Unsaturated hetero chains, part 13.: 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(-)center dot Pd(OAc)* and 4-CUCl2 when treated with palladium(II) acetate and copper(II) chloride, respectively. 4(-)center dot Pd(OAc)* shows remarkable catalytic activity in Suzuki-Miyaura cross-coupling reactions, The pincer-type ligand 5 gives the chelate complexes 5 center dot Co(CLO4)(2)center dot DMF 5 center dot CoCl2 and 5 center dot Ni(ClO4)(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 Coll complexes a cis configuration is oberserved for 5-CoCl2 and a trans configuration for 5-Co(ClO4)(2)center dot DMF In all cases 5 acts as a pentadentate ligand. All metal complexes were characterised by X-ray diffraction.