Comparison of Ligand Architecture on Vapor Deposition Precursors: Synthesis, Characterization, and Reactivity of Volatile Cadmium Bis-Amidinate Complexes.

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.

Thermal Atomic Layer Deposition of Gold: Mechanistic Insights, Nucleation, and Epitaxy.

An microbalance and infrared spectroscopic study of alternating exposures to MeAu(SCNEt) and ozone illuminates the organometallic chemistry that allows for the thermal atomic layer deposition (ALD) of gold. 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. 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.

Zirconium Modification Promotes Catalytic Activity of a Single-Site Cobalt Heterogeneous Catalyst for Propane Dehydrogenation.

The effect of Zr modification on the catalytic activity of Co/SiO was investigated for nonoxidative propane dehydrogenation. Isolated Zr on SiO surface sites were prepared by organometallic synthesis using Zr(O Bu) as a precursor. The resulting Zr/SiO support was functionalized with Co ions via strong electrostatic adsorption.

Nuclearity effects in supported, single-site Fe(ii) hydrogenation pre-catalysts.

Dimeric and monomeric supported single-site Fe(ii) pre-catalysts on SiO2 have been prepared via organometallic grafting and characterized with advanced spectroscopic techniques. Manipulation of the surface hydroxyl concentration on the support influences monomer/dimer formation. While both pre-catalysts are highly active in liquid-phase hydrogenation, the dimeric pre-catalyst is ∼3× faster than the monomer.

Evidence for Redox Mechanisms in Organometallic Chemisorption and Reactivity on Sulfated Metal Oxides.

The chemical and electronic interactions of organometallic species with metal oxide support materials are of fundamental importance for the development of new classes of catalytic materials. Chemisorption of Cp*(PMe)IrMe on sulfated alumina (SA) and sulfated zirconia (SZ) led to an unexpected redox mechanism for deuteration of the ancillary Cp* ligand. Evidence for this oxidative mechanism was provided by studying the analogous homogeneous reactivity of the organometallic precursors toward trityl cation ([PhC]), a Lewis acid known to effect formal hydride abstraction by one-electron oxidation followed by hydrogen abstraction.

Crystalline WS via Room Temperature, Solution-Phase Synthesis.

Crystalline tungsten disulfide (WS) has been prepared from the reaction of bis(cyclopentadienyl)tungsten dihydride with sulfur at room temperature and ambient pressure in organic solvents. WS 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 WS 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.

Conformal Coating of a Phase Change Material on Ordered Plasmonic Nanorod Arrays for Broadband All-Optical Switching.

Actively tunable optical transmission through artificial metamaterials holds great promise for next-generation nanophotonic devices and metasurfaces. Plasmonic nanostructures and phase change materials have been extensively studied to this end due to their respective strong interactions with light and tunable dielectric constants under external stimuli. Seamlessly integrating plasmonic components with phase change materials, as demonstrated in the present work, can facilitate phase change by plasmonically enabled light confinement and meanwhile make use of the high sensitivity of plasmon resonances to the variation of dielectric constant associated with the phase change.

Discovery of highly selective alkyne semihydrogenation catalysts based on first-row transition-metallated porous organic polymers.

Five different first-row transition metal precursors (V(III), Cr(III), Mn(II), Co(II), Ni(II)) were successfully incorporated into a catechol porous organic polymer (POP) and characterized using ATR-IR and XAS analysis. The resulting metallated POPs were then evaluated for catalytic alkyne hydrogenation using high-throughput screening techniques. All POPs were unexpectedly found to be active and selective catalysts for alkyne semihydrogenation.

Assignment of the oxidation states of Zr and Co in a highly reactive heterobimetallic Zr/Co complex using X-ray absorption spectroscopy (XANES).

The reduced heterobimetallic complex (THF)Zr(MesNP(i)Pr2)3CoN2 (1) has been examined along with a series of structurally similar reference compounds using X-ray absorption near edge structure (XANES) spectroscopy. Complex 1 has been shown to be highly reactive, often via one-electron pathways that might be expected for a d(1) Zr(III) complex. However, the presence of two strongly interacting metals in complex 1 renders the assignment of oxidation states ambiguous.

Oxygen-free atomic layer deposition of indium sulfide.

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.

Phase discrimination through oxidant selection in low-temperature atomic layer deposition of crystalline iron oxides.

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.

Oxidative reactions of the Mo(IV) dialkyl complex [{(3-CF3C6H4NCH2CH2)2NMe}Mo(CH2SiMe3)2].

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].

Synthesis of molybdenum complexes that contain "hybrid" triamidoamine ligands, [(hexaisopropylterphenyl-NCH2CH2)2NCH2CH2N-aryl]3-, and studies relevant to catalytic reduction of dinitrogen.

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.

Molybdenum triamidoamine complexes that contain hexa-tert-butylterphenyl, hexamethylterphenyl, or p-bromohexaisopropylterphenyl substituents. An examination of some catalyst variations for the catalytic reduction of dinitrogen.

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))).