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The one-step breakdown and derivatization of a panel of nine fentanyls to yield uniquely tagged products that can be detected by Electron Ionization Gas Chromatography-Mass Spectrometry (EI-GC-MS) is presented. The method involves the treatment of the synthetic opioids with 2,2,2-trichloroethoxycarbonyl chloride (TrocCl) at 60 °C for 3 h in dichloromethane and furnishes two products from one fentanyl molecule that can be used to retrospectively identify the original opioid. Parameters that were studied and fully optimized for the method included temperature, solvent, nature of scavenging base and reaction time. One of the two resulting products from the reaction bears the trichloroethoxycarbonyl (Troc) tag attached to the norfentanyl portion of the original opioid and greatly aids in the opioid detection and identification process. The methodology has been applied to the chemical modification of a panel of nine fentanyls and in all cases the molecular ion peak for the Troc-norfentanyl product bearing the distinctive trichloroethyl isotopic signature can be clearly observed. The method’s LLOD was determined to be 10 ng/mL while its LLOQ was found to be 20 ng/mL. This methodology represents the first application of chloroformates in the chemical modification of this class of synthetic opioids that are notoriously inert to common derivatization strategies available for GC–MS analysis.

High energy X-rays and neutrons can provide 3-D volumetric views of large objects made of multiple materials. Lenscoupled computed tomography using a scintillator imaged on a CCD camera obtains high spatial resolution, while a surface-mounted segmented scintillator on an amorphous silicon (A-Si) array can provide high throughput. For MeV Xray CT, a new polycrystalline transparent ceramic scintillator referred to as “GLO” offers excellent stopping power and light yield for improved contrast in sizes up to a 12” field-of-view. For MeV neutron CT, we have fabricated both contiguous and segmented plates of “Hi-LY” plastic scintillator, offering light yields 3x higher than standard plastic.

Plastic scintillators are in wide use in radiation portal monitors because of their low cost and availability in large sizes. However, due to their low density and atomic number (Z), they offer low intrinsic efficiency and little to no spectroscopic information. The addition of high-Z constituents to these plastics can greatly increase both their total stopping power and the amount of photo-electric absorption, leading to full-energy deposition and thus spectroscopic information in plastics. In this work, we present the performance of the largest bismuth-loaded plastics to date, showing useful spectroscopic information up to relatively high energy (~1 MeV) and their high stopping power compared the current commercially available plastics. These Bi-loaded plastics are based on 20 wt% Bi-pivalate (8 wt% elemental Bi) dissolved in a polyvinytoluene (PVT) matrix and conventional fast fluors (

Cs2HfCl6 (CHC) is a promising high density, high-Z, non-hygroscopic, and high energy resolution scintillator. In CHC, many crystals have CsCl inclusions that form during growth. In this paper, we investigate how material synthesis, growth rate, and thermal gradient affect the formation of CsCl inclusions and their effect on scintillation performance. First, precursor material was made through a methanol synthesis process both with and without hydrochlorination. Next, five crystals were grown using Bridgman method, at growth rates of 1 or 0.5 mm/h, and thermal gradients of 21 °C or 34 °C per millimeter. The best overall performance was observed in a 22 mm diameter crystal produced using hydrochlorination which was grown at 1 mm/h in a thermal gradient of 34 °C per millimeter. It had a light yield of 36,000 photons/MeV and an energy resolution of 4.0% at 662 keV. We have also shown that poorer scintillation performance in the lower quality crystals is most likely due to reduced light collection caused by a higher concentration of inclusions.

Plastic scintillators incorporating 8 weight percent elemental Bismuth offer enhanced sensitivity and distinct photopeak spectra in the 3 Bismuth plastic scintillator plate. Count rates compared to standard plastic scintillator of the same size reveal a sensitivity improvement of >5x in the

In this study, we describe the synthesis and crystal structures of four iridium compounds containing the 2-(4,6-difluorophenyl)pyridyl ligand. Cleavage of dichloro-bridged iridium(III) dimers with phosphorus ligands leads to (46dfppy)2Ir(L)(Cl) where L = PPh3 or P(OPh)3. Treatment of the chloro compounds with cyanide forms the cyano complexes (46dfppy)2Ir(L)(CN). All complexes exhibit a trans effect in their molecular structures due to the phosphorus ligands, with the phosphite having a greater effect than the phosphine. With L = PPh3, blue photoluminescence with CIE coordinates (x = 0.16, y = 0.24), quantum yield of 0.66 ± 0.15 and 4.5 ± 0.5 μs decay time is measured. For L = P(OPh)3, blue photoluminescence with CIE coordinates (x = 0.16, y = 0.21), quantum yield of 0.65 ± 0.15 and 2.9 ± 0.3 μs decay time is measured.

Transparent plastic scintillators based on polyvinyltoluene (PVT) have been fabricated with high loading of bismuth carboxylates for gamma spectroscopy, and with lithium carboxylates for neutron detection. When activated with a combination of standard fluors, 2,5-diphenyloxazole (PPO) and tetraphenylbutadiene (TPB), gamma light yields with 15 wt% bismuth tripivalate of 5000 Ph/MeV are measured. A PVT plastic formulation including 30 wt% lithium pivalate and 30 wt% PPO offers both pulse shape discrimination, and a neutron capture peak at ~400 keVee. In another configuration, a bismuth-loaded PVT plastic is coated with ZnS(6Li) paint, permitting simultaneous gamma and neutron detection via pulse shape discrimination with a figure-of-merit of 3.8, while offering gamma spectroscopy with energy resolution of R(662 keV)=15%.

We are working on scale up of several new plastic scintillator compositions. One composition uses Iridium complex fluors to obtain up to 3x higher light yields and high α/β ratios, for improved particle (alpha, neutron, fission product) detection and imaging. Other compositions include high loading of Bismuth for gamma spectroscopy and with Lithium for neutron detection. Plastics containing 21 wt% elemental Bismuth and an Ir fluor provide strong photopeaks and R(662 keV) ~9%. When activated with standard organic fluors, 10 in3 plastic scintillators containing 8 wt% Bismuth provide a strong photopeak with R(662 keV)~19%. A 5 in3 plastic formulation including 1 wt% Lithium-6 provides a neutron capture peak at 350 keVee, with 11% resolution for the capture peak.

Plastic scintillators are widely deployed for ionizing radiation detection, as they can be fabricated in large sizes, for high detection efficiency. However, commercial plastics are limited in use for gamma spectroscopy, since their photopeak is very weak, due to low Z, and they are also limited in use for neutron detection, since proton recoils are indistinguishable from other ionizing radiation absorption events in standard plastics. We are working on scale up and production of transparent plastic scintillators based on polyvinyltoluene (PVT) loaded bismuth metallorganics for gamma spectroscopy. When activated with standard organic fluors, PVT scintillators containing 8 wt% bismuth provide energy resolution of 11% at 662 keV. When Iridium complex fluors are used, we can load plastics up to 20 wt% bismuth, while obtaining energy resolution of 10% at 662 keV. Another formulation, activated with Ir fluors for use as neutron radiography scintillator may be used for high energy neutron radiography. Acknowledgements This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and has been supported by the US DOE National Nuclear Security Administration, Defense Nuclear Nonproliferation Research and Development under Contract No. DE-AC03-76SF00098

We have investigated methods to prepare cyclometallated iridium(III) complexes with efficient photoluminescence spanning a broad color palette. In particular, we find that addition of ancillary ligands to chloro-bridged iridium dimers proceeds cleanly in refluxing 1,2-dimethoxyethane (DME) without the need for additional product purification. This represents an improvement over the conventional use of 2-ethoxyethanol which requires column chromatographic separation. Our efforts in this work have focused on acetylacetonate complexes such as (F2ppy)2Ir(acac), where F2ppy = 2-(4′,6′-diflurophenyl)pyridinato. We have prepared fifteen compounds by the route, eight of which are newly reported; in four cases we were able to prepare complexes which were inaccessible via the conventional route. Nine of the complexes were characterized by single crystal x-ray diffraction and possess the same distorted octahedral geometry around the iridium with two bidentate phenylpyridine ligands and one bidentate acetylacetonate ligand. Seven of the complexes exhibited efficient photoluminescence with colors ranging from yellow to blue and quantum yields of 0.51–0.74. All of the compounds with trifluoromethyl or phenyl substituents on the acetylacetone displayed emission in the orange with low quantum efficiency. The use of TD-DFT calculations, along with natural transition orbitals (NTOs), permitted a detailed interpretation of the electronic structures for the complexes. The nature of the acceptor orbitals for the low energy triplet state NTOs proved to be an important predictor for the emission spectra of the compounds.

We report a new method to make heteroleptic cyclometallated iridium(III) complexes that employs 1,2-dimethoxyethane (DME) instead of the commonly used 2-ethoxyethanol for the addition of ancillary ligands to chloro-bridged dimeric iridium species. Thus, picolinic acid was quickly and cleanly added to [(F2ppy)2Ir(Cl)]2 (where F2ppy = 2-(4′,6′-difluorophenyl)pyridinato) with base under DME reflux to afford (F2ppy)2Ir(picolinate) (FIrpic) in excellent yield. The high purity of the products obviates the need for further purification, an improvement over the common route in which column chromatography is required. We prepared eleven picolinate complexes by this route, eight of which were characterized by single crystal x-ray diffraction. The complexes possess the same distorted octahedral geometry with two bidentate phenylpyridine ligands and one bidentate 2-picolinate ligand. All of the compounds exhibited efficient phosphorescence with colors ranging from blue to orange; photophysical measurements revealed emission quantum yields as high as 0.92, while most surpassed 0.5. Time-dependent density functional theory calculations, coupled with the use of natural transition orbitals (NTOs), allowed a detailed interpretation of the electronic structures for the complexes. The nature of the acceptor orbital for the lowest-energy triplet state NTO was found to be an important predictor for the emission spectra of FIrpic and its congeners.

Plastic scintillators are widely deployed for ionizing radiation detection, as they can be fabricated in large sizes, for high detection efficiency. However commercial plastics are limited in use for gamma spectroscopy, since their photopeak is too weak, due to low Z, and they are also limited in use for neutron detection, since proton recoils are indistinguishable from other ionizing radiation absorption events in standard plastics. We are working on scale up and production of transparent plastic scintillators based on polystyrene (PS) with high loading of bismuth metallorganics for gamma spectroscopy, and with lithium metallorganics for neutron detection. When activated with standard organic fluors, PS scintillators containing 8 wt% bismuth provide energy resolution of 11% at 662 keV. A PS plastic formulation including 1.3 wt% lithium-6 provides a neutron capture peak at 525 keVee, with 11% resolution for the capture peak and 90% efficiency for thermal neutron capture in 2mm thickness. Acknowledgements This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and has been supported by the US DOE National Nuclear Security Administration, Defense Nuclear Nonproliferation Research and Development under Contract No. DE-AC03-76SF00098

New scintillators for high-resolution gamma ray spectroscopy have been identified, grown and characterized. Our development efforts have focused on two classes of high-light-yield materials: europium-doped alkaline earth halides and cerium-doped garnets. Of the halide single crystals we have grown by the Bridgman method-SrI2, CaI2, SrBr2, BaI2 and BaBr2-SrI2 is the most promising. SrI2(Eu) emits into the Eu2+ band, centered at 435 nm, with a decay time of 1.2 mus and a light yield of up to 115,000 photons/MeV. It offers energy resolution better than 3% FWHM at 662 keV, and exhibits excellent light yield proportionality. Transparent ceramic fabrication allows the production of gadolinium- and terbium-based garnets which are not growable by melt techniques due to phase instabilities. The scintillation light yields of cerium-doped ceramic garnets are high, 20,000-100,000 photons/MeV. We are developing an understanding of the mechanisms underlying energy dependent scintillation light yield non-proportionality and how it affects energy resolution. We have also identified aspects of optical design that can be optimized to enhance the energy resolution.

(1,2-naphtho)(1,8-naphtho)thioindigo (PNT) has been synthesized following a simple Friedel–Crafts route and its photochemical properties in toluene and polymethylmethacrylate (PMMA) have been characterized. PNT is a photochromic molecule capable of reversible photoisomerization between a yellow form ( cis -PNT, λ max = 484 nm) and a purple form ( trans -PNT, λ max = 595 nm). The stable purple form converts to the yellow form with a trans -PNT to cis -PNT conversion quantum yield of 0.027 in toluene and 0.062 in PMMA. The unstable yellow form exhibits a cis -PNT to trans -PNT quantum efficiency of conversion of 0.27–0.85 in toluene and 0.17–0.68 PMMA, with highest conversion efficiency occurring in the vicinity of its λ max of 484 nm. trans -PNT has a strong fluorescence quantum yield, 0.14 (toluene) and 0.16 (PMMA). For samples prepared photochemically in the cis -PNT form, slow thermal relaxation to the trans form occurs in the dark, with a half life of about 17 h in toluene (25 °C) and even slower, 168 h, in PMMA. The property of photoswitching between fluorescent and non-fluorescent forms makes this material a candidate for many applications in imaging and data storage.

X-ray photoemission spectroscopy was used to study Pt–metal oxide aerogel catalysts that have been developed to respond to increased NOx emissions of lean-burn engines. Lean-burn engines, critical components of low and zero emission vehicles, produce much higher levels of engine-out NOx and current three-way catalytic converters are not sufficient to meet Clean Air Act standards. Platinum catalysts were formed by the reaction of modified Pt coordination compounds with selected transition–metal alkoxides through sol–gel techniques into aerogels. Photoemission measurements of the Pt 4f, Si 2p, Ti 2p, O 1s, and C 1s core lines were used to evaluate the chemistry of the material after each processing step. Results indicate Pt–O bonding and reduced Pt disbursed in the aerogel. In addition, Si 2p, Ti 2p, and O 1s binding energies indicate an oxo-bridged network structure.

Compatible blends of poly(vinyl acetate) and poly(methyl methacrylate) have been used to produce a series of electrically conducting carbon black composites whose resistance is sensitive to the nature and concentration of an analyte in the vapor phase. The dc electrical resistance response of the composites was found to be a nonlinear function of the mole fraction of poly(vinyl acetate) in the blend. These compatible blend composite detectors provided additional analyte discrimination information relative to a reference detector array that only contained composites formed using the pure polymer phases. The added discrimination power provided by the compatible blend detectors, and thus the added diversity of the enhanced detector array, was quantified through use of a statistical metric to assess the performance of detector arrays in various vapor classification tasks.

Linear, soluble copolymers containing titanium are of interest for use in targets for inertial-confinement fusion (ICF) experiments because the titanium is a useful spectroscopic probe for studying the nuclear fusion process. We have studied the reactions of dichloro- titanocene and diphenyltitanocene with carboxylic acids to determine if these can be used to prepare such polymers. Model reactions of dichlorotitanocene with p-toluic acid show that both mono- and di-carboxylates are formed. We have prepared a soluble titanium-containing copolymer via the reaction of poly(styrene-co-methacrylic acid) with an excess of dichlorotitanocene but attempts to remove the excess molecular titanocene from the copolymer result in crosslinking of the copolymer. Model reactions of benzoic and pivalic acids with diphenyltitanocene demonstrate that monosubstituted carboxylato(phenyl)titanocenes are formed but that these products are stable only at low temperatures and decompose readily at ambient temperature. Proton NMR studies of the reaction of diphenyltitanocene and benzoic acid at −20 °C indicate that this reaction is second order, suggesting that the reaction does not proceed through a benzyne intermediate. © 1997 by John Wiley & Sons, Ltd.

Bismuth-loaded plastic scintillators capable of gamma spectroscopy are being scaled up to multiple cubic inch sizes. High light yields of >38,888 Ph/MeV are obtained with Iridium-complex fluors due to efficient harvesting of both singlet and triplet excitons, providing energy resolution of ~10% at 662 keV for 3 in3 scintillators. Although singlet fluors provide a poorer light yield of ~12,888 Ph/MeV and resolution at 662 keV of 14% in the Bismuth-loaded plastics, the fast decay time of

Recently discovered scintillators for gamma ray spectroscopy, single crystal SrI{sub 2}(Eu), GYGAG(Ce) transparent ceramic and Bismuth-loaded plastics, offer resolution and fabrication advantages compared to commercial scintillators, such as NaI(Tl) and standard PVT plastic. Energy resolution at 662 keV of 2.7% is obtained with SrI{sub 2}(Eu), while 4.5% is obtained with GYGAG(Ce). A new transparent ceramic scintillator for radiographic imaging systems, GLO(Eu) offers high light yield of 70,000 Photons/MeV, high stopping, and low radiation damage. Implementation of single crystal SrI{sub 2}(Eu), Gd-based transparent ceramics, and Bi-loaded plastic scintillators can advance the state-of-the art in ionizing radiation detection systems.

Carbon black−chiral polymer composites were used to provide diagnostic differential resistance responses in the presence of enantiomers of chiral gaseous analytes. Vapors of (+)-2-butanol and (−)-2-butanol, (+)-α-pinene and (−)-α-pinene, (+)-epichlorohydrin and (−)-epichlorohydrin, and methyl (+)-2-chloropropionate and methyl (−)-2-chloropropionate were generated and passed over a chemically sensitive carbon black−poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate) (77% butyrate) composite resistor. Each enantiomer of a pair produced a distinct relative differential resistance change on the chiral detector, whereas both enantiomers of a set produced identical signals on achiral carbon black−poly(ethylene-co-vinyl acetate) (82% ethylene) detectors.

We are developing new scintillator materials that offer potential for high resolution gamma ray spectroscopy at low cost. Single crystal SrI 2 (Eu) offers ∼3% resolution at 662 keV, in sizes of ∼1 in3. We have developed ceramics processing technology allowing us to achieve cubic inch scale transparent ceramic scintillators offering gamma spectroscopy performance superior to NaI(Tl). Our bismuth-loaded plastic scintillator demonstrates energy resolution of ∼8% at 662 keV, for samples of ∼0.5 cm3.

Transparent ceramics combine the scintillation performance of single crystals with the ruggedness and processability of glass. We have developed a versatile, scaleable fabrication method, wherein nanoparticle feedstock is consolidated at temperatures well below melting to form inch-scale phase-pure transparent ceramics with optical scatter of α

The reduction of (η-C 5 H 5 )TaCl 4 with sodium sand in neat trimethylphosphine gives a mixture of products from which (η-C 5 H 5 ) 2 Ta(H)PMe 3 ( 1 ) may be isolated in low yield and (η-C 5 H 5 )Ta(PMe 3 ) 2 -(H)(η 2 -CH 2 PMe 2 ) ( 2 ) may be identified by NMR spectroscopy. Treatment of (η-C 5 Me 5 )TaCl 4 under similar conditions affords (η-C 5 Me 5 )Ta(PMe 3 )(H) 2 (η 2 -CHPMe 2 ) ( 3 ) which has been characterized spectroscopically and by an X-ray diffraction study. When a more conventional sodium amalgam/tetra-hydrofuran reducing medium is used, (η-C 5 Me 5 )TaCl 4 reacts with excess trimethylphosphine to give (η 7 -C 5 Me 3 (CH 2 ) 2 )Ta(H) 2 (PMe 3 ) 2 ( 4 ) in which two ring methyl Cbonds have been cleaved. 4 has been characterized spectroscopically and by an X-ray diffraction study. Complexes 3 and 4 do not undergo interconversion readily under thermal conditions, and dynamic NMR studies on 3 provide no evidence for reversible hydrogen migrations. Investigations into use of other reducing media show that the ratio of the isomers obtained is highly dependent upon reducing agent and solvent.

Transparent ceramics offer an alternative to single crystals for scintillator applications such as gamma ray spectroscopy and radiography. We have developed a versatile, scaleable fabrication method, using Flame Spray Pyrolysis (FSP) to produce feedstock which is readily converted into phase-pure transparent ceramics. We measure integral light yields in excess of 80,000 Ph/MeV with Cerium-doped Garnets, and excellent optical quality. Avalanche photodiode readout of Garnets provides resolution near 6%. For radiography applications, Lutetium Oxide offers a high performance metric and is formable by ceramics processing. Scatter in transparent ceramics due to secondary phases is the principal limitation to optical quality, and afterglow issues that affect the scintillation performance are presently being addressed.

Ceramic and single crystal Lutetium Aluminum Garnet scintillators exhibit energy resolution with bialkali photomultiplier tube detection as good as 8.6% at 662 keV. Ceramic fabrication allows production of garnets that cannot easily be grown as single crystals, such as Gadolinium Aluminum Garnet and Terbium Aluminum Garnet. Measured scintillation light yields of Cerium-doped ceramic garnets indicate prospects for high energy resolution.

(1,2-naphtho)(1,8-naphtho)thioindigo (PNT) has been synthesized following a simple Friedel-Crafts route and its photochemical properties in toluene and PMMA characterized. PNT is a photochromic molecule capable of reversible photoisomerization between a yellow form (cis-PNT, {lambda}{sub max} = 484 nm) and a purple form (trans-PNT, {lambda}{sub max} = 595 nm). The stable purple form converts to the yellow form with a trans-PNT to cis-PNT conversion quantum yield of 0.027 in toluene and 0.062 in PMMA. The unstable yellow form exhibits a cis-PNT to trans-PNT quantum efficiency of conversion of 0.27-0.85 in toluene and 0.17-0.68 PMMA, with highest conversion efficiency occurring in the vicinity of its {lambda}{sub max} of 484 nm. Trans-PNT has a strong fluorescence quantum yield, 0.14 (toluene) and 0.16 (PMMA). For samples prepared photochemically in the cis-PNT form, slow thermal relaxation to the trans form occurs in the dark, with a half life of about 17 hours in toluene (25 C) and even slower, 168 hours, in PMMA. The property of photoswitching between fluorescent and non-fluorescent forms makes this material a candidate for many applications in imaging and data storage. An anomalous excitation profile for the fluorescence from trans-PNT, showing a dip at {approx}600 nm, is an agreement with the wavelength-dependent quantum yield of conversion from trans-PNT to cis-PNT, which is highest at the absorbance peak.

Response data were collected for a carbon black-polymer composite electronic nose array during exposure to homologous series of alkanes and alcohols. At a fixed partial pressure of odorant in the vapor phase, the mean response intensity of the electronic nose signals varied significantly for members of each series of odorants. However, the mean response intensity of the electronic nose detectors, and the response intensity of the most strongly-driven set of electronic nose detectors, was essentially constant for members of a chemically homologous odorant series when the concentration of each odorant in the gas phase was maintained at a constant fraction of the odorant's vapor pressure. Because the thermodynamic activity of an odorant at equilibrium in a sorbent phase is equal to the partial pressure of the odorant in the gas phase divided by the vapor pressure of the odorant, and because the activity coefficients are similar within these homologous series of odorants for sorption of the vapors into specific polymer films, the data imply that the trends in detector response can be understood based on the thermodynamic tendency to establish a relatively constant concentration of sorbed odorant into each of the polymeric films of the electronic nose at a constant fraction of the odorant's vapor pressure. This phenomenon provides a natural mechanism for enhanced sensitivity to low vapor pressure compounds, like TNT, in the presence of high vapor pressure analytes, such as diesel fuel. In a related study to evaluate the target recognition properties of the electronic nose, a statistical metric based on the magnitudes and standard deviations along Euclidean projections of clustered array response data, was utilized to facilitate an evaluation of the performance of detector arrays in various vapor classification tasks. This approach allowed quantification of the ability of a fourteen-element array of carbon black-insulating polymer composite chemiresistors to distinguish between members of a set of nineteen solvent vapors, some of which vary widely in chemical properties (e.g. methanol and benzene) and others of which are very similar (e.g. n-pentane and n-heptane). The data also facilitated evaluation of questions such as array performance as a function of the number of detectors in the system.

Polyvinylcarbazole polymer scintillators with high loading of a bismuth organometallic exhibit good light yields, and are found to be capable of gamma-ray spectroscopy. When activated by a standard fluor, diphenylanthracene, a bismuth-loaded polymer produces ~12000 photons/MeV, exhibits an emission maximum at 420 nm, a ~15 ns decay, and energy resolution of 9% at 662 keV is measured. The same bismuth-loaded polymer doped with an iridium complex fluor has an emission maximum of 500 nm, a decay time of 1.2 μs, a light yield of ~30000 photons/MeV, and energy resolution better than 7% FWHM at 662 keV.

La synthese de Cp 2 ZrH 2 (ou Cp=C 5 Me 5 ) est effectuee. L'insertion d'olefines permet d'obtenir les complexes Cp 2 Zr(alkyl)H qui, a la suite d'une photolyse ou d'une pyrolyse donnent Cp 2 Zr(C 6 H 5 )H ainsi que l'alcane correspondant. D'autre part la pyrolyse de Cp 2 Zr(C 6 H 5 )H fournit le complexe de tetramethylfulvene Cp(η 6 -C 5 Me 4 CH 2 )Zr(C 6 H 5 )

Bis(pentamethylcyclopentadienyl)dihydridozirconium(IV), (eta/sup 5/-C/sub 5/Me/sup 5/)/sub 2/ZrH/sub 2/ (2) is prepared by the reaction of H/sub 2/ with ((eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrN/sub 2/)/sub 2/N/sub 2/ (1). 2 forms unstable adducts with PF/sub 3/ and CO at -80/sup 0/C. The carbonyl adduct (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrH/sub 2/(CO) yields ((eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrH)/sub 2/(OCH == CHO) and/or (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrH(OCH/sub 3/), depending on reaction conditions. Carbonylation of (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CH/sub 3/)/sub 2/, obtained from (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrCl/sub 2/ and methyllithium, yields successively (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CH/sub 3/)(CH/sub 3/CO) and (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(O(CH/sub 3/)C == C(CH/sub 3/)O). The zirconacyclopentane ecomplex (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CH/sub 2/(CH/sub 2/)/sub 2/CH/sub 2/) (10) is prepared from 1 and ethylene. Carbonylation of 10 affords (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(H)-(OC == OH(CH/sub 2/)/sub 2/CH/sub 2/). Treatment of 2 with isobutylene yields (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(H)(Ch/sub 2/CHMe/sub 2/) (13), which undergoes a reaction with CO to form (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(H)(OCH == CHCHMe/sub 2/) (15). The results of /sup 13/C and deuterium labeling studies indicate that the conversion of 13 to 15 is mediated by (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(H)(Me/sub 2/CHCH/sub 2/CO). The observed patterns formore » these reactions of alkyl and hydride derivatives of zirconium with CO are attributed to carbenoid character of the carbonyl carbon resulting from an unusual ''side-on'' coordination of acyl and formyl groups.« less

A styrene-1% divinylbenzene resin whose phenyl rings have been derivatized with --PPh2 groups serves as an 'anchor' for Fe(CO)(n)(n = 3,4) groups; the anchor is the Fe-P bond. The photocatalytic activity of suspensions of the polymer-anchored Fe(CO)(n) has been compared to homogeneous solutions of Fe(CO)(n)(PPh3)(5-n)(n = 5,4,3). 1-Pentene isomerization and reaction with HSiEt3 can be effected with each system. Observed quantum yields for 1-pentene isomerization exceed unity for each catalyst precursor and the initial trans- to cis-2-pentene ratio depends on the catalyst precursor implicating the retention of the triarylphospine groups in the actual catalytically active species. Irradiation of Fe(CO)n(PPh3)(5-n)(n = 4) results in loss of CO, not PPh3, suggesting a photoinert anchor to the Fe(CO)n groups in the polymer systems. These experiments establish the viability of photogenerating catalysts anchored to polymer supports without destruction of the the anchor bond in the photogeneration procedure. (Author)

Principles of M-C and M-H bonding interactions are examined experimentally by high-resolution valence photoelectron spectroscopy. Gas-phase He I and He II photoelectron spectra are reported for the following series of d{sup 0} and d{sup 2} bent metallocenes: Cp{sub 2}MH{sub 3} (M = Nb, Ta), Cp{sub 2}M(CO)L (M = Nb, Ta; L = H and M = Nb; L = CH{sub 3}), and Cp{sub 2}M(C{sub 2}H{sub 4})L (M = Nb, Ta; L = H and M = Ta; L = C{sub 2}H{sub 5}) (Cp = {eta}{sup 5}-C{sub 5}H{sub 5}). The ligand replacements represented by this series of complexes allow stepwise comparison and assignment of each individual low-energy valence ionization band. The He I/He II spectral comparisons show that the lowest ionization energy band of the carbonyl complexes is higher in metal character than the corresponding ionization of the ethylene complexes. This trend indicates extensive electron delocalization in the metal-ethylene bonding that corresponds more accurately to a metallacyclopropane description with relatively strong metal-carbon bonds. The photoelectron data for the early transition metal hydride and alkyl species show that the metal-hydrogen bonds are slightly more stable than the metal-carbon bonds. Correlation of the ionization information for these substituted early metallocenes reveals that themore » stabilization of the metallacyclopropane-hydride structures, M(C{sub 2}H{sub 4})H, relative to the olefin-inserted metal-alkyl structure, M(C{sub 2}H{sub 5}), is partly due to stabilization of the metal electron density by back-bonding to the olefin as indicated by earlier theoretical studies.« less

The structure of bis(pentamethylcyclopentadienyl)dichlorotitanium(IV) has been investigated by single-crystal X-ray diffraction techniques. [η-C 5 (CH 3 ) 5 ] 2 TiCl 2 crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with cell dimensions a = 10.816(1), b = 8.132(1), c = 22.259(1) A; Z = 4. Full matrix, least-squares refinement converged to a final R index of 0.032 based on 1429 reflections. The configuration about the titanium atom is a distorted tetrahedron comprised of the two chlorine atoms and the centroids of the two η-cyclopentadienyl rings. Several ring methyl groups are bent considerably out of the cyclopentadienyl plane and away from the titanium atom. These out-of-plane deviations are attributable to chlorine—methyl crowding and methyl—methyl contacts between the two rings.

The synthesis and characterization of (η 5 -C 5 Me 5 )TaCl 4 , (η 5 -C 5 Me 5 )TaCl 4 L (L  PMe 3 , P(OMe) 3 , Ph 2 PCH 2 CH 2 PPh 2 ), (η 5 -C 5 Me 5 )TaMe 4 , and (η 5 -C 5 Me 5 )Ta(CH 2 Ph) 2 (CHPh) is described. NMR studies of the bis(1,2-diphenylphosphino)ethane (dppe) adduct show exchange of free and ligated dppe, possibly via dissociation of the ligand from a monodentate compound.

Photochemistry offers a technique to synthesize unique catalysts, control catalytic reactions, and perturb and better understand conventional catalytic cycles. Recent studies in the author's laboratory concerning photoinduced catalysis using mono-, di-, and trinuclear organometallic catalyst precursors are summarized. Specific systems considered here are (M(CO)nL5-n) (M = Fe, Ru; L = PPh; n = 5,4,3), (M3(CO)12) (M = Fe, Ru, Os), (Ru3(CO)g(PPh3)3), and (Co2(CO)6L2) (L = P(n-Bu)3, P(OPh)3) used to effect catalytic chemistry of 1-pentene including isomerization, hydrogenation, and hydrosilation. (Author)

The photocatalyzed isomerization of 1-pentene to trans- and cis-2-pentene by Ru(CO)4PPh3 and Ru3(CO)9(PPh3)3 is reported along with data for Ru3(CO)12, Fe3(CO)12, and Fe(CO)5. The primary photoprocess in Ru(CO)4PPh3 is dissociative loss of CO giving a coordinatively unsaturated species having the same empirical formula Ru3(CO)9(PPh3)3; the trinuclear species undergoes Ru-Ru bond rupture and ultimate declusterification subsequent to photo-excitation giving a quantitative yield of Ru(CO)4PPh3 under CO or Ru(CO)3(PPh3)2 in the presence of PPh3. The crucial result is that the cluster yields a different catalytically active species compared to Ru(CO)4PPh3, since the initial ratio of trans- and cis-2-pentene is different for the two photocatalysts. The photocatalysis and primary photoprocesses suggest that the isomerization from the Ru3(CO)9(PPh3)3 results from an active form of the cluster. By way of contrast, Fe(CO)5 and Fe3(CO)12 yields the same initial ratio of photocatalytic products, implicating a common, mononuclear catalytic species. Since the clusters are good visible absorbers compared to the mononuclear species, photoactivation of cluster catalysis can be effected with low energy visible light.

Reduction of CO in moderate yields was observed when ((eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CO))/sub 2/N/sub 2/ was treated with HCl. Further studies revealed that mononuclear carbonyl and hydride complexes of bis(pentamethylcyclopentadienyl)zirconium were capable of promoting the stoichiometric H/sub 2/ reduction of CO to methoxide under very mild conditions.