Efficient and Reusable Metal Heterogeneous Catalysts for Conversion of CO₂Prepared from a Microwave Synthetized Porous Polyiminopyridine

Abstract

A stable nitrogen‐rich porous polyimine containing pyridine units (PIPy‐4Mw) was successfully synthesized under microwave heating via a simple “one‐step” polycondensation in only 30 min without adding any catalyst. This versatile polymer can incorporate different transition metals leading polyiminopyridine‐supported catalysts; in this paper we report the synthesis and catalytic performance of heterogenized complexes of abundant earth metals such as iron(II), cobalt(II) and chromium(III) (PIPy‐4MwFe, PIPy‐4MwCo and PIPy‐4MwCr). These supported metal‐polyiminopyridines have been applied as heterogeneous catalysts in the conversion of CO2 into cyclic carbonates, an interesting reaction to recycle CO2, and in another eco‐friendly reaction: the synthesis of additives for diesel fuels by acetalization of furfural. The cobalt and iron complexes have showed high efficiency and were reused without any significant change in their activities.

Accessible microwave synthetized conjugated poly(azomethine‐pyridine) network and its metal complexes for CO2conversion

“…The decomposition temperature of the metal supported poly(azomethine‐pyridine)s was around 380 °C (Fig. ), lower than the corresponding starting support as it was previously reported for metal‐containing polymers …”

“…Recently, we have reported that CO 2 can be converted into cyclic carbonates using metal porous polymers at relatively mild conditions: 7 atm of CO 2 , 100 °C, without solvent, with relationships epoxide/metal of 1500 and in the presence of a base as dimethylaminopyridine (DMAP), which improve the activity of the catalysts generating more electron‐rich centers in the metal . Following this protocol and styrene oxide as substrate model, we found that all supported metal–poly(azomethine‐pyridine)s (Table , Entries 1–4) result very effective catalysts with high conversions, between 91% and 98%, and with the formation of cyclic carbonate as unique product (see 1 H‐NMR spectrum in Supporting Information, Fig.…”

“…Besides, short the reaction time, it is a more environmentally friendly procedure than conventional synthesis of PAMs. As far as we know, microwave irradiation has only been used with tri‐ or tetra‐functionalized monomers to produce porous Schiff base polymers …”

“…Ruthenium has received extensive attention because its metal complexes are active in many organic reactions, in the cycloaddition of CO 2 to epoxides among others . However, aluminum, iron, and cobalt are also very interesting because they are abundant earth metals, less toxic, and expensive than ruthenium and other metals and some of its homogeneous or heterogeneous metal complexes are also active in the above reaction . Finally, we have tested all metal heterogeneous catalysts for the cycloaddition of CO 2 to styrene oxide and epichlorohydrin to produce the corresponding cyclic carbonates.…”

Conversion of CO2 into Chloropropene Carbonate Catalyzed by Iron (II) Phthalocyanine Hypercrosslinked Porous Organic Polymer

“…However, iron could be considered as the optimum choice from a sustainable approach because it is cheap, earth abundant, and has relatively low toxicity [ 8 ]. Thus, in the last few years, some heterogeneous iron catalysts, that effectively promote this reaction, have been reported, e.g., iron doped mesoporous zeolites [ 9 , 10 ], a porous covalent triazine-based polymer containing iron oxide nanoparticles [ 11 ] and some iron-based poly(azomethine)s [ 12 , 13 , 14 ]. All reactions carried out with iron-containing heterogeneous catalysts produced cyclic carbonates in high yields, using CO 2 pressures between 3 and 20 bar and reaction temperatures in the range of 50–120 °C [ 9 , 10 , 11 , 12 , 13 , 14 ].…”