New syntheses of Cp*2Th(Ph)2 and Cp*2Th(Me)(aryl) derivatives

The complex Cp*2ThPh2 (1) is known to be a useful precursor in elimination reactions to yield transient benzyne adduct. This complex may be prepared in improved yield from the reaction of PhMgBr with Cp*2ThCl2 in the presence of p-dioxane. Ortho-substituted precursors Cp*2Th(Me)(o-MeOC6H4) (2), Cp*2TH(Me)(o-MeC6H-4) (3), and Cp*2 Th(Me)(2,5-Me2C6H3) (4) are reported for the first time, having been prepared in one-pot procedures using a similar method. The respective intermediate monohalide complexes have also been prepared at room temperature. The tolyl and xylyl derivatives exist as pairs of rotamers in solution, demonstrating the significant steric constraints imposed on this type of complex by ortho substituents. Halide exchange is observed in the preparation of the aryl-halide complexes when arylmagnesium bromides are employed. The extent of this exchange is influenced by the addition of p-dioxane to reaction mixtures. 22 refs