Darrell P. Eyman

13C NMR spectra of organoaluminum compounds: evidence for an oxygenaluminum π-interaction

Abstract The 13C NMR spectra of some trialkylaluminum compounds and a series of alkoxy-bridged and amido-bridged organoaluminum compounds are reported and discussed. In the alkoxy-bridged compounds the OC resonance is sensitive to substitution at the aluminum atom and the degree of oligomerization. In the amido-bridged compounds the analogous carbon (NC) resonance shows no variation upon changes of substituents at the aluminum. These observations are used as evidence for the existence of an oxygen to aluminum pπdπ dative bond in the alkoxy-bridged compounds.

Reactivities of Lewis acid adducts of η5-C5H5Fe(CO)2Y (Y = SPh, SO2PH, and PPh2) with nucleophiles

Complexes of the CpFe(CO)2Y (Cp = η5-C5H5, Y = SPh (I), Y = PPh2, (II), Y = SO2Ph (III)) and Cp′Fe(CO)2SPh (Cp′ = η5-C5(CH3)5 (IV)), form adducts with the Lewis acids AlMe3, AlMe2Cl or AlBr3. All of the Lewis acid adducts of I react with one or more of the nucleophiles L (L = PBu3, PPh3, P(OEt)3, cyclohexene to form ionic products of the [CpFe(CO)2(L)][PhS(AlR3)2]. The cation of each product has been isolated as the PF6− salt and characterized. One of the proposed anions, [PhS(AlMe3)2]−, has been synthesized by an independent by an independent method and characterized as the lithium salt. The Lewis acid adducts of II, and III do not undergo substitution reactions with the same nucleophiles, whereas adducts of IV react only with PBu3 in low yield. The AlMe2Cl and AlBr3 adducts of CpFe(CO)(PPh3)SPh (V) react with PPh3 to form the halides, CpFe(CO)(PPh3)X (X = Cl− and Br− respectively), but the AlMe3 adduct is unreactive.

Trimer–dimer equilibrium studies of alkylaluminum alkoxides

Abstract The aluminum alkoxides [MeClAlOEt] 3 ( 1 ), [Et 2 AlOMe] 3 ( 2 ), [Me 2 AlOEt] 3 ( 3 ), and [EtClAlOEt] 3 ( 4 ) were investigated by 1 H NMR spectroscopy to study the o -dichlorobenzene solution equilibrium: 2 [R 2 AlOR′] 3 ⇌3 [R 2 AlOR′] 2 . The complexes are shown to exist primarily as trimers at room temperature, but increasing concentrations of the dimeric form are observed at higher temperatures. Equilibrium constants, Δ H , and Δ S were determined for the trimer–dimer equilibrium. Values of Δ H for the conversion of 2 moles of trimer are 63(4), 78(1), 85.0(8), and 99(6) kJ for 1 , 2 , 3 , and 4 , respectively. The corresponding values of Δ S are 142(7), 184(3), 218(2), and 265(17) J/K, respectively. Thermodynamic parameters are compared with those reported for [Me 2 AlOPr n ] 3 and [Me 2 AlOPh] 3 . The characterization of [EtClAlOMe] 3 is also reported.

Synthesis and Characterization Studies of V-Zr Mixed Oxides Cografted on γ-Al2O3 using OV(OPr)3 and Zr(O n Bu)4 Precursors

Steam reforming of hydrocarbons is widely used to produce clean hydrogen. A nickel-containing, V2Ox-ZrO2 cografted catalyst on γ-Al2O3, prepared from a solution of OV(O i Pr)3 and Zr(O n Bu)4 was observed to provide significant turnover rates in hydrogen generation from steam-reforming of alkanes. To investigate the effect of change in vanadium precursor ligand and other reaction parameters on the surface optimization, a compositional range of V2Ox-ZrO2 samples were synthesized from OV(OPr)3 and Zr(O n Bu)4 and characterized using, ICP-OES, XRD, and XPS. These studies indicated that the cografting process was amorphous and V5+ and Zr4+ were the only oxidation states present on the catalyst surface.

Synthesis and characterization studies of γ-Al2O3 -supported, V-Zr mixed oxide catalysts prepared from OV(OEt)3 and Zr(OnBu)4

Steam reforming of hydrocarbons is one of the methods widely used to produce clean hydrogen for fuel cells. In previous studies in this group, a nickel-containing, V2Ox-ZrO2 co-grafted catalyst on γ-Al2O3, prepared from a solution of OV(OiPr)3 and Zr(OnBu)4 (precursor feed of 1 V nm−2:4 Zr nm−2) was found to generate significant turnover rates in the production of hydrogen from steam-reforming of alkanes and light alcohols. To investigate the influence of change in vanadium precursor ligand and other reaction conditions including time, temperature, concentration of co-grafting solution etc. on the surface optimization of these supported mixed oxides a compositional range of V2Ox-ZrO2 samples were synthesized using co-grafting solutions of OV(OEt)3 and Zr(OnBu)4. Temperature Programmed reduction (TPR) and X-ray Photoelectron Spectroscopy (XPS) studies furnished further insight into the red-ox behavior of the catalysts under steam-reforming conditions. It was observed that a V5+/V4+ red-ox couple was involved in this catalytic process. Zirconium was observed to be present only in the +4 oxidation state irrespective of temperature and other reduction conditions. Based on this premise it was concluded that the refractory nature of the Zr4+ species on the surface was responsible in preventing the vanadyl groups from sintering at temperatures above 600 °C, thereby stabilizing the red-ox active species during the steam-reforming process.

Surface Density Optimization of V-Zr Mixed Oxides Cografted on γ-Al2O3 Using OV(O i Pr)3 and Zr(O n Bu)4 Precursors

Cografted catalysts are synthesized by reacting surface -OH groups of a catalyst support with a solution containing two or more metal precursors. Under these circumstances factors such as temperature, concentration of metal precursors, time of cografting, and variations in metal precursor feeds can affect the surface metal densities. To understand influence of these parameters a compositional range of V-Zr cografted catalysts were synthesized using OV(O i Pr)3 and Zr(O n Bu)4 and studied. These catalysts were then characterized using ICP-OES, XRD, and XPS. XRD revealed that cografting was amorphous and XPS studies indicated that V5+ and Zr4+ were the only species present under ambient conditions.