NHC Ligands with a Secondary Pyrimidyl Donor for Electron-Rich Palladium(0) Complexes

Several ( N -2-pyrimidyl-NHC)-palladium(0) complexes have been synthesized in very high yields and purities by transmetalation from the related silver(I) complexes with Pd 0 (tBuDAB)(ma). The coordination behavior of the heteroditopic ligands was analyzed, and the structure of their complexes was confirmed by NMR and X-ray diffraction studies. The complexes are active catalysts for the transfer hydrogenation of alkynes to Z -alkenes, with activity and selectivity depending on the pyrimidine substituents and the NHC nitrogen substituent. Selectivities toward the Z -alkene as high as 97% were observed.