Divergent reactivity of [(κ3-L)ThCl2(dme)] with Grignard reagents: Alkylation, ancillary ligand transfer to magnesium, and halide exchange caught in the act

Reaction of [(BDPP)ThCl2(dme)] (1) with 2 equivalents of MeMgBr in OEt2, followed by filtration and layering a toluene solution with hexanes at −30 °C yielded a single large crystal of [{(BDPP)ThX(μ-X)2Mg(OEt2)(μ-Me)}2]·2 toluene (X = Br0.73–0.87/Cl0.13–0.27; 3·2 toluene). This product is the result of halide exchange to form a partially brominated neutral thorium species, which is adducted with MeMgX(OEt2). The complex is then tetrametallic as a result of Mg–Me–Mg bridges. The structure of complex 3 provides direct insight into the process by which halide exchange takes place between electrophilic metal halide complexes and Grignard reagents. This reactivity stands in stark contrast to the reactions of 1 and [(XA2)ThCl2(dme)] (2) with PhCH2MgCl. In these cases the expected dialkyl products, [LTh(CH2Ph)2] [L = BDPP (4) and XA2 (5)], were formed under most conditions. However, addition of a PhCH2MgCl solution to 2 at −78 °C and warming to room temperature after 5 minutes gave [(XA2)Mg(dme)] (6), the product of ancillary ligand transfer from thorium to magnesium, in 30–50% yield.