Chemistry of azopyrimidines. Part III. Synthesis, spectral characterization and electrochemical studies of arylazopyrimidine complexes of palladium(II) and catecholato derivatives

摘要

2-(Phenylazo)pyrimidine (papm), 2-(p-tolylazo)pyrimidine (p-tapm), 2-(p-chlorophenylazo)pyrimidine (p-Clpapm) are used as N,N'-chelators. They are called arylazopyrimidines and abbreviated in general as aapm (1). They were reacted with cis-Pd(MeCN)(2)Cl-2 to yield orange-red complexes of the type Pd(aapm)Cl-2(2). Upon reaction with catechols in the-presence of triethylanine (Et3N), Pd(aapm)Cl-2 yielded the mixed-ligand complexes [Pd(aapm)(O,O)] where O,O = pyrocatecholate [cat, (3)], 4-tert-butylcatecholate [tbcat, (4)], 3,5-di-tert-butylcatecholate [dtbcat, (5)] and tetrachlorocatecholate [tccat, (6)]. The complexes were characterised by elemental analyses, IR spectra, UV-VIS spectra and H-1 NMR spectra. The redox properties were examined with cyclic voltammetry. [Pd(aapm)(O,O)] exhibits four successive redox responses and the E-1/2 Values are highly sensitive to the nature of the substituents. The electronic spectra of [Pd(aapm)(O,O)] exhibit ligand-to-ligand charge transfer transitions and are different from those of Pd(aapm)Cl-2. The band position is largely dependent on the substituent type of the catechol frame and is tentatively assigned to the 3b(1) (cat) --> pi*(aapm) transition. [References: 28]