Synthesis and separation of the constitutional isomers of 1(4),8(11),15(18),22(25)-tetrakis[(pentyloxycarbonyl)phenoxy]-phthalocyaninato zinc(II) complexes

Cyclic tetramerization of 3-[(methyloxycarbonyl)phenoxy]phthalonitrile (1a–1c) in the presence of Zn(OAc)2·2H2O and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by transesterification in refluxing n-pentanol afforded 1(4),8(11),15(18),22(25)-tetrakis[(pentyloxycarbonyl)phenoxy]phthalocyaninato zinc(II) complexes (2a–2c) as a mixture of four constitutional isomers. Simple silica-gel column chromatography leads to the successful separation of pure isomers with the C4h and D2h symmetry together with a section containing the C2v and Cs isomers, which have been characterized with a wide range of spectroscopic methods including MALDI-TOF mass, electronic absorption, 1H NMR, and 2D COSY spectroscopy. Synthesis yields in combination with the NMR spectroscopic results reveal that the distribution of the four isomers in the final product for 2a–2c does not strictly follow that expected according to statistical calculation with the ratio of C4h:C2v:Cs:D2h = 1:2:4:1, indicating the effect of steric hindrance of substituents on the formation of various constitutional isomers.

Graphical abstractCyclic tetramerization of 3-[(methyloxycarbonyl)phenoxy]phthalonitrile in the presence of Zn(OAc)2·2H2O and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by transesterification in refluxing n-pentanol afforded the four constitutional isomers of 1(4),8(11),15(18),22(25)-tetrakis[(pentyloxycarbonyl)phenoxy]phthalocyaninato zinc(II) complexes, which in particular the C4h and D2h isomers have been easily separated by simple silica-gel column chromatography.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A series of 1(4),8(11),15(18),22(25)-substituted phthalocyanines have been prepared. ► The C4h and D2h isomers have been separated on simple silica-gel column chromatography. ► The distribution of all isomers could be determined by the NMR spectroscopic results.