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ABSTRACT: Several bis(hydrosulfido)-bridged dinuclear rhodium(I) compounds, [{Rh(mu-SH)(L)(2)}(2)], have been prepared from rhodium(I) acetylacetonato complexes, [Rh(acac)(L)(2)], and H(2)S(g). Reaction of [Rh(acac){P(OPh)(3)}(2)] with H(2)S(g) affords the dinuclear bis(hydrosulfido)-bridged compound [{Rh(mu-SH){P(OPh)(3)}(2)}(2)] (1). However, reaction of complexes [Rh(acac)(CO)(PR(3))] with H(2)S(g) gives the dinuclear compound [{Rh(mu-SH)(CO)(PR(3))}(2)] (R=Cy, 2; R=Ph, 4) and the trinuclear cluster [Rh(3)(mu-H)(mu(3)-S)(2)(CO)(3)(PR(3))(3)] (R=Cy, 3; R=Ph, 5). The selective synthesis of both type of compounds has been carried out by control of the H(2)S(g) concentration in the reaction media. The trinuclear hydrido-sulfido cluster [Rh(3)(mu-H)(mu(3)-S)(2)(CO)(3)(PPh(3))(3)] (5) has been also obtained by reaction of [{Rh(mu-SH)(CO)(PPh(3))}(2)] (4) with [Rh(acac)(CO)(PPh(3))], proceeding through the trinuclear hydrosulfido-sulfido intermediate [Rh(3)(mu(3)-SH)(mu(3)-S)(CO)(3)(PPh(3))(3)]. The molecular structures of complexes 1 and 3 have been determined by X-ray diffraction methods. Compound 1 is stable in solution, but complexes 2 and 4 slowly transform in solution into the trinuclear hydrido-sulfido clusters 3 and 5, respectively, with the release of H(2)S(g) in a reversible way. (1)H NMR kinetic experiments for the transformation of 4 into 5 have revealed that this transformation follows second-order-type kinetic. The following activation parameters, DeltaH( not equal)=24+/-3 kJ mol(-1) and of DeltaS( not equal)=-223+/-8 J K(-1) mol(-1), have been calculated from the determination of the second-order rate constants in the temperature range 30-45 degrees C. The large negative value of the activation entropy is consistent with an associative character of the rate-determining step. A plausible multistep mechanism based on the chemical behaviour of hydrosulfido-metal complexes and compatible with the kinetic behaviour has been proposed.
Chemistry 10/2009; 15(45):12212-22. · 5.93 Impact Factor
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ABSTRACT: The new ligand 6-mercapto-2(1H)-pyridone (H(2)PySO) has been prepared in good yield by reaction of 6-chloro-pyridin-2-ol with NaSH. Reaction of the salt K(2)PySO, generated in situ, with the appropriate complex [M(mu-Cl)(diolefin)](2) affords the tetranuclear complexes [M(4)(mu-PySO)(2)(diolefin)(4)] [M = Rh, diolefin = 1,5-cyclooctadiene (cod) (1), tetrafluorobenzobarralene (tfbb) (2); M = Ir, diolefin = cod (3)]. The molecular structure of complex 1 has been determined by X-ray diffraction methods. The tetranuclear structure is supported by two S,N,O-tridentate ligands exhibiting a 1kappaO, 2kappaN, 3:4kappa(2)S coordination mode. Carbonylation of the rhodium diolefin complexes at atmospheric pressure gives [Rh(4)(mu-PySO)(2)(CO)(8)] (4). The carbonylation of 1 is partially reversible, and the mixed-ligand complex [Rh(4)(mu-PySO)(2)(cod)(2)(CO)(4)] (5) has been obtained as a single isomer. The reaction of 4 with triphenylphosphine gives the compound [Rh(4)(mu-PySO)(2)(CO)(4)(PPh(3))(4)] (6) which also exists as a single isomer of C(2) symmetry. The diolefin complexes are redox active and exhibit two one-electron oxidations at a platinum disk electrode in dichloromethane separated by approximately 0.5 V at potentials accessible by chemical oxidants. The tetranuclear complexes were selectively oxidized to the 63-electron mixed-valence cationic complexes [M(4)(mu-PySO)(2)(diolefin)(4)](+) (1a(+), 2(+), and 3(+)) by using AgCF(3)SO(3) as oxidant and isolated as the triflate salts. Alternatively, the oxidation with [Cp(2)Fe]PF(6) gives [Rh(4)(mu-PySO)(2)(cod)(4)][PF(6)] (1b(+)). The parameters obtained from the simulation of the electron paramagnetic resonance spectra of the oxidized species strongly suggest that the unpaired electron is delocalized over only two metal atoms in the complexes.
Inorganic Chemistry 08/2009; 48(16):7984-93. · 4.60 Impact Factor
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ABSTRACT: Surface effects on a laponite-exchanged bis(oxazoline)-copper complex modify the stereochemical course of the Mukaiyama aldol reaction between 2-(trimethylsilyloxy)furan and alpha-ketoesters, leading up to 90% ee (dr 86 : 14) becoming the best overall result obtained for this reaction and significantly improving the homogeneous process.
Chemical Communications 12/2008; · 6.17 Impact Factor
