Edward I. Stiefel

Bio: Edward I. Stiefel is an academic researcher from ExxonMobil. The author has contributed to research in topics: Molybdenum & Catalysis. The author has an hindex of 45, co-authored 170 publications receiving 5406 citations. Previous affiliations of Edward I. Stiefel include Kettering University.

Hydrotreating using self-promoted molybdenum and tungsten sulfide catalysts formed from bis(tetrathiometallate) precursors

Abstract: Hydrocarbon feeds are upgraded by contacting same, at elevated temperature and in the presence of hydrogen, with a self-promoted catalyst formed by heating one or more carbon-containing, bis(tetrathiometallate) catalyst precursor salts selected from the group consisting of (NR 4 ) 2 [M(WS 4 ) 2 ], (NR 4 ) x [M(MoS 4 ) 2 ] and mixtures thereof wherein R is one or more alkyl groups, aryl groups or mixture thereof, wherein promoter metal M is covalently bound in the anion and is Ni, Co or Fe and wherein x is 2 if M is Ni and x is 3 if M is Co or Fe composite in a non-oxidizing atmosphere in the presence of sulfur, hydrogen, and a hydrocarbon to form said supported catalyst.

Desulfurization of hydrocarbons using molybdenum or tungsten sulfide catalysts promoted with low valent group VIII metals

Abstract: Hydrocarbon feedstocks are selectively hydrodesulfurized by contacting the feedstock in the presence of hydrogen with a predecessor catalyst comprising molybdenum or tungsten sulfide which has been promoted by reaction with a transition metal containing organo-metallic complex wherein the valence of the metal is 0 or +1 at the time of reaction and the contacting is done at a temperature and pressure sufficient to substantially hydrodesulfurize the hydrocarbon.

[PdS2C2(COOMe)2](6n) (n = 0, -1, -2, -3, -4): hexanuclear homoleptic palladium dithiolene complexes.

Abstract: Reaction of a stoichiometric equivalent of the zinc-dithiolene complex, (tmeda)ZnS2C2(COOMe)2 (tmeda = tetramethylethylenediamine), with (MeCN)2PdCl2 results in a 1:1 homoleptic dithiolene that forms the hexanuclear cluster [PdS2C2(COOMe)2]6 (1). X-ray structure analysis of 1 indicates a Pd6S12 core comprised of six face-centered palladium atoms and 12 edge-centered sulfur atoms situated on an imaginary approximate cube. Complex 1 undergoes four distinct and reversible one-electron redox steps in dichloromethane at -186, -484, -1174, and -1524 mV versus a standard calomel electrode (ferrocenium+/ferrocene redox couple 409 mV). The two-electron reduction product of 1, [Bu4N]2[(PdS2C2(COOMe)2)6] (2), has been chemically isolated and characterized.

Molybdenum enzymes, cofactors, and model systems : developed from a symposium sponsored by the Division of Inorganic Chemistry at the 204th National Meeting of the American Chemical Society, Washington, DC, August 23-28, 1992

Abstract: Molybdenum enzymes, cofactors and chemistry - an introductory survey, Edward I. Stiefel. Part 1 Molybdenum cofactor enzymes: the reaction mechanism of xanthine oxidase, Russ Hille biochemistry of the molybdenum cofactors, K.V. Rajagopalan the bacterial Oxmolybdenum cofactor, O. Meyer et al. Part 2 Molybdenum cofactor models: models of pterin-containing molybdenum enzymes, Charles G. Young and Anthony G. Wedd pterins, quinoxalines and metallo-ene-dithiolates - synthetic approach to the molybdenum cofactor, Robert S. Pilato et al strategies for the synthesis of the cofactor of the oxomolybdoenzymes, C.D. Garner et al molybdenum complexes of reduced pterins, Sharon J. Nieter Burgmayer et al chemical and physical coupling of oxomolybdenum centres and iron porphyrins - models for the molybdenum-iron interaction in sulfite oxidase, Michael J. LaBarre et al. Part 3 Nitrogenase: nitrogenase structure, function and genetics, Barbara K. Burgess crystal structures of the iron protein and molybdenum-iron protein of nitrogenase, D.C. Rees et al structure and environment of metal clusters in the nitrogenase molybdenum-iron protein from clostridium pasteurianum, Jeffrey T. Bolin et al biosynthesis of the iron-molybdenum cofactor of nitrogenase, Paul W. Ludden et al role of the iron-molybdenum cofactor polypeptide environment in azotobacter vinelandii molybdenum-nitrogenase catalysis extended x-ray absorption fine structure and L-Edge spectroscopy of nitrogenase molybdenum-iron protein J. Chen et al redox properties of the nitrogenase proteins from azotobader vinelandii, G.D. Watt et al the molybdenum-iron protein of nitrogenase - structural and functional features of metal cluster prosthetic groups, W.H. Orme-Johnson protein component complex formation and adenosine triphosphate hydrolysis in nitrogenase, James Bryant Howard electron-transfer reactions associated with nitrogenase from klebsiellia pneumoniae R.N.F. Thorneley et al Part 4 Nitrogenase models: recent structure determinations of the molybdenum-iron protein of nitrogenase - impact on design of synthetic analogs for the iron-molybednum-sulfur analogs for the iron-molybdenum-sulfur active site and the iron-molybdenum cofactor, Dimitri Coucouvanis. Part of contents.

Secondary building units, nets and bonding in the chemistry of metal–organic frameworks

Abstract: This critical review presents a comprehensive study of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) towards construction and synthesis of metal–organic frameworks (MOFs). We describe the geometries of 131 SBUs, their connectivity and composition. This contribution presents a comprehensive list of the wide variety of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) in the construction and synthesis of metal–organic frameworks. The SBUs discussed here were obtained from a search of molecules and extended structures archived in the Cambridge Structure Database (CSD, version 5.28, January 2007) which included only crystals containing metal carboxylate linkages (241 references).

The Mononuclear Molybdenum Enzymes

Abstract: Molybdenum is the only second-row transition metal required by most living organisms, and is nearly universally distributed in biology. Enzymes containing molybdenum in their active sites have long been recognized,1 and at present over 50 molybdenum-containing enzymes have been purified and biochemically characterized; a great many more gene products have been annotated as putative molybdenum-containing proteins on the basis of genomic and bioinformatic analysis.2 In certain cases, our understanding of the relationship between enzyme structure and function is such that we can speak with confidence as to the detailed nature of the reaction mechanism and, with the availability of high-resolution X-ray crystal structures, the specific means by which transition states are stabilized and reaction rate is accelerated within the friendly confines of the active site. At the same time, our understanding of the biosynthesis of the organic cofactor that accompanies molybdenum (variously called molybdopterin or pyranopterin), the manner in which molybdenum is incorporated into it, and then further modified as necessary prior to insertion into apoprotein has also (in at least some cases) become increasingly well understood. It is now well-established that all molybdenum-containing enzymes other than nitrogenase (in which molybdenum is incorporated into a [MoFe7S9] cluster of the active site) fall into three large and mutually exclusive families, as exemplified by the enzymes xanthine oxidase, sulfite oxidase, and DMSO reductase; these enzymes represent the focus of the present account.3 The structures of the three canonical molybdenum centers in their oxidized Mo(VI) states are shown in Figure 1, along with that for the pyranopterin cofactor. The active sites of members of the xanthine oxidase family have an LMoVIOS-(OH) structure with a square-pyramidal coordination geometry. The apical ligand is a Mo=O ligand, and the equatorial plane has two sulfurs from the enedithiolate side chain of the pyranopterin cofactor, a catalytically labile Mo–OH group, and most frequently a Mo=S. Nonfunctional forms of these enzymes exist in which the equatorial Mo=S is replaced with a second Mo=O; in at least one member of the family the Mo=S is replaced by a Mo=Se, and in others it is replaced by a more complex –S–Cu–S–Cys to give a binuclear center. Members of the sulfite oxidase family have a related LMoVIO2(S–Cys) active site, again square-pyramidal with an apical Mo=O and a bidentate enedithiolate Ligand (L) in the equatorial plane but with a second equatorial Mo=O (rather than Mo–OH) and a cysteine ligand contributed by the protein (rather than a Mo=S) completing the molybdenum coordination sphere. The final family is the most diverse structurally, although all members possess two (rather than just one) equiv of the pyranopterin cofactor and have an L2MoVIY(X) trigonal prismatic coordination geometry. DMSO reductase itself has a catalytically labile Mo=O as Y and a serinate ligand as X completing the metal coordination sphere of oxidized enzyme. Other family members have cysteine (the bacterial Nap periplasmic nitrate reductases), selenocysteine (formate dehydrogenase H), –OH (arsenite oxidase), or aspartate (the NarGHI dissimilatory nitrate reductases) in place of the serine. Some enzymes have S or even Se in place of the Mo=O group. Members of the DMSO reductase family exhibit a general structural homology to members of the aldehyde:ferredoxin oxidoreductase family of tungsten-containing enzymes;4 indeed, the first pyranopterin-containing enzyme to be crystallographically characterized was the tungsten-containing aldehyde:ferredoxin oxidoreductase from Pyrococcus furiosus,5 a fact accounting for why many workers in the field prefer “pyranopterin” (or, perhaps waggishly, “tungstopterin”) to “molybdopterin”. The term pyranopterin will generally be used in the present account. Open in a separate window Figure 1 Active site structures for the three families of mononuclear molybdenum enzymes. The structures shown are, from left to right, for xanthine oxidase, sulfite oxidase, and DMSO reductase. The structure of the pyranopterin cofactor common to all of these enzymes (as well as the tungsten-containing enzymes) is given at the bottom.