Efficient heterogeneous catalyst of Fe(II)-based coordination complexes for Friedel-Crafts alkylation reaction

In this study, two stable Fe(II) coordination compounds, namely [Fe(Hdtp)2](H2O)3 (1) and [Fe(dtp)(H2O)3](H2O)0.5 (2) (H2dtp is 4'-(3,5- dicarboxyphenyl)-2,2':60,200-terpyridine), are constructed by hydrothermal reaction of H2dtp with different iron source (Fe(II) and Fe powder) under acidic condition, which afford the activated sites of carboxylic group and Lewis acid sites exist in 1 and 2, respectively. The catalytic activity of 2 is found superior to 1 when used as catalyst for the Friedel-Crafts reaction of beta-nitroalkenes and indoles under ambient conditions. The high activity of 2 may be attributed to the sufficient coordination sites in Fe(II) for intermediate formation by coordination interaction with beta-nitroalkenes, which enhance the electrophilic character of beta-nitroalkenes and further facilitate the attack from the indole. The catalyst 2 is high functional group and solvent tolerance, and can be readily recycled and reused at least 3 times without loss of catalytic activity significantly. This work provides a new strategy for the synthesis of indole alkaloids under ambient conditions.

Automated summary

In this study, two stable Fe(II) coordination compounds were synthesized and showed different catalytic activities when used for the Friedel-Crafts reaction. Compound 2 exhibited superior catalytic activity compared to 1 due to the coordination sites in Fe(II) facilitating intermediate formation and enhancing the electrophilic nature of beta-nitroalkenes. The high functional group and solvent tolerance of catalyst 2 allows for at least 3 times of recycling and reuse without significant loss of catalytic activity. This work presents a new strategy for the synthesis of indole alkaloids under ambient conditions.