Palladium(II) Chloride and a (Dipyridin‐2‐ylmethyl)amine‐Derived Palladium(II) Chloride Complex as Highly Efficient Catalysts for the Synthesis of Alkynes in Water or in NMP and of Diynes in the Absence of Reoxidant

The (dipyridin‐2‐ylmethyl)amine‐derived palladium chloride complex 1 and PdCl 2 are efficient catalysts for cross‐coupling reactions between terminal alkynes and aryl iodides or bromides under modified Sonogashira–Cassar–Heck conditions. The alkynylation can be performed under copper‐free conditions in water at reflux or at room temperature under air with pyrrolidine as base and tetra‐ n ‐butylammonium bromide (TBAB) as additive, with TONs of up to 7 × 10 4 and TOFs(h –1 ) of up to 6666. Terminal alkynes can be arylated in NMP as well under copper‐ and amine‐free conditions at 110 °C or room temperature, with tetra‐ n ‐butylammonium acetate (TBAA) acting as base with TONs up to 2 × 10 5 and TOFs (h –1 ) up to 66 666. In general, complex 1 displays a slightly higher efficiency than PdCl 2 as catalyst and maintains the same activity after five consecutive runs. Alternatively, these alkynylation processes can be carried out under microwave heating conditions. The homocoupling of terminal alkynes to the corresponding 1,3‐diynes proceeds under phosphane‐free conditions with the (dipyridin‐2‐ylmethyl)amine‐derived palladium chloride complex 1 or with PdCl 2 as catalysts and with CuI as cocatalyst in NMP with use of either TBAA or pyrrolidine as bases. This Glaser‐type reaction can be performed at 110 °C or at room temp. in the presence of air without the use of a reoxidant. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)