Rare-Earth-Metal-Catalyzed Addition of Terminal Monoalkynes and Dialkynes with Aryl-Substituted Symmetrical or Unsymmetrical Carbodiimides

A high-efficiency and atom-economic
route for the synthesis of
N-aryl-substituted propiolamidines was established through the addition
of terminal alkynes with aryl-substituted symmetrical or unsymmetrical
carbodiimides catalyzed by mixed TpMe2/Cp rare-earth-metal
alkyl complexes (TpMe2)­CpLnCH2Ph­(THF) (1Ln). Moreover, the gadolinium alkyl
complex 1Gd can also serve as
a catalyst for the double addition of dialkynes with carbodiimides.
Mechanism studies indicated that the variable coordination modes (κ3 or κ2) of the TpMe2 ligand on
the rare-earth-metal species may play an important role in the catalytic
cycles.