Diacylthioureas – an overlooked class of ligands; the coordination chemistry of diacylated thiourea with platinum(ii), palladium(ii) and gold(iii)

Abstract

Here, we report our initial investigations into the coordination chemistry of symmetric diacylated thiourea ligands ((RCONH)₂CS) (R = Me, Et or Ph) acting as both mono and dianionic ligands with platinum(II), palladium(II) and gold(III) metal centres. Initial investigations were centred on mixed ligand bis(triphenylphosphine) (PPh₃) complexes which were prepared by reactions between cis-[PtCl₂(PPh₃)₂] and (RCONH)₂CS. A subsequent series of mixed ligand complexes from the diethyl-diacylthiourea ligand ((CH₂CH₂CONH)₂CS) with [PtCl₂(dppe)] (dppe = Ph₂PCH₂CH₂PPh₂), [PdCl₂(phen)] (phen = 1,10-phenanthroline), [AuCl₂(anp)] (anp = cyclometallated 2-anilinopyridyl) and [PtCl₂(COD)] (COD = 1,5-cyclooctadiene) were also prepared. The complexes were characterized by a combination of common techniques (MS, NMR and SC-XRD) which determined that the ligands coordinated to the metal centres in an unexpected S,N bidentate chelate manner in all instances. The complexes showed a small degree of aqueous instability as a result of hydrolysis. Computational techniques (NCI, EDA and HS) were used to analyse complexes whose solid state structure was able to be determined crystallographically. The presence of a chalcogen bond between the thiourea sulfur and acyl oxygen atoms was revealed which dominates the molecular structure. The cyclometallated 2-anilinopyridyl gold(III) complex 1f demonstrates intermolecular dimerism in the solid state. Hirshfeld surface analysis was used to determine the percentage contribution of inherent intermolecular interactions to crystal packing and the specific contacts responsible for spatial orientations in 1a, 1b, and 1f.