Chemistry of azopyrimidines. Part IV. Aromatic hydroxylation in palladium(II)-arylazopyrimidines

摘要

2-(Arylazo)pyrimidines (aapm) are N,N'-chelating ligands and synthesise orange-red complexes of composition [Pd(aapm)Cl_2], 1, with Pd(MeCN)_2Cl_2 in MeCN. The complex has cis-PdCl_2 configuration [v(Pd-Cl): 360 cm~-1]. The Treatment of Tollen's reagent ('AgOH') leads to chelatative hydroxylation in the Pendant aryl ring, affording a green phenolato complex, Pd(aapmO)Cl, 5 (aapmO is Deprotonated 2-((8-hydroxo)arylazo)pyrimidine). The reaction is also carried out by Controlled addition of dilute sodium hydroxide in air or by the addition of PhIO/m- Chloroperbenzoic acid to a MeCN suspension of the comples. A single Pd-Cl stretch At 360 cm~-1 supports the composition of phenolato complex. Unlike Pd(aapm)Cl_2 the Hydroxylated product, Pd(aapmO)Cl, has a structured intense absorption in the visible Region near 670 nm. The Pd-Cl bond in Pd(aapmO)Cl is highly sensitive to Nucleophilic substitution and slowly hydrolyses in aqueous medium.