摘要:
The variable-temperature H-1 NMR behavior of the uranium(III) dimers [Cp"2UX](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 examined. At low temperature, the number of inequivalent CMe3 or SiMe3 groups implies that the solution structure is the same as the solid-state structure in all of these complexes. The barriers to ring rotation in the Cp" series 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 barriers are explained by the different conformations of the Cp ligands in the 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.