Journal of The Chemical Society A: Inorganic, Physical, Theoretical 

About: Journal of The Chemical Society A: Inorganic, Physical, Theoretical is an academic journal. The journal publishes majorly in the area(s): Crystal structure & Aqueous solution. Over the lifetime, 3915 publications have been published receiving 61678 citations.

The preparation and properties of tris(triphenylphosphine)halogenorhodium(I) and some reactions thereof including catalytic homogeneous hydrogenation of olefins and acetylenes and their derivatives

Abstract: Tris(triphenylphosphine)chlororhodium(I), RhCl(PPh3)3, has been prepared by the interaction of an excess of triphenylphosphine with rhodium(III) chloride hydrate in ethanol; the corresponding bromide and iodide are also described. The dissociation of the complex in various solvents has been investigated, and its reactions with hydrogen, ethylene, and carbon monoxide and aldehydes studied. Dihydrido- and ethylene complexes have been isolated and studied by nuclear magnetic resonance (n.m.r.) spectroscopy. Approximate values for the formation constants of ethylene and propylene complexes have been obtained; the latter is lower by a factor of over 103. By electron spin resonance spectroscopy, the complex RhCl(PPh3)3 has been shown to contain trace amounts of a paramagnetic species, probably a rhodium(II) complex.In homogeneous solution the tris(triphenylphosphine) complexes are exceedingly active catalysts for the rapid and homogeneous hydrogenation, at ca. 1 atmosphere of hydrogen pressure and room temperature, of unsaturated compounds containing isolated olefinic and acetylenic linkages.The rates of hydrogenation of hept-1-ene, cyclohexene and hex-1-yne have been studied quantitatively and the dependence on factors such as substrate and catalyst concentration, temperature, and pressure determined. The data can be accommodated by a rate expression of the form: Rate =Kp[S][A]//1 +K1p+K2[S] where [S] and [A] are the olefin and catalyst concentrations, respectively, and p is the concentration of hydrogen in solution.From the data for cyclohexene the activation energy for the rate determining step is Ea= 22·9 kcal. mole–1(ΔH‡= 22·3 kcal. mole–1) and the value of ΔS‡= 12·9 e.u.It is shown that the rate of hydrogen–deuterium exchange under selected conditions is quite slow compared with the rates of hydrogenation of olefins and, furthermore, that when H2–D2 mixtures are used in the reactions, alkanes and dideuteroalkanes are the major products. Reductions of maleic and fumaric acids with deuterium shows that cis-addition occurs preferentially. Similarly, in the reduction of hex-2-yne to n-hexane, cis-hex-2-ene is found to be the major olefin intermediate.A mechanism for the hydrogenation is proposed in which the metal complex serves as a template to which a hydrogen molecule and an olefin molecule are briefly co-ordinated before transfer of one to the other takes place. The low kinetic isotope effect (rate H2/rate D2= 0·9) suggests that synchronous breaking of Rh–H bonds and making of C–H bonds takes place in the transition state involving two simultaneous three-centre interactions.

Hydroformylation of alkenes by use of rhodium complex catalysts

Abstract: The use of complexes of rhodium of the type trans-RhX(CO)(PR3)2, (X = halogen, R = aryl) as hydroformylation catalysts for alkenes is studied. It is shown that an inhibition period is removed by addition of hydrogen halide acceptors and that the halide complex undergoes hydrogenolysis to form a hydrido-species. The hydrido-species is only one of several complexes in equilibrium but it appears that the principal active catalytic species is RhH(CO)2(PPh3)2. This species is formed by addition of carbon monoxide to the monocarbonyl complex RhH(CO)(PPh3)2. The latter is also formed by dissociation when the stable crystalline complex RhH(CO)(PPh3)3 is dissolved in benzene or other solvents. With RhH(CO)(PPh3)3 as catalyst, alkenes undergo rapid hydroformylation even at 25°/1 atm.; with alk-1-enes the ratio of straight- to branched-chain aldehyde formed is considerably higher than the ratios normally found in hydroformylation reactions, being ca. 20 at 25°. Hydrogen atom exchange and isomerisation reactions of alkenes with RhH(CO)(PPh3)3 are described.

Heteropolytungstate complexes of the lanthanide elements. Part I. Preparation and reactions

Abstract: Salts of the anions LnIIIW10O357–(Ln = La, Ce, Pr, Nd, Sm, Ho, Er, Yb, and Y) and CeIVW10O356– have been prepared and analysed. The formulae of the previously reported 8-tungstocerates are revised. All the anions are unstable outside the pH range 5·5–8·5, and stable solutions of the free acids cannot be obtained. Lanthanide cations react rapidly with unsaturated heteropolyanions to give complexes LnL and LnL2(L = SiW11O398–, etc.). Salts of several of the LnL2 complexes have been isolated. The mode of co-ordination of L is discussed.

The electronic properties and stereochemistry of the copper(II) ion. Part I. Bis(ethylenediamine)copper(II) complexes

Abstract: The electronic properties and i.r. spectra of a series of bis(ethylenediamine)copper(II) complexes are reported. From a gaussian analysis of the electronic spectra, measured at room temperature and at the temperature of liquid nitrogen, of the seven complexes of known crystal structure, and three transitions 2A1gâ†�2B1g, 2B2gâ†�2B1g, and 2Egâ†�2B1g in D4h symmetry are tentatively assigned. From the e.s.r. spectra of polycrystalline samples of the complexes, which yield tetragonal spectra, the values of (g‖– 2)/(g⊥– 2) have been determined. Where the ratio is 4·0 the observed g-values are considered to reflect approximately the local copper(II) ion g-values. In the latter case the g-values have been combined with the appropriate electronic transitions and the orbital reduction factors k⊥ and k‖ evaluated. From the i.r. spectra of the polyanions, an infrared criterion is established for recognising the presence of weakly co-ordinated polyanions in the long tetragonal positions above and below the [Cu en2]2+ cation. The term semi-co-ordination is introduced to describe this structural situation.

The chemistry of pernitrites. Part I. Kinetics of decomposition of pernitrous acid

Abstract: The kinetics of decomposition of pernitrite in excess of alkali have been studies at several temperatures. These show that decomposition occurs through the pernitrous acid molecule, HO·ONO, with ΔH‡= 12·5 kcal. mole–1 and ΔS‡= 26 e.u. The value of ΔH‡ is not consistent with the accepted view that pernitrous acid decomposes via homolytic fission of the O–O link. This problem is discussed and other, non-homolytic, mechanisms suggested. An upper limit for the pKA of pernitrous acid at 2° of 8·3 has been calculated. The first isolation of a solid pernitrite is reported. The extinction coefficient of the pernitrite anion at 302 mµ(λmax.) has been redetermined as 1670 ± 50.