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Issue 1, 2010
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Platinum(II) and palladium(II) metallomacrocycles derived from cationic 4,4′-bipyridinium, 3-aminopyrazinium and 2-aminopyrimidinium ligands

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Abstract

A series of cationic, ditopic N-donor ligands based on 4,4′-bipyridine (4,4′-bipy), 3-aminopyrazine (apyz) and 2-aminopyrimidine (apym), each incorporating two positively-charged N-heterocycles linked by a conformationally-flexible spacer unit, have been synthesised and treated with palladium(II) or platinum(II) precursors [M(2,2′-bipy)(NO3)2] (M = Pd(II) or Pt(II)) to form highly cationic metallocyclic species. Treatment of 1,6-bis(4,4′-bipyridinium)hexane nitrate with [M(2,2′-bipy)(NO3)2] in aqueous solution, followed by the addition of KPF6, resulted in the formation of the [2+2] species [M2(2,2′-bipy)2{4,4′-bipy(CH2)64,4′-bipy}2](PF6)8. Treatment of [Pd(PhCN)2Cl2] with 1,3-bis(4,4′-bipyridinium)propane hexafluorophosphate in MeCN afforded [Pd2Cl4{4,4′-bipy(CH2)34,4′-bipy}2](PF6)4. When the cationic apyz or apym ligands were used in aqueous solution, the analogous metallomacrocycles did not form. Instead, deprotonation of the exocyclic amino group occurred upon coordination of the ligand to afford a tetranuclear [4+2] species in the case of platinum(II), with Pt(II)⋯Pt(II) bonding supported by strong UV-vis absorption at λ = 428 nm which was assigned to a metal-metal-to-ligand charge transfer (MMLCT) band. Thus, treatment of 1,6-bis(3-aminopyrazinium)hexane nitrate with [Pt(2,2′-bipy)(NO3)2], followed by the addition of KPF6, led to the formation of the red species [Pt4(2,2′-bipy)4{apyz(CH2)6apyz–2H}2](PF6)8. No related products could be identified with palladium(II), consistent with the low propensity for this metal ion to form strong Pd(II)⋯Pd(II) bonding interactions.

Graphical abstract: Platinum(II) and palladium(II) metallomacrocycles derived from cationic 4,4′-bipyridinium, 3-aminopyrazinium and 2-aminopyrimidinium ligands

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Publication details

The article was received on 13 Aug 2009, accepted on 28 Sep 2009 and first published on 11 Nov 2009


Article type: Paper
DOI: 10.1039/B916579G
Dalton Trans., 2010,39, 239-247

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    Platinum(II) and palladium(II) metallomacrocycles derived from cationic 4,4′-bipyridinium, 3-aminopyrazinium and 2-aminopyrimidinium ligands

    D. Schilter, J. K. Clegg, M. M. Harding and L. M. Rendina, Dalton Trans., 2010, 39, 239
    DOI: 10.1039/B916579G

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