Andrew R. Lucy

Oxidative desulphurisation of oils via hydrogen peroxide and heteropolyanion catalysis

Oxidation of dibenzothiophene with hydrogen peroxide using phosphotungstic acid as catalyst and tetraoctylammonium bromide as phase transfer agent in a mixture of water and toluene has been studied. Catalysed decomposition of hydrogen peroxide competes with dibenzothiophene oxidation but by choice of suitable conditions yields of dibenzothiophene sulphone approaching 100% may be obtained. Treatment of gas oils with this technology shows that all the sulphur compounds present are oxidised by this catalyst system and highly substituted dibenzothiophenes are the most readily oxidised of species containing a thiophene nucleus. Oxidised sulphur compounds can be separated from the oil by adsorption on silica gel. The use of oxidation and adsorption in a process for desulphurisation of gas oils is discussed.

PREPARATION OF CARBONATE ESTERS

A process for preparing carbonate esters by the oxidative carbonylation of an alcohol is provided. The process comprises reacting an alcohol with carbon monoxide in the presence of a dihydrocarbyl peroxide the process being characterized by the fact that the carbon monoxide pressure at the reaction temperature is less than 15 bars and by the fact that a catalyst comprising a platinum group metal and a copper compound is employed. The process is useful for preparing dimethyl carbonate from methanol and carbon monoxide.

trans-bis(diphenylphosphine)cyclopropane; a ligand selective for binuclear complexation with ca. 4.5 Å intermetallic separation

Abstract trans-1,2-Bis(diphenylphosphinoyl)ethylene was treated with (CH3)2S(CH2) in dimethyl sulphoxide and the product reduced with HSiCl3 to give trans-bis(diphenylphosphino)cyclopropane in 56% overall yield. The new ligand was found to have a strong affinity for AgBF4 forming a 2/2 complex under conditions where related ligands gave a mixture of 2/2 and 3/2 adducts. This complex could be employed as precursor to a cationic binuclear rhodium carbonyl complex P2RH2+(CO)3Cl. When synthesis of the coresponding iridium complex was attempted, a soluble yellow adduct of P2Ir2(CO)2Cl2 and AgBF4 was obtained, assumed to contain an IrAgIr bond.

Functionalisation of alkene–carbon monoxide alternating copolymers via transketalisation reactions

Alkene–dioxolane alternating copolymers 1 and 4, formed from ethane-1,2-diol and the corresponding alkene–carbon monoxide copolymers, undergo transketalisation reactions with ethane-1,2-dithiol, propane-1,3-dithiol and sulfanylethanol to yield novel dithiolane-, dithiane- and oxathiolane-containing polymers 6, 8, 9, 11 and 12.

Synthesis and characterization of polyketoximes derived from alkene-carbon monoxide copolymers

Abstract Poly(1-hydroxyiminotrimethylene) ( 6 ) and (1-hydroxyiminotrimethylene)-(1-hydroxyimmo-3-methyltrimethylene) copolymer ( 7 ) have been prepared in high yield by reaction of hydroxylamine under neutral conditions with alternating ethene-carbon monoxide copolymer ( 1 ) and ethene/propene-carbon monoxide copolymer ( 3 ), respectively.

Stereochemistry of intermediates in homogeneous hydrogenation catalysed by tristriphenylphosphinerhodium chloride, employing nuclear magnetic resonance magnetisation transfer

The DANTE technique has been employed to observe intra- and inter-molecular exchange equilibria in Wilkinsons catalyst, ClRh(PPh3)3 and its dihydride. The parent compound undergoes automerisation much faster than dissociative exchange with free PPh3. The rate of the latter process, 0.31 s–1, is in accord with that value deduced from the kinetics of H2 addition and by other techniques. For ClH2Rh(PPh3)3 the rapid exchange of PPh3trans to hydride occurs through an intermediate with effective C2v symmetry in which the two hydrides are equivalent. A slower, previously unobserved exchange of the mutually trans-phosphines with free PPh3 occurs, which is sufficiently rapid that the intermediate so generated can participate in the catalytic cycle of homogeneous hydrogenation. These results provide a basis for suggesting that the key intermediates in homogeneous hydrogenation have two mutually cis-biphosphine ligands bound to rhodium. Further justification arises from molecular modelling of transient olefin-bound intermediates based on authentic crystal structures. For several common olefins, the bound state involving trans-disposed triphenyl-phosphines is severely destabilished by unavoidable van der Waals repulsions, whereas the corresponding intermediate with cis phosphines is stable in catalytically realistic geometry.

Synthesis, reactivity, and X-ray crystal structure of [Ag{Rh(CO)(PPh3)(η5-C5H5)}2]-[PF6].toluene : a silver-stabilised radical cation

AgPF6 and [Rh(CO)(PPh3)Cp](Cp =η-C5H5) afford [Ag{Rh(CO)(PPh3)Cp}2][PF6] which contains direct Ag–Rh bonds and is a stable source of the highly reactive radical cation [Rh(CO)(PPh3)Cp]+.

Reduction–oxidation properties of organotransition-metal complexes. Part 20. Oxidative and thermolytic cyclopropane ring-opening reactions; X-ray crystal structure of [Fe2(CO)6(η4:η′4-C16H18)]

Oxidation of [Fe2(CO)6(η4:η′4-C16H18)](1) with ferrocenium hexafluorophosphate results in regioselective cyclopropane ring-opening and the formation of [Fe2(CO)6(η5:η′5-C16H18)]2+(2), a derivative of trans-1,2-bis(cycloheptadienyl)ethylene. The same hydrocarbon ligand is formed when (1) is thermolysed to give the insoluble polymer [{Fe2(CO)2(µ-CO)2(η5:η′5-C16H18)}n](3). An X-ray diffraction study has shown that the regio- and stereo-specificity observed in the formation of (2) and (3) derives from the stereochemistry of (1). The molecule (1) as a whole has near two-fold symmetry, but this is not crystallographically required. Two ring systems comprising fused cyclopropane and cyclohepta-1,3-diene fragments are joined by a single bond between the two apical cyclopropane atoms. Four atoms of each C7 ring are essentially co-planar, giving an ‘envelope’ conformation to the ring, and are bonded to an Fe(CO)3 fragment; the remainder of the C7 ring is also planar, and incorporates the two C atoms shared with the C3 ring and the CH2 group. The C7 ring folds away from the metal atom, and there are further folds at the junction with the C3 ring and again at the apex of the C3 ring, all in the same sense. The C2 symmetry thus confers an overall S shape on the dimeric species when viewed along the two-fold axis. Along the Fe ⋯ Fe vector, by contrast, the C3 rings are seen nearly edgewise and the two C7 rings are almost eclipsed. Crystals of [Fe2(CO)6(η4:η′4-C16H18)](1) are triclinic, space group P, and the structure has been refined to R 0.043 for 3468 reflections measured at 293 K. Complex (3) undergoes metal–metal bond cleavage with iodine to yield [Fe2I2(CO)4(η5:η′5-C16H18)](4) which may also be prepared from the reaction of (2) and iodide ion. Triphenylphosphine adds to the terminal carbon atoms, adjacent to the CH2 groups, of the dienyl units of (2), giving the bis(phosphonium) salt [Fe2(CO)6{η4:η′4-C16H18(PPh3)2}][PF6]2(5).

Notes. The reaction of arenediazonium ions with cycloheptatriene (cht) and with [Fe(CO)3(η4-cht)]: azo-coupling versus hydrazone formation

The complex [Fe(CO)3(η4-cht)](cht = cycloheptatriene) and [N2C6H4NO2-p][BF4] give [Fe(CO)3{η5-C7H8N2C6H4NO2-p}][BF4](1) which is deprotonated on alumina to give syn- and anti-isomers of the hydrazone complex [Fe(CO)3{η4-C7H6NN(H)C6H4NO2-p}](2); the C7H6NN(H)C6H4NO2-p is detached from the metal on reaction with N(O)Me3·2H2O. By contrast, free cycloheptatriene and [N2C6H4NO2-p][BF4] in water yield 4-hydroxy-5-p-nitrophenylazobicyclo [4.1.0] hept-2-ene.

Stereospecific cyclopropane ring-openign via one-electron oxidation of organo-iron complexes; crystal structure of [Fe2(CO)6(η4,η′4-C16H18)]

The oxidation of [Fe2(CO)6(η4,η′4-C16H18)] and of [Fe2(CO)6(η4,η′4-C16H18)] ieads to stereospecific cyclopropane ring-opening and the isolation of (4) and (5) with exocyclic trans-and cis-double bonds, respectively; (5) is reduced to (6) with cyclobutane ring formation.