Tungsten Oxo Salicylate Complexes from Tungsten Hexachloride Reactions Systems

Tungsten hexachloride is a potent halogen-transfer agent, capable of reacting directly with salicylic acid to generate
a tungsten oxo fragment and salicoyl chloride. As a result, oxo complexes dominate the chemistry of tungsten(VI) salicylates. Both mono- and disalicylate substituted tungsten oxo complexes are accessible. The Brønsted
free acid W(O)Cl(Hsal)(sal) complex is a sparingly soluble, presumably polymeric material that can be dissolved
in THF. The THF adduct has been characterized by NMR spectroscopy, although an X-ray crystallographic study
indicates that the product cocrystallizes with a structurally analogous d1 WCl2(Hsal·THF)(sal) byproduct. The
remaining chloride ligand in W(O)Cl(Hsal)(sal) is replaced by a bridging oxo unit when the reaction contains
a significant excess of salicylic acid. The product “linear” oxo bridged ditungsten complex, [W(O)(Hsal)(sal)]2O, forms intramolecular hydrogen bonds, accounting for its high solubility in noncoordinating solvents. An
X-ray study shows that the intramolecular Hsal·sal hydrogen bonding in this complex accommodates a more
linear W−O−W arrangement than does a previously observed class of isostructural diolate derivatives. Tungsten
oxo tetrachloride, formed in the initial reaction between salicylic acid and WCl6, also reacts with the salicoyl
chloride byproduct to generate tungsten salicoylate (OAr-2-COCl) complexes.