How to insulate a reactive site from a perfluoroalkyl group

Photoelectron spectroscopy, calorimetric, and computational studies of long-range electronic effects in fluorous phosphines P((CH2)m (CF2)7CF3)3

Haijun Jiao, Sylvie Le Stang, T. Soós, Ralf Meier, Klaus Kowski, Paul Rademacher, Laleh Jafarpour, Jean Benoit Hamard, Steven P. Nolan, J. A. Gladysz

Research output: Contribution to journalArticle

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Abstract

This study advances strategy and design in catalysts and reagents for fluorous and supercritical CO2 chemistry by defining the structural requirements for insulating a typical active site from a perfluoroalkyl segment. The vertical ionization potentials of the phosphines P((CH2)mRf8)3 (m = 2 (2) to 5 (5)) are measured by photoelectron spectroscopy, and the enthalpies of protonation by calorimetry (CF3SO3H, CF3C6H5). They undergo progressively more facile (energetically) ionization and protonation (P(CH2CH3)3 > 5 > 4 ≈ P(CH3)3 > 3 > 2), as expected from inductive effects. Equilibrations of trans-Rh(CO)(Cl)(L)2 complexes (L = 2, 3) establish analogous Lewis basicities. Density functional theory is used to calculate the structures, energies, ionization potentials, and gas-phase proton affinities (PA) of the model phosphines P((CH2)mCF3)3 (2′-9′). The ionization potentials of 2′-5′ are in good agreement with those of 2-5, and together with PA values and analyses of homodesmotic relationships are used to address the title question. Between 8 and 10 methylene groups are needed to effectively insulate a perfluoroalkyl segment from a phosphorus lone pair, depending upon the criterion employed. Computations also show that the first carbon of a perfluoroalkyl segment exhibits a much greater inductive effect than the second, and that ionization potentials of nonfluorinated phosphines P((CH2)mCH3)3 reach a limit at approximately nine carbons (m = 8).

Original languageEnglish
Pages (from-to)1516-1523
Number of pages8
JournalJournal of the American Chemical Society
Volume124
Issue number7
DOIs
Publication statusPublished - Feb 20 2002

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Phosphines
Photoelectron Spectroscopy
Ionization potential
Photoelectron spectroscopy
Catalytic Domain
Protons
Protonation
Carbon
Calorimetry
Carbon Monoxide
Phosphorus
Alkalinity
Gases
Ionization
Density functional theory
Enthalpy
Catalysts

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

How to insulate a reactive site from a perfluoroalkyl group : Photoelectron spectroscopy, calorimetric, and computational studies of long-range electronic effects in fluorous phosphines P((CH2)m (CF2)7CF3)3. / Jiao, Haijun; Le Stang, Sylvie; Soós, T.; Meier, Ralf; Kowski, Klaus; Rademacher, Paul; Jafarpour, Laleh; Hamard, Jean Benoit; Nolan, Steven P.; Gladysz, J. A.

In: Journal of the American Chemical Society, Vol. 124, No. 7, 20.02.2002, p. 1516-1523.

Research output: Contribution to journalArticle

Jiao, Haijun ; Le Stang, Sylvie ; Soós, T. ; Meier, Ralf ; Kowski, Klaus ; Rademacher, Paul ; Jafarpour, Laleh ; Hamard, Jean Benoit ; Nolan, Steven P. ; Gladysz, J. A. / How to insulate a reactive site from a perfluoroalkyl group : Photoelectron spectroscopy, calorimetric, and computational studies of long-range electronic effects in fluorous phosphines P((CH2)m (CF2)7CF3)3. In: Journal of the American Chemical Society. 2002 ; Vol. 124, No. 7. pp. 1516-1523.
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T1 - How to insulate a reactive site from a perfluoroalkyl group

T2 - Photoelectron spectroscopy, calorimetric, and computational studies of long-range electronic effects in fluorous phosphines P((CH2)m (CF2)7CF3)3

AU - Jiao, Haijun

AU - Le Stang, Sylvie

AU - Soós, T.

AU - Meier, Ralf

AU - Kowski, Klaus

AU - Rademacher, Paul

AU - Jafarpour, Laleh

AU - Hamard, Jean Benoit

AU - Nolan, Steven P.

AU - Gladysz, J. A.

PY - 2002/2/20

Y1 - 2002/2/20

N2 - This study advances strategy and design in catalysts and reagents for fluorous and supercritical CO2 chemistry by defining the structural requirements for insulating a typical active site from a perfluoroalkyl segment. The vertical ionization potentials of the phosphines P((CH2)mRf8)3 (m = 2 (2) to 5 (5)) are measured by photoelectron spectroscopy, and the enthalpies of protonation by calorimetry (CF3SO3H, CF3C6H5). They undergo progressively more facile (energetically) ionization and protonation (P(CH2CH3)3 > 5 > 4 ≈ P(CH3)3 > 3 > 2), as expected from inductive effects. Equilibrations of trans-Rh(CO)(Cl)(L)2 complexes (L = 2, 3) establish analogous Lewis basicities. Density functional theory is used to calculate the structures, energies, ionization potentials, and gas-phase proton affinities (PA) of the model phosphines P((CH2)mCF3)3 (2′-9′). The ionization potentials of 2′-5′ are in good agreement with those of 2-5, and together with PA values and analyses of homodesmotic relationships are used to address the title question. Between 8 and 10 methylene groups are needed to effectively insulate a perfluoroalkyl segment from a phosphorus lone pair, depending upon the criterion employed. Computations also show that the first carbon of a perfluoroalkyl segment exhibits a much greater inductive effect than the second, and that ionization potentials of nonfluorinated phosphines P((CH2)mCH3)3 reach a limit at approximately nine carbons (m = 8).

AB - This study advances strategy and design in catalysts and reagents for fluorous and supercritical CO2 chemistry by defining the structural requirements for insulating a typical active site from a perfluoroalkyl segment. The vertical ionization potentials of the phosphines P((CH2)mRf8)3 (m = 2 (2) to 5 (5)) are measured by photoelectron spectroscopy, and the enthalpies of protonation by calorimetry (CF3SO3H, CF3C6H5). They undergo progressively more facile (energetically) ionization and protonation (P(CH2CH3)3 > 5 > 4 ≈ P(CH3)3 > 3 > 2), as expected from inductive effects. Equilibrations of trans-Rh(CO)(Cl)(L)2 complexes (L = 2, 3) establish analogous Lewis basicities. Density functional theory is used to calculate the structures, energies, ionization potentials, and gas-phase proton affinities (PA) of the model phosphines P((CH2)mCF3)3 (2′-9′). The ionization potentials of 2′-5′ are in good agreement with those of 2-5, and together with PA values and analyses of homodesmotic relationships are used to address the title question. Between 8 and 10 methylene groups are needed to effectively insulate a perfluoroalkyl segment from a phosphorus lone pair, depending upon the criterion employed. Computations also show that the first carbon of a perfluoroalkyl segment exhibits a much greater inductive effect than the second, and that ionization potentials of nonfluorinated phosphines P((CH2)mCH3)3 reach a limit at approximately nine carbons (m = 8).

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