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Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

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Abstract

Counterions can play an active role in chemical reactivity, modulating reaction pathways, energetics and selectivity. We investigated the tautomeric equilibrium resulting from protonation of Fe(PEtNMePEt)(CO)3 (PEtNMePEt = (Et2PCH2)2NMe) at Fe or N. Protonation of Fe(PEtNMePEt)(CO)3 by [(Et2O)2H]+[B(C6F5)4] occurs at the metal to give the iron hydride [Fe(PEtNMePEt)(CO)3H]+[B(C6F5)4]. In contrast, treatment with HBF4·OEt2 gives protonation at the iron and at the pendant amine. Both the FeH and NH tautomers were characterized by single crystal X-ray diffraction. Addition of excess BF4 to the equilibrium mixture leads to the NH tautomer being exclusively observed, due to NH⋯F hydrogen bonding. A quantum chemical analysis of the bonding properties of these systems provided a quantification of hydrogen bonding of the NH to BF4 and to OTf. Treatment of Fe(PEtNMePEt)(CO)3 with excess HOTf gives a dicationic complex where both the iron and nitrogen are protonated. Isomerization of the dicationic complex was studied by NOESY NMR spectroscopy.

Graphical abstract: Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

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Publication details

The article was received on 23 Sep 2018, accepted on 04 Oct 2018 and first published on 23 Nov 2018


Article type: Edge Article
DOI: 10.1039/C8SC04239J
Citation: Chem. Sci., 2019, Advance Article
  • Open access: Creative Commons BY-NC license
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    Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

    G. M. Chambers, S. I. Johnson, S. Raugei and R. M. Bullock, Chem. Sci., 2019, Advance Article , DOI: 10.1039/C8SC04239J

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