Gordon A. Melson

Supported transition metal compounds ☆: Infrared studies on the acidity of Co/ZSM-5 and Fe/ZSM-5 catalysts

The acidity of Fe/ZSM-5 and Co/ZSM-5 synthesis gas conversion catalysts, prepared by extraction of Fe3(CO)12 and Co2(CO)8, is investigated by infrared characterization of chemisorbed pyridine. A portion of the total concentration of iron or cobalt is shown to incorporate into the channels of the ZSM-5. Such incorporation involves ion-exchange during Co2(CO)8 extraction onto ZSM-5 but occurs only upon H2 reduction of Fe/ZSM-5 subsequent to Fe3(CO)12 extraction. The ion-exchange causes a redistribution of the Bronsted and Lewis acidity of the ZSM-5. As a result of this redistribution, the oxidation state of the ion-exchanged iron is calculated.

In situ Mössbauer spectroscopic characterization of FeAI2O3 and FeThO2 Fischer-Tropsch catalysts

Mossbauer spectroscopy has been used to study in situ the transformation of FeAl2O3 and FeThO2 catalysts under different stages of calcination, reduction, carburization, and Fischer-Tropsch synthesis reactions. At room temperature the calcined FeAl2O3 catalyst is composed of Fe3+ ions strongly interacting with the alumina support, and about 10% of bulk α-Fe2O3. The calcined FeThO2 sample consists of a bulk phase of α-Fe2O3. After reduction in flowing hydrogen at 400 °C, the FeAl2O3 catalyst contains about 70% of α-Fe and 30% of FeAl2O4 (a spinel phase). The calcined sample of FeThO2 is completely reduced to α-Fe in flowing H2 at 400 °C in 9 h. When the reduced FeAl2O3, catalyst is carburized at 250 °C in synthesis gas (2H2CO), all the α-Fe is converted to an interstitial alloy of a composition resembling Haggs carbide and e′-Fe2.2C. Carburization of the reduced FeThO2 catalyst at 250°C in 2H2CO converted about 50% of the α-Fe to χ-Fe5C2. However, after the Fischer-Tropsch synthesis reaction, the remaining amount of α-Fe in the catalyst is also changed to χ-Fe5C2. The product distribution in the case of FeAI2O3 reveals a high selectivity for unsaturated and saturated C3 hydrocarbons. For the FeThO2 catalyst, calcined for 24 h, a high selectivity for C5ue5f8C10 hydrocarbons is shown. For the sample FeThO2 calcined for 48 h, a high selectivity for C5 hydrocarbon and oxygenated products is obtained.

Coordination chemistry of scandium. X. Macrocyclic polyether complexes of scandium(III)

Abstract The complexes Sc(NCS) 3 (benzo-15-crown-5]·1.5- THF·2H 2 O: (ScCl 3 ) 3 (benzo-15-crown-5) 2 ·H 2 O: Sc-(NCS) 3 (dibenzo-18-crown-6) 2 · 3THF: SeCl 3 (dibenzo- 18-crown-6)·1.5THF: ScCl 3 (dibenzo-18-crown-6)· 1.5CH 3 CN have been synthesized by reaction of Sc(NCS) 3 or ScCl 3 with the appropriate polyether. The complexes have been characterized by elemental analyses, conductance measurements, and infrared, ultraviolet and 1 H NMR spectroscopy; they exhibit weak bonding between the scandium(III) ion and the polyether. Structures are proposed and discussed with reference to the ionic size-cavity size relationship; some “unusual” coordination environments for the Sc(III) ion are suggested.

Supported transition metal compounds: I. A new method for the preparation of alumina-supported iridium and osmium carbonyls☆

An extraction technique for the preparation of alumina-supported iridium and osmium carbonyls from Ir4(CO)12 and Os3(CO)12 is reported. It is concluded that the metal carbonyl species produced are highly dispersed and of small particle size (less than 50 A diameter) in contrast to the large crystallites of iridium and osmium carbonyls obtained by either the dry grinding or wet impregnation techniques. Partial decarbonylation of the metal carbonyl species can be effected by varying the conditions of the preparation and by heating the samples in air, the species [Ir(CO)2]+ and [Os(CO)n]2+, n = 2,3, have been identified from their infrared spectra. Strong interactions between the metal carbonyl species and the alumina support are present.

Mechanisms of in situ macrocyclic ligand synthesis, 2. [1] Kinetics and mechanism of formation of a nickel(II) complex containing an N4 donor macrocyclic ligand [2]

Abstract The rate of reaction of [3,3′-[Ethylenebis(nitrilomethylidyne)] di- 2,4-pentanedionato(2-)] nickel(II) with ethylenediamine has been studied in tetrahydrofuran-ethanol solution. The rate is first order in nickel complex, second order in ethylenediamine and first order in added base (hydroxide or ethoxide ion) concentration. The enthalpy of activation, ΔH‡, is 41 ± 3 kJ mol−1 and the entropy of activation, ΔS‡, is − 180 ± 20 J mol−1 K−1. A multistep mechanism is proposed for the reaction in which intial coordination of two molecules of ethylenediamine is followed by nucleophilic attack of the deprotonated amine at a coordinated CO group of the ligand and rapid ring closure to produce a macrocyclic ligand with N4 donor atoms. The role of the metal ion in the in situ macrocyclic ligand synthesis is discussed.

Coordination chemistry of scandium. IX. Scandium (III) complexes with the neutral macrocyclic ligands Me4Bz2[14] tetraeneN4 and Me4[14] tetraeneN4

Anhand von Leitfahigkeitsmessungen, IR- und elektronenspektroskopischen Untersuchungen werden den aus der l : l-Reaktion von atherischen Sc(NCS)3- Losungen mit den makrocyclischen Liganden isolierten Komplexen die Strukturen (I) und (II) zuerkannt.

Synthesis of Macrocyclic Complexes

Since the recognition of the importance of complexes containing macro- cyclic ligands, considerable effort has been directed toward the development of reliable syntheses for these interesting and important compounds. Several review articles which deal primarily with the synthesis of complexes containing synthetic macrocyclic ligands* have appeared.(1–13)