Defining Reactivity Differences in Sterically Crowded (η5-C5Me5)3M Complexes Based on Metal Size and Lanthanide vs Actinide Effects

Reactions between (eta(5)-C5Me5)(3)M and (eta(5)-O5Me5)(2)M'(mu-Ph)(2)BPh2 (M, M' = La, Ce, Pr, Nd, Sm, and U; M radius < M' radius) were examined to evaluate the relative steric crowding in the (C5Me5)(3)M series as a function of metal size and 4f vs 5f electron configuration. The sterically more crowded (C5Me5)(3)M complexes transfer (C5Me5)(-) to (C5Me5)(2)M'(mu-Ph)(2)BPh2 to generate less crowded (C5Me5)(3)M' products and (C5Me5)(2)M(mu-Ph)(2)BPh2 in mixtures with equilibrium constants in the range that allows all four components to be observed by NMR spectroscopy. The (C5Me5)(3)M to (C5Me5)(3)M' ratios depend on the difference in size of the two metals. Hence, (C5Me5)(3)Sm and (C5Me5)(2)La(mu-Ph)(2)BPh2 form a mixture with 99% (C5Me5)(3)La and 1% (C5Me5)(3)Sm, but the analogous reaction with (C5Me5)(2)Nd(mu-Ph)(2)BPh2 contains 90% (C5Me5)(3)Nd and 10% (C5Me5)(3)Sm. In analogous reactions with (C5Me5)(2)U(mu-Ph)(2)BPh2 and (C5Me5)(3)Ln lanthanide complexes, a size dependence is also observed, but the (C5Me5)3Ln complexes are favored over (C5Me5)(3)U to a greater extent than expected based on size differences.