Structure–Activity Relationship of Palladium Phosphanesulfonates: Toward Highly Active Palladium‐Based Polymerization Catalysts

Palladium phosphanesulfonate [R₂P(C₆H₄‐o‐SO₃)PdMeL] catalysts permit the copolymerization of an exceptional large number of functional olefins with ethylene. However, these catalysts usually have reduced activity. We here have conducted a systematic study on the influence of the phosphane substituent, R, on activity and molecular weight. Phosphanes with strong σ‐donating character are shown to lead to the most active catalysts. Thus, the catalyst based on phosphane bis‐tert‐butyl‐phosphanyl‐benzenesulfonic acid (R=tBu) exhibits unprecedented high activity, rapidly polymerizing ethylene at room temperature to yield a linear polymer of high molecular weight (M_w=116 000 g mol^?1). The influence of the R group on the catalyst ability to incorporate methyl acrylate is also investigated.     

Polystyrene nanoparticles doped with a luminescent europium complex

Polystyrene nanoparticles doped with a luminescent europium complex, Eu(tta)(3)phen, are prepared by miniemulsion polymerization. The influence of the complex on the miniemulsion polymerization is investigated by the systematic variation of the initial concentration of Eu(tta)(3)phen from 2 to 7 wt% relatively to styrene. A maximum doping level of about 2% by weight in the final particles can be achieved. At higher doping levels, destabilization of the miniemulsion leads to a loss of reproducibility with respect to both the degree of conversion and the final Eu content of the particles. Doped nanoparticles of varying diameter, ranging from 19 to 94 nm, are successfully prepared. Steady-state and time-resolved luminescence measurements indicate that the luminescence properties of Eu(tta)(3)phen in the doped latexes are unchanged from those found in THF solution. Aqueous dispersions of the doped particles exhibit characteristic red emission under UV light irradiation. The luminescence intensity increases linearly with Eu(tta)(3)phen content, indicating the absence of self-quenching despite the relatively high local concentrations within the particles.     

Synthesis and characterization of a novel polyester derived from substituted terfluorene

Poly(1,6‐hexane‐9,9,9′,9′,9″,9″‐hexahexyl‐7,2′;7′,2″‐terfluorene‐2,7″‐dicarboxylate) (PTFHHC6) has been synthesized and characterized. This polymer exhibits strong emission in the blue range, both in solution (quantum yield of 76%) and in the solid state. Moreover, PTFHHC6 presents some advantages over other polyfluorene derivatives since its solid‐state fluorescence spectrum does not show any excimer formation and does not vary upon thermal treatment. Electrochemical measurements have revealed a reversible p‐n dopable polymer. This aromatic polyester shows promising optical and electrical properties for the development of blue light‐emitting diodes.     

Hypervalent Silicon Compounds by Coordination of Diphosphine–Silanes to Gold

Coordination of ambiphilic diphosphine–silane ligands [o‐(iPr₂P)C₆H₄]₂Si(R)F (R=F, Ph, Me) to AuCl affords pentacoordinate neutral silicon compounds in which the metal atom acts as a Lewis base. X‐ray diffraction analyses, NMR spectroscopy, and DFT calculations substantiate the presence of Au→Si interactions in these complexes, which result in trigonal‐bipyramidal geometries around silicon. The presence of a single electron‐withdrawing fluorine atom is sufficient to observe coordination of the silane as a σ‐acceptor ligand, provided it is positioned trans to gold. The nature of the second substituent at silicon (R=F, Ph, Me) has very little influence on the magnitude of the Au→Si interaction, in marked contrast to N→Si adducts. According to variable‐temperature and 2D EXSY NMR experiments, the apical/equatorial positions around silicon exchange in the slow regime of the NMR timescale. The two forms, with the fluorine atom in trans or cis position to gold, were characterized spectroscopically and the activation barrier for their interconversion was estimated. The bonding and relative stability of the two isomeric structures were assessed by DFT calculations.     

CH Activation of Benzene by a Photoactivated NiII(azide): Formation of a Transient Nickel Nitrido Complex

Photochemical activation of nickel‐azido complex 2 [Ni(N₃)(PNP)] (PN^HP=2,2′‐di(isopropylphosphino)‐4,4′‐ditolylamine) in neat benzene produces diamagnetic complex 3 [Ni(Ph)(PN^PN^H)], which is crystallographically characterized. DFT calculations support photoinitiated N₂‐loss of the azido complex to generate a rare, transient Ni^IV nitrido species, which bears significant nitridyl radical character. Subsequent trapping of this nitrido through insertion into the Ni? P bond generates a coordinatively unsaturated Ni^II imidophosphorane P?N donor. This species shows unprecedented reactivity toward 1,2‐addition of a C? H bond of benzene to form 3 . The structurally characterized chlorido complex 4 [Ni(Cl)(PN^PN^H)] is generated by reaction of 3 with HCl or by direct photolysis of 2 in chlorobenzene. This is the first report of aromatic C? H bond activation by a trapped transient nitrido species of a late transition metal.     

Position-specific 15N isotope analysis in organic molecules: A high-precision 15N NMR method to determine the intramolecular 15N isotope composition and fractionation at natural abundance

The position-specific ¹⁵N isotope content in organic molecules, at natural abundance, is for the first time determined by using a quantitative methodology based on ¹⁵N Nuclear Magnetic Resonance (NMR) spectrometry. ¹⁵N NMR spectra are obtained by using an adiabatic “Full-Spectrum” INEPT sequence in order to make possible ¹⁵N NMR experiments with a high signal-to-noise ratio (>500), to reach a precision with a standard deviation below 1‰ (0.1%). This level of precision is required for observing small changes in ¹⁵N content associated to ¹⁵N isotope effects. As an illustration, the measurement of an isotopic enrichment factor ε for each ¹⁵N isotopomer is presented for 1-methylimidazole induced during a separation process on a silica column. The precision expressed as the long-term repeatability of the methodology is good enough to evaluate small changes in the ¹⁵N isotope contents for a given isotopomer. As observed for ¹³C, inverse and normal ¹⁵N isotope effects occur concomitantly, giving access to new information on the origin of the ¹⁵N isotope effects, not detectable by other techniques such as isotope ratio measured by Mass Spectrometry for which bulk (average) values are obtained.     

Influence of actinic wavelength on properties of light‐cured interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of different acrylate/epoxide ratios, were synthesized under UV and visible‐LED curing conditions. The formation of the IPNs was explored in terms of phase separation, polymerization mechanisms, final mechanical properties and surface morphology. For these purpose, we uniquely combined results of miscibility investigations, confocal Raman microscopy, dynamical mechanical analysis and atomic force microscopy. Transparent films were obtained for all compositions and both irradiation sources. The thermo‐mechanical properties of different IPNs were associated to the presence of acrylate‐ or epoxide‐rich phases, as well as, mixed interphases, resulting from the high interpenetration between both networks. Although the final conversions were similar under UV and visible‐LED irradiation, we have found evidence that the visible‐cured samples provide higher IPN homogeneity and lower T_g, for a higher epoxide content. To explain this trend, the mechanisms and sequence of the acrylate or epoxide networks formation, under UV or LED irradiation, is discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1378‐1390     

InCl3/CyNH2 cocatalyzed carbocyclization reaction: an entry to α-disubstituted exo-methylene cyclopentanes

An efficient and cheap synthetic approach to functionalized exo-methylene cyclopentanes has been developed from α-disubstituted formyl-alkynes by merging amine catalysis with the indium activation of alkynes. We uncovered the crucial role of the amine cocatalyst and the development of a new cooperative catalytic system allowed the cyclization of a broad range of substrates. A mechanistic study was realized in order to rationalize the determining influence of the amine cocatalyst.     

Meta-B-entacenes: new polycyclic aromatics incorporating two fused borepin rings

The synthesis of new boron-containing acenes (meta-B-entacenes) is reported. These compounds exhibit slightly non-planar core geometries with blue-shifted spectral properties and more negative electrochemical reduction potentials relative to known para isomers. Polarizable π-extended architectures were realized via cross-coupling procedures with chloro-functionalized precursors.