Synthesis and Structure of Heteroleptic [C5Me4(SiMe2 t Bu)]1- Uranium(III) Complexes

The U(III) metallocene chemistry of the [C5Me4((SiMe2Bu)-Bu-t)](1-) ligand was explored for comparison with that of (C5Me5)(1-). Reactions between UI3, UI3(dioxane)(1.5), or UI3(THF)(4) and 2 equiv of LiC5Me4((SiMe2Bu)-Bu-t) in THF yielded the dihalide salt, [Li(THF)(4)]{[C5Me4((SiMe2Bu)-Bu-t)](2)UI2}, rather than a neutral metallocene monohalide. In order to obtain neutral and alkali-metal-free complexes comparable to known uranium(III) compounds with (C5Me5)(1-) ligands, the potassium salt, KC5Me4((SiMe2Bu)-Bu-t), was synthesized. The neutral mono- and bis-cyclopentadienyl complexes, [C5Me4((SiMe2Bu)-Bu-t)]UI2(THF)(3) and [C5Me4((SiMe2Bu)-Bu-t)](2)UI(THF), were generated from the reactions between UI3(dioxane)(1.5) and 1 and 2 equiv of KC5Me4((SiMe2Bu)-Bu-t) in THF, respectively. [C5Me4((SiMe2Bu)-Bu-t)](2)UI(THF) readily oxidizes to the U(IV) complex, [C5Me4((SiMe2Bu)-Bu-t)](2)UI2, which can also be made directly from UI4(dioxane)(2) and 2 equiv of KC5Me4((SiMe2Bu)-Bu-t). The borohydride analog, [C5Me4((SiMe2Bu)-Bu-t)](2)U(BH4)(THF), was obtained starting from U(BH4)(3)(THF)(2) and is less reducing and less air-sensitive than its iodide analog, [C5Me4((SiMe2Bu)-Bu-t)](2)UI(THF). The alkyl derivative, [C5Me4((SiMe2Bu)-Bu-t)](2)U[CH(SiMe3)(2)], can be synthesized from [C5Me4((SiMe2Bu)-Bu-t)](2)UI(THF) and 0.5 equiv of LiCH(SiMe3)(2) in diethyl ether, but [C5Me4((SiMe2Bu)-Bu-t)](2)U(mu-I)(2)Li(THF)(2) is also formed as a byproduct. The ansa-metallocene uranium complex, [Me4C5(SiMe2)O(SiMe2)C5Me4]UI(THF), was crystallographically identified from a reaction containing a partially hydrolyzed sample of the [C5Me4((SiMe2Bu)-Bu-t)](1-) ligand. In general, uranium complexes of the [C5Me4((SiMe2Bu)-Bu-t)](1-) ligand are more soluble in organic solvents than the analogous (C5Me5)(1-) complexes.