Insights Into the Magnesium‐Catalyzed C−C Coupling of Terminal Alkynes with Carbodiimides

Abstract The bis‐guanidinate anion stabilized amido magnesium (II) compound [LMgN(SiMe 3 ) 2 ; L={(ArHN)(ArN)−C=N−C=(NAr)(NHAr); Ar=2,6‐Et 2 −C 6 H 3 }] ( Mg‐1 ) has been synthesized and characterized. It has been successfully employed as a pre‐catalyst for the catalytic C−C coupling of terminal alkynes with carbodiimides, producing propiolamidine products with moderate to good yields. The active catalyst bis‐guanidinate magnesium acetylide [LMgC≡C−Ph] 2 ( Mg‐2 ) and the intermediate magnesium propiolamidinate [LMg{(N i Pr) 2 C}C≡C−Ph] ( Mg‐3) involved in the catalytic reaction were isolated and thoroughly characterized through multinuclear NMR and mass spectral analyses, as well as single crystal X‐ray diffraction studies. Based on the above findings, a plausible mechanistic cycle has been proposed. Additionally, a new example of bis‐guanidinate supported structurally characterized magnesium propiolamidate compound [LMg{(4−CH 3 −C 6 H 4 )N−(C−C≡C−Ph)=O] 2 ( Mg‐4 ) has been described via the reaction between Mg‐2 and isocyanate.