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The lack of low-temperature (200 °C) and easy-to-handle vapor deposition precursors for cadmium has been a limitation for cadmium chalcogenide ALD. Here, the cadmium amidinate system is presented as a scaffold for vapor deposition precursor design because the alkyl groups can be altered to change the properties of the precursor. Thus, the molecular structure affects the precursor stability at elevated temperature, onset of volatility, and reactivity. Cadmium

An in situ microbalance and infrared spectroscopic study of alternating exposures to Me2Au(S2CNEt2) and ozone illuminates the organometallic chemistry that allows for the thermal atomic layer deposition (ALD) of gold. In situ quartz crystal microbalance (QCM) studies resolve the nucleation delay and island growth of Au on a freshly prepared aluminum oxide surface with single cycle resolution, revealing inhibition for 40 cycles prior to slow nucleation and film coalescence that extends over 300 cycles. In situ infrared spectroscopy informed by first-principles computation provides insight into the surface chemistry of the self-limiting half-reactions, which are consistent with an oxidized Au surface mechanism. X-ray diffraction of ALD-grown gold on silicon, silica, sapphire, and mica reveals consistent out-of-plane oriented crystalline film growth as well as epitaxially directed in-plane orientation on closely lattice-matched mica at a relatively low growth temperature of 180 °C. A more complete understanding of ALD gold nucleation, surface chemistry, and epitaxy will inform the next generation of low-temperature, nanoscale, textured depositions that are applicable to high surface area supports.

We describe the use of a vanadium 3+ precursor for atomic layer deposition (ALD) of thin films that span the common oxidation states of vanadium oxides. Self-limiting surface synthesis of V2O3, VO2, and V2O5 are realized through four distinct reaction mechanisms accessed via judicious choice of oxygen ALD partners. In situ quartz crystal microbalance and quadrupole mass spectrometry were used to study the reaction mechanism of the vanadium precursor with O3, H2O2, H2O/O2, and H2O2/H2. A clear distinction between nonoxidative protic ligand exchange and metal oxidation is demonstrated through sequential surface reactions with different nonmetal precursors. This synergistic effect provides greater control of the resultant metal species in the film, as well as reactive surface species during growth. In an extension of this approach, we introduce oxidation state control through reducing equivalents of H2 gas. When H2 is dosed after H2O2 during growth, amorphous films of VO2 are deposited that are readily cryst...

Single-site Ga/SiO2 catalysts exhibit up to 99% C3H6 selectivity at 4% propane conversion with an initial rate of 5.4 × 10−4 (mole C3H6) (mole Ga)−1 s−1 during propane dehydrogenation (PDH) at 550 °C. Following pre-treatment in H2 at 550 °C, only four-coordinate, Ga3+–O Lewis acid sites are observed under reaction conditions. At 650 °C in H2, an additional isolated Ga site with lower Ga–O coordination (N Ga−O

Alkyl-zinc and zinc oxide-type sites were synthesized via atomic layer deposition on high-surface-area silica using an integrated atomic layer deposition-catalysis instrument (I-ALD-CAT). One-cycle ALD experiments using diethylzinc (DEZ) afforded Zn/SiO2 systems that provided key insights into the reactivity and stability of Zn sites as a function of dispersion at the submonolayer level. The I-ALD-CAT tool design allowed for systematic comparison of the reactivity of different grafted zinc sites. Open-shell 16-electron, tricoordinate ethyl zinc-silica sites exhibit higher activity in propane hydrogenation-dehydrogenation compared to 18-electron, tetracoordinate zinc oxide-type centers. Silica surface saturation with Zn(II) sites (∼75% of a monolayer) results in facile zinc agglomeration and catalyst deactivation under reaction conditions. Reduced DEZ dosing coupled with thermal substrate pretreatment techniques (e.g., dehydration under vacuum) resulted in increased Zn dispersion and produced Zn/SiO2 catalysts with improved activity and stability under propylene hydrogenation (200 °C) and propane dehydrogenation (550 °C) conditions.

Crystalline tungsten disulfide (WS2) has been prepared from the reaction of bis(cyclopentadienyl)tungsten dihydride with sulfur at room temperature and ambient pressure in organic solvents. WS2 was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, resonance Raman spectroscopy, transmission electron microscopy, and X-ray absorption spectroscopy, and the resulting WS2 is highly crystalline by X-ray diffraction. The low-temperature synthesis is hypothesized to be a result of highly mobile surface W–Cp groups that are able to facilitate crystallization.

This study details the surface reaction chemistry relevant to the vapor deposition mechanism of SnO2 thin films by atomic layer deposition. The mechanism was elucidated by combining different spectroscopic studies. Initial nucleation of cyclic N2,N3-di-tert-butylbutane-2,3-diamidotin(II) (1) consists of surface SiOH protonation of ligands as shown by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This SiO2-surface-bound stannylene was further characterized by X-ray absorption (XAS) and resonance Raman spectroscopy. XAS, DRIFTS, and Raman spectroscopy were then used to follow the further reaction of the surface-bound stannylene with different oxygen sources and a second equivalent of 1. It was observed that water does not oxidize the initial surface-bound tin site, and a well-defined, three-coordinate tin(II) species, with two surface oxygen bonds and one coordinated water molecule, was characterized. Treatment of the surface stannylene with protic oxidants such as H2O2 or tBuOOH ful...

Substitutional alloys of several thin film semiconductors have been proposed as intermediate band (IB) materials for use in next-generation photovoltaics, which aim to utilize a larger fraction of the solar spectrum without sacrificing significant photovoltage. We demonstrate a novel approach to IB material growth, namely atomic layer deposition (ALD), to allow unique control over substitutional-dopant location and density. Two new ALD processes for vanadium sulfide incorporation are introduced, one of which incorporates a vanadium(III) amidinate previously untested for ALD. Using this process, we synthesize the first thin film VxIn(2–x)S3 intermediate band semiconductors and further demonstrate that the V:In ratio, and therefore intraband gap density of states, can be finely tuned according to the ALD dosing schedule. Deposition on a crystalline In2S3 underlayer promotes the growth of a tetragonal β-In2S3-like phase VxIn(2–x)S3, which exhibits a distinct sub-band gap absorption peak with onset near 1.1 e...

The effect of Zr modification on the catalytic activity of Co/SiO2 was investigated for nonoxidative propane dehydrogenation. Isolated Zr on SiO2 surface sites were prepared by organometallic synthesis using Zr(OtBu)4 as a precursor. The resulting Zr/SiO2 support was functionalized with Co2+ ions via strong electrostatic adsorption. Spectroscopic (diffuse reflectance infrared Fourier transform spectroscopy, UV–vis, electron paramagnetic resonance) and microscopic characterization (transmission electron microscopy, scanning transition electron microscopy) results are consistent with single-site cobalt that preferentially associates with the mono-dispersed Zr at a variety of loadings and Co/Zr ratios. The oxidation state of Co in the as-prepared Co/SiO2 and Co–Zr/SiO2 was both +2 with tetrahedral and octahedral geometries, respectively. In situ X-ray absorption near edge structure and extended X-ray absorption fine structure results confirmed that the oxidation state of Co remained as +2 under reaction condition for both Co/SiO2 and Co–Zr/SiO2 samples and both catalysts have tetrahedral Co2+ as the active catalyst. Despite similar Co coordination environments, the catalytic activity and selectivity was significantly improved by the Zr modification of the silica support versus Co/SiO2. This was attributed to the change in oxygen donor ability and Co–O bond strength of the ≡SiO–Zr–O sites of Co–Zr/SiO2 compared with the ≡SiO– ligands in Co/SiO2. These results show that tuning of the support SiO2 oxygen donation ability by use of an anchoring site (e.g., ≡SiO–Zr–O–) can be used to alter both rate and selectivity of propane dehydrogenation with single-site heterogeneous catalysts. These results also show some preference for Co2+ active sites to associate with ≡SiO–Zr–O– sites over ≡SiO–.

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order to better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. These findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.

A single-site chromium catecholate POP (catPOP A2B1) was synthesized and characterized via AT-IR, XAS, and EPR spectroscopy. The well-defined, four-coordinate, 11-electron Cr(III) centers bound to catecholate POP were demonstrated to be active hydrogenation catalysts for nonpolar unsaturated organic substrates under mild conditions (5 mol % of Cr, 200 psi of H2, 60 °C). This material constitutes the first example of a well-defined, supported organometallic chromium hydrogenation precatalyst.

We report the synthesis, characterization, and catalytic performance for gas phase propane dehydrogenation of single-site Co2+ ions supported on silica. Spectroscopic characterization by resonance Raman, electron paramagnetic resonance, and X-ray near-edge and extended absorption fine structure revealed that tetrahedrally coordinated Co2+ ions are chemisorbed into the trisiloxane rings on the surface of amorphous silica. In situ XAS shows that Co is not oxidized by air nor reduced by hydrogen even at 650 °C. For catalytic propane dehydrogenation, single-site Co2+/SiO2 exhibits selectivities >95% at 550 °C and >90% at 650 °C with stable activity over 24 h. Calculations with hybrid density functional theory support a non-redox mechanism for activation of C–H and H–H bonds by Co2+ similar to that previously reported for single-site Zn2+/SiO2.

Thin films containing germanium or tin have a great variety of current and potential applications, particularly their oxides or chalcogenides. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are popular ways to make these thin films conformally even on challenging nanostructured substrates. The success of these processes depends on having precursors that are sufficiently stable, volatile, and reactive. In this paper we optimize the syntheses of the following three precursors: 1 and 2 are racemic Ge(II) or Sn(II) cyclic amides made from N2,N3-di-tert-butylbutane-2,3-diamine, and 3 is bis(N,N′-diisopropylacetamidinato)tin(II). All three compounds are demonstrated to be effective precursors for ALD of their monosulfides, GeS or SnS, by reaction with H2S. 2 has also been reported previously to make polycrystalline SnO2 by ALD with oxidizing agents such as H2O2. The cyclic amides 1 and 2 are more volatile than the amidinate 3, vaporizing sufficiently for ALD even at precursor temperatures bel...

A single-site, rhodium(I) catecholate containing porous organic polymer was prepared and utilized as an active catalyst for the hydrogenation of olefins in both liquid-phase and gas-phase reactors. Liquid-phase, batch hydrogenation reactions at 50 psi and ambient temperatures result in the formation of rhodium metal nanoparticles supported within the polymer framework. Surprisingly, the Rh(I) complex is catalytically active and stable for propene hydrogenation at ambient temperatures under gas-phase conditions, where reduction of the Rh(I) centers to Rh(0) nanoparticles requires at least 200–250 °C under a flow of hydrogen gas. After high-temperature treatment, the Rh(0) nanoparticles are active arene hydrogenation catalysts that convert toluene to methylcyclohexadiene at a rate of 9.3 × 10–3 mol g–1 h–1 of rhodium metal at room temperature. Conversely, single-site Rh(I) is an active and stable catalyst for the hydrogenation of propylene (but not toluene) under gas-phase conditions at room temperature.

The oxidation state and coordination number of immobilized iron catecholate EtO2Fe(CAT-POP) were determined by X-ray absorption spectroscopy (XAS) under a variety of conditions. We find the as-prepared material to be three-coordinate Fe2+ that readily oxidizes to Fe3+ upon exposure to air but remains three-coordinate. Both the reduced and oxidized Fe(CAT-POP) catalyze olefin hydrogenation in batch and flow reactors. We determined the catalytic rates for both species and also observed by means of XAS that the oxidation state of the iron centers does not change in hydrogen at the reaction temperature. Therefore, we postulate that the mechanism of hydrogenation by Fe(CAT-POP) proceeds through one of several possible nonclassical mechanisms, which are discussed.

Control over the oxidation state and crystalline phase of thin-film iron oxides was achieved by low-temperature atomic layer deposition (ALD), utilizing a novel iron precursor, bis(2,4-methylpentadienyl)iron. This low-temperature (T = 120 °C) route to conformal deposition of crystalline Fe3O4 or α-Fe2O3 thin films is determined by the choice of oxygen source selected for the second surface half-reaction. The approach employs ozone to produce fully oxidized α-Fe2O3 or a milder oxidant, H2O2, to generate the Fe(2+)/Fe(3+) spinel, Fe3O4. Both processes show self-limiting surface reactions and deposition rates of at least 0.6 Å/cycle, a significantly high growth rate at such mild conditions. We utilized this process to prepare conformal iron oxide thin films on a porous framework, for which α-Fe2O3 is active for photocatalytic water splitting.

Thin film solar cells made from earth-abundant, non-toxic materials are needed to replace the current technology that uses Cu(In,Ga)(S,Se)2 and CdTe, which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (SnS). In this report, pure, stoichiometric, single-phase SnS films were obtained by atomic layer deposition (ALD) using the reaction of bis(N,N′-diisopropylacetamidinato)tin(II) [Sn(MeC(N-iPr)2)2] and hydrogen sulfide (H2S) at low temperatures (100 to 200 °C). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption (α > 104 cm−1) is observed throughout the visible and near-infrared spectral regions. The films are p-type semiconductors with carrier concentration on the order of 1016 cm−3 and hole mobility 0.82–15.3 cm2V−1s−1 in the plane of the films. The electrical properties are anisotropic, with three times higher mobility in the direction through the film, compared to the in-plane direction.

An X-ray structural study of Mo(NAd)(CHCMe2Ph)(2,5-Me2NC4H2)2 (1; Ad = 1-adamantyl) reveals it to contain one η1-2,5-Me2NC4H2 ring and one η5-2,5-Me2NC4H2 ring. The structures of Mo(NAr)(CHCMe2Ph)(...

Monosiloxide and disiloxide complexes have been prepared through the addition of silanols to Mo(NR)(CHCMe2Ph)(pyrrolyl)2 species [R = 1-adamantyl (Ad) or 2,6-i-Pr2C6H3 (Ar)]. The silanols employed ...

The structure of [(CF3N2NMe)Mo(CH2SiMe3)2] (in which (CF3N2NMe)2- is [(3-CF3C6H4NCH2CH2)2NMe]2-) is approximately trigonal bipyramidal with one axial and one equatorial alkyl ligand. Heating of solutions of [(CF3N2NMe)Mo(CH2SiMe3)2] in [D6]benzene in the presence of five equivalents of 2-butyne led to diamagnetic [(CF3N2NMe)Mo(CHSiMe3)(eta(2)-MeC[triple bond]CMe)], whose structure is approximately square pyramidal with the alkyne occupying the axial site. Addition of one equivalent of cyclohexene sulfide to [(CF3N2NMe)Mo(CH2SiMe3)2] at room temperature produced the diamagnetic, dimeric molybdenum(IV) sulfido complex, [{(CF3N2NMe)MoS}2]. This complex is composed of two approximately trigonal bipyramidal centers, each containing one axial and one equatorial sulfur atom. Oxidation of [(CF3N2NMe)Mo(CH2SiMe3)2] with hexachloroethane resulted in formation of tetramethylsilane, HCl, and the sparingly soluble, red alkylidyne complex, [{(CF3N2NMe)Mo(CSiMe3)Cl}2]. This complex forms a dimer through bridging chlorides. The oxidation reactions of [(CF3N2NMe)Mo(CH2SiMe3)2] with 2-butyne, cyclohexene sulfide, or C2Cl6 are all proposed to proceed by alpha-hydrogen abstraction in the Mo(VI) species to yield (initially) the Mo=CHSiMe3 species and tetramethylsilane.

Synchrotron characterization techniques provide some of the most powerful tools for the study of film structure and chemistry. The brilliance and tunability of the Advanced Photon Source allow access to scattering and spectroscopic techniques unavailable with in-house laboratory setups and provide the opportunity to probe various atomic layer deposition (ALD) processes in situ starting at the very first deposition cycle. Here, we present the design and implementation of a portable ALD instrument which possesses a modular reactor scheme that enables simple experimental switchover between various beamlines and characterization techniques. As first examples, we present in situ results for (1) X-ray surface scattering and reflectivity measurements of epitaxial ZnO ALD on sapphire, (2) grazing-incidence small angle scattering of MnO nucleation on silicon, and (3) grazing-incidence X-ray absorption spectroscopy of nucleation-regime Er2O3 ALD on amorphous ALD alumina and single crystalline sapphire.

An integrated atomic layer deposition synthesis-catalysis (I-ALD-CAT) tool was developed. It combines an ALD manifold in-line with a plug-flow reactor system for the synthesis of supported catalytic materials by ALD and immediate evaluation of catalyst reactivity using gas-phase probe reactions. The I-ALD-CAT delivery system consists of 12 different metal ALD precursor channels, 4 oxidizing or reducing agents, and 4 catalytic reaction feeds to either of the two plug-flow reactors. The system can employ reactor pressures and temperatures in the range of 10(-3) to 1 bar and 300-1000 K, respectively. The instrument is also equipped with a gas chromatograph and a mass spectrometer unit for the detection and quantification of volatile species from ALD and catalytic reactions. In this report, we demonstrate the use of the I-ALD-CAT tool for the synthesis of platinum active sites and Al2O3 overcoats, and evaluation of catalyst propylene hydrogenation activity.

In the Buchwald-Hartwig reaction between HIPTBr (HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3 = hexaisopropylterphenyl) and (H2NCH2CH2)3N, it is possible to obtain a 65% isolated yield of (HIPTNHCH2CH2)2NCH2CH2NH2. A second coupling then can be carried out to yield a variety of "hybrid" ligands, (HIPTNHCH2CH2)2NCH2CH2NHAr, where Ar = 3,5-Me2C6H3, 3,5-(CF3)2C6H3, 3,5-(MeO)2C6H3, 3,5-Me2NC5H3, 3,5-Ph2NC5H3, 2,4,6-i-Pr3C6H2, or 2,4,6-Me3C6H2. The hybrid ligands may be attached to Mo to yield [hybrid]MoCl species. From the monochloride species, a variety of other species such as [hybrid]MoN, {[hybrid]MoN2}Na, and {[hybrid]Mo(NH3)}+ can be prepared. [Hybrid]MoN2 species were prepared through oxidation of {[hybrid]MoN2}Na species with ZnCl2, but they could not be isolated. [Hybrid]Mo=N-NH species could be observed as a consequence of the protonation of {[hybrid]MoN2}- species, but they too could not be isolated as a consequence of a facile decomposition to yield dihydrogen and [hybrid]MoN2 species. Attempts to reduce dinitrogen catalytically led to little or no ammonia being formed from dinitrogen. The fact that no ammonia was formed from dinitrogen in the case of Ar = 3,5-Me2C6H3, 3,5-(CF3)2C6H3, or 3,5-(MeO)2C6H3 could be attributed to a rapid decomposition of intermediate [hybrid]Mo=N-NH species in the catalytic reaction, a decomposition that was shown in separate studies to be accelerated dramatically by 2,6-lutidine, the conjugate base of the acid employed in the attempted catalytic reduction. X-ray structures of [(HIPTNHCH2CH2)2NCH2CH2N{3,5-(CF3)2C6H3}]MoCl and [(HIPTNHCH2CH2)2NCH2CH2N(3,5-Me2C6H3)]MoN2}Na(THF)2 are reported.

An X-ray study of [(THF)(RF6O)2(ArN)MoCH]2(1,4-C6H4) (ORF6 = OCMe(CF3)2; Ar = 2,6-diisopropylphenyl; THF = tetrahydrofuran; 1b), which is closely related to known [(DME)(RF6O)2(ArN)MoCH]2(1,4-C6H4) (DME = 1,2-dimethoxyethane; 1a), showed it to be the expected bimetallic species in which each end is approximately a trigonal bipyramidal monoadduct of a syn alkylidene with the THF coordinated to the NOO face of the metal trans to the MoC bond. Treatment of 1a with lithium tert-butoxide yielded [(t-BuO)2(ArN)MoCH]2(1,4-C6H4) (2). Addition of divinylferrocene to Mo(CHCMe2Ph)(NAr)(ORF6)2 produced the bimetallic species {(RF6O)2(ArN)Mo[CH(C5H4)]}2Fe (3), which upon treatment with lithium tert-butoxide produced a related tert-butoxide complex (4). X-ray studies of 3 and 4 showed them to be “syn/syn” bimetallic species related to 1b. In solution two resonances can be observed in proton NMR spectra in the alkylidene region for the “syn/anti” isomer of 1a, 2, 3, and 4; the total amount varies between 4 and 20% of th...

Reactions between [HIPTN3N]Mo(N2) and ethylene, acetylene, or CO yield Mo(η2-C2H4), Mo(η2-C2H2), and Mo(CO), respectively ([HIPTN3N]3- = [3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2]3N3-; HIPT = hexaisopropylterphenyl; [HIPTN3N]Mo = Mo). All are paramagnetic C3 symmetric species. Attempts to prepare Mo(CO) through reduction of MoCl with Na/Hg in THF under carbon monoxide yielded [Mo(CO)]Na, in which the sodium ion is believed to be bound within the HIPT aryl system. Addition of a variety of acids such as [Et3NH]BAr‘4 to [Mo(CO)]Na led to formation of the carbonyl hydride, Mo(CO)H, which also could be prepared by treating MoH with CO. Reactions between MoH and ethylene, 1-hexene, or 1-octene in benzene yield paramagnetic, red Mo(CH2R) complexes (CH2R = ethyl, hexyl, or octyl). MoMe could be prepared by treating MoCl with AlMe3 at room temperature over a period of 2 days. Treatment of MoH with acetylene affords yellow diamagnetic Mo(η2-CHCH2) plus polyacetylene. The MoCH2R complexes decompose at ∼150 °C to yield the ...

The diamine rac-H2[MepyN] (rac-N,N‘-di(6-methylpyridin-2-yl)-2,2‘-diaminobinaphthalene) has been prepared in good yield through reductive amination of rac-2,2‘-diaminobinaphthalene with 6-methylpyridinecarboxaldehyde. The [MepyN]2- ligand has been employed to prepare a variety of zirconium and hafnium complexes, [MepyN]MX2 (M = Zr, X = NMe2, Cl, OSO2CF3, CH2CHMe2, CH2Ph; M = Hf, X = NMe2, OSO2CF3, CH2CHMe2). The solid state structures of [MepyN]Zr(CH2Ph)2, [MepyN]Zr(NMe2)Cl, [MepyN]Hf(CH2CHMe2)2, and [MepyN]Hf(OSO2CF3)2 have been determined by X-ray diffraction. Activation of [MepyN]Zr(CH2Ph)2 and [MepyN]Hf(CH2CHMe2)2 with various Lewis acids leads to observable cationic alkyls that are not active toward 1-hexene polymerization.

In this paper we report the synthesis of several new Mo(NR)Cl4(THF) species (R = C6F5, 3,5-(CF3)2C6H3, 1-adamantyl, CPh3, and 2,6-i-Pr2C6H3) via the treatment of MoCl4(THF)2 with azides and their r...

Two new “NNN” (diamido-N-donor) ligands have been synthesized that contain ethylene/o-phenylene “arms” and a phenyl-substituted amine donor in the central position, [MesitylNH-o-C6H4N(Ph)CH2CH2NHMesityl] (H21) and [t-Bud6-NH-o-C6H4N(Ph)CH2CH2NHMesityl] (H22). The Zr and Hf complexes that have been isolated include [1]MX2 (M = Zr or Hf, X = NMe2, Cl, or Me) and [2]MX2 (M = Zr or Hf, X = NMe2, Cl, Me). The structures of [1]ZrMe2, [2]ZrMe2, and a dimeric species with the formula [MesitylN-o-C6H4NCH2CH2NMesityl]Zr2(NMe2)5 have been determined in X-ray crystallographic studies. Abstraction of a methyl group in [1]MMe2 (M = Zr or Hf) with [Ph3C][B(C6F5)4] gives rise to cationic complexes that are active initiators for the polymerization of 1-hexene. Similar activation of [2]MMe2 (M = Zr or Hf) gives rise to dimeric monocations that eventually break up and react further to yield cationic monomethyl species. In all cases the poly[1-hexene] produced in the presence of the monometallic cations was found to be atactic.

Molybdenum and tungsten complexes have been prepared that contain three different types of diamidoamine ligands of the type [(ArNCH2CH2)2NMe]2- ([ArNMe]2-, where Ar = C6F5, 3,4,5-F3C6H2, 3-CF3C6H4). The starting materials, which are of the type [Et3NH]{[ArNMe]MCl3}, are prepared from MCl4 reagents and the ligand upon addition of triethylamine. X-ray studies for [Et3NH]{[C6F5NMe]MoCl3}, [Et3NH]{[C6F5NMe]WCl3}, and [Bu4N]{[3-CF3C6H4NMe]MoCl3} reveal that the amido nitrogens are approximately cis to one another in a distorted-pseudooctahedral environment. Addition of various alkylating reagents to various [Et3NH]{[ArNMe]MCl3} species led to the formation of [C6F5NMe]MoMe2 (3), [C6F5NMe]Mo(CH2CMe3)Cl (4b), [C6F5NMe]W(CH2CMe3)Cl (5), [3,4,5-F3C6H2NMe]Mo(CH2CMe3)Cl (8), [3,4,5-F3C6H2NMe]Mo(CH2CMe3)(CCMe3) (9), [3,4,5-F3C6H2NMe]Mo(CH2SiMe3)2 (10), [3,4,5-F3C6H2NMe]W(CH2CMe3)(CCMe3) (11a), [3,4,5-F3C6H2NMe]W(CH2SiMe3)(CSiMe3) (11b), [3-CF3C6H4NMe]Mo(CH2SiMe3)2 (13), [3-CF3C6H4NMe]Mo(CH2CMe3)Cl (14), and [3-CF3C6H...

Atomic layer deposition (ALD) of indium sulfide (In2S3) films was achieved using a newly synthesized indium precursor and hydrogen sulfide. We obtain dense and adherent thin films free from halide and oxygen impurities. Self-limiting half-reactions are demonstrated at temperatures up to 225 °C, where oriented crystalline thin films are obtained without further annealing. Low-temperature growth of 0.89 Å/cycle is observed at 150 °C, while higher growth temperatures gradually reduce the per-cycle growth rate. Rutherford backscattering spectroscopy (RBS) together with depth-profiling Auger electron spectroscopy (AES) reveal a S/In ratio of 1.5 with no detectable carbon, nitrogen, halogen, or oxygen impurities. The resistivity of thin films prior to air exposure decreases with increasing deposition temperature, reaching1 Ω·cm for films deposited at 225 °C. Hall measurements reveal n-type conductivity due to free electron concentrations up to 10(18) cm(-3) and mobilities of order 1 cm(2)/(V·s). The digital synthesis of In2S3 via ALD at temperatures up to 225 °C may allow high quality thin films to be leveraged in optoelectronic devices including photovoltaic absorbers, buffer layers, and intermediate band materials.

A few heavily substituted metal sulfides have been predicted to form intermediate band (IB) materials. While early experiments with powdered material have shown great promise, a synthetic approach to thin film growth is lacking. Here we report an atomic layer deposition (ALD) approach to fabricate V 0.25 In 1.75 SP 3 IB thin films with the potential for unique alloying control. Many commercial indium and vanadium precursors were explored, but their surface chemistries were unsatisfactory with H 2 S. Instead, a novel indium (III) amidinate precursor enables the growth of largely impurity-free In 2 S 3 films. Thin films with promising optoelectronic properties have been tested and characterized. Additionally, vanadium alloying has commenced using a novel vanadium(III) amidinate precursor, and the first evidence of sub-band gap absorption has been observed.

International audience; Trichlorotris(tetrahydrofuran)molybdenum(III) (MoCl3(THF)3), is a widely used starting material for the synthesis of a broad range of molybdenum compounds. It was first prepared by a carbonyl route, but later the compound was obtained by a reductive procedure in three steps starting from MoCl5. In spite of the various incremental improvements, the three-step procedure remains rather long and requires isolation of both the MoCl4(MeCN)2 and MoCl4(THF)2 intermediates in order to obtain product of sufficient quality. Ethereal solutions of MoCl5 are stable and their conversion to tetrachlorobis(diethyl ether)molybdenum(IV) (MoCl4(OEt2)2) by reducing agents such as norbornene or allyltrimethylsilane has been previously reported. As it turns out, this reduction can be conveniently carried out by metallic tin. This chapter describes both the synthesis and isolation of the MoCl4(OEt2)2 complex and the direct, two-step, single-flask synthesis of MoCl3(THF)3 from MoCl5.

Addition of two equivalents of lithium pyrrolide to Mo(NR)(CHCMe2R')(OTf)2(DME) (OTf = OSO2CF3; R = 2,6-i-Pr2C6H3, 1-adamantyl, or 2,6-Br2-4-MeC6H2; R' = Me or Ph) produces Mo(NR)(CHCMe2R')(NC4H4)2 complexes in good yield. All compounds can be recrystallized readily from toluene or mixtures of pentane and ether and are sensitive to air and moisture. An X-ray structure of a 2,6-diisopropylphenylimido species shows it to be an unsymmetric dimer, {Mo(NAr)(syn-CHCMe2Ph)(η5-NC4H4)(η1-NC4H4)}{Mo(NAr)(syn-CHCMe2Ph)(η1-NC4H4)2}, in which the nitrogen in the η5-pyrrolyl bound to one Mo behaves as a donor to the other Mo. All complexes are fluxional on the NMR time scale at room temperature, with one symmetric species being observed on the NMR time scale at 50 °C in toluene-d8. The dimers react with PMe3 (at Mo) or B(C6F5)3 (at a η5-NC4H4 nitrogen) to give monomeric products in high yield. They also react rapidly with two equivalents of monoalcohols (e.g., Me3COH or (CF3)2MeCOH) or one equivalent of a biphenol or binaphthol to give two equivalents of pyrrole and bisalkoxide or diolate complexes in ~100% yield.

Three new tetramines, (ArNHCH(2)CH(2))(3)N, have been synthesized in which Ar = 3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3) (H(3)[HTBTN(3)N]), 3,5-(2,4,6-Me(3)C(6)H(2))(2)C(6)H(3) (H(3)[HMTN(3)N]), or 4-Br-3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(2) (H(3)[pBrHIPTN(3)N]). The diarylated tetramine, [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(2), has also been isolated, and the "hybrid" tetramine [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(4-t-BuC(6)H(4)) has been prepared from it. Monochloride complexes, [(TerNCH(2)CH(2))(3)N]MoCl, have been prepared, as well as a selection of intermediates that would be expected in a catalytic dinitrogen reduction such as [(TerNCH(2)CH(2))(3)N]Mo[triple bond]N and [[(TerNCH(2)CH(2))(3)N]Mo(NH(3))][BAr'(4)] (Ter = HTBT, HMT, or pBrHIPT and Ar' = 3,5-(CF(3))(2)C(6)H(3))). Intermediates that contain the new terphenyl-substituted ligands are then evaluated for their efficiency for the catalytic reduction of dinitrogen under conditions where analogous [HIPTN(3)N]Mo species give four turnovers to ammonia under "standard" conditions with an efficiency of approximately 65%. Only [pBrHIPTN(3)N]Mo compounds are efficient catalysts for dinitrogen reduction. The reasons are explored and discussed.