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 ol igomers, dimers and/or trimers, of terminal alkynes. The method allows cont rol of the extent of and, in some cases, the regiospecificity in the cataly zed oligomerization of terminal alkynes promoted by bis (pentamethylcyclope ntadienyl) actinide dimethyl complexes (Cp*(2)AnMe(2); Cp* = C5Me5, An = Th , U). These metallocene precursors are known to promote the simultaneous pr oduction of a large number of differently sized oligomers in the presence o f terminal alkynes. However, the addition of specific amines ensures the se lective synthesis of short oligomers. Catalytic "tailoring" to dimers or a mixture of dimers and trimers can be achieved by using nonbulky or bulky am ines, respectively. The kinetics in the catalytic oligomerization of 1-hexy ne, in the presence of i-BuNH2, mediated by Cp*2ThMe2 are first order in [a lkyne], first order in [Th], and inverse first, order in [amine]. Kinetic, spectroscopic, and mechanistic data argue that the turnover-limiting step i nvolves the formation of the mono(amido)thorium acetylide complex with rapi d insertion of the alkyne and protonolysis by the amine.