Thomas R. B. Mitchell

Oxidation of alcohols by transition metal complexes part V. Selective catalytic monoalkylation of arylacetonitriles by alcohols

Abstract Selective catalytic monoalkylation of arylacetonitriles by primary alcohols can be achieved at ≤ 100° using a catalyst prepared in situ from rhodium trichloride, triphenylphosphine and sodium carbonate. RuH 2 (PPh 3 ) 4 is a more effective catalyst for this process.

Oxidation of alcohols by transition metal complexes—iv : The rhodium catalysed synthesis of esters from aldehydes and alcohols

Abstract Both RhH(CO)PPh3)3 and a catalyst made in situ from RhCl3·3H2O, PPh3 and Na2CO3 catalyse the reaction of a range of aldehydes with simple primary alcohols to give esters together with alcohols formed by reduction of the aldehydes. The proportion of ester can be increased by adding an efficient hydrogen acceptor. The reaction can also be used to produce 5- and 7-membered lactones from aromatic dialdehydes. Propan-2-ol and the in situ catalyst reduce some aromatic aldehydes to the corresponding alcohols without concomitant ester formation.

A kinetic and mechanistic study of the thermal decomposition of nickel acetate

An isothermal kinetic and mechanistic study of the thermal decomposition of nickel acetate is reported. Plots of yields of volatile products against time were sigmoid. Calculated activation energies were 150 ± 8 (548–578 K) and 80 ± 8 (578–618 K) kJ mol−1. There were systematic variations in kinetic behaviour with temperature. At the upper end of the temperature interval studied here ( > 580 K) a second rate process became apparent during the final stages of reaction ( > 80%). It is concluded that the autocatalytic reaction is a nucleation and growth process in which anion breakdown is promoted by the predominant solid product, nickel carbide. Towards the end of reaction, and increasingly at higher temperatures, nickel, produced by Ni3C decomposition, more effectively accelerates reaction and this acccounts for the second rate process. These mechanistic proposals are based also on scanning electron micrographs which showed that the salt did not comprehensively melt during pyrolysis. Little information could, however, be obtained concerning the structure of the reaction interface because textural features were below the limits of resolution. Analytical determinations failed to reveal the existence of any anionic reaction intermediate.

Gas-phase reactions on platinum. Synthesis and crystal structure of anti- tetramantane, a large diamondoid fragment

anti-Tetramantane, a C22H28 hydrocarbon having the regular topology of the diamondoid lattice, has been synthesised by a double homologation of diamantane, the key step involving a ring expansion–cyclisation reaction of a polycyclic diene in hydrogen in the gas phase on a platinum-silica catalyst; the structure has been established by an X-ray crystal analysis.

Palladium- and rhodium-catalysed cyclisation of 1,6-, 1,7- and 1,8-dienes to cyclopentenes and methylenecyclopentenes. Crystal structure of dichloro(4,4-diacetylhepta-1,6-diene)platinum(II)

Hepta-1,6-dienes disubstituted at C-4 with certain carbonyl-containing groups cyclise, in good yield, to the corresponding 4,4-disubstituted 1,2-dimethylcyclopent-2-enes when treated with a catalytic amount of palladium acetate in chloroform containing hydrogen chloride. Changing the catalyst precursor to chlorotris(triphenylphosphine)rhodium(I) led to the formation of the corresponding 1-methyl-2-methylenecyclopentanes which, in turn, isomerised to 1,2-dimethylcyclopent-1-enes in ethanolic hydrogen chloride containing the rhodium complex. The effect of terminal substitution of the dienes with methyl groups was examined. 1,7- and 1,8-Dienes give rise to mixtures of five-membered ring products. Possible mechanisms for the catalytic processes are discussed. The X-ray crystal structure analysis of dichloro(4,4-diacetylhepta-1,6-diene)platinum(II) is reported.

Catalytic synthesis of substituted cyclopentenes

4,4-Disubstituted 1,6-dienes undergo a palladium(II) catalysed cyclisation in boiling chloroform to give substituted cyclopentenes in good yield.

Rhodium-catalysed synthesis of substituted methylene cyclopentanes

4,4-Disubstituted 1,6-dienes are cyclised in good yield by Wilkinsons catalyst [RhCl(PPh3)3], in boiling chloroform, to methylene cyclopentanes.

Transition metal-catalysed N-alkylation of amines by alcohols

Primary and secondary alcohols effect alkylation of primary and secondary amines in the presence of rhodium, iridium, and ruthenium compounds at ⩽ 100 °C, whereby selective monoalkylation of primary amines can be achieved and heterocyclic rings can be constructed by both inter- and intra-molecular processes.

Reactions of O-alkyl and O-cycloalkyl S-methyl xanthates with MCI(PPh3)3(M = Rh, Ir) and M(PPh3)4(M = Pd, Pt). Easy 1,2-bond shifts in alkyl and cycloalkyl–metal intermediates

Reactions of O-alkyl and O-cycloalkyl S-methyl xanthates with RhCl(PPh3)3(1), IrCl(PPh3)3(2), Pd(PPh3)4(3), or Pt(PPh3)4(4) at temperatures from 373 to 423 K give olefinic products whose structures clearly reveal 1,2-bond shift skeletal rearrangements in alkyl–metal intermediates; these rearrangements are exactly analogous to several of those occurring in hydroisomerisation of cycloalkanes and alkanes at elevated temperatures on transition metal surfaces.

Evidence for a novel mechanism of the 1,2-bond shift rearrangements catalysed by coenzyme-B12

The olefinic products arising from he oxidative addition at ambient temperatures of 2,2,6,6-tetramethyl-cyclohex-1-yl toluene-p-sulphonate to (PPh3)2CoBr2,(PPh3)2NiBr2, and hydroxo-cobalamin, all reduced with sodium borohydride, or to (Me)2CuLi, provide firm evidence for a novel mechanism of the 1,2-bond shift rearrangements catalysed by vitamin B12 coenzyme.