Organo-f-element-based heterogeneous catalysts. Kinetics and mechanism of olefin hydrogenation by supported pentamethylcyclopentadienyl actinide complexes

Ralph D. Gillespie, Robert L. Burwell, Tobin J Marks

Research output: Contribution to journalArticle

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Abstract

This contribution reports a detailed kinetic and mechanistic study of heterogeneous olefin hydrogenation by Cp′2Th(CH3)2 (Cp′ = η5-(CH3)5C5) adsorbed on dehydroxylated alumina (DA). For both propylene and isobutylene, the kinetics can be accommodated by a two-step sequence: (i) olefin insertion into Th-H (rate constant ν2); (ii) hydrogenolysis of the resulting Th-alkyl bond (rate constant ν3). Kinetic data can be fit to the rate law Nt (turnover frequency) = ν2ν3PH2/(ν2 + ν3PH2), where the reaction is zero-order in olefin and where ν23 = 0.55 bar-1 (-63°C) and 0.47 bar-1 (0°C) for propylene and isobutylene, respectively. Kinetic isotope measurements indicate Nt(H2)/Nt(D2) = 1.5(1) for propylene hydrogenation at -63°C and 2.0(2) for isobutylene hydrogenation at 0°C. In reaction with D2, propylene yields exclusively 1,2-propane-d2. Arrhenius activation energies for catalytic hydrogenation are 3.6(2) kcal mol-1 (propylene, -63 to -23°C) and 5.3(2) kcal mol-1 (isobutylene, -23 to +64°C); for isobutylene, it could be determined that the activation enthalpies for olefin insertion and alkyl hydrogenolysis are comparable (6.2(10) and 4.2(10) kcal mol-1, respectively). Protonolytic poisoning experiments indicate that ≤4 ± 1% and ≤2 ± 1% of the thorium surface sites are responsible for the bulk of the propylene and isobutylene hydrogenation, respectively. As a function of olefin, the relative rates of Cp′2Th(CH3)2/DA-catalyzed hydrogenation are cis-2-butene > trans-2-butene > propylene > isobutylene; 1,3-butadiene yields only 1-butene and cis-2-butene as initial hydrogenation products. For several organoactinides supported on DA, the relative ordering of propylene hydrogenation activity is Cp′2Th(CH3)2 ≥ Me2SiCp″2Th(n-Bu)2 (Cp″ = n5-(CH3)4C5) ≥ [Me2SiCp″2Th(μ-H)2]2 ≥ Cp′2Th(CH3)(O3SCF3) ≥ [Me2SiCp″2U(μ-H)2]2, ≫ U(η8-n-BuC8H7)2. As a function of support, the relative rates of Cp′2Th(CH3)2catalyzed propylene hydrogenation are DA > dehydroxylated SiO2-Al2O3 > dehydroxylated MgCl2 ≫ dehydroxylated SiO2-MgO. Protonolytic poisoning experiments indicate that 35 ± 10% of the Cp′2Th(CH3)2/MgCl2 sites are catalytically significant. Informative parallels can be drawn between these observations and homogeneous solution phenomenology for similar types of compounds.

Original languageEnglish
Pages (from-to)1465-1477
Number of pages13
JournalLangmuir
Volume6
Issue number9
Publication statusPublished - 1990

Fingerprint

Actinoid Series Elements
Actinides
Alkenes
butenes
Chemical elements
alkenes
Olefins
Hydrogenation
hydrogenation
Propylene
propylene
catalysts
Catalysts
Kinetics
kinetics
Aluminum Oxide
Butenes
Alumina
aluminum oxides
Hydrogenolysis

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Colloid and Surface Chemistry

Cite this

Organo-f-element-based heterogeneous catalysts. Kinetics and mechanism of olefin hydrogenation by supported pentamethylcyclopentadienyl actinide complexes. / Gillespie, Ralph D.; Burwell, Robert L.; Marks, Tobin J.

In: Langmuir, Vol. 6, No. 9, 1990, p. 1465-1477.

Research output: Contribution to journalArticle

@article{904d4d5f7d8c4af496c445d90607c007,
title = "Organo-f-element-based heterogeneous catalysts. Kinetics and mechanism of olefin hydrogenation by supported pentamethylcyclopentadienyl actinide complexes",
abstract = "This contribution reports a detailed kinetic and mechanistic study of heterogeneous olefin hydrogenation by Cp′2Th(CH3)2 (Cp′ = η5-(CH3)5C5) adsorbed on dehydroxylated alumina (DA). For both propylene and isobutylene, the kinetics can be accommodated by a two-step sequence: (i) olefin insertion into Th-H (rate constant ν2); (ii) hydrogenolysis of the resulting Th-alkyl bond (rate constant ν3). Kinetic data can be fit to the rate law Nt (turnover frequency) = ν2ν3PH2/(ν2 + ν3PH2), where the reaction is zero-order in olefin and where ν2/ν3 = 0.55 bar-1 (-63°C) and 0.47 bar-1 (0°C) for propylene and isobutylene, respectively. Kinetic isotope measurements indicate Nt(H2)/Nt(D2) = 1.5(1) for propylene hydrogenation at -63°C and 2.0(2) for isobutylene hydrogenation at 0°C. In reaction with D2, propylene yields exclusively 1,2-propane-d2. Arrhenius activation energies for catalytic hydrogenation are 3.6(2) kcal mol-1 (propylene, -63 to -23°C) and 5.3(2) kcal mol-1 (isobutylene, -23 to +64°C); for isobutylene, it could be determined that the activation enthalpies for olefin insertion and alkyl hydrogenolysis are comparable (6.2(10) and 4.2(10) kcal mol-1, respectively). Protonolytic poisoning experiments indicate that ≤4 ± 1{\%} and ≤2 ± 1{\%} of the thorium surface sites are responsible for the bulk of the propylene and isobutylene hydrogenation, respectively. As a function of olefin, the relative rates of Cp′2Th(CH3)2/DA-catalyzed hydrogenation are cis-2-butene > trans-2-butene > propylene > isobutylene; 1,3-butadiene yields only 1-butene and cis-2-butene as initial hydrogenation products. For several organoactinides supported on DA, the relative ordering of propylene hydrogenation activity is Cp′2Th(CH3)2 ≥ Me2SiCp″2Th(n-Bu)2 (Cp″ = n5-(CH3)4C5) ≥ [Me2SiCp″2Th(μ-H)2]2 ≥ Cp′2Th(CH3)(O3SCF3) ≥ [Me2SiCp″2U(μ-H)2]2, ≫ U(η8-n-BuC8H7)2. As a function of support, the relative rates of Cp′2Th(CH3)2catalyzed propylene hydrogenation are DA > dehydroxylated SiO2-Al2O3 > dehydroxylated MgCl2 ≫ dehydroxylated SiO2-MgO. Protonolytic poisoning experiments indicate that 35 ± 10{\%} of the Cp′2Th(CH3)2/MgCl2 sites are catalytically significant. Informative parallels can be drawn between these observations and homogeneous solution phenomenology for similar types of compounds.",
author = "Gillespie, {Ralph D.} and Burwell, {Robert L.} and Marks, {Tobin J}",
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TY - JOUR

T1 - Organo-f-element-based heterogeneous catalysts. Kinetics and mechanism of olefin hydrogenation by supported pentamethylcyclopentadienyl actinide complexes

AU - Gillespie, Ralph D.

AU - Burwell, Robert L.

AU - Marks, Tobin J

PY - 1990

Y1 - 1990

N2 - This contribution reports a detailed kinetic and mechanistic study of heterogeneous olefin hydrogenation by Cp′2Th(CH3)2 (Cp′ = η5-(CH3)5C5) adsorbed on dehydroxylated alumina (DA). For both propylene and isobutylene, the kinetics can be accommodated by a two-step sequence: (i) olefin insertion into Th-H (rate constant ν2); (ii) hydrogenolysis of the resulting Th-alkyl bond (rate constant ν3). Kinetic data can be fit to the rate law Nt (turnover frequency) = ν2ν3PH2/(ν2 + ν3PH2), where the reaction is zero-order in olefin and where ν2/ν3 = 0.55 bar-1 (-63°C) and 0.47 bar-1 (0°C) for propylene and isobutylene, respectively. Kinetic isotope measurements indicate Nt(H2)/Nt(D2) = 1.5(1) for propylene hydrogenation at -63°C and 2.0(2) for isobutylene hydrogenation at 0°C. In reaction with D2, propylene yields exclusively 1,2-propane-d2. Arrhenius activation energies for catalytic hydrogenation are 3.6(2) kcal mol-1 (propylene, -63 to -23°C) and 5.3(2) kcal mol-1 (isobutylene, -23 to +64°C); for isobutylene, it could be determined that the activation enthalpies for olefin insertion and alkyl hydrogenolysis are comparable (6.2(10) and 4.2(10) kcal mol-1, respectively). Protonolytic poisoning experiments indicate that ≤4 ± 1% and ≤2 ± 1% of the thorium surface sites are responsible for the bulk of the propylene and isobutylene hydrogenation, respectively. As a function of olefin, the relative rates of Cp′2Th(CH3)2/DA-catalyzed hydrogenation are cis-2-butene > trans-2-butene > propylene > isobutylene; 1,3-butadiene yields only 1-butene and cis-2-butene as initial hydrogenation products. For several organoactinides supported on DA, the relative ordering of propylene hydrogenation activity is Cp′2Th(CH3)2 ≥ Me2SiCp″2Th(n-Bu)2 (Cp″ = n5-(CH3)4C5) ≥ [Me2SiCp″2Th(μ-H)2]2 ≥ Cp′2Th(CH3)(O3SCF3) ≥ [Me2SiCp″2U(μ-H)2]2, ≫ U(η8-n-BuC8H7)2. As a function of support, the relative rates of Cp′2Th(CH3)2catalyzed propylene hydrogenation are DA > dehydroxylated SiO2-Al2O3 > dehydroxylated MgCl2 ≫ dehydroxylated SiO2-MgO. Protonolytic poisoning experiments indicate that 35 ± 10% of the Cp′2Th(CH3)2/MgCl2 sites are catalytically significant. Informative parallels can be drawn between these observations and homogeneous solution phenomenology for similar types of compounds.

AB - This contribution reports a detailed kinetic and mechanistic study of heterogeneous olefin hydrogenation by Cp′2Th(CH3)2 (Cp′ = η5-(CH3)5C5) adsorbed on dehydroxylated alumina (DA). For both propylene and isobutylene, the kinetics can be accommodated by a two-step sequence: (i) olefin insertion into Th-H (rate constant ν2); (ii) hydrogenolysis of the resulting Th-alkyl bond (rate constant ν3). Kinetic data can be fit to the rate law Nt (turnover frequency) = ν2ν3PH2/(ν2 + ν3PH2), where the reaction is zero-order in olefin and where ν2/ν3 = 0.55 bar-1 (-63°C) and 0.47 bar-1 (0°C) for propylene and isobutylene, respectively. Kinetic isotope measurements indicate Nt(H2)/Nt(D2) = 1.5(1) for propylene hydrogenation at -63°C and 2.0(2) for isobutylene hydrogenation at 0°C. In reaction with D2, propylene yields exclusively 1,2-propane-d2. Arrhenius activation energies for catalytic hydrogenation are 3.6(2) kcal mol-1 (propylene, -63 to -23°C) and 5.3(2) kcal mol-1 (isobutylene, -23 to +64°C); for isobutylene, it could be determined that the activation enthalpies for olefin insertion and alkyl hydrogenolysis are comparable (6.2(10) and 4.2(10) kcal mol-1, respectively). Protonolytic poisoning experiments indicate that ≤4 ± 1% and ≤2 ± 1% of the thorium surface sites are responsible for the bulk of the propylene and isobutylene hydrogenation, respectively. As a function of olefin, the relative rates of Cp′2Th(CH3)2/DA-catalyzed hydrogenation are cis-2-butene > trans-2-butene > propylene > isobutylene; 1,3-butadiene yields only 1-butene and cis-2-butene as initial hydrogenation products. For several organoactinides supported on DA, the relative ordering of propylene hydrogenation activity is Cp′2Th(CH3)2 ≥ Me2SiCp″2Th(n-Bu)2 (Cp″ = n5-(CH3)4C5) ≥ [Me2SiCp″2Th(μ-H)2]2 ≥ Cp′2Th(CH3)(O3SCF3) ≥ [Me2SiCp″2U(μ-H)2]2, ≫ U(η8-n-BuC8H7)2. As a function of support, the relative rates of Cp′2Th(CH3)2catalyzed propylene hydrogenation are DA > dehydroxylated SiO2-Al2O3 > dehydroxylated MgCl2 ≫ dehydroxylated SiO2-MgO. Protonolytic poisoning experiments indicate that 35 ± 10% of the Cp′2Th(CH3)2/MgCl2 sites are catalytically significant. Informative parallels can be drawn between these observations and homogeneous solution phenomenology for similar types of compounds.

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