Synthesis and structure‐optoelectronic property relationships of a series of PPV and SFTV derived polymers

Engineering of the highest occupied molecular orbital and lowest unoccupied molecular orbitals through synthetic chemical structural modification has been the most widely used method to tuning optoelectronic properties in conjugated polymers. The electronic, thermal, optical, and physical properties can be tuned and exploited for optimization of optoelectronic devices. Through copolymerization of donor and acceptor type conjugated monomers, the frontier orbitals of four polymers were tailored. Through this synthetic engineering, the relationship between structural features, frontier orbital tailoring, and changes in optoelectronic and physical properties are discussed. Spectroscopic, thermal, and electronic analysis of the polymers indicated that polymers containing carbazole monomer moieties gave overall improved optoelectronic properties, but higher band gaps (2.61 and 2.18 eV) in comparison to their phenyl‐ based counterparts. This result is attributed to the higher electron density of the carbazole than the terephthaldicarboxaldehyde, and the possible deviation from planarity in the polymer main chain due to possible steric hindrance of the branched substituents. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2202–2213     

Selective Iridium‐Catalyzed Alkylation of (Hetero)Aromatic Amines and Diamines with Alcohols under Mild Reaction Conditions

Selective amine alkylation : A P,N‐ligand‐stabilized iridium complex has been used as an efficient catalyst for the alkylation of (hetero)aromatic amines with alcohols at mild reaction temperatures and catalyst loadings as low as 0.1 mol % Ir (see scheme). The excellent selectivity of the catalyst for monoalkylation of the amine function has also been exploited for the N,N′‐dialkylation of diamines in both symmetric and nonsymmetric fashions.

     

Single and Double C?Cl‐Activation of Methylene Chloride by P,N‐ligand Coordinated Rhodium Complexes

Two in one : The simultaneous formation of bimetallic μ‐methylene bridged Rh^III complexes as well as dimeric Rh^III complexes with terminal chloromethyl groups is observed for P,N‐ligand stabilized Rh^I complexes by C? Cl bond activation of methylene chloride. A mechanistic proposal for the formation of both activation products is also discussed.

     

Synthesis of the macrocyclic core of leiodermatolide

The macrocyclic core (2) of the marine macrolide leiodermatolide (1) has been synthesized in 19 steps through a convergent strategy exploiting boron aldol methodology to install the requisite stereochemistry and a selective Stille coupling reaction for controlled fragment assembly, followed by a Yamaguchi macrolactonization and carbamate introduction at the C9-OH.     

Non-Heme FeII Diastereomeric Complexes Bearing a Hexadentate Ligand: Unexpected Consequences for the Spin State and Catalytic Oxidation Properties

The reactivity and selectivity of non-heme Fe^II complexes as oxidation catalysts can be substantially modified by alteration of the ligand backbone or introduction of various substituents. In comparison with the hexadentate ligand N,N,N′,N′-tetrakis(pyridin-2-ylmethyl)ethane-1,2-diamine (TPEN), N,N′-bis[1-(pyridin-2-yl)ethyl]-N,N′-bis(pyridin-2-ylmethyl)ethane-1,2-diamine (_2MeL₆²) has a methyl group on two of the four picolyl positions. Fe^II complexation by _2MeL₆² yields two diastereomeric complexes with very similar structures, which only differ in the axial/equatorial positions occupied by the methylated pyridyl groups. In solution, these two isomers exhibit different magnetic behaviors. Whereas one isomer exhibits temperature-dependent spin-state conversion between the S=0 and S=2 states, the other is more reluctant towards this spin-state equilibrium and is essentially diamagnetic at room temperature. Their catalytic properties for the oxidation of anisole by H₂O₂ are very different and correlate with their magnetic properties, which reflect their lability/inertness. These different properties most likely depend on the different steric constraints of the methylated pyridyl groups in the two complexes.     

The Synthesis,Characterization and Dehydrogenation of Sigma‐Complexes of BN‐Cyclohexanes

The coordination chemistry of the 1,2‐BN‐cyclohexanes 2,2‐R₂‐1,2‐B,N‐C₄H₁₀ (R₂=HH, MeH, Me₂) with Ir and Rh metal fragments has been studied. This led to the solution (NMR spectroscopy) and solid‐state (X‐ray diffraction) characterization of [Ir(PCy₃)₂(H)₂(η²η²‐H₂BNR₂C₄H₈)][BAr^F₄] (NR₂=NH₂, NMeH) and [Rh(iPr₂PCH₂CH₂CH₂PiPr₂)(η²η²‐H₂BNR₂C₄H₈)][BAr^F₄] (NR₂=NH₂, NMeH, NMe₂). For NR₂=NH₂ subsequent metal‐promoted, dehydrocoupling shows the eventual formation of the cyclic tricyclic borazine [BNC₄H₈]₃, via amino‐borane and, tentatively characterized using DFT/GIAO chemical shift calculations, cycloborazane intermediates. For NR₂=NMeH the final product is the cyclic amino‐borane HBNMeC₄H₈. The mechanism of dehydrogenation of 2,2‐H,Me‐1,2‐B,N‐C₄H₁₀ using the {Rh(iPr₂PCH₂CH₂CH₂PiPr₂)}⁺ catalyst has been probed. Catalytic experiments indicate the rapid formation of a dimeric species, [Rh₂(iPr₂PCH₂CH₂CH₂PiPr₂)₂H₅][BAr^F₄]. Using the initial rate method starting from this dimer, a first‐order relationship to [amine‐borane], but half‐order to [Rh] is established, which is suggested to be due to a rapid dimer–monomer equilibrium operating.     

Mechanical Reversibility of Strain‐Promoted Azide–Alkyne Cycloaddition Reactions

Mechanophores, that is, molecules that show a defined response to force, are crucial building blocks of mechanoresponsive materials. The possibility of mechanically induced cycloreversion for a series of triazoles formed via strain‐promoted azide–alkyne cycloaddition reactions was investigated by density functional theory calculations, and these triazoles were compared to the 1,4‐ and 1,5‐regioisomers formed in the reaction of an azide with a terminal alkyne. We show that cycloreversion is in principal possible and that the pulling geometry is the most important parameter that determines the probability of cycloreversion. We further compared triazole stability to the mechanical stability of polymers that are frequently used as force transducers in mechanochemical experiments and identified DIBAC (azadibenzylcyclooctyne) as a promising mechanophore for future applications.     

Synthesis and characterization of polyimides based on new fluorinated 3,3′-diaminobiphenyls

Two new fluorinated diamine monomers, 3,3′-diamino-5,5′-bis(trifluoromethyl)biphenyl and 3,3′-diamino-6,6′-bis(trifluoromethoxy)biphenyl, as well as a known nonfluorinated analog, 3,3′-diaminobiphenyl, were synthesized. Reaction of these diamines with rigid, highly rod-like dianhydrides produced poly(amic acid)s and polyimides, which were spin coated and thermally treated to produce polyimide films for evaluation in electronics applications. It was hoped that these polyimide films would exhibit an ideal combination of low thermal expansion, reduced water absorption, and low dielectric constant but with improved elongation due to the “crankshaft” nature of the 3,3′-biphenyl unit. Unlike polyimide films from analogous 4,4′-diaminobiphenyls, however, the 3,3′-diaminobiphenyl-based polyimides did not yield low in-plane thermal expansion coefficient in spin-coated films. In some cases high elongation was achieved, but with high thermal expansion. These new diamines may nevertheless find utility in polyimides and polyaramides for membrane, fiber, and other applications. Additionally, they may be useful in modifying the properties of polymer backbones via copolymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2441–2451, 1997     

Quantitative chromatographic method for the determination of low levels of nitrilotriacetic and ethylenediaminetetraacetic acids in diethylenetriaminepentaacetic acid

A quantitative method for determination of low levels (0.05%, w/w) of nitrilotriacetic and ethylenediaminetetraacetic acids in diethylenetriaminepentaacetic acid is described. Palmitic acid is added to the chelator as an internal standard before esterification with methanol containing 2%(v/v)H2SO4. The methyl esters of palmitic, nitrilotriacetic, and ethylenediaminetetraacetic acids are first separated from diethylenetriaminepentaacetate by silicic acid column chromatography and are subsequently quantitated by gas-liquid chromatography. The method is both accurate and reproducible with less than 10% relative error. Thin-layer chromatographic separations of the methyl esters, and quantitation at the 1% level, are also described.