Solution structure and behavior of dimeric uranium(III) metallocene halides

The variable-temperature H-1 NMR behavior of the uranium(III) dimers [Cp"2U X](2) and [(Cp2UX)-U-double dagger](2), where X is F, Cl, Br, or I, Cp" is 1,3-(Me3Si)(2)C5H3, and Cp-double dagger is 1,3-(Me3C)(2)C5H3, has been exa mined. At low temperature, the number of inequivalent CMe3 or SiMe3 groups implies that the solution structure is the same as the solid-state structur e in all of these complexes. The barriers to ring rotation in the Cp" serie s are strongly dependent upon the U-X distance, but all of the barriers to ring rotation in the Cp" series are the same. The trends in ring rotation b arriers are explained by the different conformations of the Cp ligands in t he dimers. In addition to the homo-halide dimers, the variable-temperature NMR, behavior of the hetero-halide dimers Cp'U-4(2)(mu-X)(mu-Y), where Cp' is Cp" or Cp-double dagger and X and Y are halides where X not equal Y, was examined. Above room temperature, the halide atoms exchange sites rapidly on the NMR time scale.