A kinetic, mechanistic, and molecular mechanics investigation of olefin insertion into organoactinide-hydride bonds. Metal, olefin, ancillary ligand, and diastereoselection effects

Zerong Lin, Tobin J Marks

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Abstract

This contribution reports a kinetic/mechanistic/stereochemical/molecular mechanics study of olefin insertion into the actinide-hydrogen bonds of Cp′2An(H)(OR) complexes (Cp′ = η5-(CH3)5C5; An = Th, U; R = achiral or chiral alkyl group). For the reaction Cp′2An(H)(O-t-Bu) + cyclohexene (An = Th), the rate law is first order in organoactinide and first order in olefin, with kTh-H/kTh-D = 1.4 (1), kTHF/ktoluene = 0.59 (5), ΔH = 9.0 (5) kcal/mol, and ΔS = -47.2 (1) eu; kU/kTh ≈ 1.5. For Cp′2Th(H)[OCH(t-Bu)2] + 1-hexene, kTh-H/kTh-D = 1.3 (2). Alkoxide effects on insertion rates can be large, and for Cp′2Th(H)(OR) + cyclohexene, kO-t-Bu/kOCH(t-Bu)2 ≳ 103. For Cp′2Th(H)[OCH(t-Bu)2], relative insertion rates follow the ordering ethylene > 1-hexene > 4-methoxystyrene > styrene ≫ cyclohexene; k4-methoxystyrene/kstyrene = 2.2 (5). For cis-2-butene, insertion reactions yield sec-butyl derivatives that slowly rearrange to the n-butyl isomers. Insertion experiments with Cp2′An(H)(OR*) complexes having chiral alkoxide ligands (OR* = (1R,2S,5R)-menthoxide; (R)-2-butoxide; [(1S)-endo]-bornoxide; (1S,2S,5R)-neomenthoxide) and prochiral olefins (norbornene, cis-2-butene) or ketones (acetophenone, butyrophenone) demonstrate that maximum diastereoselection occurs for sterically encumbered reagents at low temperatures (de = 36% for norbornene at -45°C). A molecular mechanics/molecular graphics analysis suggests that the sterically most favorable direction of olefin approach toward the actinide center is between the U-H and U-O bonds rather than from the side. These results provide additional insight into ancillary ligand effects on the kinetics of organo-f-element-catalyzed olefin hydrogenation.

Original languageEnglish
Pages (from-to)5515-5525
Number of pages11
JournalJournal of the American Chemical Society
Volume112
Issue number14
Publication statusPublished - Jul 4 1990

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Molecular mechanics
Alkenes
Mechanics
Hydrides
Olefins
Metals
Ligands
Kinetics
Actinoid Series Elements
Actinides
Butenes
Molecular graphics
Butyrophenones
Styrene
Hydrogenation
Ketones
Isomers
Hydrogen
Hydrogen bonds
Ethylene

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{e49d4bc3f3b94511bb1936d8e436a860,
title = "A kinetic, mechanistic, and molecular mechanics investigation of olefin insertion into organoactinide-hydride bonds. Metal, olefin, ancillary ligand, and diastereoselection effects",
abstract = "This contribution reports a kinetic/mechanistic/stereochemical/molecular mechanics study of olefin insertion into the actinide-hydrogen bonds of Cp′2An(H)(OR) complexes (Cp′ = η5-(CH3)5C5; An = Th, U; R = achiral or chiral alkyl group). For the reaction Cp′2An(H)(O-t-Bu) + cyclohexene (An = Th), the rate law is first order in organoactinide and first order in olefin, with kTh-H/kTh-D = 1.4 (1), kTHF/ktoluene = 0.59 (5), ΔH‡ = 9.0 (5) kcal/mol, and ΔS‡ = -47.2 (1) eu; kU/kTh ≈ 1.5. For Cp′2Th(H)[OCH(t-Bu)2] + 1-hexene, kTh-H/kTh-D = 1.3 (2). Alkoxide effects on insertion rates can be large, and for Cp′2Th(H)(OR) + cyclohexene, kO-t-Bu/kOCH(t-Bu)2 ≳ 103. For Cp′2Th(H)[OCH(t-Bu)2], relative insertion rates follow the ordering ethylene > 1-hexene > 4-methoxystyrene > styrene ≫ cyclohexene; k4-methoxystyrene/kstyrene = 2.2 (5). For cis-2-butene, insertion reactions yield sec-butyl derivatives that slowly rearrange to the n-butyl isomers. Insertion experiments with Cp2′An(H)(OR*) complexes having chiral alkoxide ligands (OR* = (1R,2S,5R)-menthoxide; (R)-2-butoxide; [(1S)-endo]-bornoxide; (1S,2S,5R)-neomenthoxide) and prochiral olefins (norbornene, cis-2-butene) or ketones (acetophenone, butyrophenone) demonstrate that maximum diastereoselection occurs for sterically encumbered reagents at low temperatures (de = 36{\%} for norbornene at -45°C). A molecular mechanics/molecular graphics analysis suggests that the sterically most favorable direction of olefin approach toward the actinide center is between the U-H and U-O bonds rather than from the side. These results provide additional insight into ancillary ligand effects on the kinetics of organo-f-element-catalyzed olefin hydrogenation.",
author = "Zerong Lin and Marks, {Tobin J}",
year = "1990",
month = "7",
day = "4",
language = "English",
volume = "112",
pages = "5515--5525",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "14",

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TY - JOUR

T1 - A kinetic, mechanistic, and molecular mechanics investigation of olefin insertion into organoactinide-hydride bonds. Metal, olefin, ancillary ligand, and diastereoselection effects

AU - Lin, Zerong

AU - Marks, Tobin J

PY - 1990/7/4

Y1 - 1990/7/4

N2 - This contribution reports a kinetic/mechanistic/stereochemical/molecular mechanics study of olefin insertion into the actinide-hydrogen bonds of Cp′2An(H)(OR) complexes (Cp′ = η5-(CH3)5C5; An = Th, U; R = achiral or chiral alkyl group). For the reaction Cp′2An(H)(O-t-Bu) + cyclohexene (An = Th), the rate law is first order in organoactinide and first order in olefin, with kTh-H/kTh-D = 1.4 (1), kTHF/ktoluene = 0.59 (5), ΔH‡ = 9.0 (5) kcal/mol, and ΔS‡ = -47.2 (1) eu; kU/kTh ≈ 1.5. For Cp′2Th(H)[OCH(t-Bu)2] + 1-hexene, kTh-H/kTh-D = 1.3 (2). Alkoxide effects on insertion rates can be large, and for Cp′2Th(H)(OR) + cyclohexene, kO-t-Bu/kOCH(t-Bu)2 ≳ 103. For Cp′2Th(H)[OCH(t-Bu)2], relative insertion rates follow the ordering ethylene > 1-hexene > 4-methoxystyrene > styrene ≫ cyclohexene; k4-methoxystyrene/kstyrene = 2.2 (5). For cis-2-butene, insertion reactions yield sec-butyl derivatives that slowly rearrange to the n-butyl isomers. Insertion experiments with Cp2′An(H)(OR*) complexes having chiral alkoxide ligands (OR* = (1R,2S,5R)-menthoxide; (R)-2-butoxide; [(1S)-endo]-bornoxide; (1S,2S,5R)-neomenthoxide) and prochiral olefins (norbornene, cis-2-butene) or ketones (acetophenone, butyrophenone) demonstrate that maximum diastereoselection occurs for sterically encumbered reagents at low temperatures (de = 36% for norbornene at -45°C). A molecular mechanics/molecular graphics analysis suggests that the sterically most favorable direction of olefin approach toward the actinide center is between the U-H and U-O bonds rather than from the side. These results provide additional insight into ancillary ligand effects on the kinetics of organo-f-element-catalyzed olefin hydrogenation.

AB - This contribution reports a kinetic/mechanistic/stereochemical/molecular mechanics study of olefin insertion into the actinide-hydrogen bonds of Cp′2An(H)(OR) complexes (Cp′ = η5-(CH3)5C5; An = Th, U; R = achiral or chiral alkyl group). For the reaction Cp′2An(H)(O-t-Bu) + cyclohexene (An = Th), the rate law is first order in organoactinide and first order in olefin, with kTh-H/kTh-D = 1.4 (1), kTHF/ktoluene = 0.59 (5), ΔH‡ = 9.0 (5) kcal/mol, and ΔS‡ = -47.2 (1) eu; kU/kTh ≈ 1.5. For Cp′2Th(H)[OCH(t-Bu)2] + 1-hexene, kTh-H/kTh-D = 1.3 (2). Alkoxide effects on insertion rates can be large, and for Cp′2Th(H)(OR) + cyclohexene, kO-t-Bu/kOCH(t-Bu)2 ≳ 103. For Cp′2Th(H)[OCH(t-Bu)2], relative insertion rates follow the ordering ethylene > 1-hexene > 4-methoxystyrene > styrene ≫ cyclohexene; k4-methoxystyrene/kstyrene = 2.2 (5). For cis-2-butene, insertion reactions yield sec-butyl derivatives that slowly rearrange to the n-butyl isomers. Insertion experiments with Cp2′An(H)(OR*) complexes having chiral alkoxide ligands (OR* = (1R,2S,5R)-menthoxide; (R)-2-butoxide; [(1S)-endo]-bornoxide; (1S,2S,5R)-neomenthoxide) and prochiral olefins (norbornene, cis-2-butene) or ketones (acetophenone, butyrophenone) demonstrate that maximum diastereoselection occurs for sterically encumbered reagents at low temperatures (de = 36% for norbornene at -45°C). A molecular mechanics/molecular graphics analysis suggests that the sterically most favorable direction of olefin approach toward the actinide center is between the U-H and U-O bonds rather than from the side. These results provide additional insight into ancillary ligand effects on the kinetics of organo-f-element-catalyzed olefin hydrogenation.

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