On the use of “fast kinetics” to determine the mechanism of ligand substitution at a solvated transition‐metal intermediate

Schultz, Richard H.

doi:10.1002/kin.20007

Cited by 10 publications

(11 citation statements)

References 29 publications

(30 reference statements)

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“…Unfortunately, under the experimental conditions and as previously noted, a linear dependence of k obs on ligand concentration does not assist in distinguishing between associative, dissociative, or interchange mechanisms of solvent displacement from the metal center. Some insight into the mechanism of the substitution reaction was obtained by determining the relevant activation parameters.…”

Section: Resultsmentioning

confidence: 82%

Reactivity of the CpMn(CO)₂−XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy

Bengali

Fan

2008

Organometallics

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The mechanism and energetics of the displacement of dihaloalkanes from the photolytically generated CpMn(CO)2−XR (X = Cl, Br) complexes by 2,6-lutidine have been studied using rapid-scan FTIR. The substitution reactions proceed through an Id mechanism, and theoretical calculations indicate that the Mn−XR bond is mostly broken in the transition state. Activation enthalpies of 16−17 kcal/mol for the Mn−ClR and 18−19 kcal/mol for the Mn−BrR complexes are only slightly lower than previous thermodynamic measurements of the Mn−haloalkane bond dissociation enthalpies. The rate of displacement of bromoalkanes was found to be ∼10 times slower than for the analogous chloroalkanes. Ab initio calculations suggest that this difference in reactivity is primarily due to a more stable interaction between the Mn center and bromoalkanes.

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Section: Resultsmentioning

confidence: 82%

Reactivity of the CpMn(CO)₂−XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy

Bengali

Fan

2008

Organometallics

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“…As shown in Figure , k obs exhibits a linear dependence on [cyclooctene] at all the temperatures studied. Such dependence does not allow for a determination of the reaction mechanism, as it is consistent with an associative, dissociative, and interchange pathway of ligand substitution . The temperature dependence of the second-order rate constants (Table ) yield activation parameters of Δ H ⧧ = 13.7 ± 0.3 kcal/mol and Δ S ⧧ = +8 ± 1 eu.…”

Section: Resultsmentioning

confidence: 94%

Time-Resolved Infrared Spectroscopy Studies of Olefin Binding in Photogenerated CpRu(CO)X (X = Cl, I) Transients

et al. 2012

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The mechanism and energetics of ligand (L) substitution (L = THF, cyclopentene, cyclohexene, cyclooctene) from photogenerated CpRu-(CO)(X)L (X = Cl, I) complexes were studied using time-resolved infrared spectroscopy. The reactions proceed through a dissociative mechanism, and the Ru−L binding enthalpies were estimated. The trend in the bond enthalpies, Ru− (η 2 -cyclooctene) ≈ Ru−(η 2 -cyclopentene) > Ru−(η 2 -cyclohexene), is correlated with the strain energy of the cycloalkene ring. For all ligands investigated, CpRu(CO)(Cl)−L binding enthalpies were lower than those for the analogous CpMn(CO) 2 −L and BzCr(CO) 2 −L complexes. DFT calculations indicate that the lower binding enthalpy for the Ru−L complexes is due to a greater reorganizational energy for the CpRu(CO)Cl fragment as it adopts a configuration suitable for interaction with the ligand. ■ INTRODUCTIONTransition-metal-containing organometallic compounds have been shown to catalyze a variety of organic transformations. 1 Complexes containing the ruthenium metal center are particularly active catalysts in a variety of reactions. For example, many key reactions such as alkene isomerization, hydroformylation, C−H activation of arenes, CO 2 fixation, and others have been successfully catalyzed by derivatives of the Ru 3 (CO) 12 cluster. 2 Other Ru carbonyls such as Ru-(CO) 3 (PR 3 ) 2 have also been used as catalysts for the hydrodesulfurization of benzothiophenes. 3 The hydroformylation of 1-octene by CpRu(CO) 2 Cl has also been reported, and despite its high catalytic activity, there are no mechanistic studies that have been undertaken to identify and study the chemistry of the relevant intermediates. 4 Photoinduced time-resolved infrared spectroscopy is a powerful tool for identifying and studying the reactivity of intermediates that may be formed during a catalytic cycle. 5 A vacant coordination site on a metal complex, necessary for catalytic activity, can be generated by photolytic loss of a ligand. Upon binding of the substrate, the reactivity of the resulting intermediate can be probed with infrared light over a range of time scales. Metal carbonyls tend to be the best candidates for such studies, since photolytic loss of CO often proceeds with high quantum efficiency and the remaining CO's attached to the metal center are ideal infrared tags for probing the temporal profile of the resulting intermediates. This technique is therefore well suited to study the reactions of Ru carbonyl intermediates, given their importance in promoting several catalytic processes.As mentioned above, the reaction of CpRu(CO) 2 Cl with 1-octene in the presence of H 2 /CO leads to hydroformylation of the alkene with high selectivity and yield. 4 The mechanism of the reaction was not determined, although it was found that a key species was most likely the CpRu(CO) 2 H complex, presumably formed upon reaction of the parent compound with H 2 . Since this 18-electron coordinatively saturated hydride complex is unlikely to be the active species, it is reasonable to suggest ...

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“…2, k obs , is a linear function of the 1-hexene concentration which was varied over a ten-fold range (0.21-2.1 M). Unfortunately, as noted in previous studies, a linear dependence of k obs on [L] does not assist in distinguishing between associative, dissociative, or interchange mechanisms of solvent displacement from the metal center [8]. We therefore investigated the reactivity of the CpRe(CO) 2 (heptane) complex with other nucleophiles to assist in the determination of the substitution mechanism.…”

Section: Resultsmentioning

confidence: 98%

Displacement of the heptane solvent from (η5-C5H5)Re(CO)2(heptane): A flash photolysis study using infrared detection

Bengali

2005

Journal of Organometallic Chemistry

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On the use of “fast kinetics” to determine the mechanism of ligand substitution at a solvated transition‐metal intermediate

Cited by 10 publications

References 29 publications

Reactivity of the CpMn(CO)₂−XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy

Reactivity of the CpMn(CO)₂−XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy

Time-Resolved Infrared Spectroscopy Studies of Olefin Binding in Photogenerated CpRu(CO)X (X = Cl, I) Transients

Displacement of the heptane solvent from (η5-C5H5)Re(CO)2(heptane): A flash photolysis study using infrared detection

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On the use of “fast kinetics” to determine the mechanism of ligand substitution at a solvated transition‐metal intermediate

Cited by 10 publications

References 29 publications

Reactivity of the CpMn(CO)2−XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy

Reactivity of the CpMn(CO)2−XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy

Time-Resolved Infrared Spectroscopy Studies of Olefin Binding in Photogenerated CpRu(CO)X (X = Cl, I) Transients

Displacement of the heptane solvent from (η5-C5H5)Re(CO)2(heptane): A flash photolysis study using infrared detection

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Reactivity of the CpMn(CO)₂−XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy

Reactivity of the CpMn(CO)₂−XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy