Charles E. Hammond

Bio: Charles E. Hammond is an academic researcher from Indiana University. The author has contributed to research in topics: Molybdenum & Alkoxide. The author has an hindex of 8, co-authored 24 publications receiving 293 citations.

Metal alkoxides: models for metal oxides. 17. Reductive cleavage of carbon monoxide to carbide and oxide by ditungsten and tetratungsten alkoxides. Crystal and molecular structures of W4(.mu.4-C)(OCH2-c-Pen)14, W4(.mu.4-C)(O)(OCH2-tert-Bu)12 and W4(.mu.4-C)(O)(O-i-Pr)12

Abstract: Two synthetic strategies for the reductive cleavage of C≡O to carbide and oxide ligands have been explored. Both were successful but both had competing side reactions. Addition of CO to W 4 (OCH 2 -c-Pen) 12 , where Pen=pentyl, leads to the formation of three carbonyl derived products, W 4 (μ 4 -C)(OCH 2 -c-Pen) 14 , W 4 (μ 4 -CO)(Co) 2 -(OCH 2 -c-Pen) 12 , and an oxo-tungsten alkoxide.

Carbon-nitrogen bond formation in the reaction between tetrakis(dimethylamido)molybdenum(IV) and 2,6-dimethylphenyl isocyanide. Preparation and characterization of the first homoleptic metallaamidine complex: Mo(.eta.2-Me2NC:NC6H3Me3-2,6)4

Abstract: La reaction du titre semble le premier exemple d'une insertion d'isocyanure dans une liaison metal de transition amide. Structure moleculaire

Metal alkoxides: models for metal oxides. 16. Synthesis and characterization of a new class of homoleptic 12-electron molybdenum and tungsten alkoxide clusters of formula M4(OR)12: structural characterization of Mo4(OCH2-c-Bu)12.cntdot.(HOCH2-c-Bu)

Abstract: Addition of primary alcohols, RCH{sub 2}OH (> 6 equiv), to hydrocarbon solutions of M{sub 2}(O-t-Bu){sub 6} compounds has led to the isolation of the first homoleptic series of cluster alkoxides M{sub 4}(OCH{sub 2}R){sub 12} for both M = Mo and W where R = i-Pr, Cy (Cy = cyclohexyl), Cp (Cp = cyclopentyl), and c-Bu (c-Bu = cyclobutyl). The NMR data ({sup 1}H and {sup 13}C) indicate a common structural unit for this class of compounds containing a molecular mirror plane. For each M{sub 4}(OCH{sub 2}R){sub 12} compound there are eight types of alkoxide ligands in the integral intensity 2:2:2:2:1:1:1:1. Those having integral intensity two possess diastereotopic methylene protons, indicating that they do not lie on the mirror plane, whereas the other four alkoxides (1:1:1:1) are contained within the mirror plane. Though these compounds yield crystals from 1,2-dimethoxyethane, they failed to diffract beyond 10{degree} indicating a molecular disorder within hexagonal packing of M{sub 4} units. However, the cyclobutylmethoxide derivatives crystallize with an additional molecule of alcohol, M{sub 4}(CH{sub 2}-c-Bu){sub 12}(HOCH{sub 2}-c-Bu), and the molecular structure of the molybdenum compound was determined by an X-ray study. Crystal data for Mo{sub 4}(OCH{sub 2}-c-Bu){sub 12}(HOCH{sub 2}-c-Bu) at {minus}156{degree}C: a = b = 19.952more » (7) {angstrom}, c = 34.755 (16) {angstrom}, Z = 8, d{sub calcd} = 1.43 g cm{sup {minus}3}, and space group Pr{sub 1}. The unit cell contains two crystallographically independent molecules that are essentially equivalent with respect to M-M and M-O distances and angles. In each there is a central Mo{sub 4} butterfly with a dihedral angle between the Mo{sub 3} triangles of 132.5{degree}.« less

A new class of homoleptic 12-electron molybdenum and tungsten alkoxide clusters of formula [M4(OR)12]

Abstract: The authors are interested in developing efficient synthetic routes to alkoxide-supported molybdenum and tungsten clusters that may prove to be excellent models for fragments of reduced oxides of the same metals. These clusters should include both coordinative unsaturation and redox flexibility at the metal centers to initiate organometallic chemistry upon substrate reduction. Complementary metal oxide model systems such as polyoxoanions may prove effective for oxidation catalysis. They have recently demonstrated that W/sub 2/(O-i-Pr)/sub 6/ (I) exists in reversible equilibrium with its 12-electron cluster W/sub 4/(O-i-Pr)/sub 12/ (II) in solution at room temperature, eq 1, whereas Mo/sub 2/(O-i-Pr)/sub 6/ is indefinitely stable with respect to cluster formation. Even by reducing the steric demands at the molybdenum center they were unable to induce the formation of new metal-metal bonds in (Mo/sub 2/(O-i-Pr)/sub 5/(OMe))/sub 2/ (III), which instead retains isolated, unbridged Mo-Mo triple bonds. The authors report here the isolation and characterization of members of a new class of 12-electron tetranuclear alkoxide clusters, IV-XI, which are spectroscopically isostructural for both molybdenum and tungsten together with the single-crystal X-ray diffraction structure of one derivative, (Mo/sub 4/(O-CH/sub 2/-c-Bu)/sub 12/(HO-CH/sub 2/-c-Bu)) (XI) (where c-Bu = cyclobutyl). This represents the first group of structurally related homoleptic alkoxidemore » clusters for molybdenum and tungsten in oxidation state (3+).« less

Efficient synthesis of chiral ansa-metallocenes by amine elimination. synthesis, structure, and reactivity of rac-(ebi)zr(nme2)2

Abstract: The amine elimination reaction of Zr(NMe2)4 (2) and (EBI)H2 (1,2-bis(3-indenyl)ethane, 3) in toluene at 100 °C affords pure rac-(EBI)Zr(NMe2)2 (rac-4, EBI = ethylene-1,2-bis(1-indenyl)) in 68% isolated yield. This reaction proceeds via the rapidly formed mono-indenyl intermediate (η5-C9H6CH2CH2C9H7)Zr(NMe2)3 (6) which undergoes reversible intermolecular amine elimination with a second equivalent of 2 to give the binuclear species (μ-η5,η5-EBI){Zr(NMe2)3}2 (5, rac and meso isomers) or reversible intramolecular amine elimination to give either rac-4 or meso-4. The kinetic metallocene product is a 1/1 mixture of rac-4 and meso-4, the thermodynamic product is rac-4, and the meso-4 to rac-4 isomerization is catalyzed by the NMe2H co-product. The rac-4/meso-4 product ratio can be controlled by adjusting the rate of NMe2H removal from the reaction vessel and the steady state concentration of amine in the reaction mixture. The molecular structure of rac-4 has been determined by X-ray crystallography. rac-4 is con...