On the synthesis and chemical behaviour of the elusive bis(hydrosulfido)-bridged dinuclear rhodium(I) complexes [{Rh(mu-SH)(CO)(PR(3))}(2)].
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.
Pérez-Torrente
Jesús J
JJ
Departamento de Química Inorgánica, Instituto Universitario de Catálisis Homogénea, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-C.S.I.C., 50009-Zaragoza, Spain. perez@unizar.es
Jiménez
M Victoria
MV
Hernandez-Gruel
Marc A F
MA
Fabra
María J
MJ
Lahoz
Fernando J
FJ
Oro
Luis A
LA
D001952:Bridged-Ring Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D012238:Rhodium / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*
D001952:Bridged-Ring Compounds; D056831:Coordination Complexes; D013438:Sulfhydryl Compounds; D012238:Rhodium