Cerium Pyrazolates Grafted onto Mesoporous Silica SBA-15: Reversible CO₂ Uptake and Catalytic Cycloaddition of Epoxides and Carbon Dioxide

Abstract

The activation and catalytic conversion of CO2 is a current topic relating to molecular chemistry and materials science alike. As a transdisciplinary field of research, surface organometallic chemistry (SOMC) might be applicable to perform synergistically, thus striking a new path in sustainable chemistry. Both ceric and cerous rare-earth-metal pyrazolates, which were recently shown to reversibly insert CO2 and to promote the catalytic cycloaddition of epoxides and carbon dioxide, were grafted onto large-pore mesoporous silica SBA-15500, thermally pretreated at 500 °C. The obtained hybrid materials [Ce­(Me2pz)4]2@SBA-15500, Ce­(Me2pz)4(thf)@SBA-15500, Ce4(Me2pz)12@SBA-15500, and [Ce­(Me2pz)3(thf)]2@SBA-15500 (Me2pz = 3,5-dimethyl­pyrazolato) were characterized by DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy), solid-state 1H/13C NMR spectroscopy, elemental analysis, ICP/OES, and N2 physisorption. The lanthanum­(III)-based material [La­(Me2pz)3(thf)]2@SBA-15500 was synthesized for better assessment of the cerous materials being highly sensitive to oxidation. To mimic ceric surface species, Ce­[OSi­(OtBu)3]3Cl was treated with 1 equiv of K­(Me2pz), generating the mixed pyrazolyl/siloxy complex KCe­[OSi­(OtBu)3]4(Me2pz) featuring a cerium­(IV)-bonded terminal pyrazolato ligand. All hybrid materials show efficient and reversible carbon dioxide uptake of maximum 20 wt % in the solid state. When combined with tetra-n-butyl­ammonium bromide (TBAB), the hybrid materials catalyze the cycloaddition of CO2 and epoxides, displaying good conversion of various epoxides and reusability.

Direct coupling of CO2 with epoxides catalyzed by lanthanum(III) supported on magnetic mesoporous organosilica nanoparticles

“…As consequence, the presence of both lanthanum species and dipicolinic in the catalyst pores are crucial in getting high activity. We have also tried to experimentally show the affinity of pyridine's basic site to carbon dioxide according to the methods has already been reported by Anwander et al 43 . To do this, a pre-weighted sample of La@MON and MON were stored under 1 bar CO 2 pressure for 16 h at ambient temperature.…”

“…The use of 0.3 mol% Lanthanum chloride heptahydrate (LaCl 3 ⋅H 2 O) in homogenous form (unsupported) instead of La@MON resulted in inferior yields of styrene carbonate (Table 3 , entry 18). The higher catalytic activity of La@MON with regard to LaCl 3 ⋅H 2 O may be attributed to the presence of dipicolinic amide unites incorporated inside of mesoporous channels of catalyst, which would favor the CO 2 capturing through pyridine basic site during the reaction process as well as enchantment of metal center life time via its complexation on a solid network 43 . The studies also showed that the use of several selected catalysts such as MON, Fe 3 O 4 @mSiO 2, and Fe 3 O 4 under the same reaction conditions and with essentially the same weight, resulted in very poor yields of styrene carbonate (Table 3 , entries 19–21).…”

Recent developments on the transformation of CO2utilising ligand cooperation and related strategies

“…This allowed for complexes such as 74 to be synthesised and for the development of materials able to adsorb up to 20 wt% of CO2. 99 The insertion is reversible, acting as a "CO2 sponge" and could be exploited for the catalytic formation of cyclic carbonates from epoxides. Scheme 18.…”

Near-Infrared Photothermal Catalysis for Enhanced Conversion of Carbon Dioxide under Mild Conditions

“…Inspired by UV–vis photothermal catalysis applied in green chemistry recently, − we herein present a strategy of using composite catalysts bearing a matrix with near-infrared (NIR) photothermal effects to realize enhanced conversion of CO 2 . Based on Lewis acidity and structural priority, , cobalt and cerium monosubstituted Keggin-type POMs, K 6 SiW 11 Co­(H 2 O)­O 39 (SiWCo) and H 4 SiW 11 Ce­(H 2 O) 4 O 39 (SiWCe), are electrostatically attached on a graphene oxide (GO)­with covalently grafted branched polyethyleneimine (PEI), forming NIR photothermal catalysts, SiWCo@GO-PEI and SiWCe@GO-PEI composites (Scheme ). While PEI serves as both the connector of GO and POMs and the Lewis base, the SiWCo and SiWCe afford Lewis acid catalysts in the cycloaddition reaction.…”