Superparamagnetic Poly(aniline-co-m-phenylenediamine)@Fe3O4 Nanocomposite as an Efficient Heterogeneous Catalyst for the Synthesis of 1H-pyrazolo[1,2-a]pyridazine-5,8-diones & 1H-pyrazolo[1,2-b]phthalazine-5, 10-diones Derivatives
Authors: Nezhad Shefa Mirani , Pourmousavi Seied Ali , Zare Ehsan Nazarzadeh 
Published: November 2021

Background:
The use of polymer-based catalysts has increased because of their high potential application as an effective catalyst in organic reactions. They have benefits such as high efficiency and reactivity, simple separation, and safety compared to other heterogeneous catalysts.

Aim and Objective:
The objective of the current research is to prepare solid polymer-based catalysts, poly(aniline-co-m-phenylenediamine) (PAmPDA), and its superparamagnetic nanocomposite. Then, the catalytic activity of the resulting superparamagnetic nanocomposite was investigated in the synthesis of 1H-pyrazolo[1,2-b]phetalazine-5,10-diones and 1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives. A series of some 1H-pyrazolo[1,2-b]phetalazine-5,10-diones and 1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives was tested for its antibacterial properties against the Staphylococcus aureus and E. coli bacteria.

Materials and Methods:
PAmPDA copolymer was synthesized in a 1:2 molar ratio of Ani to mPDA via radical oxidative polymerization at room temperature. Superparamagnetic PAmPDA@Fe3O4 nanocompo-site was synthesized from a mixture of Fe(II), Fe(III) solution, and PAmPDA copolymer via the in-situ co-precipitation technique. 1H-pyrazolo[1,2-b]phetalazine-5,10-diones were synthesized via one-pot three-component condensation reaction of Phthalhydrazide, aromatic aldehyde derivatives, and malono-nitrile in the presence of PAmPDA under solvent-free conditions at 80 °C. The synthesis of 1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives was carried out via a one-pot three-component condensa-tion reaction of maleic hydrazide, aromatic aldehyde derivatives, and malononitrile in the presence of PAmPDA under reflux conditions at EtOH/H2O 1:1. The antibacterial activity of some derivatives was tested against Gram-positive and Gram-negative bacteria.

Results:
First, superparamagnetic PAmPDA@Fe3O4 nanocomposite was synthesized and characterized successfully, and then the resulting nanocatalyst was used for the synthesis of pyrazolo[1,2-b]phthalazine and pyrazolo[1,2-a]pyridazine. We obtained the maximum yield of the desired 1H-pyrazolo[1,2-b]phthalazine-5,10 dione derivatives with 0.05 g of catalyst at 80°C, under solvent free conditions, whereby the reaction was complete within 30 min. A wide range of 1H-pyrazolo[1,2-b]phthalazine-5,10 dione derivatives were synthesized in good to excellent yield. On the other hand, pyrazolo[1,2-a]pyridazine derivative was synthesized successfully in high yield using PAmPDA as a nanocatalyst.
The antibacterial activity of some derivatives, according to the data (inhibition zone%), showed good ac-tivity against Staphylococcus aureus and E. coli.

Conclusion:
In this research, PAmPDA was used for mild preparation of 1H-pyrazolo [1,2-a]pyridazine-5,8-diones & 1H-pyrazolo[1,2-b]phetalazine-5,10-diones derivatives with excellent yields and short reac-tion times. The attractive features of this protocol are simple procedure, cleaner reaction, and the use of recyclable nanocatalyst. Satisfactory yields of products and easy workup make this a useful protocol for the green synthesis of this class of compounds. The antibacterial activity of some derivatives, according to the data (inhibition zone%), showed good activity against Staphylococcus aureus and E. coli.