New olefinic centred binuclear clamshell type phthalocyanines: Design, synthesis, structural characterisation, the stability and the change in the electron cloud at olefine-based symmetrical diphthalonitrile fragment by the combined application of UV–Vis

The olefinic centred Schiff base (3) was obtained from the condensation of substituted dialdehyde (1) with 2-amino-4-methylphenol (2) in a 1:2 ratio. The diphthalonitrile derivative (5) was prepared by the reaction of 4-nitrophthalonitrile (4) and compound (3) in dry dimethylformamide/potassium carbonate. The key product (5) was obtained by nucleophilic substitution of an activated nitro group into an aromatic ring. The cyclotetramerization of compound (5) with phthalonitrile (6) in 1:6.15 ratio gave the expected metal-free phthalocyanine of clamshell type (7), and with metal salts of Zn(II), Ni(II), Co(II) and Cu(II) gave metallophthalocyanines of clamshell types (8–11), respectively in dimethylaminoethanol/1,8-diazabycyclo[5.4.0]undec-7-ene system. The products were purified by several techniques such as crystallization and preparative thin layer chromatography. The newly prepared compounds were characterised by a combination of elemental analyses, IR, 1H/13C NMR, MS and UV–Vis spectroscopy.

Graphical abstractThe synthesis of diphthalonitrile derivative (5) was performed by the reaction of 4-nitrophthalonitrile (4) and compound (3) in dry dimethylformamide/potassium carbonate. The cyclotetramerization of compound (5) with phthalonitrile (6) in 1:6.15 ratio gave the expected metal-free phthalocyanine of clamshell type (7), and with metal salts of Zn(II), Ni(II), Co(II) and Cu(II) gave metallophthalocyanines of clamshell types (8–11), respectively in dimethylaminoethanol/1,8-diazabycyclo[5.4.0]undec-7-ene system. The products were purified by several techniques such as crystallization and preparative thin layer chromatography. The newly prepared compounds were characterised by a combination of elemental analyses, IR, 1H/13C NMR, MS and UV–Vis spectroscopy.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Schiff base (3) was synthesized with no solvent. ► Diphthalonitrile (5) was synthesized in DMF at 60 °C. ► The structure of key product (5) was also established by theoretical criterion. ► H2Pc (7) was synthesized directly by compoumds (5) and (6). ► MPcs (8-11) were obtained from (5), (6) and corresponding metal salts.