Organometallic molecule-inorganic surface coordination and catalytic chemistry. In Situ CPMAS NMR delineation of organoactinide adsorbate structure, dynamics, and reactivity

William C. Finch, Ralph D. Gillespie, David Hedden, Tobin J Marks

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Abstract

A 75.4-MHz 13C CPMAS NMR spectroscopic study of the surface structures and reaction chemistry of a series of organoactinides adsorbed on various inorganic supports is reported. On Lewis acid surfaces such as dehydroxylated Al23, MgCl2, and Si2-Al23, it is found that organothorium complexes of the type Cp'2ThR2 (Cp' = η5-(CH3)5C5; R = 13CH3, 13CH213CH3), Cp'ThR3 (R = 13CH2C6H5), and Cp3ThR (Cp = η5-C5H5; R = 13CH3), undergo heterolytic Th - C scission to transfer an alkyl anion to the surface forming Cp'2ThR, CpThR3-n, or Cp3Th adsorbate species with "cation-like" character. Probe studies with paramagnetic Cp'2U(13CH3)2 indicate that the majority of the transferred methyl groups of Cp'2U(13CH3)2/DA and Cp'2U(13CH3)2/MgCl2 are located ≳5 Å from the U(IV) ion. On less dehydroxylated or more basic supports such as Si2-MgO, Si2, and MgO, μ-oxo species of the type Cp'2Th(CH3)O- are formed, by Th - C protonolysis or by transfer of an alkyl group to the surface. For Cp'2U(13CH3)2/Si2, the majority of the resulting 13CH3-Si(surface) functionalities are ≳5 Å from the actinide center. In agreement with heterogeneous catalytic studies, the NMR data reveal that only a small percentage of Cp'2Th(13CH3)2/DA or Cp'Th(13CH2C6H5)3/DA surface sites undergo reaction with ethylene or H2 at 25 °C. In contrast, 50 ± 10% of Cp'2Th(13CH3)2/MgCl2 sites undergo reaction with ethylene; >90 ± 10% of ethylene insertion/polymerization occurs at Th - CH3 with k(propagation)/k(initiation) ≈ 12 in the initial stages. There is no evidence for methane evolution via C - H functionalization nor for significant rates of Th(CH2CH2)n13CH3- 13CH3Mg(surface) alkyl group permutation. At 25 °C, a large percentage of Cp'2Th(13CH3)2/MgCl2 Th - CH3 and Mg - CH3 functionalities undergo hydrogenolysis, with Th-CH3 being slightly more reactive. In competition experiments, Th - CH3 is far more reactive than Mg - CH3 in migratory CO insertion, and products are inferred to be, inter alia, η2-acyl complexes. Cp'2Th(13CH3)2/MgCl2 undergoes reaction with propylene to yield methane (derived from Th-CH3), a Th(η3-allyl) complex, and what appear to be propylene oligomers.

Original languageEnglish
Pages (from-to)6221-6232
Number of pages12
JournalJournal of the American Chemical Society
Volume112
Issue number17
Publication statusPublished - 1990

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Magnesium Chloride
Organometallics
Adsorbates
Nuclear magnetic resonance
Molecules
Methane
Ethylene
Propylene
Actinoid Series Elements
Lewis Acids
Carbon Monoxide
Hydrogenolysis
Polymerization
Actinides
Surface reactions
Anions
Cations
Oligomers
Surface structure
Ions

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{fbc72d3d9d434b88b56dd5389f7c6b74,
title = "Organometallic molecule-inorganic surface coordination and catalytic chemistry. In Situ CPMAS NMR delineation of organoactinide adsorbate structure, dynamics, and reactivity",
abstract = "A 75.4-MHz 13C CPMAS NMR spectroscopic study of the surface structures and reaction chemistry of a series of organoactinides adsorbed on various inorganic supports is reported. On Lewis acid surfaces such as dehydroxylated Al23, MgCl2, and Si2-Al23, it is found that organothorium complexes of the type Cp'2ThR2 (Cp' = η5-(CH3)5C5; R = 13CH3, 13CH213CH3), Cp'ThR3 (R = 13CH2C6H5), and Cp3ThR (Cp = η5-C5H5; R = 13CH3), undergo heterolytic Th - C scission to transfer an alkyl anion to the surface forming Cp'2ThR, CpThR3-n, or Cp3Th adsorbate species with {"}cation-like{"} character. Probe studies with paramagnetic Cp'2U(13CH3)2 indicate that the majority of the transferred methyl groups of Cp'2U(13CH3)2/DA and Cp'2U(13CH3)2/MgCl2 are located ≳5 {\AA} from the U(IV) ion. On less dehydroxylated or more basic supports such as Si2-MgO, Si2, and MgO, μ-oxo species of the type Cp'2Th(CH3)O- are formed, by Th - C protonolysis or by transfer of an alkyl group to the surface. For Cp'2U(13CH3)2/Si2, the majority of the resulting 13CH3-Si(surface) functionalities are ≳5 {\AA} from the actinide center. In agreement with heterogeneous catalytic studies, the NMR data reveal that only a small percentage of Cp'2Th(13CH3)2/DA or Cp'Th(13CH2C6H5)3/DA surface sites undergo reaction with ethylene or H2 at 25 °C. In contrast, 50 ± 10{\%} of Cp'2Th(13CH3)2/MgCl2 sites undergo reaction with ethylene; >90 ± 10{\%} of ethylene insertion/polymerization occurs at Th - CH3 with k(propagation)/k(initiation) ≈ 12 in the initial stages. There is no evidence for methane evolution via C - H functionalization nor for significant rates of Th(CH2CH2)n13CH3- 13CH3Mg(surface) alkyl group permutation. At 25 °C, a large percentage of Cp'2Th(13CH3)2/MgCl2 Th - CH3 and Mg - CH3 functionalities undergo hydrogenolysis, with Th-CH3 being slightly more reactive. In competition experiments, Th - CH3 is far more reactive than Mg - CH3 in migratory CO insertion, and products are inferred to be, inter alia, η2-acyl complexes. Cp'2Th(13CH3)2/MgCl2 undergoes reaction with propylene to yield methane (derived from Th-CH3), a Th(η3-allyl) complex, and what appear to be propylene oligomers.",
author = "Finch, {William C.} and Gillespie, {Ralph D.} and David Hedden and Marks, {Tobin J}",
year = "1990",
language = "English",
volume = "112",
pages = "6221--6232",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "17",

}

TY - JOUR

T1 - Organometallic molecule-inorganic surface coordination and catalytic chemistry. In Situ CPMAS NMR delineation of organoactinide adsorbate structure, dynamics, and reactivity

AU - Finch, William C.

AU - Gillespie, Ralph D.

AU - Hedden, David

AU - Marks, Tobin J

PY - 1990

Y1 - 1990

N2 - A 75.4-MHz 13C CPMAS NMR spectroscopic study of the surface structures and reaction chemistry of a series of organoactinides adsorbed on various inorganic supports is reported. On Lewis acid surfaces such as dehydroxylated Al23, MgCl2, and Si2-Al23, it is found that organothorium complexes of the type Cp'2ThR2 (Cp' = η5-(CH3)5C5; R = 13CH3, 13CH213CH3), Cp'ThR3 (R = 13CH2C6H5), and Cp3ThR (Cp = η5-C5H5; R = 13CH3), undergo heterolytic Th - C scission to transfer an alkyl anion to the surface forming Cp'2ThR, CpThR3-n, or Cp3Th adsorbate species with "cation-like" character. Probe studies with paramagnetic Cp'2U(13CH3)2 indicate that the majority of the transferred methyl groups of Cp'2U(13CH3)2/DA and Cp'2U(13CH3)2/MgCl2 are located ≳5 Å from the U(IV) ion. On less dehydroxylated or more basic supports such as Si2-MgO, Si2, and MgO, μ-oxo species of the type Cp'2Th(CH3)O- are formed, by Th - C protonolysis or by transfer of an alkyl group to the surface. For Cp'2U(13CH3)2/Si2, the majority of the resulting 13CH3-Si(surface) functionalities are ≳5 Å from the actinide center. In agreement with heterogeneous catalytic studies, the NMR data reveal that only a small percentage of Cp'2Th(13CH3)2/DA or Cp'Th(13CH2C6H5)3/DA surface sites undergo reaction with ethylene or H2 at 25 °C. In contrast, 50 ± 10% of Cp'2Th(13CH3)2/MgCl2 sites undergo reaction with ethylene; >90 ± 10% of ethylene insertion/polymerization occurs at Th - CH3 with k(propagation)/k(initiation) ≈ 12 in the initial stages. There is no evidence for methane evolution via C - H functionalization nor for significant rates of Th(CH2CH2)n13CH3- 13CH3Mg(surface) alkyl group permutation. At 25 °C, a large percentage of Cp'2Th(13CH3)2/MgCl2 Th - CH3 and Mg - CH3 functionalities undergo hydrogenolysis, with Th-CH3 being slightly more reactive. In competition experiments, Th - CH3 is far more reactive than Mg - CH3 in migratory CO insertion, and products are inferred to be, inter alia, η2-acyl complexes. Cp'2Th(13CH3)2/MgCl2 undergoes reaction with propylene to yield methane (derived from Th-CH3), a Th(η3-allyl) complex, and what appear to be propylene oligomers.

AB - A 75.4-MHz 13C CPMAS NMR spectroscopic study of the surface structures and reaction chemistry of a series of organoactinides adsorbed on various inorganic supports is reported. On Lewis acid surfaces such as dehydroxylated Al23, MgCl2, and Si2-Al23, it is found that organothorium complexes of the type Cp'2ThR2 (Cp' = η5-(CH3)5C5; R = 13CH3, 13CH213CH3), Cp'ThR3 (R = 13CH2C6H5), and Cp3ThR (Cp = η5-C5H5; R = 13CH3), undergo heterolytic Th - C scission to transfer an alkyl anion to the surface forming Cp'2ThR, CpThR3-n, or Cp3Th adsorbate species with "cation-like" character. Probe studies with paramagnetic Cp'2U(13CH3)2 indicate that the majority of the transferred methyl groups of Cp'2U(13CH3)2/DA and Cp'2U(13CH3)2/MgCl2 are located ≳5 Å from the U(IV) ion. On less dehydroxylated or more basic supports such as Si2-MgO, Si2, and MgO, μ-oxo species of the type Cp'2Th(CH3)O- are formed, by Th - C protonolysis or by transfer of an alkyl group to the surface. For Cp'2U(13CH3)2/Si2, the majority of the resulting 13CH3-Si(surface) functionalities are ≳5 Å from the actinide center. In agreement with heterogeneous catalytic studies, the NMR data reveal that only a small percentage of Cp'2Th(13CH3)2/DA or Cp'Th(13CH2C6H5)3/DA surface sites undergo reaction with ethylene or H2 at 25 °C. In contrast, 50 ± 10% of Cp'2Th(13CH3)2/MgCl2 sites undergo reaction with ethylene; >90 ± 10% of ethylene insertion/polymerization occurs at Th - CH3 with k(propagation)/k(initiation) ≈ 12 in the initial stages. There is no evidence for methane evolution via C - H functionalization nor for significant rates of Th(CH2CH2)n13CH3- 13CH3Mg(surface) alkyl group permutation. At 25 °C, a large percentage of Cp'2Th(13CH3)2/MgCl2 Th - CH3 and Mg - CH3 functionalities undergo hydrogenolysis, with Th-CH3 being slightly more reactive. In competition experiments, Th - CH3 is far more reactive than Mg - CH3 in migratory CO insertion, and products are inferred to be, inter alia, η2-acyl complexes. Cp'2Th(13CH3)2/MgCl2 undergoes reaction with propylene to yield methane (derived from Th-CH3), a Th(η3-allyl) complex, and what appear to be propylene oligomers.

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