An insight into the vicarious nucleophilic substitution reaction of 2-nitro-5,10,15,20-tetraphenylporphyrin with p-chlorophenoxyacetonitrile: Synthesis and gas-phase fragmentation studies

Meso-tetraarylporphyrins bearing nitro groups are considered as excellent templates to introduce new functionalities in the porphyrin core, namely through reactions with nucleophiles. Here the reaction of 2-nitro-5,10,15,20-tetraphenylporphyrin with p-chlorophenoxyacetonitrile was revisited and it was found that the reaction profile was strongly dependent on the presence or absence of a metal ion in the porphyrinic inner core and on the solvent used. Under the studied synthetic conditions several porphyrins modified at neighbouring β-positions with nitro, amino, ether, ester, nitrile, methylcyano and formyl functionalities were isolated. Most of them are suitable for further modifications and/or conjugation to other substrates or materials. The gas-phase fragmentation studies corroborated the proposed structures. In general, the formation of the main fragment ions involves intramolecular cyclization processes with the formation of five or six-membered rings between the β-pyrrolic and the ortho position of the adjacent meso-phenyl group.