Synthesis Of Pyridine-Based Tridentate N-Ligands And The Application In Homogeneous Catalysis

With good stability and high reactivity, pyridine-based tridentate N-ligands have been widely used in the fields of coordination chemistry, organic synthesis and homogeneous catalysis. Among which, the ligands with a so-called "pincer" structure have been investigated deeply recent years with regard to their synthesis as well as their potential application in homogeneous catalysis.In this paper, the pyridine-based tridentate ligands, functionalized and un-functionalized in the 4 position of the pyridine rings, were synthesized. A bis(imino)pyridine-Ru complex, RuCl₂(BIP)PPh₃, was synthesized. The complex was further studied in the catalytic transfer hydrogenation of acetophenone.(1) Synthesis of the bis(imino)pyridine ligands.The synthetic routes for 2,6-diacetylpyridne and 4-allyloxy-2,6-diacetylpyridine were designed respectively from the starting substrates of 2,6-dicarboxylpyridine and chelidamic acid. Beside obtaining the above end products, two purified derivatives, 6-acetyl-2-carbethoxypyridine and 4-allyloxy-6-acetyl-2-carbethoxypyridine, were also prepared. The effects of the conditions upon the yields were studied. To the best of our knowledge, the synthesis of 4-allyloxy-6-acetyl-2-carbethoxypyridine has not been reported before. When the molar ratio of EtONa to 4-allyloxy-2,6-dicarbethoxypyridine was approximately 0.9:1, only 4-allyloxy-6-acetyl-2-carbethoxypyridine was obtained; while the ratio was approximately 5:1, only 4-allyloxy-2,6-diacetyl -pyridine was obtained.Two bis(imino)pyridine ligands, 2,6-{1-[(phenyl)imino]ethyl}pyridine and 4-allyloxy-2,6-{1l-[(2,6-dimethylphenyl)imino]ethyl}pyridine, were synthesized from 2,6- diacetylpyridine and 4-allyloxy-2,6-diacetylpyridine through Schiff-Base condensations with aniline and 2,6-dimethylaniline,...