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

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journal contribution
posted on 2011-03-14, 00:00 authored by Thomas J. Mueller, Gregory W. Nyce, William J. Evans
Reactions between (η5-C5Me5)3M and (η5-C5Me5)2M′(μ-Ph)2BPh2 (M, M′ = La, Ce, Pr, Nd, Sm, and U; M radius < M′ radius) were examined to evaluate the relative steric crowding in the (C5Me5)3M series as a function of metal size and 4f vs 5f electron configuration. The sterically more crowded (C5Me5)3M complexes transfer (C5Me5) to (C5Me5)2M′(μ-Ph)2BPh2 to generate less crowded (C5Me5)3M′ products and (C5Me5)2M(μ-Ph)2BPh2 in mixtures with equilibrium constants in the range that allows all four components to be observed by NMR spectroscopy. The (C5Me5)3M to (C5Me5)3M′ ratios depend on the difference in size of the two metals. Hence, (C5Me5)3Sm and (C5Me5)2La(μ-Ph)2BPh2 form a mixture with 99% (C5Me5)3La and 1% (C5Me5)3Sm, but the analogous reaction with (C5Me5)2Nd(μ-Ph)2BPh2 contains 90% (C5Me5)3Nd and 10% (C5Me5)3Sm. In analogous reactions with (C5Me5)2U(μ-Ph)2BPh2 and (C5Me5)3Ln lanthanide complexes, a size dependence is also observed, but the (C5Me5)3Ln complexes are favored over (C5Me5)3U to a greater extent than expected based on size differences.