Binaphtholate and Binaphtholate Chloride Complexes of Tungsten(VI)

A range of 1,1′-bi-2-naphthol (H₂BINO) derivatives react with WCl₆ in toluene to generate a new family of W(R₂BINO)_3−nCl_2n derivatives. Reactions between excess 3,3′-diphenyl-1,1′-bi-2-naphthol (H₂Ph₂BINO) and WCl₆ generate only the monosubstituted W(Ph₂BINO)Cl₄ product. The less sterically demanding H₂Me₂BINO ligand produces minor quantities of various bis-Me₂BINO-substituted isomers, together with trans-(R*,R*)-W(Me₂-BINO)₂Cl₂, which is the overwhelmingly favored product. The parent H₂BINO ligand generates two of four possible W(BINO)₃ diastereomers, with (S*,S*,S*)-W(BINO)₃ and (S*,S*,S*)-W(BINO)₃ diastereomers being produced in statistically predicted quantities. Molecular modeling and spectroscopic studies indicate that the S*,S*,S* and S*,S*,R* isomers prefer to adopt Δ* rather than Λ* overall complex stereochemistry. This preference stems from a minimization of interligand interactions between (S)-BINO ligands in Δ diastereomers. There is relatively little difference between the stereochemistry of polynorbornene prepared employing the W(R₂BINO)_3−nCl_2n complexes as precatalysts. This may arise, in part, from the ability of the catalysts to engage in secondary metathesis reactions. The (BINO)₃W complexes are not activated for ring opening metathesis polymerization catalysis at −70 °C, apparently because the slow rate of ligand exchange at this temperature does not allow the metal to open a coordination site.