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 Pd0(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.