Synthesis and characterization of salen-type ligands functionalized with pyrrole derivative pendant arms

Several salen-type ligands functionalized with two pyrrole derivative pendant arms were prepared. These Schiff base ligands, which differ in the imine bridge, were prepared by a multi-step procedure that includes (i) synthesis of 3-pyrrol-1-ylpropanoic acid, (ii) transformation of the latter compound into the mixed carboxylic-carbonic anhydride (MCCA) intermediate followed by reaction with 2,3-dihydroxybenzaidehyde to give (3-formyl-2-hydroxyphenyl) 3-(pyrrol-1-yl)propanoate and finally (iii) Schiff condensation of the different 1,2-diamines with (3-formyl-2-hydroxyphenyl) 3-(pyffol-1-yl)propanoate. The key step in the Schiff base ligand preparation is the functionalization of the 2,3-dihydroxybenzaldehyde at the C-3 hydroxyl group without protection of the C-2 hydroxyl group, by a regiospecific acylation of the ortho-hydroxyl group via esterification with the mixed carboxylic-carbonic anhydride of 3-pyrrol-1-ylpropanoic acid. The compounds were characterized by elemental analyses, H-1 and C-13 NMR spectroscopy, mass spectrometry and FTIR and UV-visible spectrophotometry. Copyright (c) 2005 John Wiley & Sons, Ltd.