Metal-alkyl group effects on the thermodynamic stability and stereochemical mobility of B(C6F5)3-derived Zr and Hf metallocenium ion-pairs

C. L. Beswick, T. J. Marks

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Abstract

This paper reports significant dependence of ion-pair formation energetics and stereomutation rates upon the metal-bound alkyl substituent (R) and the solvent dielectric constant in the metallocenium series (1,2-Me2Cp)2MR+ MeB(C6F5)3 - where R = Me, CH2(t)Bu, CH2TMS, CH(TMS)2, and M = Zr and Hf, as determined by reaction titration calorimetry and dynamic NMR spectroscopy. For the ion-pair forming reaction, (1,2-Me2Cp)2M(R)Me + B(C6F5)3 → (1,2-Me2Cp)2MR+ MeB(C6F5)3 -, enthalpies in toluene solution at 25 °C for M = Zr and R = Me, CH2TMS, and CH(TMS)2 are -24.6(0.8), -22.6(1.0), and -59.2(1.4) kcal/mol, respectively. Corresponding values for M = Hf and R = Me and CH2TMS are -20.8(0.5) and -31.1(1.6) kcal/mol, respectively. ΔH((+))(reorg) values for the reorganization process that interchanges the ion-pair enantiotopic sites for M = Zr and R = Me, CH2(t)Bu, CH2TMS, and CH(TMS)2 are 22(1), 18(1), 17(1), and 9(2) kcal/mol, respectively. Corresponding ΔH((+))(reorg) values for M = Hf and R = Me, CH2(t)Bu, and CH2TMS are >24, 12(3), and 15(2) kcal/mol, respectively. ΔH((+))(reorg) values are highest in low dielectric constant solvents such as C6D12. Activation parameters for β-Me elimination in the complexes (1,2-Me2Cp)2MCH2(t)Bu+ MeB(C6F5)3 - for M = Zr and Hf are found to be ΔH((+))(β-Me) = 22.5(0.9) and 17.3(0.9) kcal/mol, and ΔS((+))(β-Me) = 4.3(3.3) and -11.9-(3.4) cal/mol·K, respectively.

Original languageEnglish
Pages (from-to)10358-10370
Number of pages13
JournalJournal of the American Chemical Society
Volume122
Issue number42
DOIs
Publication statusPublished - Oct 25 2000

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Thermodynamics
Thermodynamic stability
Metals
Ions
Permittivity
Calorimetry
Interchanges
Toluene
Titration
Nuclear magnetic resonance spectroscopy
Enthalpy
Magnetic Resonance Spectroscopy
Chemical activation

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{7c6cd063a6df476298d26739258d7dee,
title = "Metal-alkyl group effects on the thermodynamic stability and stereochemical mobility of B(C6F5)3-derived Zr and Hf metallocenium ion-pairs",
abstract = "This paper reports significant dependence of ion-pair formation energetics and stereomutation rates upon the metal-bound alkyl substituent (R) and the solvent dielectric constant in the metallocenium series (1,2-Me2Cp)2MR+ MeB(C6F5)3 - where R = Me, CH2(t)Bu, CH2TMS, CH(TMS)2, and M = Zr and Hf, as determined by reaction titration calorimetry and dynamic NMR spectroscopy. For the ion-pair forming reaction, (1,2-Me2Cp)2M(R)Me + B(C6F5)3 → (1,2-Me2Cp)2MR+ MeB(C6F5)3 -, enthalpies in toluene solution at 25 °C for M = Zr and R = Me, CH2TMS, and CH(TMS)2 are -24.6(0.8), -22.6(1.0), and -59.2(1.4) kcal/mol, respectively. Corresponding values for M = Hf and R = Me and CH2TMS are -20.8(0.5) and -31.1(1.6) kcal/mol, respectively. ΔH((+))(reorg) values for the reorganization process that interchanges the ion-pair enantiotopic sites for M = Zr and R = Me, CH2(t)Bu, CH2TMS, and CH(TMS)2 are 22(1), 18(1), 17(1), and 9(2) kcal/mol, respectively. Corresponding ΔH((+))(reorg) values for M = Hf and R = Me, CH2(t)Bu, and CH2TMS are >24, 12(3), and 15(2) kcal/mol, respectively. ΔH((+))(reorg) values are highest in low dielectric constant solvents such as C6D12. Activation parameters for β-Me elimination in the complexes (1,2-Me2Cp)2MCH2(t)Bu+ MeB(C6F5)3 - for M = Zr and Hf are found to be ΔH((+))(β-Me) = 22.5(0.9) and 17.3(0.9) kcal/mol, and ΔS((+))(β-Me) = 4.3(3.3) and -11.9-(3.4) cal/mol·K, respectively.",
author = "Beswick, {C. L.} and Marks, {T. J.}",
year = "2000",
month = "10",
day = "25",
doi = "10.1021/ja000810a",
language = "English",
volume = "122",
pages = "10358--10370",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
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TY - JOUR

T1 - Metal-alkyl group effects on the thermodynamic stability and stereochemical mobility of B(C6F5)3-derived Zr and Hf metallocenium ion-pairs

AU - Beswick, C. L.

AU - Marks, T. J.

PY - 2000/10/25

Y1 - 2000/10/25

N2 - This paper reports significant dependence of ion-pair formation energetics and stereomutation rates upon the metal-bound alkyl substituent (R) and the solvent dielectric constant in the metallocenium series (1,2-Me2Cp)2MR+ MeB(C6F5)3 - where R = Me, CH2(t)Bu, CH2TMS, CH(TMS)2, and M = Zr and Hf, as determined by reaction titration calorimetry and dynamic NMR spectroscopy. For the ion-pair forming reaction, (1,2-Me2Cp)2M(R)Me + B(C6F5)3 → (1,2-Me2Cp)2MR+ MeB(C6F5)3 -, enthalpies in toluene solution at 25 °C for M = Zr and R = Me, CH2TMS, and CH(TMS)2 are -24.6(0.8), -22.6(1.0), and -59.2(1.4) kcal/mol, respectively. Corresponding values for M = Hf and R = Me and CH2TMS are -20.8(0.5) and -31.1(1.6) kcal/mol, respectively. ΔH((+))(reorg) values for the reorganization process that interchanges the ion-pair enantiotopic sites for M = Zr and R = Me, CH2(t)Bu, CH2TMS, and CH(TMS)2 are 22(1), 18(1), 17(1), and 9(2) kcal/mol, respectively. Corresponding ΔH((+))(reorg) values for M = Hf and R = Me, CH2(t)Bu, and CH2TMS are >24, 12(3), and 15(2) kcal/mol, respectively. ΔH((+))(reorg) values are highest in low dielectric constant solvents such as C6D12. Activation parameters for β-Me elimination in the complexes (1,2-Me2Cp)2MCH2(t)Bu+ MeB(C6F5)3 - for M = Zr and Hf are found to be ΔH((+))(β-Me) = 22.5(0.9) and 17.3(0.9) kcal/mol, and ΔS((+))(β-Me) = 4.3(3.3) and -11.9-(3.4) cal/mol·K, respectively.

AB - This paper reports significant dependence of ion-pair formation energetics and stereomutation rates upon the metal-bound alkyl substituent (R) and the solvent dielectric constant in the metallocenium series (1,2-Me2Cp)2MR+ MeB(C6F5)3 - where R = Me, CH2(t)Bu, CH2TMS, CH(TMS)2, and M = Zr and Hf, as determined by reaction titration calorimetry and dynamic NMR spectroscopy. For the ion-pair forming reaction, (1,2-Me2Cp)2M(R)Me + B(C6F5)3 → (1,2-Me2Cp)2MR+ MeB(C6F5)3 -, enthalpies in toluene solution at 25 °C for M = Zr and R = Me, CH2TMS, and CH(TMS)2 are -24.6(0.8), -22.6(1.0), and -59.2(1.4) kcal/mol, respectively. Corresponding values for M = Hf and R = Me and CH2TMS are -20.8(0.5) and -31.1(1.6) kcal/mol, respectively. ΔH((+))(reorg) values for the reorganization process that interchanges the ion-pair enantiotopic sites for M = Zr and R = Me, CH2(t)Bu, CH2TMS, and CH(TMS)2 are 22(1), 18(1), 17(1), and 9(2) kcal/mol, respectively. Corresponding ΔH((+))(reorg) values for M = Hf and R = Me, CH2(t)Bu, and CH2TMS are >24, 12(3), and 15(2) kcal/mol, respectively. ΔH((+))(reorg) values are highest in low dielectric constant solvents such as C6D12. Activation parameters for β-Me elimination in the complexes (1,2-Me2Cp)2MCH2(t)Bu+ MeB(C6F5)3 - for M = Zr and Hf are found to be ΔH((+))(β-Me) = 22.5(0.9) and 17.3(0.9) kcal/mol, and ΔS((+))(β-Me) = 4.3(3.3) and -11.9-(3.4) cal/mol·K, respectively.

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