-2-pyridylmethyl)-η¹ (N_py);η¹:η¹(N); η¹:η¹(S)-2-thiolatoethylamido]pentacarbonyldiiron (7), and μ-[N-(6-methyl-2-pyridylmethylidene)-η²(C,N);η¹:η¹(S)-2- thiolethylamino]hexacarbonyldiiron (8). Reactions of both complex 7 and 8 with NOBF₄ gave μ-[(6-methyl-2-pyridylmethyl)-η¹(N_py);η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido](acetonitrile)tricarbonylnitrosyldiiron (9). These reaction products were well characterized spectrally. The molecular structures of complexes 3, 7-9 have been determined by means of X-ray diffraction. Intramolecular 1,5-hydrogen shift from the thiol to the methine carbon was observed in complexes 3, 7, and 9.     

Convenient synthesis of 3-fluoro-4,5-diphenylfuran-2(5H)-one from benzoin ethers : Novel and efficient Z-E isomerisation and cyclisation of 2-fluoroalkenoate precursors, substitution of vinylic fluorine

Mixtures of ethyl (E)- and (Z)-4-alkoxy-2-fluoro-3,4-diphenylbut-2-enoates (6-8) prepared from benzoin ethers and ethyl 2-(diethoxyphosphoryl)-2-fluoroacetate were transformed in high yields to the target 3-fluoro-4,5-diphenylfuran-2(5H)-one (14) using bromine in tetrachloromethane at room temperature. The non-cyclisable Z-isomers 6b-8b were gradually isomerised to the cyclisable E-isomers 6a-8a during the process. The reaction of the (E)-butenoates 6a-8a with boron trifluoride led to furanone 14, while in Z-isomers 6b-8b both alkoxy group and vinylic fluorine were substituted with bromine during the reaction. Mechanisms for both complex reactions have been proposed. Furanone 14 was transformed to 2-[tert-butyl(dimethyl)silyloxy]-3-fluoro-4,5-diphenylfuran (18) as a novel building block.     

Ultrasound-assisted convenient synthesis of hypolipidemic active natural methoxylated (E)-arylalkenes and arylalkanones

An ultrasound-assisted convenient method was developed for the conversion of toxic methoxylated cis-isomer of arylalkenes into its hypolipidemic active trans-isomer. Treatment of cis-isomer or mixture of all three isomers (1a-1j) with ammonium formate and 10% Pd/C gave arylalkanes (2a-2j), which upon oxidation with DDQ in anhydrous dioxane containing a little amount of silica gel, provided (E)-arylalkenes (3a-3g) in 42-72% yield depending upon the substituents attached at the aryl ring. The same method, upon addition of a few drops of water, provided hypolipidemic active arylalkanones (3h-3j) in 59-65% yield.     

A facile stereoselective synthesis of difunctionalized 1,3-dienes containing tin and halogen via hydrozirconation of (Z)-3-(tributylstannyl)alk-3-en-1-ynes

Sonogashira coupling of (E)-α-iodovinylstannanes 1 with (trimethylsilyl)acetylene gave (Z)-1-(trimethylsilyl)-3-(tributylstannyl)alk-3-en-1-ynes 2, which underwent a desilylation reaction to afford (Z)-3-(tributylstannyl)alk-3-en-1-ynes 3 in high yields. (1E,3Z)-1-Halo-3-(tributylstannyl)-substituted 1,3-dienes 5 could be synthesized stereoselectively via hydrozirconation of (Z)-3-(tributylstannyl)alk-3-en-1-ynes 3, followed by trapping with iodine or NBS.     

Crystal and solution structures of di-n-butyltin(IV) complexes of 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol and benzoic acid derivatives: En route to elegant self-assembly via modulation of the tin coordination geometry

Reactions of ⁿBu₂SnCl(L¹) (1), where L¹ = acid residue of 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol, with various substituted benzoic acids in refluxing toluene, in the presence of triethylamine, yielded dimeric mixed ligand di-n-butyltin(IV) complexes of composition [ⁿBu₂Sn(L¹)(L^2-6)]₂ where L² = benzene carboxylate (2), L³ = 2-[(E)-2-(2-hydroxy-5-methylphenyl)-1-diazenyl]benzoate (3), L⁴ = 5-[(E)-2-(4-methylphenyl)-1-diazenyl]-2-hydroxybenzoate (4), L⁵ = 2-{(E)-4-hydroxy-3-[(E)-4-chlorophenyliminomethyl]-phenyldiazenyl}benzoate (5) and L⁶ = 2-[(E)-(3-formyl-4-hydroxyphenyl)-diazenyl]benzoate (6). All complexes (1-6) have been characterized by elemental analyses, IR, ¹H, ¹³C and ¹¹⁷Sn NMR and ¹¹⁹Sn Mössbauer spectroscopy and their structures were determined by X-ray crystallography, complemented by ¹¹⁷Sn CP-MAS NMR spectroscopy studies in the solid state. The crystal structure of 1 reveals a distorted trigonal bipyramidal coordination geometry around the Sn-atom where the Cl- and N-atoms of ligand L¹ occupy the axial positions. In complexes 2-5, the molecules are centrosymmetric dimers in which the Sn-atoms are connected by asymmetric μ-O bridges through the quinoline O-atom to give an Sn₂O₂ core. The differences in the Sn-O bond lengths within the bridge range from 0.28 to 0.48 Å, with the longer of the Sn-O distances being in the range 2.56-2.68 Å and the most symmetrical bridge being in 5. The carboxylate group is almost symmetrically bidentate coordinated to the tin atom in 5 (Sn-O distances of 2.327(2) and 2.441(2) Å), unlike the other complexes in which the distance of the carboxylate carbonyl O-atom from the tin atom is in the range 2.92-3.03 Å. The structure of 5 displays a more regular pentagonal bipyramidal coordination geometry about each tin atom than in 2-4. In contrast, the centrosymmetric dimeric structure of 6 involves asymmetric carboxylate bridges, resulting in a different Sn₂C₂O₄ motif. The Sn-O bond lengths in the bridge differ by about 0.6 Å, with the longer distance involving the carboxylate carbonyl O-atom (2.683(2) and 2.798(2) Å for two molecules in the asymmetric unit). The carboxylate carbonyl O-atom has a second, even longer intramolecular contact to the Sn-atom to which the carboxylate group is primarily coordinated, with these Sn?O distances being as high as 3.085(2) and 2.898(2) Å. If the secondary interactions are considered, all the di-n-butyltin(IV) complexes (2-6) display a distorted pentagonal bipyramidal arrangement about each tin atom in which the n-butyl groups occupy the axial positions.     

Dibutyltin(IV) complexes of the 5-[(E)-2-(Aryl)-1-diazenyl]-2-hydroxybenzoic acid ligand: an investigation of structures by X-ray diffraction, solution and solid state tin NMR, electrospray ionisation MS and assessment of in vitro cytotoxicity

A series of dibutylbis{5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoato}tin(IV) complexes, Bu₂Sn(LH)₂, have been prepared and characterized by ¹H, ¹³C, ¹¹⁹Sn NMR and ESI mass spectrometry in solution. The structures of the complexes Bu₂Sn(L¹H)₂ (1), Bu₂Sn(L³H)₂ (3), Bu₂Sn(L⁴H)₂ (4), and Bu₂Sn(L⁶H)₂ (6) (L = 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoate: aryl = phenyl (L¹H), 3-methylphenyl (L³H), 4-methylphenyl (L⁴H) and 4-bromophenyl (L⁶H)) were determined by X-ray crystallography and ¹¹⁷Sn CP-MAS NMR spectroscopy in the solid state. In general, the complexes were found to adopt a skew-trapezoidal bipyramidal arrangement around the tin atom. In addition, there are weak bridging intermolecular Sn?O contacts in complexes 1 and 3, but not in 4 and 6, where one of the hydroxy oxygen atoms from a neighboring molecule coordinates weakly with the Sn atom, thereby completing a seventh coordination site in the extended Sn coordination sphere. The Sn?O distance is 3.080(2) and 3.439(2) Å in 1 and 3, respectively, which are significantly shorter than the sum of the van der Waals radii of the Sn and O atoms (∼3.8 Å). In 1, this Sn?O interaction links the molecules into polymeric chains. In 3, these interactions link pairs of molecules into head-to-head dimeric units. The in vitro cytotoxicity of compound 2 indicates better results than cisplatin and etoposide against seven well characterized human tumor cell lines.     

Zn(II), Cd(II) and Hg(II) complexes with 1-(p-methoxybenzyl)-2-(p-methoxyphenyl)benzimidazole: Syntheses, structures and luminescence

Five coordination compounds Zn(mbmpbi)₂Cl₂ (1), Zn(mbmpbi)₂Br₂ (2), Cd(mbmpbi)₂Cl₂ (3), Hg(mbmpbi)₂Cl₂ (4) and Hg(mbmpbi)₂Br₂ (5) were synthesized by the reaction of 1-(p-methoxybenzyl)-2-(p-methoxyphenyl)benzimidazole (mbmpbi) with the corresponding metal halides. The complexes have been characterized by elemental analysis, conductance measurements, FT-IR, ¹H NMR and photoluminescence spectral studies. The ligand mbmpbi exhibits the N-benzimidazole coordination. The structures of 3-5 have been determined by single crystal X-ray diffraction. These three complexes are isostructural, crystallizing in the monoclinic system, P2/n space group with a distorted tetrahedral geometry around the metal ion. Zn(II) and Cd(II) complexes show strong blue emission in solid state at room temperature.     

Ti(III)-promoted cyclizations. Application to the synthesis of (E)-endo-bergamoten-12-oic acids. Moth oviposition stimulants isolated from Lycopersicon hirsutum

The Ti(III)-promoted radical cyclization of epoxyenone 8 is described as the key step to access the diol 10 as a convenient starting material of the target molecules. The synthesis of β-(E)-endo-bergamoten-12-oic acid 2a from (+)-8,9-epoxycarvone 8 was successfully achieved by Suzuki-Miyaura coupling of the terminal alkene 20 with β-iodomethacrylate 21c, followed by deprotection and dehydration processes. Moreover, synthesis of the α-(E)-endo-1-hydroxy-bergamoten-12-oic acid derivative 34 was achieved by iterative elongation processes of the diol 10 lateral chain.     

Highly stereoselective synthesis of para-substituted (E)-N-styrylcarbazoles via sequential silylative coupling-Hiyama coupling reaction

A series of new para-substituted (E)-(N)-styrylcarbazoles, i.e., eight (E)-9-[2-(aryl)ethenyl]-9H-carbazoles (5-12) and 1,4-bis[(E)-2-(9H-carbazol-9-yl)vinyl]benzene (13), have been synthesized in high yield and stereoselectively by a sequential silylative coupling-Hiyama coupling reaction, i.e., coupling of commercially available 9-vinylcarbazole with vinyltriethoxysilane or divinyltetramethyldisiloxane in the presence of [RuHCl(CO)(PCy₃)₂] (I), followed by Pd (II) catalyzed cross-coupling with para-substituted iodobenzenes.The tandem procedure has facilitated the synthesis of 13. X-ray structures of the intermediate silylvinylcarbazole (4), as well as products 12 and 13 have been obtained.     

Cobalt(II), nickel(II) and zinc(II) coordination compounds derived from aromatic amines

The structural and spectroscopic characterization of coordination compounds of four aromatic amines derived from benzimidazole, 2-aminobenzimidazole (L1), 1-(S-methylcarbodithioate)-2-aminobenzimidazole (L2), 2-(2-aminophenyl)-1H-benzimidazole (L3) and 6,6-dimethyl-5H-benzimidazolyl[1,2-c]quinazoline (L4) are reported. Cobalt(II) [Co(L1)₂(CH₃COO)₂] (1) and nickel(II) [Ni(L1)₂(CH₃COO)₂] (2) acetate coordination compounds of L1 are discussed. The synthesis and the X-ray crystal structure of the new 1-(S-methylcarbodithioate)-2-aminobenzimidazole (L2) is informed, together with its cobalt(II) [Co(L2)₂Cl₂] (3), [Co(L2)₂Br₂] (4) and zinc(II) [Co(L2)₂Cl₂] (5), [Zn(L2)₂Br₂] (6) coordination compounds. In these compounds the imidazolic nitrogen is coordinated to the metal center, while the ArNH₂ and the S-methylcarbodithioate groups do not participate as coordination sites. A co-crystal of L1 and L2 is analyzed. Structural analyses of the coordination compounds of L3 showed that this ligand behaves as a bidentate ligand through the aniline and the imidazole groups forming six membered rings in the cobalt(II) [Co(L3)Cl₂] (7) and zinc(II) [Zn(L3)Cl₂] (8) compounds, as well as the nickel(II) nitrate [Ni(L3)₂(H₂O)₂](NO₃)₂ (9). The quinazoline L4 was produced by insertion of one acetone molecule and water elimination in L3, its X-ray crystal diffraction analysis, as well as that of its zinc(II) coordination compound [Zn(L4)₂Cl₂] (10), are discussed.     

Microwave-assisted synthesis of novel bis(2-thioxothiazolidin-4-one) derivatives as potential GSK-3 inhibitors

(5Z,5′Z)-3,3′-(1,4-Phenylenebis(methylene)-bis-(5-arylidene-2-thioxothiazolidin-4-one) derivatives (5a-r) have been synthesized by the condensation reaction of 3,3′-(1,4- or 1,3-phenylenebis(methylene))bis(2-thioxothiazolidin-4-ones) (3a,b) with suitably substituted aldehydes (4a-f) or 2-(1H-indol-3-yl)2-oxoacetaldehydes (8a-c) under microwave conditions. The bis(2-thioxothiazolidin-4-ones) were prepared from the corresponding primary alkyl amines (1a,b) and di-(carboxymethyl)-trithiocarbonyl (2). The 2-(1H-indol-3-yl)-2-oxoacetaldehydes (8a-c) were synthesized from the corresponding acid chlorides (7a-c) using HSnBu₃.     

Synthesis of 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-ones via Pd-catalyzed regioselective cross-coupling reaction and cyclization

An efficient and novel route for the synthesis of 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-one 1 via palladium-catalyzed site-selective cross-coupling reaction and cyclization process was described. Reaction of 3-bromo-4-trifloxy-quinolin-2(1H)-one 3 with arylboronic acid catalyzed by PdCl₂(PPh₃)₂ afforded 3-bromo-4-aryl-quinolin-2(1H)-one 4, which then reacted with 2-ethynylaniline 5 via Pd-catalyzed Sonogashira coupling and CuI-mediated cyclization leading to the desired 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-one 1 in good yields.     

Self-assembly of diorganotin(IV) 2-{[(E)-1-(2-oxyaryl)alkylidene]amino}acetates: An investigation of structures by X-ray diffraction, solution and solid-state tin NMR, and electrospray ionization MS

The diorganotin(IV) compounds, [Me₂SnL²(OH₂)]₂ (1), [ⁿBu₂SnL²(OH₂)]₂ (2), [ⁿBu₂SnL¹]₃ · 0.5C₃H₆O (3), [ⁿBu₂SnL³]₃ · 0.5C₆H₆ (4) and [Ph₂SnL³]_n · 0.5C₆H₆ (5) (L = carboxylic acid residue, i.e., 2-{[(E)-1-(2-oxyaryl)alkylidene]amino}acetate), were synthesized by treating the appropriate diorganotin(IV) dichloride with the potassium salt of the ligand in anhydrous methanol.The reaction of Ph₂SnL² (L = 2-{[(E)-1-(2-oxyphenyl)ethylidene]amino}acetate) with 1,10-phenanthroline (Phen) yielded a 1:1 adduct of composition, [Ph₂SnL²(Phen)] (6).The crystal structures of 1-6 were determined.The crystal of 1 is composed of centrosymmetric dimers of the basic Me₂SnL²(OH₂) moiety, where the two Sn-centres are linked by two asymmetric Sn-O?Sn bridges involving the carboxylic acid O atom of the ligand and a long Sn?O distance of 3.174(2) Å.The dimers are further linked into columns by hydrogen bonds.The coordination geometry about the Sn atom is a distorted pentagonal bipyramid with the two methyl groups in axial positions.The structure of 2 is similar.The same Sn atom coordination geometry is observed in compound 3, which is a cyclic trinuclear[ⁿBu₂SnL¹]₃ compound. Each Sn atom is coordinated by the phenoxide O atom, one carboxylate O atom and the imino N atom from one ligand and both the exo- and endo-carboxylate O atoms (mean Sn-O(exo): 2.35 Å; Sn-O(endo): 2.96 Å) from an adjacent ligand to form the equatorial plane, while the two butyl groups occupy axial positions. Compound 4 was found to crystallize in two polymorphic forms. The Sn-complex in both forms has a trinuclear [ⁿBu₂SnL³]₃ structural motif similar to that found in 3. In compound 5, distorted trigonal bipyramidal Ph₂SnL³ units are linked into polymeric cis-bridged chains by a weak Sn?O interaction (3.491(2) Å) involving the exocyclic O atom of the tridentate ligand of a neighboring Sn-complex unit. This interaction completes a highly distorted octahedron about the Sn atom, where the weakly coordinated exocyclic O atom and one phenyl group are trans to one another. In contrast, a monomeric distorted pentagonal bipyramidal geometry is found for adduct 6 where the Sn-phenyl groups occupy the axial positions. The solution and solid-state structures are compared by using ¹¹⁹Sn NMR chemical shift data. Compounds 1-6 were also studied using ESI-MS and their positive- and negative-ions mass fragmentation patterns are discussed.     

Photochemistry of 3,6-bis(styryl)pyridazines in solution and in neat liquid crystalline phase—optical switching and imaging techniques

3,6-Bis(styryl)pyridazines 1a-f with 2-6 alkoxy groups show on irradiation in solution a stereoisomerization which leads to a photostationary state of (E,E)- and (E,Z)-isomer. Sensitizing and quenching experiments reveal that the (E,E)→(E,Z) route is a pure triplet process, whereas the (E,Z)→(E,E) route can have a minor singlet by-reaction.Hexyloxy or dodecyloxy chains on the terminal benzene rings convey the (E,E)-isomers of compounds 1a,b,d-f thermotropic liquid crystalline properties. In particular S_A, S_C, and S_F/I phases were studied with regard to their photochemical behavior. Depending on the system, photodegradation of the smectic phase to the isotropic melt (S→I) or photoinduction of the smectic phase (I→S) can be achieved by alteration of the (E,E)/(E,Z) ratio. These processes represent the basis for imaging techniques (writing and erasing of information).     

Cyclopalladated complexes with N-(benzoyl)-N-(2,4-dimethoxybenzylidene)hydrazine: syntheses, characterization and structural studies

Cyclopalladated complexes with the Schiff base N-(benzoyl)-N^′-(2,4-dimethoxybenzylidene)hydrazine (H₂L, 1) have been described. The reaction of 1 with Li₂[PdCl₄] in methanol yields the complex [Pd(HL)Cl] (2). [Pd(HL)(CH₃CN)Cl] (3) has been prepared by dissolving 2 in acetonitrile. In methanol-acetonitrile mixture, treatment of 2 with two mole equivalents of PPh₃ produces [PdL(PPh₃)] (4) and that with one mole equivalent of PPh₃ produces [Pd(HL)(PPh₃)Cl] (5). Crystallization of 2 from dmso-d₆ results into isolation of [Pd(HL)((CD₃)₂SO)Cl] (6). In 2, the monoanionic ligand (HL⁻) is C,N,O-donor and the Cl-atom is trans to the azomethine N-atom. In 3, 5 and 6, HL⁻ is C,N-donor and the Cl-atom is trans to the metallated C-atom. The remaining fourth coordination site is occupied by the N-atom of CH₃CN, the P-atom of PPh₃ and the S-atom of (CD₃)₂SO in 3, 5 and 6, respectively. Thus on dissolution in acetonitrile and dmso and in reaction with stoichiometric PPh₃ the incoming ligand imposes a rearrangement of the coordinating atoms on the palladium centre. On the other hand, in presence of excess PPh₃ deprotonation of the amide functionality in 2 occurs and the Cl-atom is replaced by the P-atom of PPh₃ to form 4. Here the dianionic ligand (L²⁻) remains C,N,O-donor as in 2. The compounds have been characterized with the help of elemental analysis (C, H, N), infrared, ¹H NMR and electronic absorption spectroscopy. Molecular structures of 3, 4, and 6 have been determined by X-ray crystallography.