Chiral phosphine ligands in the structural chemistry of gold

The reaction of chloro(dimethylsulfide)gold(I) with (2-hydroxybutyl)diphenylphosphine (L) (racemic mixture) in dichloromethane affords high yields of the racemic chiral complex (L)AuCl. Metathesis reactions with KBr or KI, respectively, in a two-phase solvent mixture (CH₂C1₂/H₂O) lead to a conversion into the corresponding bromide and iodide complexes (L)AuBr and (L)AuI. Treatment of silver chloride with the ligand L in acetonitrile yields the analogous 1:1 adduct (L)AgCl. The compounds have been characterized by their analytical and spectroscopic data, and the structures of (L)AuCl and (L)AuBr have been determined by single-crystal X-ray diffraction. The compounds build isomorphous crystal lattices (monoclinic, P2₁/c) in which pairs of enantiomers (R- and S-configuration of L) are aggregated by two long hydrogen bonds between the hydroxyl group of the ligand and the halogen substituent of the neighbouring molecule. Cationic, linear two-coordinate 1:2 complexes (L)₂Au⁺ X^- (X = BF₄, ClO₄, SO₃CF₃) and (L)₂Ag⁺ X^- (X = BF₄) are obtained in good yields by reaction of L with Me₂SAuCl and AgX (molar ratio 2:1:1) or with AgBF₄ (molar ratio 2:1), respectively. ³¹P NMR studies at variable temperature show an equilibrium between all possible stereoisomers (RR, SS, RS, SR) in solution with rapid ligand exchange at ambient temperatures.