Strongly fluorescent ethylene‐bridged poly(para‐phenylene) ladder polymers

We have synthesized novel, fully soluble ethylene‐bridged para‐phenylene ladder polymers. The synthesis of our ladder poly(dihydrophenanthrene)s (LPDPs) was achieved via an aryl‐aryl homocoupling according to Yamamoto, followed by a polymer‐analogous pinacolization with SmI₂. The resulting, strongly fluorescent polymers were characterisized by NMR, UV/Vis‐ and PL measurements.     

Characterization of para‐substituted benzamidoximes and benzamidinium salts by 15N NMR spectroscopy

¹⁵N NMR data for a series of 12 para‐substituted benzamidoximes and benzamidinium salts were determined in dimethyl sulfoxide. For the amino group of benzamidoximes ¹J(N,H) coupling constants were determined using polarization transfer techniques; the other ¹⁵N atoms were not detectable owing to fast exchange processes and, thus, standard proton noise decoupled spectra had to be measured. The ¹⁵N NMR chemical shifts of the oxime‐type nitrogen atom and the benzamidinium amino group (with two exceptions) correlate with Hammett σ° values (r²>0.95). ¹⁵N NMR shift data are a suitable and sensitive means for characterizing far‐ranging electronic substituent effects in these functional groups. Additionally, ¹³C NMR data in dimethyl sulfoxide solution are given. All spectroscopic data will be used for investigations into the mechanisms of the enzymes involved in the metabolic cycle of oxidation and reduction of benzamidines and benzamidoximes. Copyright © 2002 John Wiley & Sons, Ltd.     

Ethylene polymerization by chromium complexes with phosphorous‐bridged bisphenoxy ligand

Chromium catalysts combined with phosphorous‐bridged bisphenoxy ligands were found to be highly active for ethylene polymerization. The most efficient catalyst precursor among them, generated by combining bis[3‐tert‐butyl‐5‐methyl‐2‐hydroxyphenyl](phenyl)phosphine hydrochloride ( 1a ) and CrCl₃(THF)₃, was characterized. X‐ray analysis of (3‐tert‐butyl‐5‐methyl‐2‐phenoxy)(3‐tert‐butyl‐5‐methyl‐ 2‐hydroxyphenyl)(phenyl)phosphine bis(tetrahydrofuran)chromium dichloride ( 6 ), obtained by the reaction of 1a and CrCl₃(THF)₃ in the presence of NaH, revealed a unique structure in which one phenol moiety of the bisphenol did not coordinate to the chromium center. Complex 6 showed higher activities than those observed in the in situ catalyst system. Polyethylene of various molecular weights was obtained with differing activators. The highest activity (113.5 kg mmol (cat)^?1 h^?1) was observed when TIBA/TB was used as a cocatalyst. A medium molecular weight polymer with narrow molecular weight distribution (M_w = 128,700, M_w/M_n = 1.8) was obtained using a 6 ‐TIBA/B(C₆F₅)₃ system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3668–3676, 2007     

Variation of hydrogen‐bonded networks in hexa­fluoro­phosphate salts of amidate‐bridged dirhodium(II,III) complexes with axial aqua ligands

In diaqua­tetra‐μ‐acetamidato‐κ⁴N:O;κ⁴O:N‐di­rhodium(II,III) hexa­fluoro­phosphate, [Rh₂(C₂H₄NO)₄(H₂O)₂]PF₆, and diaqua­tetra‐μ‐acetamidato‐κ⁴N:O;κ⁴O:N‐di­rho­dium(II,III)hexa­fluoro­phosphate dihydrate, [Rh₂(C₂H₄NO)₄(H₂O)₂]PF₆·2H₂O, the cations and anions lie on inversion centers. Diaqua­tetra‐μ‐propionamidato‐κ⁴N:O;κ⁴O:N‐dirhodium(II,III) hexa­fluoro­phosphate dihydrate, [Rh₂(C₃H₆NO)₄(H₂O)₂]PF₆·2H₂O, and diaqua­tetra‐μ‐butyramidato‐κ⁴N:O;κ⁴O:N‐dirhodium(II,III) hexa­fluoro­phosphate, [Rh₂(C₄H₈NO)₄(H₂O)₂]PF₆, crystallize with two crystallographically independent complexes that lie on inversion centers. In all of the structures, the dirhodium units are hydrogen bonded to one another. The hydrogen‐bonded networks vary with the alkyl substituents.     

Solvent and substituent effects on the electrochemical oxidation of para‐ and meta‐substituted anilines

Electrochemical oxidation of 15 para‐ and meta‐substituted anilines in different mole fractions of water in 2‐methylpropan‐2‐ol has been investigated in the presence of 0.1 M sulfuric acid as a supporting electrolyte. The oxidation potential data of anilines correlate well with the Brown–Okamoto's substituent constants affording a negative reaction constant. The effect of para‐ and meta‐substituents on the oxidation potential confirms to Swain's F and R, affording negative reaction constants. The oxidation potential values also correlate satisfactorily with macroscopic solvent parameter such as relative permittivity, ε_r. The results of Kamlet–Taft multiple correlation analysis show that specific solute–solvent interactions play a dominant role in governing the reactivity. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 289–297, 2007     

Synthesis of highly branched polyethylene using para‐phenyl‐substituted α‐diimine nickel catalysts

A series of para‐phenyl‐substituted α‐diimine nickel complexes, [(2,6‐R₂‐4‐PhC₆H₂N═C(Me))₂]NiBr₂ (R = ⁱPr ( 1 ); R = Et ( 2 ); R = Me ( 3 ); R = H ( 4 )), were synthesized and characterized. These complexes with systematically varied ligand sterics were used as precatalysts for ethylene polymerization in combination with methylaluminoxane. The results indicated the possibility of catalytic activity, molecular weight and polymer microstructure control through catalyst structures and polymerization temperature. Interestingly, it is possible to tune the catalytic activities ((0.30–2.56) × 10⁶ g (mol Ni·h)^?1), polymer molecular weights (M_n = (2.1–28.6) × 10⁴ g mol^?1) and branching densities (71–143/1000 C) over a very wide range. The polyethylene branching densities decreased with increasing bulkiness of ligand and decreasing polymerization temperature. Specifically, methyl‐substituted complex 3 showed high activities and produced highly branched amorphous polyethylene (up to 143 branches per 1000 C).     

Two new oximate‐bridged square‐planar dinuclear nickel(II) complexes

The synthesis and characterization of two new dinuclear nickel(II) complexes, namely bis{μ‐3‐[2‐(dimethylamino)ethylimino]butan‐2‐one oximato}dinickel(II) bis(perchlorate) acetonitrile solvate, [Ni₂(C₈H₁₆N₃O)₂](ClO₄)₂·CH₃CN, (I), and bis{μ‐3‐[2‐(dimethylamino)ethylimino]‐3‐phenylpropan‐2‐one oximato}dinickel(II) bis(perchlorate), [Ni₂(C₁₃H₁₈N₃O)₂](ClO₄)₂, (II), are reported. Single‐crystal X‐ray analyses of the complexes reveal that the nickel(II) ions are in square‐planar N₃O environments and form six‐membered (NiNO)₂ metallacycles. The cation in (II) possesses crystallographically imposed inversion symmetry.     

Synthesis and structures of cycloalkylidene‐bridged mixed cyclopentadienyl‐indenyl tetracarbonyl diruthenium complexes

A series of cycloalkylidene‐bridged mixed cyclopentadienyl‐indenyl tetracarbonyl diruthenium complexes (η⁵:η⁵‐RC₅H₃CR′₂C₉H₆)Ru₂(CO)₂(µ‐CO)₂ [R = H, R′, R′ = Me₂ (1), (CH₂)₄ (2), (CH₂)₅ (3), (CH₂)₆ (4); R = ^tBu, R′, R′ = Me₂ (5), (CH₂)₄ (6), (CH₂)₅ (7)] have been synthesized by reactions of the corresponding ligands RC₅H₄CR′₂C₉H₇ with Ru₃(CO)₁₂ in refluxing xylene. The molecular structures of 2, 6 and 7 have been determined by X‐ray diffraction. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of electroactive polystyrene derivatives para‐substituted with π‐conjugated oligothiophene via postgrafting functionalization

Two electroactive polystyrene derivatives para‐ substituted with π‐conjugated oligothiophene, poly(5‐hexyl‐5″‐(4‐vinylphenyl)‐2,2′:5′,2″‐terthiophene) ( PH3TS ), and poly(5‐hexyl‐5″″‐(4‐vinylphenyl)‐2,2′:5′,2″:5″,2″′:5″′,2″″‐quinquethiophene) ( PH5TS ) have been successfully synthesized via the Stille coupling reaction between tributyltin postfunctionalized poly(4‐(2‐thiophenyl)styrene) ( PTS ) and bromo‐oligothiophene. The effect of the chain length of the pendant oligothiophenes on properties of the resulting polymers including solubility, thermal stability, optical absorption, and electroactivation energy levels has been studied by using a variety of techniques such as thermogravimetric analyzer, differential scanning calorimetry, UV–Vis, Fluorescence, and cyclic voltammetry. With shielding of the hexyl terminal groups attached to the pendant oligothiophene units, no obvious chain aggregation was observed for both PH3TS and PH5TS even in a poor solvent environment. When compared with conventional linear conjugated polymer systems, the concept of grafting electroactive units as pendant side chains via postfunctionalizing aliphatic polymers might offer a strategy to precisely synthesize new electroactive polymer materials for a number of organic electronic applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Intricacies of ligand coordination in tricarbonylchromium(0) complexes with ortho‐ and para‐fluorobiphenyls

The steric and electronic factors that influence which of the two rings of a substituted biphenyl ligand coordinates to chromium are of interest and it has been suggested that haptotropic rearrangements within these molecules may be limited if the arene–arene dihedral angle is too large. Two tricarbonylchromium(0) complexes and their respective free ligands have been characterized by single‐crystal X‐ray diffraction. In the solid state, tricarbonyl[(1′,2′,3′,4′,5′,6′‐η)‐2‐fluoro‐1,1′‐biphenyl]chromium(0), [Cr(C₁₂H₉F)(CO)₃], (I), exists as the more stable isomer with the nonhalogenated arene ring ligated to the metal center. Similarly, tricarbonyl[(1′,2′,3′,4′,5′,6′‐η)‐4‐fluoro‐1,1′‐biphenyl]chromium(0) crystallizes as the more stable isomer with the phenyl ring bonded to the Cr⁰ center. The arene–arene dihedral angles in these complexes are 55.77 (4) and 52.4 (5)°, respectively. Structural features of these complexes are compared to those of the DFT‐optimized geometries of ten tricarbonyl[(η⁶‐C₆H₅)(4‐F‐C₆H₄)]chromium model complexes. The solid‐state structures of the free ligands 2‐fluoro‐1,1′‐biphenyl and 4‐fluoro‐1,1′‐biphenyl, both C₁₂H₉F, exhibit arene–arene dihedral angles of 54.83 (7) and 0.71 (8)°, respectively. The molecules of the free ligands occupy crystallographic twofold axes and exhibit positional disorder. Weak intermolecular C—H…F interactions are observed in all four structures.     

A photochemical route to ferrocenyl‐substituted ferrapyrrolinone complexes

In the presence of iron pentacarbonyl, photochemical reaction between phenylisocyanate and ferrocenylacetylene results in ferrapyrrolinone complex [Fe₂(CO)₆(μ₂‐η³‐FcC═C(H)C(O)NPh)] ( 1 ) and maleimide 3‐ferrocenyl‐1‐phenyl‐1H ‐pyrrole‐2,5‐dione ( 2 ). Under similar experimental conditions, ferrocenyl−/phenyl‐substituted butadiyne primarily shows the activation of only one C☰C bond and results in ferrapyrrolinone complexes [Fe₂(CO)₆(μ₂‐η³‐FcC═C(C☰CR)C(O)NPh)] ( 3 , R = Fc; 3a , R = Ph), maleimides 3‐ferrocenyl‐1‐phenyl‐4‐(ferrocenylethynyl)‐1H –pyrrole‐2,5‐dione ( 5 ) and 3‐ferrocenyl‐1‐phenyl‐4‐(phenylethynyl)‐1H –pyrrole‐2,5‐dione ( 5a ) and [Fe₂(CO)₆(μ₂‐η³‐FcC═C(R)C(O)NPh)] ( 4 ; R  = 3‐ferrocenyl‐1‐phenyl‐1H ‐pyrrole‐2,5‐dione). Compound 4 consists of ferrapyrrolinone and a maleimide unit, formed by the activation of both C☰C bonds of diferrocenylbutadiyne. Activation of both C☰C bonds in a substituted butadiyne is a rare observation. Formation of the ferrapyrrolinone compounds is an advance over the earlier reported methods which generally use internal alkynes and involve prior synthesis of other clusters.     

Density functional crystal orbital study of cyano‐substituted poly(para‐phenylene‐vinylene) and poly(quinoxaline‐vinylene)

We have calculated the optical and electronic properties of several conjugated organic polymers: poly(p‐phenylene‐vinylene) (PPV) and its derivatives. Cyano substitutions on the phenylene ring: poly(2,5‐dicyano‐p‐phenylene‐vinylene) (2,5‐DCN‐PPV) and on the vinylene linkage: poly(p‐phenylene‐7(,8)‐(di)cyano‐vinylene) are considered. In addition, poly(quinoxaline‐vinylene) (PQV) is studied. The infinite isolated quasi‐1D chains are treated with periodic boundary conditions, using atomic basis sets. In a comparative study of PPV, some issues regarding the selection of the functionals and basis sets are discussed and excitation energies derived from time‐dependent and from ordinary methods are compared. It is concluded that for these polymers the calculations are informative at the B3LYP/6‐31G** density functional theory (DFT) level. The absolute values might change with improved methods, but the similarity of the polymers suggests that the relative characterization is adequate. Band structures are communicated along with characteristics of the highest occupied and the lowest unoccupied crystal orbitals (HOCO and LUCO). Electron affinities, ionization potentials, valence and conduction bandwidths, and effective masses at the bandgap are given. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Studies on the kinetics of imidazolium fluorochromate oxidation of some meta‐ and para‐substituted anilines in nonaqueous media

The imidazolium fluorochromate (IFC) oxidation of meta‐ and para‐substituted anilines, in seven organic solvents, in the presence of p‐toluenesulfonic acid (TsOH) is first order in IFC and TsOH and is zero order with respect to substrate. The IFC oxidation of 15 meta‐ and para‐substituted anilines at 299–322 K complies with the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental range. The specific rate of oxidizing species‐anilines reaction (k₂) correlates with substituent constants affording negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ε_r and E^N_T. A correlation of rate data with Kamlet–Taft solvatochromic parameters (α, β, π*) suggests that the specific solute–solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute–solvent complexation. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 166–175, 2006     

Synthesis and Spectra Characteristics of Novel 3‐(para‐Bromophenyl)‐7‐(substituted vinyl) Coumarins

Five new coumarin derivatives ( 5a , 5b , 5c , 5d , 5e ) with extending para‐bromophenyl at the 3‐position and substituted vinyl at the 7‐position were synthesized and characterized by FT‐IR, ¹H NMR, and element analysis. The absorption and fluorescence characteristics of compounds 5a , 5b , 5c , 5d , 5e showed significant dependences on its molecular structure, which possessed large Stokes shifts (up to 8309 cm^?1) and high fluorescence quantum yield (up to 0.80) in CH₂Cl₂. These advantageous spectral properties should allow use in many areas.     

Copolymerization of ethylene with 1‐hexene promoted by novel multi‐chelated non‐metallocene complexes with imine bridged imidazole ligand

A series of novel bridged multi‐chelated non‐metallocene catalysts is synthesized by the treatment of N,N‐imidazole, N,N‐dimethylimidazole, and N,N‐benzimidazole with n‐BuLi, 2,6‐dimethylaniline, and MCl₄ (M = Ti, Zr) in THF. These catalysts are used for copolymerization of ethylene with 1‐hexene after activated by methylaluminoxane (MAO). The effects of polymerization temperature, Al/M molar ratio, and pressure of monomer on ethylene copolymerization behaviors are investigated in detail. These results reveal that these catalysts are favorable for copolymerization of ethylene with 1‐hexene featured high catalytic activity and high comonomer incorporation. The copolymer is characterized by ¹³C NMR, WAXD, GPC, and DSC. The results confirm that the obtained copolymer features broad molecular weight distribution (MWD) about 33–35 and high 1‐hexene incorporation up to 9.2 mol %, melting temperature of the copolymer depends on the content of 1‐hexene incorporation within the copolymer chain and 1‐hexene unit in the copolymer chain isolates by ethylene units. The homopolymer of ethylene has broader MWD with 42–46. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 417–424, 2010