Pyridine-based oligonitriles as pincer ligands for palladium(II), copper(II), cobalt(II), and nickel(II) ions

Abstract

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-(ClO4) 2·DMF, 5·CoCl2 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 CoII complexes a cis configuration is oberserved for 5·CoCl2 and a trans configuration for 5·Co(ClO4)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, 2005.