Coordination chemistry and catalytic applications of Pd(II)-, and Ni(II)-sulfosalan complexes in aqueous media

Abstract

With the aim of identifying new types of water-soluble catalyst precursors for modification of biological membranes by homogeneous hydrogenation in aqueous solution and under mild conditions, we have performed detailed equilibrium and spectroscopic characterization of complex formation between nickel(II) or palladium(II) and salan-type ligands sulfonated in their aromatic rings (N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminoethane (HSS), N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminopropane (PrHSS) and N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminobutane (BuHSS)) in the slightly acidic-alkaline pH range. The stability constants of the metal complexes were determined using pH-potentiometry. The catalytic activities of the [Ni(HSS)] and [Pd(HSS)] complexes in hydrogenation and redox isomerization of oct-1-en-3-ol were also studied. The results indicate, that all of the investigated ligands exhibit excellent nickel(II) and palladium(II) binding ability via the formation of (O^-,N,N,O^-) linked chelate system. Both [Ni(HSS)] and [Pd(HSS)] catalyze the hydrogenation and redox isomerization of oct-1-en-3-ol. [Pd(HSS)] shows excellent activity and the reaction was highly selective to the formation of octan-3-ol. [Ni(HSS)] is also an active and selective catalyst for this hydrogenation reaction and to the best of our knowledge, [Ni(HSS)] is the first nickel(II)-based, hydrolytically stable, water-soluble catalyst bearing sulfonated salan moiety.

Keywords: Allylic alcohols; Hydrogenation; Nickel(II); Palladium(II); Stability; Sulfonated salan.