Controlling conformations and physical properties of meso-tetrakis(phenylethynyl)porphyrins by ring fusion: synthesis, properties and structural characterizations

The boron trifluoride-catalyzed Rothemund condensations of phenylpropargylaldehyde with 4,7-dihydro-4,7-ethano-2H-isoindole or 3,4-diethylpyrrole in dichloromethane at low temperature give 5,10,15,20-tetrakis(phenylethynyl)porphyrins bearing bicyclo[2.2.2]octadiene and octaethyl substituents, respectively. The former undergoes a retro Diels-Alder reaction to afford 5,10,15,20-tetrakis(phenylethynyl)benzoporphyrin quantitatively. The different conformations of the porphyrin periphery were determined by X-ray diffraction and their redox and spectroscopic properties have been investigated.     

Electrophilic behavior of the pi delocalized azepinium ion: Friedel-Crafts reactions with benzenes and five-membered aromatic heterocycles

[reaction: see text] Although the reactivity of tropylium ion with aromatic substrates is low, the reaction of azepinium ion with aromatic substrates such as benzene, phenol, furan, and thiophene resulted in the formation of 2-aryl-2H-azepine as a major product. An exceptional result in the formation of ring-contracted product was observed in the reaction with pyrrole.     

PHOTOLYSIS MECHANISM OF AQUEOUS TYROSINE UPON EXCITATION OF THE SECOND ABSORPTION BAND

Abstract— The formation mechanism of tyrosinyl radical was studied for aqueous solutions of tyrosine under irradiation at 235 nm which falls into the second absorption band. The work is based upon the analysis of the rate of bityrosine production for steady-state excitation at low intensity. The results indicate that monophotonic O-H bond cleavage of tyrosine, presumably involving the upper excited triplet state, is the initial photoprocess leading to the tyrosinyl radical when tyrosine is excited into the second absorption band.     

Thermal cis–trans isomerization and decomposition of polyacetylene

Thermal cis-trans isomerization and decomposition of polyacetylene film prepared with a Ti(OC₄H₉)₄–Al(C₂H₅)₃ (Al/Ti = 4) system were investigated under inert gas or in vacuum by means of thermal analysis and infrared spectroscopy. Thermograms of differential thermal analysis of cis-polyacetylene revealed the existence of two exothermic peaks at 145 and 325°C and one endothermic peak at 420°C which were assigned to cis-trans isomerization, hydrogen migration accompanied with crosslinking reaction, and thermal decomposition, respectively. The isomerization was followed by infrared spectroscopy over the temperature range 75–115°C. The reaction did not obey simple kinetics. The apparent activation energy for the cis-trans isomerization was 17.0 kcal/mole for the polymer containing 88% cis configuration and increased with increasing trans content up to 38.8 kcal/mole for 80% trans content.     

Innovative reactions mediated by zirconocene

Radical reactions mediated by Schwartz reagent and zirconocene(alkene) complex are firstly described. Schwartz reagent is a promising alternative to tributyltin hydride and the first transition metal hydrido complex used as a radical mediator in organic synthesis. A zirconocene(alkene) complex effects single electron transfer to alkyl halide to generate the corresponding alkyl radical. Secondly, serendipitous allylic C-H bond activation of the coordinating alkene of zirconocene(alkene) complex and its application to organic synthesis are summarized. By utilizing equilibrium between zirconocene(alkene) and zirconocene 2-alkenyl hydride, reaction of acid chloride with zirconocene(alkene) provides the corresponding homoallylic alcohol by sequential attacks of the hydride and 2-alkenyl moieties. A set of hydride and 2-alkenyl attacks on 1,4-diketone yields 6-heptene-1,4-diol derivative in high yield with high stereoselectivity. Selective capture of the hydride with diisopropyl ketone gives zirconocene 2-alkenyl alkoxide, which is a useful reagent for stereoselective allylation of aldehyde and imine. alpha-Halo carbonyl compounds undergo radical allylation with the zirconocene 2-alkenyl alkoxide which serves as a substitute for allyltin.     

Synthesis and reactivity of a (mu-1,1-hydroperoxo)(mu-hydroxo)dicopper(II) complex: ligand hydroxylation by a bridging hydroperoxo ligand

A new tetradentate tripodal ligand (L3) containing sterically bulky imidazolyl groups was synthesized, where L3 is tris(1-methyl-2-phenyl-4-imidazolylmethyl)amine. Reaction of a bis(mu-hydroxo)dicopper(II) complex, [Cu2(L3)2(OH)2]2+ (1), with H2O2 in acetonitrile at -40 degrees C generated a (mu-1,1-hydroperoxo)dicopper(II) complex [Cu2(L3)2(OOH)(OH)]2+ (2), which was characterized by various physicochemical measurements including X-ray crystallography. The crystal structure of 2 revealed that the complex cation has a Cu2(mu-1,1-OOH)(mu-OH) core and each copper has a square pyramidal structure having an N3O2 donor set with a weak ligation of a tertiary amine nitrogen in the apex. Consequently, one pendant arm of L3 in 2 is free from coordination, which produces a hydrophobic cavity around the Cu2(mu-1,1-OOH)(mu-OH) core. The hydrophobic cavity is preserved by hydrogen bondings between the hydroperoxide and the imidazole nitrogen of an uncoordinated pendant arm in one side and the hydroxide and the imidazole nitrogen of an uncoordinated pendant arm in the other side. The hydrophobic cavity significantly suppresses the H/D and 16O/18O exchange reactions in 2 compared to that in 1 and stabilizes the Cu2(mu-1,1-OOH)(mu-OH) core against decomposition. Decomposition of 2 in acetonitrile at 0 degrees C proceeded mainly via disproportionation of the hydroperoxo ligand and reduction of 2 to [Cu(L3)]+ by hydroperoxo ligand. In contrast, decomposition of a solid sample of 2 at 60 degrees C gave a complex having a hydroxylated ligand [Cu2(L3)(L3-OH)(OH)2]2+ (2-(L3-OH)) as a main product, where L3-OH is an oxidized ligand in which one of the methylene groups of the pendant arms is hydroxylated. ESI-TOF/MS measurement showed that complex 2-(L3-OH) is stable in acetonitrile at -40 degrees C, whereas warming 2-(L3-OH) at room temperature resulted in the N-dealkylation from L3-OH to give an N-dealkylated ligand, bis(1-methyl-2-phenyl-4-imidazolylmethyl)amine (L2) in approximately 80% yield based on 2, and 1-methyl-2-phenyl-4-formylimidazole (Phim-CHO). Isotope labeling experiments confirmed that the oxygen atom in both L3-OH and Phim-CHO come from OOH. This aliphatic hydroxylation performed by 2 is in marked contrast to the arene hydroxylation reported for some (mu-1,1-hydroperoxo)dicopper(II) complexes with a xylyl linker.     

Synthesis of block copolymer segments containing different ratios of ethylene and 5-norbornen-2-yl acetate

Block copolymerization of ethylene with 5-norbornen-2-yl acetate (1) by the nickel catalyst system [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide]Ni(eta1-CH2Ph)(PMe3) (2) and Ni(COD)2 (bis(1,4-cyclooctadiene)nickel) (3) produces a variety of block copolymer structures that demonstrate microphase separation. Typical block copolymerizations were carried out in an autoclave charged with a solution of the catalyst mixture and 1 (0.15 M) in toluene. The autoclave was sealed and exposed to PC2H4 = 50 psi for a period of time (T1). A pressure jump to PC2H4 = 1100 psi was then applied and the reaction allowed to proceed for another predetermined interval (T2). Independent experiments were performed to isolate and examine the molecular weight and comonomer composition of the first block. Narrow molecular weight distributions and the increase of polymer molecular weight with increases in T1 or T2 are consistent with a product in which an initial block is formed at low ethylene pressures and quantitatively converted to a block copolymer by the jump to high pressure. Transmission electron microscopy confirms that the materials are microphase separated.     

Control of particle alignment in water by an alternating electric field

We attempted to align a large number of silica particles dispersed in aqueous solution by controlling the alternating electric field between the two electrodes (400 microm apart). Relatively large particles (9.9 microm) were found to align forming strings in the direction parallel to the electric field while relatively small particles (2.0 and 4.9 microm) were observed to align making stripes in the direction perpendicular to the field. The number of stripes formed by particles between the electrodes increased with increasing frequency of the alternating field. This peculiar perpendicular particle alignment appeared when the contribution to particle alignment of electroosmotic flow exceeded that of dielectric polarization and the osmotic flow was found to be stronger around the particles than in the vicinity of the electrode surface.     

Stable metallic behavior and antiferromagnetic ordering of Fe(III) d spins in (EDO-TTFVO)2.FeCl4

We report the crystal structure and physical properties of the 2:1 FeCl4- salt of a new donor molecule, EDO-TTFVO. Crystal structure analysis of this salt revealed that the donor molecules formed a beta' '-type two-dimensional conducting layer, and there is a short S...Cl contact between the donor molecules and the FeCl4- ions, which is expected to mediate a strong pi-d interaction. This salt showed a stable metallic conducting behavior down to 0.3 K and an antiferromagnetic ordering at TN approximately 3.0 K, indicating that this salt becomes a new antiferromagnetic molecular metal at ambient pressure. The appearance of the magnetic ordering is considered to originate from the strong pi-d interactions between the donor molecules and the FeCl4- ions because the field dependence of magnetoresistances was remarkably affected below the antiferromagnetic transition temperature.     

Palladium-catalyzed [3 + 2] cycloaddition reaction using 2-(sulfonylmethyl)- or 2-(cyanomethyl)allyl carbonate

Reaction of ethyl 2-(sulfonylmethyl)- or 2-(cyanomethyl)allyl carbonate with α,β-unsaturated esters or ketones in the presence of PD₂(dba)₃·.CHCl₃-dppe catalyst gave highly functionalized cyclopentanes regio-selectively in good yields.