Advanced search
1 file | 830.62 KB

The intramolecular dynamics of a rigid yet twisty 'Ferrocenyl' TetraPhosphine : served with some 31P-NMR delicacy

Author
Organization
Abstract
Polydentate ferrocenyl phosphines equipped with bulky functional groups are regarded as rigid ligands capable of stabilizing and/or activating a broad range of chemical compounds such as smaller complexes (being formed e.g. in transition metal-catalyzed cross coupling reactions), nanoparticles, or even larger surfaces. The fruitful rigidity of these fascinating molecular species originates from the internal steric constraints imposed by the substituents; hence, the rotational reorientation of the Cp rings around the vertical 5-fold symmetry axis is hampered, and a permanent polydentate phosphine ‘cage’ is created (see figure). Latter construction then provides a large variety of coordination modes for the actual substrate what is the core structural feature being responsible for the diverse applicability spectrum. If such ferrocenyl phosphine is investigated on a sufficiently long i.e. ‘NMR time scale’ however, its decelerated intramolecular motions might be discovered and quantitatively characterized. Indeed, selective 1D 31P-{1H} EXSY {Exchange Spectroscopy} pointed out the exchange of the chemically distinct phosphoruses (green and red spheres below) in the scrutinized Fc(P)4tBu ligand and thus successfully demonstrated the previously unknown rotation (i.e. antiparallel twisting) of the Cp rings around the Fe centre. Series of measurements performed at different temperatures enabled the evaluation of the respective thermodynamic parameters (ΔS#, ΔH#, ΔG#) for which the influence of the solvent was also studied – while the confrontation of the experimental and theoretical values computed by DFT methods completed the analysis of the motion. In fact, the four 31P-s of Fc(P)4tBu composes an AA’BB’ spin system giving rise to a puzzling second order 31P NMR spectrum. Although the respective J-couplings had already been presented reclining upon the output of in silico simulations, a side track of the current work covered the full deduction of the results by the means of a quantum mechanical approach. Besides, the internal ring rotations shed new light on the ’through space’ nature of the JAA’ coupling affecting the inner phosphoruses (red spheres). That is, the interaction showed unquenchable and endured higher ring rotation rates than its actual frequency value what highlighted the intricacy of the magnetization transfer phenomena between the two nuclei. Finally, exchange phenomena were revealed for the complexed state of the ligand as well. According to 2D 1H–1H EXSY spectra, in case of [Pd(II)Br2-Fc(P)4tBu] the familiar twisting of the cyclopentadienyl rings was complemented with the periodic transconnection of the [Pd(II)Br2-] moiety between the bidentate (-PPH2)2 sites – perfectly illustrating the possibility for multiple coordination ways offered by polydentate phosphines.

Downloads

  • poster euromar 2018.pdf
    • full text
    • |
    • open access
    • |
    • PDF
    • |
    • 830.62 KB

Citation

Please use this url to cite or link to this publication:

Chicago
Kovács, Benjámin, José Martins, César Alejandro Urbina Blanco, Mark Saeys, and Jean-Cyrille Hierso. 2018. “The Intramolecular Dynamics of a Rigid yet Twisty ‘Ferrocenyl’ TetraPhosphine : Served with Some 31P-NMR Delicacy.” In European Magnetic Resonance, Meeting Abstracts.
APA
Kovács, B., Martins, J., Urbina Blanco, C. A., Saeys, M., & Hierso, J.-C. (2018). The intramolecular dynamics of a rigid yet twisty “Ferrocenyl” TetraPhosphine : served with some 31P-NMR delicacy. European Magnetic Resonance, Meeting abstracts. Presented at the European Magnetic Resonance meeting (EUROMAR) 2018.
Vancouver
1.
Kovács B, Martins J, Urbina Blanco CA, Saeys M, Hierso J-C. The intramolecular dynamics of a rigid yet twisty “Ferrocenyl” TetraPhosphine : served with some 31P-NMR delicacy. European Magnetic Resonance, Meeting abstracts. 2018.
MLA
Kovács, Benjámin, José Martins, César Alejandro Urbina Blanco, et al. “The Intramolecular Dynamics of a Rigid yet Twisty ‘Ferrocenyl’ TetraPhosphine : Served with Some 31P-NMR Delicacy.” European Magnetic Resonance, Meeting Abstracts. 2018. Print.
@inproceedings{8587646,
  abstract     = {Polydentate ferrocenyl phosphines equipped with bulky functional groups are regarded as rigid ligands capable of stabilizing and/or activating a broad range of chemical compounds such as smaller complexes (being formed e.g. in transition metal-catalyzed cross coupling reactions), nanoparticles, or even larger surfaces. The fruitful rigidity of these fascinating molecular species originates from the internal steric constraints imposed by the substituents; hence, the rotational reorientation of the Cp rings around the vertical 5-fold symmetry axis is hampered, and a permanent polydentate phosphine {\textquoteleft}cage{\textquoteright} is created (see figure). Latter construction then provides a large variety of coordination modes for the actual substrate what is the core structural feature being responsible for the diverse applicability spectrum.
If such ferrocenyl phosphine is investigated on a sufficiently long i.e. {\textquoteleft}NMR time scale{\textquoteright} however, its decelerated intramolecular motions might be discovered and quantitatively characterized. Indeed, selective 1D 31P-\{1H\} EXSY \{Exchange Spectroscopy\} pointed out the exchange of the chemically distinct phosphoruses (green and red spheres below) in the scrutinized Fc(P)4tBu ligand and thus successfully demonstrated the previously unknown rotation (i.e. antiparallel twisting) of the Cp rings around the Fe centre. Series of measurements performed at different temperatures enabled the evaluation of the respective thermodynamic parameters (\ensuremath{\Delta}S\#, \ensuremath{\Delta}H\#, \ensuremath{\Delta}G\#) for which the influence of the solvent was also studied -- while the confrontation of the experimental and theoretical values computed by DFT methods completed the analysis of the motion.
In fact, the four 31P-s of Fc(P)4tBu composes an AA{\textquoteright}BB{\textquoteright} spin system giving rise to a puzzling second order 31P NMR spectrum. Although the respective J-couplings had already been presented reclining upon the output of in silico simulations, a side track of the current work covered the full deduction of the results by the means of a quantum mechanical approach. Besides, the internal ring rotations shed new light on the {\textquoteright}through space{\textquoteright} nature of the JAA{\textquoteright} coupling affecting the inner phosphoruses (red spheres). That is, the interaction showed unquenchable and endured higher ring rotation rates than its actual frequency value what highlighted the intricacy of the magnetization transfer phenomena between the two nuclei.
Finally, exchange phenomena were revealed for the complexed state of the ligand as well. According to 2D 1H--1H EXSY spectra, in case of [Pd(II)Br2-Fc(P)4tBu] the familiar twisting of the cyclopentadienyl rings was complemented with the periodic transconnection of the [Pd(II)Br2-] moiety between the bidentate (-PPH2)2 sites -- perfectly illustrating the possibility for multiple coordination ways offered by polydentate phosphines. },
  author       = {Kov{\'a}cs, Benj{\'a}min and Martins, Jos{\'e} and Urbina Blanco, C{\'e}sar Alejandro and Saeys, Mark and Hierso, Jean-Cyrille},
  booktitle    = {European Magnetic Resonance, Meeting abstracts},
  language     = {eng},
  location     = {Nantes, France},
  title        = {The intramolecular dynamics of a rigid yet twisty 'Ferrocenyl' TetraPhosphine : served with some 31P-NMR delicacy},
  year         = {2018},
}