Anion and platinum group metal binding of bis(thioureido) ligands

Abstract

A series of bis(thioureido) ligands have been synthesised, which show anion binding in acetone-d(_6). Their structures have been determined by X-ray crystallography and some exhibit hydrogen bonding interactions with the π-electrons of the the thiocarbonyl bond. This hydrogen bonding interaction has been investigated for the general thiocarbonyl and carbonyl bond using the CSD, and a marked difference in the interaction of hydrogen bond donors with the π-electrons of carbonyl and thiocarbonyl bonds has been shown. The bis(thioureido) ligands have been coordinated to platinum group metals and the differing binding modes of the ligands investigated. The reaction of ligands with 2 carbon atoms between thiourea groups with [(_շ)], yields a mixture of products that may be consolidated into a single product with a water wash. The water instigates a deprotonation of an NH group that allows nitrogen coordination to ruthenium, yielding a S,S,N terdentate Ru(II) half-sandwich complex, with four- and seven-membered adjoining metallacycles. A chiral metal centre is formed and in the solid state, opposite enantiomers hydrogen-bond to each other through chloride counter-ions. Ruthenium complexes with an interaction from the pyridyl nitrogen in ligands containing pyridyl binding moieties have also been characterised. Bidentate S,S coordination is observed for the reaction of bisthiourea ligands with [Pd(dppe)Cl(_2)], forming nine- and ten-membered metallacycles. A similar binding mode is observed in a Pt(II) analogue. A polymer analogue of the bisthiourea ligands has been synthesised, and has been tested to extract metals from mixed metal solutions. Using well-defined metal salts in methanol, ruthenium(II) may be loaded onto the polymer from a single metal solution, acetontrile solvent inhibits the uptake of platinum group metals from mixed metal solutions, the polymer is selective for Cu(II) even when acetonitrile solvent is present and in the absence of Cu(II) or acetonitrile, can selectively extract Pt(II) over Ru(II), Fe(II), Cr(III) and Ni(II). The ruthenium loaded resin may be stripped of Ru(II) effectively using concentrated nitric acid solution in two hours. Testing the bisthiourea polymer in an acetic acid mixed metal solution demonstrated that the polymer was not suitable for platinum group metal extraction from the acetic acid medium, when compared to a commercially available resin.