1,8-Naphthyridine Complexes of Dimethylgold Halides and Pseudohalides. A Simple Case of Fluxional Behavior

A series of 1:1 complexes of dimethylgold halides and pseudohalides with 2,7-dimethyl-l,8-naphthyridine has been prepared and characterized by elemental analysis, molecular weight, conductivity, and spectral data. A study of the temperature dependence of the proton magnetic resonance spectra revealed a fluxional behavior of these nonionic molecular compounds in dichloromethane and chloroform solutions. Whereas at very low temperatures the gold atom is associated with only one of the two nitrogen donors of the ligand, there is rapid intramolecular two-site exchange at elevated temperatures (>200°K). It is only above ambient temperature that the intermolecular exchange of ligand and/or (pseudo)halide ion becomes rapid on the nmr time scale, whereby the low-temperature nonequivalence of the two methyl groups attached to gold is eliminated. Analogous dimethylgold halide complexes of 2,2 ′-bipyridyl, on the contrary, are classical ionic chelate compounds, which do not show this kind of nonrigidity.