Organic-soluble optically pure anionic metal complexes PPh4[MIII(S,S-EDDS)]·2H2O (M = Fe, Co, Cr)

Abstract

The first organic-soluble, optically and diastereomerically pure EDDS metal complexes have been synthesised. A number of synthetic approaches were attempted, but finally the tetraphenylphosphonium series emerged as providing readily accessible compounds of trivalent Cr, Fe and Co in reasonable yields via the silver salts without the need to perform ion-exchange chromatography. The species PPh₄[M^III(S,S-EDDS)] are very soluble in methanol, acetonitrile and even THF but isolation was facilitated by addition of stoichiometric water giving the highly crystalline but still conveniently soluble title compounds. The structures of the three isomorphous crystals comprise H₂O-bridged extended hydrogen bonded structures with large channels occupied by the counterion molecules. The magnetic properties and circular dichroism spectra are reported along with comparative data for water-soluble NH₄[Fe^III(S,S-EDDS)]. Phase purity (and hence diastereomeric purity) in the paramagnetic systems is assessed through powder XRD. The practical utility of this type of compound was confirmed by optical resolution of (±)-[Ru^II(bpy)₃]Cl₂.