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 ](H 2 O) 3 ( 1 ) and [Fe(dtp)(H 2 O) 3 ](H 2 O) 0.5 ( 2 ) (H 2 dtp is 4'-(3,5- dicarboxyphenyl)-2,2':6′,2″-terpyridine), are constructed by hydrothermal reaction of H 2 dtp 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 β- 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 β- nitroalkenes, which enhance the electrophilic character of β- 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. Two new Fe(II) complexes containing dangling carboxylic group (compound 1 ) and Lewis acid site (compound 2 ) as active sites were successfully synthesized. A series of heterocyclic compounds with indole and β -nitrostyrene derivatives were synthesized in good yields by Friedel-Crafts alkylation reaction with 2 as catalyst, suggesting a higher catalytic activity of Lewis acid site over H-bond interaction. • Two Fe(II) complexes containing dangling carboxylic groups and Lewis acid site as active sites are presented. • Complex 2 shows good applicability in catalyzing the synthesis of a series of FC reactions with high stability for recycling. • The higher activity ​of ​Lewis ​acid ​site ​over ​H-bond ​interaction in ​catalyzing ​the ​FC ​reaction was witnessed in this case.