Christian Monsé

P(SiiPr3)3: the First Trisilylphosphane Derivative with an almost Planar Three‐Coordinated Phosphorus Atom

The title compound (1) was obtained by salt-metathesis reaction of iPr3SiPLi2 with two molar equiv. of iPr3SiOTf (OTf = OSO2CF3) in 34% yield. Surprisingly, (1) consists of an 4 : 1 mixture of the two diastereomers (1 a) and (1 b), which do not interconvert to each other even at their decomposition temperature (> 70 °C). They represent different iPr-rotational isomers which are separated by an unusual high rotational barrier (> 25 kcal mol–1), resulting from hindered rotations around the Si–C and C–C bonds. The unexpectedly small magnitude of the 1J(Si, P) coupling constant of (1 a) (9.4 Hz) and (1 b) (9.0 Hz) reflects unusual electronic properties of the Si3P skeleton. Hitherto only (1 a) could be isolated in the form of single-crystals and its structure was determined by X-ray diffraction analysis. The P-atom in (1 a) is almost planar coordinated (sum of bond angles = 359.789(3)°), but the Si–P-distance (2.264(7) A) resembles those values of related silylphosphanes with pyramidally coordinated P atoms. Although MNDO calculations revealed two other iPr-rotational isomers with similar energy, they prove that the Si3P skeleton prefers the trigonal-planar arrangement due to steric congestion. P(SiiPr3)3: Das erste Trisilylphosphanderivat mit einem fast planar dreifachkoordinierten Phosphoratom Die Titelverbindung (1) wurde durch Salzmetathesereaktion von iPr3SiPLi2 mit zwei Molaquivalent iPr3SiOTf (OTf = OSO2CF3) in 34% Ausbeute erhalten. Uberraschenderweise besteht (1) aus einer 4 : 1 Mischung der zwei Diastereomere (1 a) und (1 b), die sich auch bis zu ihrer Zersetzungstemperatur (70 °C) nicht ineinander umwandeln. Sie reprasentieren verschiedene iPr-Rotamere, die durch eine ungewohnlich hohe Rotationsbarriere (> 25 kcal · mol–1) voneinander getrennt sind und die von gehinderten Rotationen um die Si–C- und C–C-Bindungen herruhren. Der unerwartet kleine Betrag der 1J(Si, P)-Kopplungskonstante von (1 a) (9.4 Hz) und (1 b) (9.0 Hz) spiegelt die ungewohnlichen elektronischen Eigenschaften des Si3P-Gerusts wider. Bisher konnte nur (1 a) in einkristalliner Form isoliert werden, und seine Struktur wurde durch Rontgenbeugungsanalyse bestimmt. Das P-Atom in (1 a) ist annahernd planar koordiniert (Summe der Bindungswinkel = 359.789(3)°), aber der Si–P-Abstand (2.264(7) A) gleicht den Werten von verwandten Silylphosphanen mit pyramidal-koordinierten P-Atomen. Obwohl MNDO-Berechnungen zwei andere Rotamere ergaben, beweisen sie, dass das Si3P-Gerust die trigonal-planare Anordnung wegen der sterischen Uberladung bevorzugt.

Modular Chemistry with Aluminum Phosphanides: Cluster Formation of (AlP)n (n=3,6,7), Al4P3, and Al4Li4P6 Frameworks

The Al3P3 heterocycle 1 is formed in 94% yield by the reaction of the primary silylphosphane 6a with Me3Al in toluene at 70 degrees C. While 1 crystallizes in an isomerically pure form, in which the six-membered Al3P3 ring prefers the chair conformation and the P-H hydrogen atoms adopt exo positions, it isomerizes in solution to give different diastereomers as shown by 1H and 31P NMR spectroscopy. Intermolecular cyclocondensation of 1 at 110 degrees C in toluene leads, under liberation of methane, to the distorted hexameric-prismatic (AlP)6 cluster 2 in 98% yield. The capability of 1 to function as a building block was further used for the synthesis of the solvent-separated ion pair [Li(thf)2]+ [(Me2Al)4(PR)3]- (3) which was prepared by a one-pot reaction of 1 with nBuLi and Me2AlCl in 15% yield. The structure of 3 was established by an X-ray diffraction analysis. Double deprotonation at phosphorus in 1 with RPLi2 (R = iPr3Si) (molar ratio 1:2), and subsequent transformation of the reaction mixture with Me3Al afforded the novel donor-solvent-free cluster 4 in 62% yield. The latter consists of a rhombododecahedral Al4Li4P6 framework, in which the Li centers are three-coordinate. The reaction of the silylphosphane 6b with the trimethylamine adduct of alane furnishes not only the hexamer (RPAIH)6 (R = (iPrMe2C)-Me2Si) but also the corresponding heptamer 5, which has a nonregular polyhedral (AIP)7 framework and represents the first cluster of this type.

E(SiMe3)4+ Ions (E=P, As): Persilylated Phosphonium and Arsonium Ions

Only strong Lewis acidic, arene-solvated Me3 Si+ ions react with E(SiMe3 )3 compounds (E=P, As) to give the crystallographically characterized E(SiMe3 )4+ onium ions 1 (left hand picture), which contain highly negative polarized P and As atoms, respectively. The masked Me3 Si+ ions in 1 can be easily transferred to Et2 O, to give the first structurally characterized planar silyloxonium ion [Et2 (Me3 Si)O]+ 2 (right hand picture).

Synthesis of the first fluoro(phosphanyl)- and diphosphanyl-stannanes and surprising formation of [P(SnMe3)4]+SiF5−

Monophosphanylation of the difluorostannane Is2SnF2 (Is = 2,4,6-triisopropylphenyl) with Si(PH2)4 furnishes the first isolable fluoro(phosphanyl)stannane Is2Sn(F)PH2 1, which readily undergoes unique SiO2-assisted decompostion to [Is2Sn(PH)]2 2 and HF, while further phosphanylation of 1 leads to the remarkably stable diphosphanylstannane Is2Sn(PH2)2 3; the latter reacts with Me3SnF at the glass-wall to give the first perstannylphosphonium pentafluorosilicate [P(SnMe3)4]+ SiF5- 4.

Considerations for the design and technical setup of a human whole-body exposure chamber.

Exposures to air contaminants, such as chemical vapors and particulate matter, pose important health hazards at workplaces. Short-term experimental exposures to chemical vapors and particles in humans are a promising attempt to investigate acute effects of such hazards. However, a significant challenge in this field is the determination of effects of co-exposures to more than one chemical or mixtures of chemical vapors and/or particles. To overcome such a challenge, studies have to be conducted under standardized exposure characterization and real time measurements, if possible. A new exposure laboratory (ExpoLab) was installed at IPA, combining sophisticated engineering designs with new analytical techniques, to fulfill these requirements. Low-dose as well as high-dose exposure scenarios are achieved by means of a calibration-gas-generator. Exposure monitoring can be carried out with a high performance real time mass spectrometer and other suitable analyzers (e.g. gas chromatograph). Numerous automated security facilities guarantee the physical integrity of the volunteers, and the waste atmosphere is removed using either charcoal filtration or catalytic post-combustion. Measurements of sulfur hexafluoride, carbon dioxide, aniline and carbon black are presented to demonstrate the performance of the exposure unit with respect to the temporal and spatial stability of generated atmospheres. The variations of generated contents in the atmospheres at steady state are slightly higher than the measurement precision of the analyzers (the typical standard deviation of generated atmospheres is < 2%). The technical components of ExpoLab and its monitoring systems ensure high quality standards in validity and reliability of generating and measuring exposure atmospheres.

Synthesis and crystal structure analysis of tetraphosphanylsilane and identification of tetraphosphanylgermane.

Inversion-symmetric pairs, each with two weak P-H⋅⋅⋅P interactions, form molecules of Si(PH2 )4 in the crystal (see drawing). The title compounds are formed from ECl4 (E=Si,Ge) on reaction with [LiAl(PH2 )4 ] and could serve as single-source CVD precursors for phosphides.

Development and Evaluation of a Nanoparticle Generator for Human Inhalation Studies with Airborne Zinc Oxide

In the EU there is an increasing need for regulatory agencies to derive health based threshold limits based on human inhalation studies with airborne particles. A necessary prerequisite for such projects is the development of a suitable generator system to produce nanoparticle test aerosols for human whole-body inhalation studies. We decided to use a generator with flame-based heating of aqueous precursor solutions. Validation of the test system was done by generating zinc oxide (ZnO) nanoparticles with minimal contamination of trace gases, i.e., nitric oxides or carbon monoxide that could confound the effects seen in exposed subjects. ZnO was selected based on the uncertainties surrounding its health effects after exposure at the workplace. The generation process of the developed flame generator yields ZnO nanoparticles with monomodal size distribution and very good temporal stability. The maximum target exposure mass concentration of 2 mg/m3 ZnO, with a resulting median particle diameter of 57 nm, is attainable in our human exposure laboratory. The morphological examination shows typical agglomerates and aggregates formed by high temperature processes. Overall, the performed experiments confirm that a constant exposure can be provided for all subjects at all times. Copyright 2014 American Association for Aerosol Research

In vivo monitoring of epidermal absorption of hazardous substances by confocal Raman micro-spectroscopy.

Background: Presently, percutaneous absorption of potentially hazardous chemicals in humans can only be assessed in animal experiments, in vitro, or predicted mathematically. Our aim was to demonstrate the proof‐of‐principle of a novel quantitative in vivo assay for percutaneous absorption: confocal Raman micro‐spectroscopy (CRS). The advantages and limitations of CRS for health risk assessments are discussed.

Different Patterns in Changes of Exhaled Breath Condensate pH and Exhaled Nitric Oxide After Ozone Exposure

Study objective was the evaluation of pH in exhaled breath condensate (EBC-pH) and nitric oxide in exhaled breath (FeNO) as biomarkers of ozone induced inflammation. We recently demonstrated that an ozone exposure of 240 ppb is sufficient to reduce lung function indices. We enrolled ten healthy subjects exposed in an intermittent exercise protocol to ozone concentrations of 240 ppb and 40 ppb (sham exposure). EBC-pH and FeNO were assessed before (pre), immediately post (post), and 16 h after exposure (16 h). Findings are that compared to baseline, EBC-pH was significantly higher immediately after sham and ozone exposures, but not 16 h later. There was a negative net change in EBC-pH after adjusting for effects after sham exposure (net-ΔpHpost -0.38%, net-ΔpH16h -0.23%). Concerning FeNO, we observed no changes of values after sham exposure compared to baseline, but measured a significant lower net response at the end of exposure (net-ΔFeNOpost -17.5%) which was transient within 16 h (net-ΔFeNO16h -9.4%). We conclude that exercise known to enhance EBC-pH may compensate for EBC acidification associated with inflammation resulting in diminished change of this biomarker. Ozone imposes an oxidative burden and reactions between reactive oxygen species and NO might be an explanation for reduced FeNO levels.

Reproducibility of Sensitivity to Capsaicin Assessed by Single Breath Inhalation Methodology

The hallmark of sensory hyperreactivity is an enhanced capsaicin induced cough reflex. The cough reflex can be modified by activation of nociceptive (capsaicin-sensitive) nerve terminals. The aim of our study was to assess the influence of exposure to CO(2) concentrations up to 2.0 vol% on capsaicin induced cough reflex on four different occasions. Sixteen healthy volunteers were exposed to CO(2) concentrations of 0.5, 1.0, and 2.0 vol% for 4 h and to clean air in a repeated measures cross-over design. After exposure the capsaicin induced cough reflex was assessed by the single breath dose-response method according to ERS 2007 guidelines. After blank solutions, capsaicin doses (n=12, range 0.49 to 1000 μM) were administrated from a nebulizer combined with a provocation system (Masterscope, software APS version 5.02). Doses were doubled every minute and the concentration causing five or more coughs (C5) was fixed as the end point. The inter-individual C5 capsaicin responsiveness reflected a representative range (0.95-1000 μM). On an intra-individual basis, a good reproducibility could be demonstrated for four tests within 3 weeks. There was no influence of CO(2) challenge on the cough reflex. The first capsaicin test demonstrated a lower C5 threshold independent of the CO(2) concentration applied. In conclusion, assessing the capsaicin cough reflex by single breath inhalation is reliable. However, the at cough sensitivity might be overestimated at the first test occasion. Exposure to CO(2) in concentrations of up to 2.0 vol% has no effect on sensory reactivity.