Kinetics and mechanisms of homogeneous catalytic reactions

Rosales, Merlín; González, A.; Guerrero, YusbeIi; Pacheco, Inés; Sánchez‐Delgado, Roberto A.

doi:10.1016/j.molcata.2007.01.044

Cited by 21 publications

(5 citation statements)

References 28 publications

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“…For the hydroformylation reactions under syngas conditions, the systems containing one equivalent of the diphosphine ligand produce the trigonal bipyramidal species RhH(CO) 2 (diphos), which were more active than those containing two equivalents, as reported before by some of us for the dppe system [23]; the results are showed in Table 1. As it can be observed, both the reaction rate and the selectivity, measured as the linear to branch ratio (l/b), increase with the enlargement of the carbon chain of the bridge between the two phosphorous atoms of the diphosphine (dppb [ dppp [ dppe) which may be explained by the bite angle of the corresponding diphosphine.…”

Section: Resultssupporting

confidence: 62%

A Comparative Study of the 1-Hexene Hydroformylation Either Under Syngas Conditions or with Paraformaldehyde Catalyzed by Rhodium/Diphosphine Systems

et al. 2008

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In order to carry out a comparison, the hydroformylation of 1-hexene to their corresponding aldehydes (heptanal and 2-methyl-hexanal) was studied both under syngas conditions and with paraformaldehyde using the catalytic rhodium/diphosphine precatalysts; the catalytic systems were formed in situ by the addition of one or two equivalents of the corresponding diphosphine, Ph 2 P(CH 2 ) n PPh 2, n = 2 (dppe), 3 (dppp) and 4 (dppb), to the carbonyl complex Rh(acac)(CO) 2 . For the hydroformylation reactions under syngas conditions, the more active systems were the ones containing one equivalent of the diphosphine, which produce trigonal bipyramidal species like RhH(CO) 2 (diphos). The activity and selectivity of these systems strongly depend on the bite angle of the ligand: when the bite angle increases both parameters are higher (dppb [ dppp [ dppe). Contrary to these results, for the reaction with paraformaldehyde, the systems containing two equivalents of the diphosphine ligand, which produce the cationic square planar species [Rh (diphos) 2 ] ? , were more active than those containing one equivalent; the reaction rate decreases with the enlargement of the carbon chain of the bridge between the two phosphorous atoms of the diphosphine (dppe [ dppp [ dppb). These results may be explained by a higher steric effect on the metal center, which probably produces a decreasing of the rate of the CH 2 O oxidative addition reactions. For both reactions, these effects were explained through DFT calculations of the corresponding resting states.

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Section: Resultssupporting

confidence: 62%

A Comparative Study of the 1-Hexene Hydroformylation Either Under Syngas Conditions or with Paraformaldehyde Catalyzed by Rhodium/Diphosphine Systems

et al. 2008

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“…A detailed structural and quantitative description of the catalyst system, which often represents a mixture of several components, is the basis of any kinetic and mechanistic study. It has to be noted that due to the higher stability of iridium carbonyl complexes compared to rhodium congeners they have been frequently used as model complexes in mechanistic studies. − Many complex structures have been thoroughly characterized, but mostly no quantitative informations are available when dealing with mixtures of complexes.…”

Section: Iridium-catalyzed Hydroformylationmentioning

confidence: 99%

Investigation into the Equilibrium of Iridium Catalysts for the Hydroformylation of Olefins by Combining In Situ High-Pressure FTIR and NMR Spectroscopy

et al. 2014

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A detailed quantitative study of phosphine-modified hydrido iridium complexes relevant for the hydroformylation reaction has been performed using HP-FTIR and HP-NMR spectroscopy. The equilibrium composition under typical reaction conditions has been characterized. Investigation of the temperature dependency allowed even for a distinction between both configurational isomers of [HIr(CO)2(PPh3)2]. The trihydride complex [H3Ir(CO)(PPh3)2] is part of the investigated equilibrium depending on the ratio of p(H2)/p(CO). Single rate constants for the sequence of corresponding equilibrium reactions have been estimated from stopped-flow experiments and conventional measurements, monitoring the concentrations after changing reactant concentrations.

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“…In this case, the acetylacetonato entity plays the role of counteranion. The formation of rhodium cationic species with diphosphine ligands and acac – as counterion was already described. , Attempts to isolate the complex [Rh(CO) 2 (NHC 5 H 10 ){( R,R )-Ph-BPE}]acac C3 were unsuccessful, since the stabilization of the rhodium cation by acac – is somewhat less efficient than by BF 4 – .…”

Section: Results and Discussionmentioning

confidence: 99%

“…The formation of rhodium cationic species with diphosphine ligands and acac − as counterion was already described. 40,41 Attempts to isolate the complex [Rh-(CO) 2 (NHC 5 H 10 ){(R,R)-Ph-BPE}]acac C3 were unsuccessful, since the stabilization of the rhodium cation by acac − is somewhat less efficient than by BF 4 − . 16 31 P NMR analyses under 30 bar CO/H 2 (1:2) revealed after 15 min the presence of the doublet of the monohydride species C2 at 97.9 ppm due to a fast exchange phenomenon of the two phosphorus atoms on the NMR time scale and the two doublet of doublets of C3 at 73.7 and 80.2 ppm.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Hydroaminomethylation of Styrene Catalyzed by Rhodium Complexes Containing Chiral Diphosphine Ligands and Mechanistic Studies: Why Is There a Lack of Asymmetric Induction?

et al. 2014

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Various chiral diphosphine ligands (P−P) have been introduced in the coordination sphere of neutral or cationic rhodium complexes, and the generated species catalyze efficiently the hydroaminomethylation reaction of styrene with piperidine. The diphospholane ligand family is particularly adapted to this tandem reaction leading to the branched amine with good chemo-and regioselectivity. We analyzed in detail the main reasons why the reaction proceeds with no enantioselectivity. Catalytic and HP-NMR experiments reveal the presence of the [Rh(H)(CO) 2 (P−P)] species as the resting state. DFT calculations allow us to elucidate the mechanism of the hydrogenation of the branched (Z) or (E)-enamine. From the [Rh(H)(CO)(P−P)] active species, the coordination of the two enamine isomers, the hydride transfer, the H 2 activation, and then the final reductive elimination follow similar energetic pathways, explaining the lack of enantioselectivity for the present substrates. Analysis of the energy-demanding steps highlights the formation of the active species as crucial for this rate-limiting hydrogenation reaction.

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Kinetics and mechanisms of homogeneous catalytic reactions

Cited by 21 publications

References 28 publications

A Comparative Study of the 1-Hexene Hydroformylation Either Under Syngas Conditions or with Paraformaldehyde Catalyzed by Rhodium/Diphosphine Systems

A Comparative Study of the 1-Hexene Hydroformylation Either Under Syngas Conditions or with Paraformaldehyde Catalyzed by Rhodium/Diphosphine Systems

Investigation into the Equilibrium of Iridium Catalysts for the Hydroformylation of Olefins by Combining In Situ High-Pressure FTIR and NMR Spectroscopy

Hydroaminomethylation of Styrene Catalyzed by Rhodium Complexes Containing Chiral Diphosphine Ligands and Mechanistic Studies: Why Is There a Lack of Asymmetric Induction?

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