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Issue 15, 2015
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Homoleptic borates and aluminates containing the difluorophosphato ligand – [M(O2PF2)x]y – synthesis and characterization

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Abstract

Weakly coordinating anions (WCAs) with the difluorophosphato ligand (O2PF2) were the target of this study. Initial experiments were conducted towards the preparation of homoleptic aluminates of the well-studied [Al(OR)4]-type. The preparation of the initial target structure Li[Al(O2PF2)4] failed due to the remaining Lewis acidic character of the central aluminum atom. Instead, the formation of Li3[Al(O2PF2)6] and Al(O2PF2)3 was observed with hexacoordinate aluminum atoms and verified by NMR, IR and X-ray crystallography. A possible mechanism towards these compounds was postulated in the solvent induced dismutation of the tetracoordinate Li[Al(O2PF2)4]. A singly charged WCA was realized by the exchange of the central aluminum atom for boron. The [B(O2PF2)4] anion was prepared starting from BH3·S(CH3)2 and boron tribromide leading to the protic room temperature Ionic Liquid (IL) [H(S(CH3)2)][B(O2PF2)4] and the neat liquid Brønsted acid H[B(O2PF2)4], respectively, representing a significantly improved synthesis with regard to the first experiments of Dove et al. The basicity of the [B(O2PF2)4] anion and its WCA quality were investigated on the basis of the IR-spectroscopic NH-scale and the salt [H(N(Oct)3)][B(O2PF2)4] that places it better than all oxyanions and close to the carboranate based WCAs. A pathway to the solvent free pure Li[B(O2PF2)4] salt was established on a multi-gram scale with excellent purities enabling electrochemical applications (verified by NMR, IR, X-ray crystallography and cyclovoltammetry).

Graphical abstract: Homoleptic borates and aluminates containing the difluorophosphato ligand – [M(O2PF2)x]y− – synthesis and characterization

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Publication details

The article was received on 02 Feb 2015, accepted on 02 Mar 2015 and first published on 18 Mar 2015


Article type: Paper
DOI: 10.1039/C5DT00469A
Dalton Trans., 2015,44, 7048-7057
  • Open access: Creative Commons BY-NC license
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    Homoleptic borates and aluminates containing the difluorophosphato ligand – [M(O2PF2)x]y – synthesis and characterization

    C. Schulz, P. Eiden, P. Klose, A. Ermantraut, M. Schmidt, A. Garsuch and I. Krossing, Dalton Trans., 2015, 44, 7048
    DOI: 10.1039/C5DT00469A

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