Helmut Weigold

Insertion reactions of dicyclopentadienyldimethylzirconium and related cyclopentadienyl compounds with sulphur dioxide and nitric oxide

Abstract The reactions of (π-C 5 H 5 ) 2 Zr(CH 3 ) 2 are characterized by lability of the methyl groups, one or both of which may be displaced by reaction with hydrogen, phenylacetylene, methanol or lead chloride. Sulphur dioxide will insert between both methyl groups and the zirconium atom and also between one of the cyclopentadienyl ligands and the metal atom. Nitric oxide will insert between one of the methyls and the zirconium leading to a novel zirconium complex of methylnitrosohydroxylamine. Insertion reactions of SO 2 and NO were also observed with the monomethyl derivative (π-C 5 H 5 ) 2 Zr(Cl)CH 3 , and with (C 5 H 5 ) 4 Zr.

Hydrido complexes of zirconium: III. Reactions with acetylenes to give alkenylzirconium derivatives

Abstract The zirconium hydride (C5H5)2Zr(H)Cl reacts with both mono and disubstituted acetylenes by addition of Zr-H across the triple bond. Generallytrans-alkenyl derivatives result although in some cases mixtures of isomers are formed. With monosubstituted acetylenes (C5H5)2ZrH2 behaves similarly giving di(trans-alkenyl)zirconium compounds, but with diarylacetylenes hydrogen is evolved and tetraarylbutadiene complexes result.

Sulphur dioxide insertion reactions with dicyclopentandienyltitanium and -zirconium alkyl and aryl compounds

Abstract Sulphur dioxide was found to react in the expected manner with alkyl- and aryldicyclopentadienyltitanium compounds to yield the red monomeric O-sulphinates (π-C5H5)2Ti(O2SCH3)2, (π-C5H5)2Ti(O2SCH3Cl, and (π-C5H5)2Ti(O2SC6H5)2. With dicyclopentadienylzirconium compounds, the sulphur dioxide inserts into the zirconium-alkyl bond also into the zirconium-cyclopentadienyl bond in certain cases, even though the cyclopentadienyl group is π-bonded to zirconium. The preparations of the O-sulphinates [π-C5H5(C5H5SO2)Zr(O2SCH3)Cl]n, [π-C5H5(C5H5SO2) ZrO]n and [π-C5H5(C5H5SO2)ZrSO3]n are reported.

Behaviour of Co-Mo-Al2O3 catalysts in the hydrodeoxygenation of phenols☆

Abstract The activity of a number of ring alkyl-substituted phenols in the direct hydrodeoxygenation reaction (i.e. C-O bond scission without prior ring hydrogenation) in the presence of a commercial Co-Mo-Al2O3 catalyst has been investigated. The results indicate that the catalytically active site is stereochemically demanding. It is proposed that the phenol ring hydrogenation and the direct hydrodeoxygenation reaction proceed on the same catalytic site. The ease of the direct hydrodeoxygenation reaction is retarded mainly when transfer of the substrate hydroxyl group onto a co-ordinatively unsaturated metal site on the catalyst is inhibited. This occurs when the catalyst hydroxyl group receptor site is occupied by a co-ordinating ligand (poison) or when substituents on the substrate direct the phenolic hydroxyl group away from this metal site. The catalytic behaviour of Co-Mo-Al2O3 can be ‘transformed’ to resemble more closely that of Ni-Mo-Al2O3 (high reductive capacity) when the reaction medium contains both excess H2S and a co-ordinating ligand. It is proposed that this ‘transformed’ species is of importance in hydrodenitrogenation reactions in an H2S-rich environment.

The nature of molybdenum oxide species mounted on alumina: An oligomer model

Abstract A model for the structure of the molybdenum species mounted on alumina is developed on the basis of the following considerations. (1) The alumina surface hydroxyl groups remaining after thermal depopulation are found largely in rows. (2) Molybdate species react with the support hydroxyl groups. (3) Molybdate species undergo oligomerization on the alumina support. The structure developed using these criteria has the molybdenum species attached in rows to the support with μ-oxo linkages between adjacent molybdenum atoms along these rows. This requires each alumina surface oxygen atom in these rows to carry one molybdenum atom. The average interatomic molybdenum to molybdenum separation along these surface-attached polymer chains is therefore equal to the ionic diameter of the alumina oxygen atoms (viz., approx. 2.8 A). On reduction of the molybdenum atoms in these rows, metal-metal bond formation is proposed to occur. On the (111)-face of the alumina steric and charge considerations suggest that in the formation of the polymer chain, one oxygen atom per two molybdenum(VI) atoms is placed in the support in a vacancy formed during partial dehydration of the surface alumina layer. This oxygen is difficult to remove either by reduction or sulfidation. “Fixed” hydrogen, formed on reduction of the catalyst with hydrogen, is associated with isolated relatively immobile μ-OH groups. Catalytic hydrodesulfurization activity is ascribed to dimer species and the utility of alumina as a catalyst support is thought to reside in its ability to promote both the oligomerization and the dispersion of the molybdenum species over the support.

Continuous hydrogenation of Yallourn brown-coal tar

Abstract Hydrogenation of brown-coal tar offers a source of liquid fuel or chemical feedstock. In order to make a preliminary assessment of its potential, tar from pyrolysis of Yallourn brown-coal briquettes has been hydrogenated in a laboratory scale continuous-flow hydrogenation unit over sulphided nickel molybdate and cobalt molybdate catalysts. Over a 148 h running period the product oil was characterized by periodical measurement of refractive index, infrared spectrum, density, viscosity, elemental analyses and boiling range. Effluent gases were also monitored. The fifty most abundant compounds in the product were identified by gas chromatography/mass spectrometry. The oils contain 50–60% aromatics and boil over a wide range, including gasoline to gas oil fractions. Carbon and iron deposition on the catalyst caused a decrease in surface area and a consequent deterioration in product quality. The use of an efficient pre-coking furnace should increase catalyst life significantly.