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Sylviane Sabo-Etienne

Publications and source records attributed to Sylviane Sabo-Etienne.

8 recordsLinked to original sources
PubMed2005

Synthesis, neutron structure, and reactivity of the bis(dihydrogen) complex RuH2(eta(2)-H2)2(PCyp3)2 stabilized by two tricyclopentylphosphines.

Treatment of Ru(eta4-C8H12)(eta6-C8H10) with 3 bar H2 in the presence of 2 equiv of tricyclopentylphosphine (PCyp3) in pentane resulted in the isolation of the new bis(dihydrogen) complex RuH2(eta2-H2)2(PCyp3)2 (2), characterized by NMR and single-crystal X-ray and neutron diffraction. The single-crystal neutron diffraction study is the first carried out for a bis(dihydrogen) complex. The coordination geometry around the metal center is a distorted octahedron defined by the two phosphines in a trans configuration (making an angle of 168.9(1) degrees ), two cis dihydrogen ligands, and two hydrides trans to them, defining the equatorial plane. The H-H bond distances (0.825(8) and 0.835(8) A) are characteristic of two "unstretched" dihydrogen ligands. H/D exchange between the Ru-H and the C-D bonds of deuterated benzene is observed within 1 h, leading to the formation of various isotopomers RuHxD6-x(PCyp3)2 (with x = 0-6). 2 is a catalyst precursor for ethylene coupling (20 bar, 293 K) to a functionalized arene (Murai reaction). We found a 90% conversion of acetophenone to 2-ethylacetophenone within 35 min, whereas 10 h was needed in the same conditions using the analogous tricyclohexylphosphine complex, RuH2(eta2-H2)2(PCy3)2, the best catalyst precursor, at room temperature, prior to this work.

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PubMed2004

Bridging the gap between homogeneous and heterogeneous catalysis: ortho/para H(2) conversion, hydrogen isotope scrambling, and hydrogenation of olefins by Ir(CO)Cl(PPh(3))(2).

Some transition metal complexes are known to catalyze ortho/para hydrogen conversion, hydrogen isotope scrambling, and hydrogenation reactions in liquid solution. Using the example of Vaska's complex, we present here evidence by NMR that the solvent is not necessary for these reactions to occur. Thus, solid frozen solutions or polycrystalline powdered samples of homogeneous catalysts may become heterogeneous catalysts. Comparative liquid- and solid-state studies provide novel insight into the reaction mechanisms.

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PubMed2003

Photochemical oxidative addition of B-H bonds at ruthenium and rhodium.

Metal phosphine hydrides of type RuP(4)H(2) and RhP(3)H(3) react photochemically with HB(pin)(pin = pinacolate) to form metal boryl hydride complexes via 16-electron intermediates generated by H(2) loss; the second order rate constants for reaction of the intermediates with HB(pin) are even larger than those for reaction with Et(3)SiH.

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PubMed2003

Ruthenium dihydrogen complexes with wide bite angle diphosphines.

The wide bite angle diphosphines homoxantphos (10,11-dihydro-4,5,-bis(diphenylphosphino)dibenzo[b,f]oxepine), sixantphos (4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin), and thixantphos (2,8-dimethyl-4,6-bis(diphenylphosphino)phenoxathiin) were used to prepare cis[MH(2)(diphosphine)(2)] complexes (1a-f) by reaction of [Ru(cod)(cot)] (cod = cyclo-octa-1,5-diene, cot = cyclo-octa-1,3,5-triene) with 2 equiv of the diphosphine under dihydrogen pressure. The electronic properties of the thixantphos ligand were varied. Complexes 1a-f can be protonated with HBF(4) or CF(3)COOH to yield hydrido(dihydrogen) complexes cis[MH(H(2))(diphosphine)(2)](+) (2a-f), which were characterized by VT (variable temperature) NMR and T(1) measurements. These complexes show fast hydrogen atom exchange between the eta(2)-H(2) and the terminal hydride at all temperatures studied. They are thermally unstable toward dihydrogen loss yielding the cationic monohydride complexes cis[MH(diphosphine)(2)](+) (3a-f). Coordination of the eta(2)-H(2) is dominated by sigma --> d donation, and hence, the H-H distance is hardly influenced by the electronic properties of the ligands.

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PubMed2002

sigma-Borane and dihydroborate complexes of ruthenium.

Room temperature reaction of the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1) with excess pinacol borane (HBpin) generates the novel complex RuH[(mu-H)(2)Bpin](sigma-HBpin)(PCy(3))(2) (2) by loss of dihydrogen. Complex 2 was characterized spectroscopically and by X-ray crystallography. It contains two pinacolborane moieties coordinated in a different fashion, one as a dihydroborate (B-H distances : 1.58(3) and 1.47(3) A) and the other as a sigma-borane (B-H distance: 1.35(3) A). In addition, reaction of 1 with one equiv of HBpin yields total conversion to a new complex tentatively formulated as RuH[(mu-H)(2)Bpin](H(2))(PCy(3))(2) (3) on the basis of NMR data. In the presence of excess HBpin, 3 is converted to 2. Furthermore, under an atmosphere of dihydrogen, a C(7)D(8) solution of 2 rapidly converts to 3 and finally regenerates 1 over a much longer period. Thus, complex 3 is an intermediate in the formation of 2 from 1. In these processes the borane is eliminated as HBpin later hydrolyzed to BpinOBpin. Selective hydroboration of ethylene (3 bar) into C(2)H(5)Bpin is achieved using 1 or 2 as catalyst precursors in toluene, whereas in THF, competitive formation of the vinylborane C(2)H(3)Bpin (56% under 20 bar of C(2)H(4)) can be favored.

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PubMed1998

Fluxionality and Isomerism of the Bis(dihydrogen) Complex RuH(2)(H(2))(2)(PCy(3))(2): INS, NMR, and Theoretical Studies.

To study the fluxionality of the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1), NMR spectra were recorded in Freons (mixture of CDCl(3), CDFCl(2), and CDF(2)Cl). 1 was found to remain fluxional at all temperatures, but the presence of CDCl(3) necessary for its solubilization induces its transformation into, first, RuHCl(H(2))(2)(PCy(3))(2) (3) and the new ruthenium(IV) dihydride RuH(2)Cl(2)(PCy(3))(2) (4). 4 is produced selectively in pure CDCl(3) but reacts further to give a mixture of chloro complexes. 4 was isolated from the reaction of 1 with aqueous HCl in Et(2)O and shows a fluxional process attributed to the interconversion between two symmetrical isomers. The activation parameters of this process were obtained by (1)H NMR line shape analysis, as well as those corresponding to the exchange between 3 and free dihydrogen. The fluxionality of the dihydrogen-hydride system is also evident at a much faster time scale than that of NMR studies in the inelastic neutron scattering observations of the rotation of the dihydrogen ligands. The geometries and relative energies of several isomers of complexes 1, 3, and 4 were studied using density functional theory (DFT) and MP2 methods, together with a few coupled-cluster (CCSD(T)) calculations. In contrast to what might have been expected, the two hydrides and the two H(2) units of 1 lie in the same plane, due to the attractive "cis effect" created by the hydrides. The two H(2) ligands adopt cis positions in the lowest-energy isomer. Rotation of the two dihydrogen ligands has been analyzed using DFT calculations. A slight preference for a C(2) conrotatory pathway has been found with a calculated barrier in good agreement with the experimental INS value. Two low-energy isomers of 4 have been characterized computationally, both of which have C(2)(v)() symmetry, consistent with the solution NMR spectra.

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