Carbonylation of nitrobenzene in methanol with palladium bidentate phosphane complexes: an unexpectedly complex network of catalytic reactions, centred around a Pd-imido intermediate

The reactivity of palladium complexes of bidentate diaryl phosphane ligands (P₂) was studied in the reaction of nitrobenzene with CO in methanol. Careful analysis of the reaction mixtures revealed that, besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MPC), N,N′‐diphenylurea (DPU), aniline, azobenzene (Azo) and azoxybenzene (Azoxy)], large quantities of oxidation products of methanol were co‐produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H₂O, and CO). From these observations, it is concluded that several catalytic processes operate simultaneously, and are coupled via common catalytic intermediates. Starting from a P₂Pd⁰ compound formed in situ, oxidation to a palladium imido compound P₂Pd^II?NPh, can be achieved by de‐oxygenation of nitrobenzene 1) with two molecules of CO, 2) with two molecules of CO and the acidic protons of two methanol molecules, or 3) with all four hydrogen atoms of one methanol molecule. Reduction of P₂Pd^II?NPh to P₂Pd⁰ makes the overall process catalytic, while at the same time forming Azo(xy), MPC, DPU and aniline. It is proposed that the Pd–imido species is the central key intermediate that can link together all reduction products of nitrobenzene and all oxidation products of methanol in one unified mechanistic scheme. The relative occurrence of the various catalytic processes is shown to be dependent on the characteristics of the catalysts, as imposed by the ligand structure.     

Tetracyanoquinodimethane Reduction by Complexed Guanidinyl‐Functionalized Aromatic Compounds

In this work, we report on the reduction of tetracyanoquinodimethane (TCNQ) with dicationic complexes of guanidinyl‐functionalized aromatic (GFA) electron donors. In contrast to reduction with free GFAs, milder reduction conditions were achieved, and this led to semiconducting materials with extended TCNQ π stacking. The charge on the TCNQ units was estimated from the structural data obtained by single‐crystal X‐ray diffraction analysis and from IR spectroscopic data. The electrical conductivity was studied and the activation energy of the semiconducting materials was estimated from the temperature dependence of the conductivity.     

Hybrid phospholipid bilayer coatings for separations of cationic proteins in capillary zone electrophoresis

Protein separations in CZE suffer from nonspecific adsorption of analytes to the capillary surface. Semipermanent phospholipid bilayers have been used to minimize adsorption, but must be regenerated regularly to ensure reproducibility. We investigated the formation, characterization, and use of hybrid phospholipid bilayers (HPBs) as more stable biosurfactant capillary coatings for CZE protein separations. HPBs are formed by covalently modifying a support with a hydrophobic monolayer onto which a self‐assembled lipid monolayer is deposited. Monolayers prepared in capillaries using 3‐cyanopropyldimethylchlorosilane (CPDCS) or n‐octyldimethylchlorosilane (ODCS) yielded hydrophobic surfaces with lowered surface free energies of 6.0 ± 0.3 or 0.2 ± 0.1 mJ m^?2, respectively, compared to 17 ± 1 mJ m^?2 for bare silica capillaries. HPBs were formed by subsequently fusing vesicles comprised of 1,2‐dilauroyl‐sn‐glycero‐3‐phosphocholine or 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine to CPDCS‐ or ODCS‐modified capillaries. The resultant HPB coatings shielded the capillary surface and yielded reduced electroosmotic mobility (1.3–1.9 × 10^?4 cm² V^?1s^?1) compared to CPDCS‐ and ODCS‐modified or bare capillaries (3.6 ± 0.2 × 10^?4 cm² V^?1s^?1, 4.8 ± 0.4 × 10^?4 cm² V^?1s^?1, and 6.0 ± 0.2 × 10^?4 cm² V^?1s^?1, respectively), with increased stability compared to phospholipid bilayer coatings. HPB‐coated capillaries yielded reproducible protein migration times (RSD ≤ 3.6%, n ≥ 6) with separation efficiencies as high as 200 000 plates/m.     

Comparison of direct mass spectrometry methods for the on‐line analysis of volatile compounds in foods

For the on‐line monitoring of flavour compound release, atmospheric pressure chemical ionization (APCI) and proton transfer reaction (PTR) combined to mass spectrometry (MS) are the most often used ionization technologies. APCI‐MS was questioned for the quantification of volatiles in complex mixtures, but direct comparisons of APCI and PTR techniques applied on the same samples remain scarce. The aim of this work was to compare the potentialities of both techniques for the study of in vitro and in vivo flavour release. Aroma release from flavoured aqueous solutions (in vitro measurements in Teflon bags and glass vials) or flavoured candies (in vivo measurements on six panellists) was studied using APCI‐ and PTR‐MS. Very similar results were obtained with both techniques. Their sensitivities, expressed as limit of detection of 2,5‐dimethylpyrazine, were found equivalent at 12 ng/l air. Analyses of Teflon bag headspace revealed a poor repeatability and important ionization competitions with both APCI‐ and PTR‐MS, particularly between an ester and a secondary alcohol. These phenomena were attributed to dependency on moisture content, gas/liquid volume ratio, proton affinities and product ion distribution, together with inherent drawbacks of Teflon bags (adsorption, condensation of water and polar molecules). Concerning the analyses of vial headspace and in vivo analyses, similar results were obtained with both techniques, revealing no competition phenomena. This study highlighted the equivalent performances of APCI‐MS and PTR‐MS for in vitro and in vivo flavour release investigations and provided useful data on the problematic use of sample bags for headspace analyses. Copyright © 2013 John Wiley & Sons, Ltd.     

Formation of an Imino‐Stabilized Cyclic Tin(II) Cation from an Amino(imino)stannylene

The novel amino(imino)stannylene 1 was prepared by conversion of HNIPr (NIPr=bis(2,6‐diisopropylphenyl)imidazolin‐2‐imino) with one equivalent of Lappert’s tin reagent (Sn[N(SiMe₃)₂]₂). Treatment of 1 with DMAP (4‐dimethylaminopyridine) yields its Lewis acid–base adduct 2 . The reaction of 1 with one equivalent of trimethylsilyl azide results in replacement of the amino group at the tin center by an N₃ substituent with concomitant elimination of N(SiMe₃)₃ to afford dimeric [N₃SnNIPr]₂ ( 3 ). Remarkably, the reaction of 1 with B(C₆F₅)₃ produces the novel tin(II) monocation 4 ⁺[MeB(C₆F₅)₃]^? comprising a four‐membered stannacycle through methyl‐abstraction from the trimethylsilyl group.     

Comparison of monomethoxy‐, dimethoxy‐, and trimethoxysilane anchor groups for surface‐initiated RAFT polymerization from silica surfaces

The immobilization of reversible addition–fragmentation chain transfer (RAFT) agents on silica for surface‐initiated RAFT polymerizations (SI‐RAFT) via the Z‐group approach was studied systematically in dependence of the functionality of the RAFT‐agent anchor group. Monoalkoxy‐, dialkoxy‐, and trialkoxy silyl ether groups were incorporated into trithiocarbonate‐type RAFT agents and bound to planar silica surfaces as well as to silica nanoparticles. The immobilization efficiency and the structure of the bound RAFT‐agent film varied strongly in dependence of the used solvent (toluene vs. 1,2‐dimethoxyethane) and the anchor group functionality, as evidenced by atomic force microscopy, transmission electron microscopy, dynamic light scattering, and UV/Vis spectroscopy. Surface‐initiated RAFT polymerizations using functionalized silica nanoparticles revealed that grafted oligomers, which often occur in SI‐RAFT, are not formed within the crosslinked structures that originate from the immobilization, and that RAFT‐agent films that show less aggregation during the immobilization are more efficient during SI‐RAFT in terms of polymer grafting density. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 103–113     

Functional polymethacrylates as bacteriostatic polymers

Two copolymers, P(PCEMA-co-MMA) and P(t-BMA-block-PCEMA), were prepared via ATRP using 2-(phenoxycarbonyloxy)ethyl methacrylate (PCEMA) as reactive monomer and methyl methacrylate (MMA) or tert-butyl methacrylate (t-BMA) as co-monomers. Alternatively phenoxycarbonyloxy decorated polymethacrylates were obtained via polymer analogous reaction: P(HEMA) was reacted with phenyl chloroformate to yield P(PCEMA). The highly reactive phenoxycarbonyloxy groups were used for polymer analogous reactions with nucleophiles to obtain polymers with ionic/hydrophilic and hydrophobic side groups. Different amines with long alkyl chains or tertiary amine groups were reacted with phenoxycarbonyloxy decorated polymers and subsequently reacted with methyl iodide to obtain amphipathic polymers with bacteriostatic properties.     

Concise Synthesis of [1,1′‐Biisoquinoline]‐4,4′‐diol via a Protecting Group Strategy and Its Application for Potential Liquid‐Crystalline Compounds

The [1,1′‐biisoquinoline]‐4,4′‐diol ( 4a ), which was obtained as hydrochloride 4a ?2 HCl in two steps starting from the methoxymethyl (MOM)‐protected 1‐chloroisoquinoline 8 (Scheme 3), opens access to further O‐functionalized biisoquinoline derivatives. Compound 4a ?2 HCl was esterified with 4‐(hexadecyloxy)benzoyl chloride ( 5b ) to give the corresponding diester 3b (Scheme 4), which could not be obtained by Ni‐mediated homocoupling of 6b (Scheme 2). The ether derivative 2b was accessible in good yield by reaction of 4a ?2 HCl with the respective alkyl bromide 9 under the conditions of Williamson etherification (Scheme 4). Slightly modified conditions were applied to the esterification of 4a ?2 HCl with galloyl chlorides 10a – h as well as etherification of 4a ?2 HCl with 6‐bromohexyl tris(alkyloxy)benzoates 11b , d – h and [(6‐bromohexyl)oxy]‐substituted pentakis(alkyloxy)triphenylenes 14a – c (Scheme 5). Despite the bulky substituents, the respective target 1,1′‐biisoquinolines 12, 13 , and 15 were isolated in 14–86% yield (Table).     

Red‐ and Green‐Emitting Iridium(III) Complexes for a Dual Barometric and Temperature‐Sensitive Paint

A new dual luminescent sensitive paint for barometric pressure and temperature (T) is presented. The green‐emitting iridium(III) complex [Ir(ppy)₂(carbac)] (ppy=2‐phenylpyridine; carbac=1‐(9H‐carbazol‐9‐yl)‐5,5‐dimethylhexane‐2,4‐dione) was applied as a novel probe for T along with the red‐emitting complex [Ir(btpy)₃], (btpy=2‐(benzo[b]thiophene‐2‐yl)pyridine) which functions as a barometric (in fact oxygen‐sensitive) probe. Both iridium complexes were dissolved in different polymer materials to achieve optimal responses. The probe [Ir(ppy)₂(carbac)] was dispersed in gas‐blocking poly(acrylonitrile) microparticles in order to suppress any quenching of its luminescence by oxygen. The barometric probe [Ir(btpy)₃], in turn, was incorporated in a cellulose acetate butyrate film which exhibits good permeability for oxygen. The effects of temperature on the response of the oxygen probe can be corrected by simultaneous optical determination of T, as the poly(acrylonitrile) microparticles containing the temperature indicator are incorporated into the film. The phosphorescent signals of the probes for T and barometric pressure, respectively, can be separated by optical filters due to the ≈75 nm difference in their emission maxima. The dual sensor is applicable to luminescence lifetime imaging of T and barometric pressure. It is the first luminescent dual sensor material for barometric pressure/T based exclusively on the use of Ir^III complexes in combination with luminescence lifetime imaging.