New perspectives in hydroformylation : a para-hydrogen study

Godard, Cyril; Duckett, Simon B.; Henry, Céline; Polas, Stacey; Toose, Robert; Whitwood, Adrian C.

doi:10.1039/b404547e

Cited by 36 publications

(32 citation statements)

References 14 publications

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“…Species including iridium acyl and alkyl dihydride intermediates were detected. The results confirmed that the CO-deficient atmosphere favors hydrogenation over carbonylation [76].…”

Section: Iridium Catalystssupporting

confidence: 71%

Carbonylation of Alkenes and Dienes

Kégl

2008

Modern Carbonylation Methods

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In the beginning, only cobalt catalysts were utilized for hydroformylation under relatively vigorous conditions. The moderate selectivity of the generally more desired linear isomers, the substantial formation of by-products, and the low stability of the catalysts forced more appropriate catalytic systems to be developed. Using donor ligands such as phosphanes resulted in an increase in the linear selectivity. Rhodium-containing catalysts, however, permitted the use of much milder conditions in combination with suitable ligands. Other transition metals such as ruthenium, palladium, platinum, and iridium also tended to show activity for hydroformylation, albeit a vast majority of works on hydroformylation still concentrated on rhodium-containing systems. Cobalt CatalystsThe initial rate of Co 2 (CO) 8 -catalyzed cyclohexene hydroformylation, triethyl orthoformate carbonylation, and CoH(CO) 4 formation from Co 2 (CO) 8 and H 2 is reduced by the addition of dinitrogen, argon, or xenon. It is assumed that the additional gas competes with one or more reactants for a coordinatively unsaturated site responsible for their activation, thus affecting the reaction rate [1].The carbonylation reaction of propylene oxide in the presence of various [Lewis acid] þ [Co(CO) 4 ] À salts was investigated using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. b-Alkoxy-acyl-cobalttetracarbonyl species were found to be key intermediates from which two reaction routes start depending on the applied Lewis acid. Labile Lewis acid-alkoxy combinations primarily favor the production of lactone products [2].The reaction of olefins (1-octene, 3,3-dimethylbutene, cyclohexene) introduced into a preequilibrated Co 2 (CO) 8 þ H 2 system was investigated by high-pressure infrared spectroscopy. Based on the observed induction period for the formation of the corresponding aldehyde, the decrease in HCo(CO) 4 concentration and increase in Co 2 (CO) 8 concentration during the induction period, the active catalytic species of the type H x Co y (CO) z was proposed [3]. Experiments with isotope mixtures of H 2 /D 2 in the gas phase during the various steps of the reaction showed that the ratio of H/D isotopes in the hydrocarbon portion of the aldehyde product correlates with the HCo(CO) 4 /DCo(CO) 4 ratio in solution, whereas the RC(¼O)H/RC(¼O)D product ratio correlates with the H 2 /D 2 in the gas phase. It was concluded that the dominant pathway for the hydrogenolysis step in this type of hydroformylation is the direct reaction of hydrogen or deuterium with the acyl complex intermediate [4].The effect of argon (280 bar) on the rate of aldehyde formation in 1-hexene hydroformylation catalyzed by Co 2 (CO) 8 at 50 C, 70 bar P(CO) and 85 bar P(H 2 ) in toluene was investigated by high-pressure FT-IR spectroscopy. The initial rate of the reaction was found to be reduced by the presence of argon. A similar effect was observed in the RhH(CO)(PPh 3 ) 3 -catalyzed cyclohexene hydroformylation reaction [5]. 162j 7 Carbonylation of Alkenes and D...

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“…Species including iridium acyl and alkyl dihydride intermediates were detected. The results confirmed that the CO-deficient atmosphere favors hydrogenation over carbonylation [76].…”

Section: Iridium Catalystssupporting

confidence: 71%

Carbonylation of Alkenes and Dienes

Kégl

2008

Modern Carbonylation Methods

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“…Another use of parahydrogen enhancement in monitoring hydroformylation was reported by Godard et al, in which allyl complexes such as Ir( 3 -C 3 H 5 )(CO)(PPh 3 ) 2 were used as catalyst precursors [86]. In the presence of a mixture of parahydrogen and carbon monoxide, two significant intermediates were detected via their enhanced signals, corresponding to an acyl dihydride complex and an alkyl dihydride complex.…”

Section: Studies Of Catalytic Hydroformylation With Parahydrogenmentioning

confidence: 95%

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Duckett

Wood

2008

Coordination Chemistry Reviews

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121

127

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“…6 The nature of the hydrogen activation at intermediate 6 remains uncertain, despite efforts to study this reaction with highly sensitive spectroscopic techniques 7. Aldehyde elimination with regeneration of complex 1 may rather occur reductively from a rhodium(III) dihydrido complex intermediate than from a η 2 ‐H 2 educt in a reaction related to sigma bond metathesis 7d. 8…”

Section: Introductionmentioning

confidence: 99%

Exploring Between the Extremes: Conversion‐Dependent Kinetics of Phosphite‐Modified Hydroformylation Catalysis

Kubis

Selent

Sawall

et al. 2012

Chemistry A European J

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The kinetics of the hydroformylation of 3,3-dimethyl-1-butene with a rhodium monophosphite catalyst has been studied in detail. Time-dependent concentration profiles covering the entire olefin conversion range were derived from in situ high-pressure FTIR spectroscopic data for both, pure organic components and catalytic intermediates. These profiles fit to Michaelis-Menten-type kinetics with competitive and uncompetitive side reactions involved. The characteristics found for the influence of the hydrogen concentration verify that the pre-equilibrium towards the catalyst substrate complex is not established. It has been proven experimentally that the hydrogenolysis of the intermediate acyl complex remains rate limiting even at high conversions when the rhodium hydride is the predominant resting state and the reaction is nearly of first order with respect to the olefin. Results from in situ FTIR and high-pressure (HP) NMR spectroscopy and from DFT calculations support the coordination of only one phosphite ligand in the dominating intermediates and a preferred axial position of the phosphite in the electronically saturated, trigonal bipyramidal (tbp)-structured acyl rhodium complex.

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New perspectives in hydroformylation : a para-hydrogen study

Abstract: NMR studies on the reaction of Ir(CO)(PPh(3))(2)(eta(3)-C(3)H(5)) with para-H(2) and CO enable the complete mapping of the hydroformylation mechanism for an iridium monohydride catalyst via the detection of species which include iridium acyl and alkyl dihydride intermediates.

Cited by 36 publications

References 14 publications

Carbonylation of Alkenes and Dienes

Carbonylation of Alkenes and Dienes

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Exploring Between the Extremes: Conversion‐Dependent Kinetics of Phosphite‐Modified Hydroformylation Catalysis

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