posted on 2016-06-02, 19:37authored byRebecca J. Warr, Katherine J. Bell, Anastasia Gadzhieva, Rafel Cabot, Ross J. Ellis, Jy Chartres, David K. Henderson, Eleni Lykourina, A. Matthew Wilson, Jason B. Love, Peter A. Tasker, Martin Schröder
Extraction
and binding studies of [PtCl6]2– are
reported for 24 mono-, bi-, and tripodal extractants containing tris(2-aminoethyl)amine
(TREN) or tris(3-aminopropyl)amine (TRPN) scaffolds. These
reagents are designed to recognize the outer coordination sphere of
[PtCl6]2– and to show selectivity over
chloride anion under acidic conditions. Extraction from 0.6 M HCl
involves protonation of the N-center in tertiary
amines containing one, two, or three urea, amide, or sulfonamide hydrogen-bond
donors to set up the following equilibrium: 2L(org) + 2H+ + [PtCl6]2– ⇌ [(LH)2PtCl6](org). All reagents show
higher Pt loading than trioctylamine, which was used as a positive
control to represent commercial trialkylamine reagents. The loading
of [PtCl6]2– depends on the number of
pendant amides in the extractant and follows the order tripodal >
bipodal > monopodal, with urea-containing extractants outperforming
amide and sulfonamide analogues. A different series of reagents in
which one, two, or three of the alkyl groups in tris-2-ethylhexylamine
are replaced by 3-N′-hexylpropanamide groups
all show a comparably high affinity for [PtCl6]2– and high selectivity over chloride anion in extractions from aqueous
acidic solutions. 1H NMR titration of three extractants
[LH·Cl] with [(Oct4N)2PtCl6] in CDCl3 provides evidence for high selectivity for
[PtCl6]2– over chloride for tri- and
bipodal extractants, which show higher binding constants than a monopodal
analogue.