Coupling of o and/or m-substituted arylamines with the ortho-C–H function of the pendant aryl ring in coordinated arylazopyrimidinepalladium(II) complexes. Spectral and electrochemical characterisation of the products

Abstract

2-(Arylazo)pyrimidines (aapm) are N,N′-chelators which form palladium(II) complexes, Pd(aapm)Cl2(1). The reaction of Pd(aapm)Cl2(1) with arylamines (ArNH2) yields Pd(aapm-N-Ar)Cl, (2)–(7), complexes of the tridentate N,N′,N″-donor system in which arylamines are fused to the ortho C–H function of the pendant aryl ring in the coordinated 2-(arylazo)pyrimidine, leading to the C–N coupled product. Pd(aapm-N-Ar)Cl, complexes (2)–(7), exhibit a broad intense absorption band in n.i.r. region (870–920 nm), while the parent complex, Pd(aapm)Cl2, shows an intense absorption at 425 nm. Cyclic voltammograms of (2)–(7) exhibit an oxidation couple at positive potential to s.c.e. together with three reductions at negative side. The oxidation may involve conversion of the chelated azoarylamine to semibenzoquinone azoarylamine fragment. The reduction is due to the accommodation of electrons in the azoimine function. The absorption spectra in the n.i.r. region may be regarded as HOMO → LUMO intravalence charge transfer (i.v.c.t.) transitions.