Gold(III) Adducts with Chiral Pyridinyl-Oxazolines. Synthesis, Reactivity of the Coordinated Ligands, and Structural Characterizations

Novel gold(III) pyridinyl-oxazoline cationic complexes [Au(pyox R )Cl 2 ][X] [pyox R = ( S )-4-R-2-(pyridin-2-yl)-4,5-dihydrooxazole, with R = i Pr, Bn, and ( R )-4-phenyl-2-(pyridin-2-yl)-4,5-dihydrooxazole; X = PF 6, AuCl 4, or mixtures of the two anions] were synthesized and structurally characterized. Reaction of the adducts with NaOAc in aqueous solution afforded the neutral complexes [Au(N,N′,O)Cl] of the deprotonated ligands N -(1-hydroxy-3-R-2-yl)pyridine-2-carboxamide (R = i Pr, Ph), N,N′H,OH, resulting from ring-opening of the bound pyox ligand by hydroxide ions and incorporation of hydroxide into the ring-opened products. Reaction of [Au(N,N′,O)Cl] (R = i Pr) with HX (X = Cl, BF 4, OTf) in aqueous solution resulted in protonation of the coordinated alkoxo group and its displacement from the coordination sphere to give the adducts [Au(N,N′,OH)ClX] (X = OTf, Cl) or the aquo complex [Au(N,N′,OH)(OH 2 )Cl] + (X = BF 4 ). Crystal structure characterizations were carried out on both [Au(N,N′,O)Cl] and [Au(N,N′,OH)Cl 2 ] (R = i Pr). Equimolar mixtures of the ring-opened derivative [Au(N,N′,O)Cl] (R = i Pr) and either silver salts or HBF 4 were found to promote, under mild conditions, polymerization of styrenes.