Isocyanide adducts of tri- and tetravalent uranium metallocenes supported by tetra(isopropyl)cyclopentadienyl ligands.

Reaction of the uranium(III) metallocenium salt [(Cp-iPr4)(2)U][B(C6F5)(4)] withtert-butyl isocyanide ((BuNC)-Bu-t) yielded the dicationic uranium(iv) complex [(Cp-iPr4)(2)U((CNBu)-Bu-t)(4)][B(C6F5)(4)](2)(1), which displays a linear metallocene geometry. Use of crude mixtures of [(Cp-iPr4)(2)U][B(C6F5)(4)], which contain a soluble source of iodide, led instead to isolation of the monocationic uranium(IV) iodide complex [(Cp-iPr4)(2)U(I)((CNBu)-Bu-t)(2)][B(C6F5)(4)] (2). Adduct formation with no change in oxidation state was observed upon addition of(t)BuNC to the neutral uranium(iii) species (Cp-iPr4)(2)UI, resulting in isolation of (Cp-iPr4)(2)U(I)((CNBu)-Bu-t) (3). X-ray crystallographic and IR spectroscopic studies both showed effects ascribed to the presence of multiple strongly donating isocyanide ligands in 1.