Nonrigidity in Eight-Coordinate Tetrakis Chelates: the Stereochemical Integrity and Geometrical Isomerism of Tungsten (5-Methylpicolinato) (5,7-Dichloro-8-quinolinolato) Complexes.

摘要

All previous reports of eight-coordinate transition metal tetrakis chelates indicate nonrigidity on a nuclear magnetic resonance time scale at temperatures appreciably below room temperature. In fact, Fay and his co-workers have designated the tetrakis (N,N-dimethyldithiocarbamato) tantalum(V) cation as stereochemically rigid based on its nonequivalent proton magnetic resonance (H NMR) methyl resonances below -62 C. Slow exchange limit H NMR methyl signals at and above room temperature for the tetrakis eight-coordinate heterochelate tris(5-methylpicolinato) (5,7-dichloro-8-quinolinolato)tungsten(IV), abbreviated WP3O are reported here. Furthermore, to our knowledge, Geometrical isomers of an eight-coordinate transition metal complex in solution have not been obtained previously. We wish to report the solution evidence for two isomers of bis(5-methylpicolinato)bis (5,7-dichloro-8-quinolinolato)tungsten(IV), abbreviated WP3Q, is reported.