Synthesis of air-stable mixed bis-carboxylate titanocene complexes and their catalytic behaviors in cross-aldol and Mannich reactions

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• 作者：Jing Wang ; Xi Chen ; Xiu Wang ; Wei-Qiang Zhang ; Hua-Ming Sun…
• 刊名：Transition Metal Chemistry
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：41
• 期：7
• 页码：731-738
• 全文大小：877 KB
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry
  Catalysis
  Physical Chemistry
  Inorganic Chemistry
  
• 出版者：Springer Netherlands
• ISSN：1572-901X
• 卷排序：41

文摘

Tunable organometallic Lewis acid catalysts were developed by combining salicylic acid (H₂-Sal) with benzoic acid (H-Ben), 4-fluorobenzoic acid (H-BenF) and 3-thiophenic acid (H-Th), as coligands for mixed bis-carboxylate titanocene complexes. Three air-stable complexes [Cp₂Ti(η1-HSal)(η1-Ben)] (1), [Cp₂Ti(η1-HSal)(η1-BenF)] (2) and [Cp₂Ti[η1-HSal][(η1-Th)] (3) were prepared in high yields by the reaction of salicylato titanocene chelate with carboxylate ligands. The mixed bis-carboxylate titanocene complexes were fully characterized by physicochemical and spectroscopic methods. Single-crystal X-ray diffraction studies revealed Ti–O_(H-Sal) bond distances in 1, 2 and 3 of 1.972(3), 1.9245(18) and 1.912(5) Å, respectively, while the bond distances involving the coligands of 1, 2 and 3 are 1.908(3) Å (Ti–O_Ben), 1.9296(19) Å (Ti–O_BenF) and 1.945(5) Å (Ti–O_Th), respectively. These bis-carboxylate titanocene complexes showed satisfactory activities and selectivities in Mannich and cross-aldol reactions. Notably, complex 3 bearing the labile thiophene carboxylate ligand gave high yields with a diastereomer ratio (d.r.) as high as 1:99 for the direct Mannich reactions of benzaldehyde, cyclohexanone and aniline. In cross-aldol reaction of benzaldehyde and cyclohexanone, 1 and 2 successfully catalyzed the formation of double-aldol products in up to 99 % yield.