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

Reactions of [UMe(2)(C(5)Me(5))(2)] with primary; aromatic or aliphatic amines led to the rapid formation of monomeric uranium(IV) complexes [U(C(5)Me(5))(2)(NHR)(2)] (R=2,6-dimethylphenyl 1, Et 2 or Bu(t) 3). 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(C(5)Me(5))(2){N(C(6)H(3)Me(2)-2,6)}]. thf 4, whereas in non-co-ordinating solvents the base-free [U(C(5)Me(5))(2){N(C(6)H(3)Me(2)-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. sigma-Bond metathesis reactions of the bis(amido) and/or imido complexes with terminal alkynes produced the bis(acetylide) complexes [U(C(5)Me(5))(2)(C=CR)(2)] (R=Ph 6 or Bu(t) 7) active species for the regioselective oligomerization of terminal alkynes, which can be prepared also from the reaction of [UMe(2)(C(5)Me(5))(2)] with 2 equivalents of the corresponding terminal alkyne. Reactivity studies show the possible interconversion among these bis(amido), imido and bis(acetylide) complexes.