FACILE REGIOSPECIFIC AROMATIC HYDROXYLATION IN PALLADIUM AZOPYRIDINESAND STRUCTURAL CHARACTERIZATION OF PHENOLATO PRODUCT

The reaction of Na2PdCl4 with 2-(arylazo)pyridines (A) in ethanol affo rds yellow complexes of composition [PdACl2] in which the PdCl2 fragme nt has a cis configuration [nu(Pd-Cl): 350, 365 cm-1]. Upon treating [ PdACl2] with dilute sodium hydroxide in air the pendent aryl group is selectively hydroxylated at the ortho position, affording the phenolat o complex [PdBCl] in high yields [B- is deprotonated 2-(2'-hydroxyaryl azo)pyridine]. A possible reaction pathway is proposed by analogy with the hydroxylation of certain organic compounds by OH-/O2. The crystal and molecular structure of one [PdBCl] complex is reported. In the hi ghly planar complex, the Pd-N(azo) length is significantly shorter tha n the Pd-N(pyridine) length. A single Pd-Cl stretch at 365 cm-1 charac terizes [PdBCl] which, unlike [PdACl2], has a structured intense absor ption in the visible region near 670 nm.