The imidazolium ligand precursors [L1H1H 2]Cl and [L2H12H2]C1 (H1 = NHC=O, H2 = NCHN) for the potentially bidentate and pincer-type amido-NHC ligands were synthesized in 66-78% yields. Selective deprotonation of H2 in these salts with pyridine in the presence of palladium chloride resulted in the monodentate palladium(II) complexes Pd(L 1H1)(py)Cl2 and Pd(L2H 12)(py)Cl2. The use of K2CO 3 in pyridine or DMF led to the double and triple deprotonations of the ligand precursors, giving the bis-bidentate and pincer-type palladium(II) complexes PdL12 and PdL2(py), respectively. Intriguingly, in certain cases, both the cis and the trans isomers of PdL 12 were formed and isolated in pure forms. A theoretical study indicates that the trans-PdL12 is thermodynamically more stable than the cis isomer (ca. 5.8 kcal mol-1). All the new complexes are characterized by NMR (ID and 2D) and single-crystal X-ray diffraction studies. A systematic study of the new complexes in Suzuki coupling reactions revealed the following order of activities: Pd(L1H 1)(py)Cl2 > PdL2(py) > PdL 12.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry