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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...

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.

The electronic structures of two uranium compounds supported by redox-active α-diimine ligands, ((Mes)DAB(Me))(2)U(THF) (1) and Cp(2)U((Mes)DAB(Me)) (2) ((Mes)DAB(Me) = [ArN═C(Me)C(Me)═NAr]; Ar = 2,4,6-trimethylphenyl (Mes)), have been investigated using both density functional theory and multiconfigurational self-consistent field methods. Results from these studies have established that both uranium centers are tetravalent, that the ligands are reduced by two electrons, and that the ground states of these molecules are triplets. Energetically low-lying singlet states are accessible, and some transitions to these states are visible in the electronic absorption spectrum.

The uranium(IV) terminal oxo species Tp*(2)U(O) has been synthesized by oxygen-atom transfer from pyridine-N-oxide to Tp*(2)U(2,2'-bipyridine), a trivalent uranium species with a monoanionic bipyridine ligand. Full characterization of the oxo species using (1)H NMR and IR spectroscopies, X-ray crystallography, and computational studies was performed.

A series of tris- and tetrakis(phosphinoamide) U/Co complexes has been synthesized. The uranium precursors, (η(2)-Ph2PN(i)Pr)4U (1), (η(2)-(i)Pr2PNMes)4U (2), (η(2)-Ph2PN(i)Pr)3UCl (3), and (η(2)-(i)Pr2PNMes)3UI (4), were easily accessed via addition of the appropriate stoichiometric equivalents of [Ph2PN(i)Pr]K or [(i)Pr2PNMes]K to UCl4 or UI4(dioxane)2. Although the phosphinoamide ligands in 1 and 4 have been shown to coordinate to U in an η(2)-fashion in the solid state, the phosphines are sufficiently labile in solution to coordinate cobalt upon addition of CoI2, generating the heterobimetallic Co/U complexes ICo(Ph2PN(i)Pr)3U[η(2)-Ph2PN(i)Pr] (5), ICo((i)Pr2PNMes)3U[η(2)-((i)Pr2PNMes)] (6), ICo(Ph2PN(i)Pr)3UI (7), and ICo((i)Pr2PNMes)3UI (8). Structural characterization of complexes 5 and 7 reveals reasonably short Co-U interatomic distances, with 7 exhibiting the shortest transition metal-uranium distance ever reported (2.874(3) Å). Complexes 7 and 8 were studied by cyclic voltammetry to examine the influence of the metal-metal interaction on the redox properties compared with both monometallic Co and heterobimetallic Co/Zr complexes. Theoretical studies are used to further elucidate the nature of the transition metal-actinide interaction.

Hydrotris(3,5-dimethylpyrazolyl)borate uranium(III) diiodide derivatives have been prepared as an entry into low-valent uranium chemistry with these ligands. The bis(tetrahydrofuran) adduct, Tp*UI(2)(THF)(2) (1) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate), was synthesized by addition of sodium hydrotris(3,5-dimethylpyrazolyl)borate (NaTp*) to an equivalent of UI(3)(THF)(4). Addition of 2,2'-bipyridine (2,2'-bpy) to 1 displaced the THF molecules producing Tp*UI(2)(2,2'-bpy) (2). Both derivatives were characterized by (1)H NMR and IR spectroscopies, magnetic measurements, and X-ray crystallography. Reduction of both species was attempted with two equivalents of potassium graphite. The reduction of 1 did not result in a clean product, but rather decomposition and ligand redistribution. However, compound 2 was reduced to form Tp*(2)U(2,2'-bpy), 3, which is composed of a uranium(III) ion with a radical monoanionic bipyridine ligand. This was confirmed by X-ray crystallography, which revealed distortions in the bond lengths of the bipyridine consistent with reduction. Further support was obtained by (1)H NMR spectroscopy, which showed resonances shifted far upfield, consistent with radical character on the 2,2'-bipyridine ligand. Future studies will explore the reactivity of this compound as well as the consequences for redox-activity in the bipyridine ligand.