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

The bis‐guanidinate anion stabilized amido magnesium (II) compound [LMgN(SiMe3)2; L = {(ArHN)(ArN)‐C=N−C=(NAr)(NHAr); Ar = 2,6‐Et2‐C6H3}] (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{(NiPr)2C}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‐CH3‐C6H4)N‐(C‐C≡C−Ph)=O]2 (Mg‐4) has been described via the reaction between Mg‐2 and isocyanate.