# Advances and Challenges in the Creation of Porous Metal Phosphonates
## 3 Applications
### Catalysis
In a later study, the above hybrid materials were evaluated as catalysts for the cycloaddition of CO\({}_{2}\) with aziridines to obtain oxazolidinones at 120 \({}^{\circ}\)C under 3 MPa pressure of CO\({}_{2}\) for 6 h under solvent-free conditions. The three zirconium phosphonate hybrids showed a high conversion of \(>\)98% and regioselectivity with yields of 85%, 79% and 90% for Zr-HEDP, Zr-ATMP, and Zr-EDTMP, respectively. Among these three hybrid catalyst systems, the Zr-HEDP displayed the highest regioselectivity of 96:4 in the formation of 3-ethyl-5-phenyloxazolidin-2-one with respect to 3-ethyl-4-phenyloxazolidin-2-one, in comparison to the Zr-ATMP (95:5) and Zr-EDTMP (90:10) hybrids. The authors proposed a mechanism wherein the proton from the -P-OH group coordinated with the N-containing aziridine and the adsorbed CO\({}_{2}\) interacted with the -OH group of the HEDP moiety. This way, the aziridine was attacked by the activated CO\({}_{2}\) (nucleophilic), leading to the formation of carbamate, followed by intramolecular ring closure resulting in oxazolidinone formation [121]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Metal Precursor** &
\begin{tabular}{c} **Phosphonic** \\ **Linker** \\ \end{tabular} & **Synthesis** & **Application—Catalysis** & **Reference** \\ \hline V(O)(\(i\)-ZrO)\({}_{3}\) & TPPHA & Non-hydrolytic condensation & Oxidation of benzylic alcohols & [81] \\ Ti(SO\({}_{4}\))\({}_{2}\) & (IR, 2S)-(-)-2-P & Precipitation & Enantioselective addition of benzaldehyde & [110] \\  & (IR, 2S)-(+)-2-P & (Hydrothermal) & benzaldehyde & \\  & Polypeptide & & & \\ Ti(O’Pr)\({}_{4}\) & capped with phosphonic acid & Non-hydrolytic condensation & Enantioselective hydration of styrene oxide & [111] \\  & moiety & & & \\ ZrCl\({}_{4}\) & HEDP & Precipitation/Hydrothermal & methyl-2,3-O-isopropylidene-\(\beta\)-D-ribofuranoside & [112] \\ SnCl\({}_{4}\) & PEHMP & Precipitation/Hydrothermal & Oxidation of cyclohexanone to adipic acid in absence of peroxides & [116] \\ FeCl\({}_{3}\) & BTP & Precipitation/Hydrothermal & Transesterification for synthesis of biofuels & [115] \\ SnCl\({}_{4}\) & BTP & Precipitation/Hydrothermal & Synthesis of 1,4-dihydropypropylidines & [117] \\ MoCl\({}_{5}\) & BTP & Precipitation/Hydrothermal & Synthesis of benzimidazolees & [118] \\ CoCl\({}_{2}\) & DPTMP & Hydrothermal & Catalytic oxidation of methylene blue & [119] \\  & HEDP & & Hydrolysis of ethyl acetate; & \\ ZrOCl\({}_{2}\) & ATMP & Precipitation/Hydrothermal & esterification of acetic acid with ethanol and cyclohexanol & [114] \\  & EDTMP & & ethanol and cyclohexanol & \\ ZrOCl\({}_{2}\) & ATMP & Precipitation/Hydrothermal & Cycloaddition of aziridines and CO\({}_{2}\) & [121] \\  & EDTMP & & Oxidation of cyclohexanone to adipic acid & [120] \\ FeCl\({}_{3}\) & HEDP & Precipitation/Hydrothermal & adipic acid & \\ \hline Abbreviation: TPPHA = tetrakis-1,3,5,7-(4-diethylphosphonatophenyl)adamantane; (IR,2S)-(-)-P = (IR,2S)-(-)-2-[N-(diethylethylphosphononate)]imino-1,2-diphenylethanol; (IR, 2S)-(+)-P = (1R,2S)-(+)-2-[N-(diethylethylphosphononate)]imino-1,2-diphenylethanol; HEDP = 1-hydroxyethane 1,1-diphosphonic acid; PEMP = pentachloryleneamine-octakis-(methylphosphonic acid); BTP = benzene 1,3,5-triphosphonic acid; DTPMP = diethylenediamine penta(methylphosphonic acid); ATMP = aminotri(methylene phosphonic acid); EDTAMP = ethylenediamine tetra(methylbenzene phosphonic acid). & [120] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of the porous metal phosphonates for catalytic application. Figure 9: (**A**)—probable reaction mechanism and the role of the HSnP-2 catalyst in selective synthesis of 1,4-dihydropyproidines. Reprinted with permission from [117]. Copyright (2013), The Royal Society of Chemistry and (**B**)—dependence of the product yield on various catalysts for the aerobic oxidation of cyclohexanone at 75 \({}^{\circ}\)C. Reprinted with permission from [120]. Copyright (2016), American Chemical Society.