Ruthenium(II) complexes bearing pyridine-functionalized N-heterocyclic carbene ligands: Synthesis, structure and catalytic application over amide synthesis

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• 作者：MUTHUKUMARAN NIRMALA ; PERIASAMY VISWANATHAMURTHI
• 关键词：Pyridine ; functionalized carbene ligand ; [Ru–NHC] complexes ; transmetalation ; aldehyde to amide conversion
• 刊名：Journal of Chemical Sciences
• 出版年：2016
• 出版时间：November 2016
• 年：2016
• 卷：128
• 期：11
• 页码：1725-1735
• 全文大小：2,154 KB
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry
  Chemistry
  
• 出版者：Springer India
• ISSN：0973-7103
• 卷排序：128

文摘

A series of four imidazolium salts was synthesized by the reaction of 2-bromopyridine with 1-substituted imidazoles. These imidazolium salts (1a–d) were successfully employed as ligand precursors for the syntheses of new ruthenium(II) complexes bearing neutral bidentate ligands of N-heterocyclic carbene and pyridine donor moiety. The NHC-ruthenium(II) complexes (3a–d) were synthesized by reacting the appropriately substituted pyridine-functionalized N-heterocyclic carbenes with Ag₂O forming the NHC–silver bromide in situ followed by transmetalation with [RuHCl(CO)(PPh₃)₃]. The new complexes were characterized by elemental analyses and spectroscopy (IR, UV-Vis,1H,13C,31P-NMR) as well as ESI mass spectrometry. Based on the spectral results, an octahedral geometry was assigned for all the complexes. The complexes were shown to be efficient catalysts for the one-pot conversion of various aldehydes to their corresponding primary amides with good to excellent isolated yields using NH₂OH.HCl and NaHCO₃. The effects of solvent, base, temperature, time and catalyst loading were also investigated. A broad range of amides were successfully synthesized with excellent isolated yields using the above optimized protocol. Notably, the complex 3a was found to be a very efficient and versatile catalyst towards amidation of a wide range of aldehydes.