Chemistry of Azopyrimidines. Part III. Synthesis, Spectral Characterization and Electrochemical Studies of Arylazopyrimidine Complexes of Palladium(II) and Catecholato Derivatives

Abstract

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)2Cl2 to yield orange-red complexes of the type Pd(aapm)Cl2 (2). Upon reaction with catechols in the presence of triethylamine (Et3N), Pd(aapm)Cl2 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 1H NMR spectra. The redox properties were examined with cyclic voltammetry. [Pd(aapm)(O,O)] exhibits four successive redox responses and the E12 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)Cl2 The band position is largely dependent on the substituent type of the catechol frame and is tentatively assigned to the 3bi (cat)→π*(aapm) transition.