50520-11-1Relevant articles and documents
Kinetics and mechanisms of homogeneous catalytic reactions. Part 7. Hydroformylation of 1-hexene catalyzed by cationic complexes of rhodium and iridium containing PPh3
Rosales, Merlin,Durán, Jesús A.,González, ángel,Pacheco, Inés,Sánchez-Delgado, Roberto A.
, p. 250 - 256 (2008/10/09)
Cationic rhodium and iridium complexes of the type [M(COD)(PPh3)2]PF6 (M = Rh, 1a; Ir, 1b) are efficient precatalysts for the hydroformylation of 1-hexene to its corresponding aldehydes (heptanal and 2-methylhexanal), under mild pressures (2-5 bar) and temperatures (60 °C for Rh and 100 °C for Ir) in toluene solution; the linear to branched ratio (l/b) of the aldehydes in the hydroformylation reaction varies slightly (between 3.0 and 3.7 for Rh and close to 2 for Ir). Kinetic and mechanistic studies have been carried out using these cationic complexes as catalyst precursors. For both complexes, the reaction proceeds according to the rate law ri = K1K2K3k4[M][olef][H2][CO]/([CO]2 + K1[H2][CO] + K1K2K3[olef][H2]). Both complexes react rapidly with CO to produce the corresponding tricarbonyl species [M(CO)3(PPh3)2]PF6, M = Rh, 2a; Ir, 2b, and with syn-gas to yield [MH2(CO)2(PPh3)2]PF6, M = Rh, 3a; Ir, 3b, which originate by CO dissociation the species [MH2(CO)(PPh3)2]PF6 entering the corresponding catalytic cycle. All the experimental data are consistent with a general mechanism in which the transfer of the hydride to a coordinated olefin promoted by an entering CO molecule is the rate-determining step of the catalytic cycle.
HDS model systems. 2,3-Dihydrothiophene as an intermediate in the homogeneous hydrogenation of thiophene to tetrahydrothiophene at iridium
Bianchini, Claudio,Meli, Andrea,Peruzzini, Maurizio,Vizza, Francesco,Herrera, Verónica,Sánchez-Delgado, Roberto A.
, p. 721 - 730 (2008/10/08)
Thermolysis of the bis(thiophene) (T) dihydride [(PPh3)2Ir(H)2(η1-SC 4H4)2]PF6 (1) in 1,2-dichloroethane at 80°C gives the thioallyl complex [(PPh3)2IrH(η4-SC4H 5)]PF6 (2) by a stereospecific endo migration of one of the coordinated hydrides. Reaction of the thioallyl complex with H2 under mild conditions yields the bis(tetrahydrothiophene) (THT) dihydride [(PPh3)2Ir(H)2(η1-SC 4H8)2]PF6 (3) plus the pentahydride [{(PPh3)2IrH}2(μ2-H) 3]PF6 (4); if the hydrogenation is carried out in the presence of excess T, complex 3 is obtained exclusively. Interaction of 2 with CO at room temperature produces the two novel isomeric derivatives [(PPh3)2Ir(H)(CO)(η2-C 5,S-SC4H5)]PF6 (7) and [(PPh3)2Ir(H)(CO)(η2-C 3,S-SC4H5)]PF6 (8) in a 5:1 ratio, which do not interconvert from -50 to +80°C; longer reaction times (24 h, 25°C) or higher temperatures (3 h, 50°C) result in quantitative conversion of the complex to [(PPh3)2-Ir(CO)3]PF6 with concomitant liberation of 2,5-dihydrothiophene (2,5-DHT) and 2,3-DHT in a 5:1 ratio. Reaction of 2 with 2,5-DHT under H2 at 80°C produces the new bis(2,5-DHT) dihydride complex [(PPh3)2Ir(H)2(η1-2,5-S-SC 4H6)2]PF6 (5), whereas the analogous reaction with 2,3-DHT results in hydrogenation to yield the bis(THT) dihydride derivative 3. Complex 5 and its 2,3-DHT analog [(PPh3)2Ir(H)2(η1-2,3-SC 4H6)2]PF6 (6) may also be prepared by displacement of coordinated acetone in [(PPh3)2Ir(H)2(Me2CO) 2]PF6 (5) by the appropriate ligand. Complex 5 does not react with H2 at 80°C, whereas 6 is readily transformed into 3 under analogous conditions. Interaction of 2 with syngas results in the production of 7 and 8, together with free 2,5-DHT and 2,3-DHT, plus small amounts of [(PPh3)2Ir(H2)(CO)(η1-SC 4H8)]PF6 (10) and [(PPh3)2Ir(H)2(CO)2]PF6 (11). These combined results clearly establish that only the 2,3-DHT isomer is an intermediate in the homogeneous hydrogenation of T to THT (via the isolated thioallyl (2) and hydrido-η2-C,S (8) intermediates) with this Ir system, a result of relevance in connection with the HDS mechanisms. The THT complex 10 crystallizes in monoclinic space group P21 (No. 4) with a = 9.563(4) A?, b = 23.201(4) A?, c = 11.221(2) A?, β = 97.87° (2), Z = 2, and V = 2466.16 A?3. The structure of the complex cation consists of a distorted octahedron with mutually cis-hydrides, cis-THT, and CO and trans-PPh3 ligands.
