Thomas Straub

Designing new catalytic C–C and C–N bond formations promoted by organoactinides

Abstract Organoactinides of the type Cp 2 * AnMe 2 (Cp * =C 5 Me 5 ; An=Th; U) are active catalytic precursors for the oligomerization of terminal alkynes HC≡CR (R=alkyl, aryl, SiMe 3 ). The regioselectivity and the extent of oligomerization depend strongly on the alkyne substituent R, whereas the catalytic reactivity is similar for both organoactinides. Reaction with tert -butylacetylene yields regioselectively the E-2,4-disubstituted 1-buten-3-yne dimer whereas trimethylsilylacetylene is regioselective trimerized to the E,E-1,4,6-tris(trimethylsilyl)-1,3-hexadiene-5-yne, with small amounts (3–5%) of the corresponding E-2,4-disubstituted 1-buten-3-yne dimer. Oligomerization with less bulky alkyl and aryl substituted alkynes produces a mixture of higher oligomers with no regioselectivity. Using the Cp 2 * ThMe 2 catalyst, we have recently developed a strategic method to control the extent and in some cases the regioselectivity of the catalyzed oligomerization of nonbulky terminal alkynes to dimers and/or trimers. The metallocene catalytic precursors ensure the selective synthesis of small oligomers by the addition of specific amines. Catalytic “tailoring” to dimer and trimers can be achieved by using small or bulky amines, respectively. Kinetic and mechanistic data for the controlling experiments argue that the turnover-limiting step involves the acetylide actinide complex formation with the rapid insertion of the alkyne and protonolysis by the amine. The analog Cp 2 * UMe 2 in the presence of primary amines induce the selective C–N bond formation, producing enamines which are tautomerized to the corresponding imines.

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

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 But3). 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 But7) 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.