Silica nanospheres supported diazafluorene iron complex: an efficient and versatile nanocatalyst for the synthesis of propargylamines from terminal alkynes, dihalomethane and amines

We present the synthesis of an efficient heterogeneous silica nanosphere supported iron catalyst (SiO2@APTES@DAFO-Fe) and its catalytic application in a one pot three-component coupling reaction of terminal alkynes, dihalomethane and secondary amines for the facile synthesis of propargylamines. The synthesized SiO2@APTES@DAFO-Fe nanocatalyst has been systematically characterized by solid-state C-13 CPMAS and Si-29 CPMAS NMR spectroscopy, fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), atomic absorption spectroscopy (AAS), energy dispersive X-ray fluorescence spectroscopy (ED-XRF), and elemental analysis. The nanocatalyst exhibits high catalytic performance for the coupling reaction of aromatic terminal alkynes, dichloromethane and secondary amines to afford propargylamines. In order to achieve high catalytic efficacy, the effect of various reaction parameters such as temperature, base, the amount of catalyst, reaction time, type of solvent, substrate molar ratio etc. have been investigated. Furthermore, the recovery and reuse of the quasi-homogeneous nanocatalyst have been demonstrated several times without any appreciable loss in its catalytic activity. Apart from this, FT-IR, SEM and HRTEM techniques are employed in order to prove the stability of the reused nano-catalyst. The present protocol works under mild reaction conditions with the additional advantages of a simple work-up procedure, high product yield, and easy recovery and reusability of the nanostructured catalyst. It is noteworthy that this atom economical methodology does not require an additional co-catalyst or activator. A tentative mechanism is also proposed for the one pot coupling reaction for the synthesis of propargylamines.