Pyridine‐Based Oligonitriles as Pincer Ligands for Palladium( II ), Copper( II ), Cobalt( II ), and Nickel( II ) Ions

Nucleophilic ring opening of the 1‐oxa‐3,5‐diazinium salts 2 and 3 by propylamine furnishes the new polydentate, branched, pincer‐type ligands 4 and 5 , respectively, in 34 and 57 % yield. The 1‐oxa‐3,5‐diazinium salts 2 and 3 were prepared from pyridine‐2,6‐dicarbonyl dichloride ( 1 ) by treatment with dimethylcyanamide and diisopropylcyanamide in the presence of antimony pentachloride and tin tetrachloride, respectively. The structure of 4 , which is characterised by a strongly twisted N ‐acyloligonitrile arm, was determined by X‐ray crystallography. The ligand 4 , with its short and long arms, forms chelate complexes 4 – ·Pd(OAc) + and 4·CuCl 2 when treated with palladium( II ) acetate and copper( II ) chloride, respectively. 4 – ·Pd(OAc) + shows remarkable catalytic activity in Suzuki–Miyaura cross‐coupling reactions. The pincer‐type ligand 5 gives the chelate complexes 5·Co(ClO 4 ) 2 ·DMF , 5·CoCl 2 and 5·Ni(ClO 4 ) 2 ·DMF upon treatment with the respective metal salts. These three complexes show octahedral configuration, with DMF or chloride occuping the sixth coordination site. For the Co II complexes a cis configuration is oberserved for 5·CoCl 2 and a trans configuration for 5·Co(ClO 4 ) 2 ·DMF . In all cases 5 acts as a pentadentate ligand. All metal complexes were characterised by X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)