Selective dimerization of terminal alkynes promoted by the cationic actinide compound [(Et2N)(3)U][BPh4]. Formation of the alkyne pi-complex [(Et2N)(2)U(C equivalent to(CBu)-Bu-t) (eta(2)-HC equivalent to(CBu)-Bu-t)][BP4]

The cationic actinide complex [(Et2N)(3)U]-[BPh4] is an active catalytic pr ecursor for the selective dimerization of terminal alkynes. The regioselect ivity is mainly toward the geminal dimer, but for bulky alkyne substituents the unexpected cis dimer is also obtained. Mechanistic NMR studies show th at a eta(2)-pi-complex is formed between a terminal alkyne and an uranium-a cetylide intermediate. This latter complex has been characterized spectrosc opically. A plausible mechanistic scenario is proposed for the dimerization process.