Chelate [2‐(Iminoethyl)pyridine N ‐oxide]metal Complexes – Synthesis and Structural Comparison with Their Chemically Related 2‐(Iminoethyl)pyridine‐Derived Systems

The N,O‐chelate ligands 2‐(iminoethyl)pyridine N ‐oxide ( 2a ) and 2‐(iminoethyl)‐6‐isopropylpyridine N ‐oxide ( 2b ) were prepared by conventional synthetic routes, the latter involving a variant of the Reissert–Henze reaction. Treatment of 2a with FeCl 2 resulted in a deoxygenation reaction of the ligand and formation of the salt [bis{2‐(iminoethyl)pyridine}FeCl] + [FeCl 4 ] – ( 18a ). In contrast, the reaction of 2a with PdCl 2 or CoCl 2 cleanly furnished the six‐membered chelate [κ N , O ‐2(iminoethyl)pyridine N ‐oxide]MCl 2 complexes ( 19a , M = Pd) or ( 20a , M = Co), respectively, which were both characterised by X‐ray diffraction. Treatment of 2b with [NiBr 2 (dme)], followed by crystallisation from THF, gave the complex [(κ N , O ‐ 2b )NiBr 2 (THF)] ( 21b ), which features a distorted trigonal‐bipyramidal coordination geometry of the central metal atom. The reaction of 2a with [NiBr 2 (dme)] gave the structurally related complex [(κ N , O ‐ 2a )NiBr 2 (κ O ‐ 2a )] ( 21a ). The N,O‐chelate Pd complex 19a was shown to be an active catalyst for the Suzuki coupling reaction. The ligand systems 2a , b and their related 2‐(iminoethyl)pyridines 3a , b and a variety of metal complexes of ligands 3 were also prepared and characterised for comparison by X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)