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Issue 46, 2007
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Bis(ketopyrrolyl) complexes of Co(II) stabilised by trimethylphosphine ligands

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2-Formylpyrrole and 2-acetylpyrrole were deprotonated with NaH to give the corresponding Na salts 1a and 1b, respectively. The reactivity of these salts towards cobalt chloride compounds was studied. The resulting new bis(ketopyrrolyl) Co(II) 19-electron complexes [Co(κ2N,O-2-NC4H3C(R)[double bond, length as m-dash]O)2(PMe3)2] (R = H 2a, and Me 2b) were characterised by single crystal X-ray diffraction, to show an octahedral geometry with the PMe3 ligands in trans positions to each other, and two bidentate ketopyrrolyl ligands occupying the remaining coordination positions in a transoid conformation. Powder and solution magnetic susceptibility measurements together with EPR and UV/Vis/NIR spectra revealed a low-spin ground state (dz2, S = 1/2) for Co(II) in these compounds. Analysis of the EPR superhyperfine couplings suggested that the longer distances (z axis) of the hexacoordinate Co coordination sphere are occupied by the keto-O atoms of the bidentate ligand, leaving the pyrrolyl N and the phosphine P atoms within the equatorial plane. This is confirmed by means of DFT calculations, which also indicate that the most thermodynamically stable isomers are low-spin (S = 1/2) complexes with coordination geometries corresponding to the molecular structures obtained by X-ray crystallography.

Graphical abstract: Bis(ketopyrrolyl) complexes of Co(ii) stabilised by trimethylphosphine ligands

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Publication details

The article was received on 04 Jul 2007, accepted on 19 Sep 2007 and first published on 05 Oct 2007

Article type: Paper
DOI: 10.1039/B710162G
Citation: Dalton Trans., 2007, 5460-5470
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    Bis(ketopyrrolyl) complexes of Co(II) stabilised by trimethylphosphine ligands

    S. A. Carabineiro, P. T. Gomes, L. F. Veiros, C. Freire, L. C. J. Pereira, R. T. Henriques, J. E. Warren and S. I. Pascu, Dalton Trans., 2007, 5460
    DOI: 10.1039/B710162G

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