The effect of steric hindrance in the synthesis of corrolates via the cobalt catalyzed cycliztion of 2-(α-hydroxyalkyl)pyrroles

Article abstract of DOI:10.1016/0020-1693(95)90040-D

2-(α-hydroxyalkyl)pyrroles react in the presence of cobalt ions leading to the formation of corrolates or porphyrinates as function of the2-substituents. The nature of the cyclic tetrapyrrole obtained can be r elated to the steric hindrance of the substituent present in the starting pyrrole. The presence of cobalt ions is essential to drive the reaction towards the formation of the contracted corrole macroring. When 3-ethyl-4-methyl-2-(α-hydroxybenzyl)pyrrole-5-carboxylic acid is used asstarting material an etio-like cobalt corrolate, i.e. with alternate me thyl and ethyl groups on the β-pyrrolic positions, has been obtained as demonstrated by detailed analysis of the NMR spectrum of the complex. A possible reaction pathway explaining the formation of such a species is reported.