Heterobimetallic [LAu(μ-H)2WCp2]BF4 complexes undergo selective ion pairing in solution arising from a pronounced accumulation of positive charge on the metallocene fragment. The charge depletion on the Cp2W unit is strong enough to override ligand effects, so that the electrostatic potential of these species is not affected by the nature of the ancillary ligand on gold.
The interionic structure in solution of a series of [LAu(μ-H)2WCp2][BF4] ion pairs (L=N-heterocyclic carbene, phosphine or phosphite) has been elucidated by means of heteronuclear NOE and diffusion NMR. Selective ion pairing based on specific metallocene-anion interactions has been observed for all species. The ancillary ligand L plays only a minor role in dictating the availability of secondary ion pair structures, mainly owing to steric factors. DFT calculations have indicated that the tungstenocene fragment delocalizes most of the positive charge and acts as the preferential anion anchoring point. Even though the interaction is highly specific, ion association in CD2Cl2 is not enhanced and the typical aggregation behavior of linear Au(I) ion pairs is observed.Zum Volltext