Protonation of ferrous dinitrogen complexes containing a diphosphine ligand with a pendent amine

Zachariah M. Heiden, Shentan Chen, Michael T. Mock, William G. Dougherty, W. Scott Kassel, Roger Rousseau, R Morris Bullock

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The addition of acids to ferrous dinitrogen complexes [FeX(N 2)(PEtNMePEt)(dmpm)]+ (X = H, Cl, or Br; PEtNMePEt = Et 2PCH2N(Me)CH2PEt2; and dmpm = Me2PCH2PMe2) gives protonation at the pendent amine of the diphosphine ligand rather than at the dinitrogen ligand. This protonation increased the νN2 band of the complex by 25 cm -1 and shifted the Fe(II/I) couple by 0.33 V to a more positive potential. A similar IR shift and a slightly smaller shift of the Fe(II/I) couple (0.23 V) was observed for the related carbonyl complex [FeH(CO)(P EtNMePEt)(dmpm)]+. [FeH(P EtNMePEt)(dmpm)]+ was found to bind N2 about three times more strongly than NH3. Computational analysis showed that coordination of N2 to Fe(II) centers increases the basicity of N2 (vs free N2) by 13 and 20 pK a units for the trans halides and hydrides, respectively. Although the iron center increases the basicity of the bound N2 ligand, the coordinated N2 is not sufficiently basic to be protonated. In the case of ferrous dinitrogen complexes containing a pendent methylamine, the amine site was determined to be the most basic site by 30 pKa units compared to the N2 ligand. The chemical reduction of these ferrous dinitrogen complexes was performed in an attempt to increase the basicity of the N2 ligand enough to promote proton transfer from the pendent amine to the N2 ligand. Instead of isolating a reduced Fe(0)-N2 complex, the reduction resulted in isolation and characterization of HFe(Et 2PC(H)N(Me)CH2PEt2)(PEtN MePEt), the product of oxidative addition of the methylene C-H bond of the PEtNMePEt ligand to Fe.

Original languageEnglish
Pages (from-to)4026-4039
Number of pages14
JournalInorganic Chemistry
Volume52
Issue number7
DOIs
Publication statusPublished - Apr 1 2013

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Protonation
Amines
amines
Ligands
ligands
Alkalinity
Proton transfer
shift
Carbon Monoxide
methylene
Hydrides
hydrides
halides
isolation
Iron
iron
acids
Acids
protons
products

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Protonation of ferrous dinitrogen complexes containing a diphosphine ligand with a pendent amine. / Heiden, Zachariah M.; Chen, Shentan; Mock, Michael T.; Dougherty, William G.; Kassel, W. Scott; Rousseau, Roger; Bullock, R Morris.

In: Inorganic Chemistry, Vol. 52, No. 7, 01.04.2013, p. 4026-4039.

Research output: Contribution to journalArticle

Heiden, Zachariah M. ; Chen, Shentan ; Mock, Michael T. ; Dougherty, William G. ; Kassel, W. Scott ; Rousseau, Roger ; Bullock, R Morris. / Protonation of ferrous dinitrogen complexes containing a diphosphine ligand with a pendent amine. In: Inorganic Chemistry. 2013 ; Vol. 52, No. 7. pp. 4026-4039.
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abstract = "The addition of acids to ferrous dinitrogen complexes [FeX(N 2)(PEtNMePEt)(dmpm)]+ (X = H, Cl, or Br; PEtNMePEt = Et 2PCH2N(Me)CH2PEt2; and dmpm = Me2PCH2PMe2) gives protonation at the pendent amine of the diphosphine ligand rather than at the dinitrogen ligand. This protonation increased the νN2 band of the complex by 25 cm -1 and shifted the Fe(II/I) couple by 0.33 V to a more positive potential. A similar IR shift and a slightly smaller shift of the Fe(II/I) couple (0.23 V) was observed for the related carbonyl complex [FeH(CO)(P EtNMePEt)(dmpm)]+. [FeH(P EtNMePEt)(dmpm)]+ was found to bind N2 about three times more strongly than NH3. Computational analysis showed that coordination of N2 to Fe(II) centers increases the basicity of N2 (vs free N2) by 13 and 20 pK a units for the trans halides and hydrides, respectively. Although the iron center increases the basicity of the bound N2 ligand, the coordinated N2 is not sufficiently basic to be protonated. In the case of ferrous dinitrogen complexes containing a pendent methylamine, the amine site was determined to be the most basic site by 30 pKa units compared to the N2 ligand. The chemical reduction of these ferrous dinitrogen complexes was performed in an attempt to increase the basicity of the N2 ligand enough to promote proton transfer from the pendent amine to the N2 ligand. Instead of isolating a reduced Fe(0)-N2 complex, the reduction resulted in isolation and characterization of HFe(Et 2PC(H)N(Me)CH2PEt2)(PEtN MePEt), the product of oxidative addition of the methylene C-H bond of the PEtNMePEt ligand to Fe.",
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AU - Heiden, Zachariah M.

AU - Chen, Shentan

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AU - Kassel, W. Scott

AU - Rousseau, Roger

AU - Bullock, R Morris

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AB - The addition of acids to ferrous dinitrogen complexes [FeX(N 2)(PEtNMePEt)(dmpm)]+ (X = H, Cl, or Br; PEtNMePEt = Et 2PCH2N(Me)CH2PEt2; and dmpm = Me2PCH2PMe2) gives protonation at the pendent amine of the diphosphine ligand rather than at the dinitrogen ligand. This protonation increased the νN2 band of the complex by 25 cm -1 and shifted the Fe(II/I) couple by 0.33 V to a more positive potential. A similar IR shift and a slightly smaller shift of the Fe(II/I) couple (0.23 V) was observed for the related carbonyl complex [FeH(CO)(P EtNMePEt)(dmpm)]+. [FeH(P EtNMePEt)(dmpm)]+ was found to bind N2 about three times more strongly than NH3. Computational analysis showed that coordination of N2 to Fe(II) centers increases the basicity of N2 (vs free N2) by 13 and 20 pK a units for the trans halides and hydrides, respectively. Although the iron center increases the basicity of the bound N2 ligand, the coordinated N2 is not sufficiently basic to be protonated. In the case of ferrous dinitrogen complexes containing a pendent methylamine, the amine site was determined to be the most basic site by 30 pKa units compared to the N2 ligand. The chemical reduction of these ferrous dinitrogen complexes was performed in an attempt to increase the basicity of the N2 ligand enough to promote proton transfer from the pendent amine to the N2 ligand. Instead of isolating a reduced Fe(0)-N2 complex, the reduction resulted in isolation and characterization of HFe(Et 2PC(H)N(Me)CH2PEt2)(PEtN MePEt), the product of oxidative addition of the methylene C-H bond of the PEtNMePEt ligand to Fe.

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