The cationic complex [(Et2N)3U][BPh4] reacts with a mixture of terminal alkynes inducing the synthesis of the cross dimerization products. For equimolar amounts of aliphatic alkynes (iPrC /CH, tBuC/CH) the head-to-tail geminal dimer of iPrC /CH and the geminal cross dimer resulting from the insertion of iPrC /CH into the U/C/CR(R/ iPr, tBu) moiety are obtained. When a mixture of PhC /CH is reacted with either iPrC /CH or tBuC /CH, different products are obtained depending on the molar ratio of the alkynes. The dimerization of iPrC /CH with an excess of PhC /CH produces the geminal head-to-tail cross dimer issued from the insertion of the aliphatic alkyne into the U/C/CPh moiety, and the geminal dimer of PhC /CH. Inverting the molar ratio of the alkynes and using the deuterium labeled aliphatic alkyne iPrC/CD,the deuterated geminal head-to-tail cross dimer is obtained preferentially with small amounts of the deuterated head-to-tail dimer of iPrC/CD. The mixture of tBuC/CH and PhC /CH is converted into the geminal head-to-tail cross dimer in good yield if the former alkyne is in large excess. The addition of external EtNH2 in the cross dimerization of iPrC /CH with PhC /CH induces a different chemoselectivity producing mainly the cis-dimer of PhC/CH. The use of a bulky amine, tBuNH2, with tBuC /CH causes the decomposition of the catalytic complex, forming the salt [tBuNH3][BPh4]/tBuNH2