Ted S. Sorensen

A comparison of alumina, carbon and carbon-covered alumina as supports for NiMoF additives: gas oil hydroprocessing studies

Abstract Catalysts with 3 wt% NiO, 15 wt% MoO 3 and 0–6.9 nominal wt% fluoride supported on alumina, carbon and carbon-covered alumina were studied to examine the role of fluoride and the influence of the support on hydroprocessing on Alberta gas oil. Experiments were carried out in a batch reactor at 410 °C and 6.9 MPa initial H 2 pressure. It was found that fluoride promotion enhances cracking and hydrogenation reactions resulting in decreased aromatic and sulphur contents in the gas oil. The promotion is dependent on the type of support and is related to the strength of the fluoride-support interaction and the accessibility of the fluoride to the surface hydroxyl groups on the support. A maximum in activity at 3.6 wt% fluoride was observed for the alumina-supported catalysts whereas higher loadings of fluoride were required for carbon-covered alumina-supported catalysts to see an improvement over their carbon supported counterparts. However, the carbon-covered alumina supported catalysts seem to have a lower propensity for coke deposition than their alumina counterparts.

μ-H-Bridged Bicyclo[3.3.3]undecyl Cations. Theoretical Calculations of Physical and Chemical Properties

Abstractμ-H-Bridged carbocations 1 and 2, which are still unknown experimentally, are structures with fascinating possibilities as intermediates for the synthesis of very strained in-bicyclic and tricyclic alkanes and alkenes. They are also expected to possess record high pKa values. In conjunction with our experimental program to try to prepare 1 and 2, we have carried out ab initio calculations on these structures and various reference compounds, with the aim of assessing just how stable these cations might be, and what physical and chemical properties they might possess. The results of these studies confirm that 1 and 2 should be viable species; they have energies similar to those of the conventional out-cations, and the μ-H bond distances are not very different from those calculated for known μ-H cations. The calculated 1H NMR chemical shift for the mu-H of 1 is –12 ± 0.5 and –9.5 ± 0.5 for 2, both values considerably more negative than in known μ-H cations. The possible effect of large amplitude motions of the μ-H on the 1H NMR chemical shift was investigated and not found to be significant. The pKas for 1 and 2 are estimated to be 17-18 with respect to an alkene conjugate base, a virtually unimaginable size for a formally alkyl cation. The paper also discusses the possibility of the μ-H being involved in the acid-conjugate base chemistry, since this is shown to be a hugely exothermic reaction. Finally, the alkenes and alkanes associated with cations 1 and 2 have been calculated, the in-alkene 7 from cation 1 is shown, for example, to possess a large steric strain, yet this structure should be accessible via deprotonation of 1 with a strong base.

5b,7b-Diaza-3b,9b-diborabenzo[ ghi ]perylenes

Treatment of a precursor to the chelating Lewis acid 2,2′-diborabiphenyl with 2,6-bisalkynyl-substituted pyridazines, leads to elimination of 2 equiv. of ClSiMe3; subsequent treatment of the mixtur...

The characterization of and the evolution of molecular hydrogen by the μ-hydrido-bridged cyclodecyl cation. Relevance to the question of hydrocarbon protonation by superacids

Abstract The observable cyclodecyl cation is established as having a 1,5-μ-hydrido-bridged structure and most probably exists as a mixture of conformational isomers. This solution carbocation is unique in organic chemistry in that it evolves molecular H2 at temperatures below -100°C to give the 9-decalyl cation. The mechanism of this reaction is postulated to involve a pentacoordinated carbocation intermediate or transition state with a structure identical to what one would get by protonating the bridgehead C-H bond of decalin. Since conversion of decalin to the decalyl cation in superacids is not accompanied by significant H2 production, the mechanism of these two reactions must be different, and in the latter case could not involve a protonated pentacoordinate carbocation intermediate, as has been postulated.

The 1,6-dimethylcyclodecyl cation. Nuclear magnetic resonance evidence for a 1,6-µ-hydrido structure

The 1H and 13C n.m.r. spectra of the observable 1,6-dimethyl-cyclodecyl cation are consistent with a 1,6-hydrogen-bridged structure, a previously unknown class of observable carbocations of both historical and current interest.

New Developments in Superacid Chemistry: Characterization of HC+=O and FC+=O Cations

A high gas pressure and use of the superacid HF/SbF5 (1/1) were required for direct spectroscopic characterization of the HC+ =O cation, which was until recently discussed as the short-lived intermediate of carbonylation reactions. The fluorocarbonyl cation FC+ =O, which was equally difficult to characterize, was also directly observed with NMR spectroscopy as the product of protolytic cleavage of tert-butyl fluoroformate [Eq. (a)].

Low temperature ketene preparations using nitrosyltetracarbonylchromium (-II) anion

Abstract Methylene and cyclopropyl ketenes can be generated at −100°C by the dehalogenation of α-bromoacylhalides using nitrosyltetracarbonylchromium (-II) anion. This facilitates the trapping of these ketenes with more stable ketenes to give mixed ketene dimers.

13C NMR spectra of η3 -allylmanganesetetracarbonyl compounds; structural implications

The 13C NMR spectra of η3-allylmanganese tetracarbonyl complexes are consistent with an overall Cs, symmetry and involving a σv plane in the Mn(CO)4 fragment. A dynamic carbonyl interchange process was looked for but the results are inconclusive, however the barrier for this process is certainly greater than 42 kJ/mol. This observation suggests an octahedral type geometry rather than a square pyramid type configuration.

Tricarbonyl (triquinacene)-molybdenum and-tungsten

Summary Triquinacene reacts with hexacarbonylmolybdenum to give tricarbonyl(triquinacene)molybdenum, and with tris(acetonitrile)tricarbonyltungsten to give tricarbonyl(triquinacene)tungsten, whereas efforts to synthesize the corresponding chromium complex, tricarbonyl(triquinacene)chromium, were unsuccessful. The molybdenum complex was characterized by 1H and 13C NMR spectroscopy, mass spectra, and a single crystal X-ray structure determination. The tungsten complex is thermally less stable and more susceptible to oxidation than its molybdenum analogue and was characterized by the mass spectrum and the 1H NMR spectrum. The crystal structure of the tricarbonyl(triquinacene)molybdenum is compared to that for the free ligand. Besides the expected lengthening of the C=C bonds, the complex shows a deepening of the triquinacene “basket”, presumably to give better overlap of the C=C bonds with molybdenum orbitals.

A deepseated carbodication rearrangement. Limited paths because of charge repulsion

Abstract The 1,5-manxyl dication undergoes a very specific skeletal rearrangement to give the 3,7-dimethylbicyclo[3.3.1]nona-3,7-diyl dication. The corresponding manxyl monocation is also labile but forms an apparent myriad of rearrangement products. This result is an indication that the dication rearrangement involves many fewer branching reactions.