Synthesis, characterization and application of nickel(II) complexes modified with N,N′,N″-pincer ligands

• Ni(II) complexes with [N,N″,N‴]-pincer ligands have been studied.
• A square planar geometry was observed for nickel hydroxido and nickel chlorido complexes.
• The Ni(II) complexes were applied as precatalysts in hydrosilylation reactions.

Different N,N″-substituted pyridine-2,6-dicarboxamides 1a–d have been synthesized and treated with nickel(II) trifluoromethanesulfonate in the presence of an excess of tetraethylammonium hydroxide to form after double-deprotonation the nickel hydroxido complexes 4a–c. These square planar complexes have been characterized by various techniques, which indicate a tridentate N,N′,N″-coordination mode of the ligands. The other coordination site on the nickel center is occupied by a hydroxido ligand. The reactivity of the complexes was studied in dehalogenation reactions and allows access to square planar nickel chlorido complexes 5a–c. Moreover, by NMR studies it was found that nickel hydroxido complexes as well as chlorido complexes can be converted with diphenylsilane or lithium borohydride to nickel hydrido complexes, which can be seen as a possible catalytic intermediate in reduction chemistry. Based on that, the potential of complexes 4 and 5 were evaluated in the hydrosilylation of ketones to produce alcohols after work-up.

Nickel(II) N,N′,N″-pincer complexes with deprotonated N,N″-substituted pyridine-2,6-dicarboxamides ligands have been synthesized and characterized. In more detail, a square planar geometry for nickel hydroxido and nickel chlorido complexes was observed. The catalytic activity of Ni(II) complexes was investigated in the hydrosilylation of ketones.Figure optionsDownload as PowerPoint slide