Structural studies of copper catalyzed hydroxylation reactions

The reaction of 2,6-diacetylpyridine, CuCl2, and semicarbazide hydrochloride was studied as a function of pH to yield three different products: aqua(2-acetylsemicarbazone-3-hydroxo-6-acetylpyridine) chlorocopper(II) hemihydrate, 1, bis(2,6-diacetylpyridinedisemicarbazone)copper(I) chloride dimer, 2, and bis(2,6-diacetylpyridinedisemicarbazone)copper(II) chloride dimer, 3. The reaction of 1 with a mol of semicarbazide hydrochloride gave chloro(3-hydroxo-2,6-diacetylpyridinedisemicarbazone)copper(II) chloride hydrate, 4, and with a mol of semicarbazide hydrochloride and cupric chloride gave aquachlorocopper(II)(μ-chloro)(μ′-[2-acetylsemicarbazone-O,N-3-hydroxy-6-acetylsemicarbazonepyridine-O,N,N])aquacopper(II) trihydrate, 5. The crystal structures of compounds 1–5 were determined by X-ray diffraction. Some observations on the course of the reactions are given.

The reaction of CuCl2 with 2,6-diacetylpyridine and semicarbazone hydrochloride gives 3 different products depending on the pH. At a of 2. the pyridine ring was hydroxylated. while at a pH of 4.95 a Cu(I) dimer was formed. A Cu(II) dimer is the product at a pH of 7.0. The crystal structures of the three products together with two copper complexes from the reaction of the hydroxylated product are reported.Figure optionsDownload as PowerPoint slide