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 aliphati c 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 no t to be in equilibrium with bulk solvents, and different proton chemic al shifts for the adducted base were observed as a function of tempera ture following a Curie-Weiss behaviour. sigma-Bond metathesis reaction s of the bis(amido) and/or imido complexes with terminal alkynes produ ced 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 ter minal alkynes, which can be prepared also from the reaction of [UMe(2) (C(5)Me(5))(2)] with 2 equivalents of the corresponding terminal alkyn e. Reactivity studies show the possible interconversion among these bi s(amido), imido and bis(acetylide) complexes.