Defining reactivity differences in sterically crowded (η~5- C_5Me_5)_3M complexes based on metal size and lanthanide vs actinide effects

摘要

Reactions between (η~5-C_5Me_5) _3M and (η~5-C_5Me_5) _2M′(μ-Ph)_2BPh_2 (M, M′ = La, Ce, Pr, Nd, Sm, and U; M radius < M′ radius) were examined to evaluate the relative steric crowding in the (C_5Me_5)_3M series as a function of metal size and 4f vs 5f electron configuration. The sterically more crowded (C_5Me_5)_3M complexes transfer (C_5Me_5)~- to (C_5Me _5)_2M′(μ-Ph)_2BPh_2 to generate less crowded (C_5Me_5)_3M′ products and (C_5Me_5)_2M(μ-Ph)_2BPh _2 in mixtures with equilibrium constants in the range that allows all four components to be observed by NMR spectroscopy. The (C_5Me _5)_3M to (C_5Me_5)_3M′ ratios depend on the difference in size of the two metals. Hence, (C _5Me_5)_3Sm and (C_5Me_5) _2La(μ-Ph)_2BPh_2 form a mixture with 99% (C_5Me_5)_3La and 1% (C_5Me _5)_3Sm, but the analogous reaction with (C _5Me_5)_2Nd(μ-Ph)_2BPh_2 contains 90% (C_5Me_5)_3Nd and 10% (C _5Me_5)_3Sm. In analogous reactions with (C _5Me_5)_2U(μ-Ph)_2BPh_2 and (C_5Me_5)_3Ln lanthanide complexes, a size dependence is also observed, but the (C_5Me_5)_3Ln complexes are favored over (C_5Me_5)_3U to a greater extent than expected based on size differences.