Controlling the catalytic oligomerization of terminal alkynes promoted by organoactinides: A strategy to short oligomers

A novel strategy has been developed for the catalytic synthesis of short oligomers, dimers and/or trimers, of terminal alkynes. The method allows control of the extent of and, in some cases, the regiospecificity in the catalyzed oligomerization of terminal alkynes promoted by bis (pentamethylcyclopentadienyl) actinide dimethyl complexes (Cp*(2)AnMe(2); Cp* = C(5)Me(5), An = Th, U). These metallocene precursors are known to promote the simultaneous production of a large number of differently sized oligomers in the presence of terminal alkynes. However, the addition of specific amines ensures the selective synthesis of short oligomers. Catalytic "tailoring" to dimers or a mixture of dimers and trimers can be achieved by using nonbulky or bulky amines, respectively. The kinetics in the catalytic oligomerization of 1-hexyne, in the presence of i-BuNH(2), mediated by Cp*(2)ThMe(2) are first order in [alkyne], first order in [Th], and inverse first, order in [amine]. Kinetic, spectroscopic, and mechanistic data argue that the turnover-limiting step involves the formation of the mono(amido)thorium acetylide complex with rapid insertion of the alkyne and protonolysis by the amine.