Uranium(IV) bis(amido), imido and bis(acetylide) complexes: synthesis, molecular structure, solution dynamics and interconversion reactions

Abstract

Reactions of [UMe₂(C₅Me₅)₂] with primary aromatic or aliphatic amines led to the rapid formation of monomeric uranium(IV) complexes [U(C₅Me₅)₂(NHR)₂](R = 2,6-dimethylphenyl 1, Et 2 or Bu^t3). The compounds were characterized by standard techniques and for 1, by X-ray diffraction. In co-ordinating solvents like tetrahydrofuran (thf) compound 1 reacted intramolecularly releasing one primary amine and forming the imidouranium(IV)[U(C₅Me₅)₂{N(C₆H₃Me₂-2,6)}]·thf 4, whereas in non-co-ordinating solvents the base-free [U(C₅Me₅)₂{N(C₆H₃Me₂-2,6)}]5 was obtained. The thf in 4 was found not to be in equilibrium with bulk solvents, and different proton chemical shifts for the adducted base were observed as a function of temperature following a Curie–Weiss behaviour. σ-Bond metathesis reactions of the bis(amido) and/or imido complexes with terminal alkynes produced the bis(acetylide) complexes [U(C₅Me₅)₂(CCR)₂](R = Ph 6 or Bu^t7) active species for the regioselective oligomerization of terminal alkynes, which can be prepared also from the reaction of [UMe₂(C₅Me₅)₂] with 2 equivalents of the corresponding terminal alkyne. Reactivity studies show the possible interconversion among these bis(amido), imido and bis(acetylide) complexes.