Design of base metal extractants. Part 1. Inter-ligand hydrogen bonding in the assembly of pseudo-macrocyclic bis(aminosulfonamidato)M(ii) complexes?

Dalton Transactions Pub Date: 2006-02-01 DOI: 10.1039/B515650P

Abstract

Monosulfonyl derivatives of simple 1,2- and 1,3-diamines (R2HN–R–NHSO2R1 = L) have been shown to be easily deprotonated to give neutral 2 : 1 complexes, [M(L ? H)2], with Co(II), Ni(II), Cu(II) or Zn(II). The Ni(II) and Cu(II) complexes with deprotonated N-tosyl-1,2-diaminoethane have a planar N42? donor set and a 14-membered pseudo-macrocyclic structure based on head-to-tail S[double bond, length as m-dash]O?H–N(amine) bonding between the two bidentate ligands. In the related tetrahedral Zn(II) complex the ends of the mutually perpendicular bidentate N2? units are too far apart to form a cyclic H-bonded system. X-Ray structure determinations on five free ligands provide evidence for extensive inter-molecular H-bonding, which in the case of N-tosyl-1,3-diaminopropane and its N′-tert-butyl derivative involves formation of dimeric 16-membered pseudo-macrocycles. Despite favourable inter-ligand H-bonding in the neutral 2 : 1 complexes, these ligands are relatively weak extractants, showing >50% loading of Cu(II) in “pH-swing” equilibria, 2?L(org) + M2+ = [M(L ? H)2](org) + 2?H+, only when the pH of the aqueous phase is raised above 4.

Graphical abstract: Design of base metal extractants. Part 1. Inter-ligand hydrogen bonding in the assembly of pseudo-macrocyclic bis(aminosulfonamidato)M(ii) complexes
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