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

摘要

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 7Xl0~4 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 deg C or room temperature,with tetra-n-butylammonium acetate(TBAA)acting as base with TONs up to 2Xl0~5 and TOFs(h~(-1))up to 66666.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 Cul as cocatalyst in NMP with use of either TBAA or pyrrolidine as bases.This Glaser-type reaction can be performed at 110 deg C or at room temp,in the presence of air without the use of a reoxidant.