Preorganized tridentate analogues of mixed hydroxyoxime/carboxylate nickel extractants

James W. Roebuck, Jennifer R. Turkington, David M. Rogers, Philip J. Bailey, Violina Griffin, Adam J. Fischmann, Gary S. Nichol, Max Pelser, Simon Parsons, Peter A. Tasker

Research output: Contribution to journalArticlepeer-review

Abstract

A series of 22 tridentate unsatd. mono-anionic ligands having the atom-sequence Y-C=C-N=CH-C=C-Z-1, with Y = N, O, or S and Z = O or S, was studied to establish whether this backbone could be used to develop strong solvent extractants for nickel(II) which will preferably also show a high selectivity over iron(III) in the pH-dependent process: 2LHorg + NiSO4 = [(L)2Ni]org + H2SO4. All are capable of forming octahedral [(L)2Ni] complexes with a mer-arrangement of the YNZ-1 donor set. X-ray crystal structures of three salicylaldimine proligands derived from 3-bromo-5-t-butyl-2-hydroxybenzaldehyde show these to have pre-organized donor sets in which the three donors are held in an approx. orthogonal arrangement by intramol. hydrogen bonds. The tautomers obsd. are dependent on the nature of the Y atom and the extent to which it is favorable for this to form a bonding interaction with the acidic hydrogen atom on the salicylaldimine unit. X-ray crystal structure detns. of seven of the [(L)2Ni] complexes show these to have significantly distorted octahedral coordination geometries which partly account for the proligands proving to be fairly weak Ni-extractants. DFT calcns. show that extractant strength is dependent on a combination of the binding strength of the YNZ-1 donor set to the nickel ion and on the ease of deprotonation of the extractant. On this basis 3-nitro-4-t-octyl-6-(quinolin-8-imino)phenol is predicted, and is found, to be the strongest Ni-extractant. The extractants have low hydrolytic stability, reverting to their aldehyde precursors when solns. in water-immiscible solvents are contacted with aq. acid, making them poor candidates for development as reagents for nickel recovery based on pH-swing processes of the type shown above. [on SciFinder(R)]
Original languageEnglish
Pages (from-to)3734-3742
Number of pages9
JournalDalton Transactions
Volume45
Issue number9
Early online date14 Jan 2016
DOIs
Publication statusE-pub ahead of print - 14 Jan 2016

Keywords

  • nickel salicylaldimine acylpyrazoloneimine acylthiopyrazoloneimine complex prepn extractant
  • crystal structure nickel salicylaldimine acylpyrazoloneimine acylthiopyrazoloneimine

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