# Phenylphosphonic acid corroles: corroles that link and bind

Gaëlle Divoux, Margerie Loze, Yoann Rousselin, Stéphane Brandès, Claude P Gros, Nicolas Desbois, Laurie André

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Gaëlle Divoux, Margerie Loze, Yoann Rousselin, Stéphane Brandès, Claude P Gros, et al.. Phenylphosphonic acid corroles: corroles that link and bind. Dalton Transactions, 2025, 54 (5), pp.1784-1790. 10.1039/d4dt03197k. hal-05401335

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Submitted on 5 Dec 2025

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# Phenylphosphonic acid corroles: corroles that link, corroles that bind

Gaëlle Divoux,† Margerie Loze,† Yoann Rousselin, Stéphane Brandès, Claude P. Gros,*

Nicolas Desbois,* and Laurie André*

**Abstract.** We report herein the synthesis and full spectroscopic characterization of two A₂B-corroles phosphonic acid. Thanks to the presence of a phosphonic acid functional group at the 10-meso position, the corroles were covalently linked to the hexanuclear Zr clusters of a PCN-222 Metal Organic Framework (MOF). After the insertion of cobalt into the corrole macrocycle, the metal complexes are able to bind small volatile molecules such as carbon monoxide (CO). Interestingly, the resulting doped porous materials were used for selective detection of CO, with excellent selectivity for CO vs. CO₂, N₂, and O₂.

**Introduction.** Carboxylic and phosphonic acid functional groups have been widely used to anchor porphyrins onto the surface of organic and inorganic materials. While various substituted corroles bearing carboxylic groups, clickable functional groups or vinylic groups for further NIP and MIP polymerization have been widely described in the literature, only A₃-corrole bearing phosphonic acid groups has been reported so far in the literature.¹, ² At the same time, many examples of surface modifications using organophosphonates and organophosphonic acids have appeared in many different different fields such as immobilization of catalysts, biological microarrays...³⁻⁵ In this work, two A₂B-corroles functionalized with a phosphonic acid function at the *para*-position of the *meso*-10-phenyl substituent were synthesized (*Scheme* 1) and fully characterized. The difference between the two corroles lies on the electron withdrawing groups added at the 2,6-aryl positions which were expected to affect the Lewis acid character of the cobalt(III) centre,⁶,⁷ and thus influence the efficiency of the CO binding to the corrole complex at low pressure. Indeed, we have previously reported that the affinity of cobalt corroles for CO depends both on the presence of a cobalt(III) ion but also on the Lewis acid character of the metal center.⁸⁻¹¹

<figure><img src="image_2.png" /><figcaption>**Scheme 1.** Synthesis of phenylphosphonic acid corroles 2a and 2b</figcaption></figure>

## Results.

**Synthesis of corroles 2a and 2b.** 5,15-(2,6-dichlorophenyl)-10-diethylphenylphosphonic acid corrole (2a) and 5,15-(2,3,5,6-tetrafluorophenyl)-10-diethylphenylphosphonic acid corrole (2b) were prepared following the standard procedure described for the synthesis of A₂B-corroles using 0.5 equiv. of diethyl(4-formylphenyl)phosphonate and 1.0 equiv. of the corresponding dipyrrromethane (Supporting Information). Hydrolysis of the diethylphosphonate groups was then performed using bromotrimethylsilane leading to the target acid phosphonic corroles in almost quantitative yields and with no further purification. The compounds were fully characterized by MALDI/TOF (low MS) and ESI (HRMS), UV-Vis. and FTIR spectroscopy, ¹H, ³¹P and ¹⁹F NMR spectroscopy. An X-ray diffraction experiment was also carried out to fully confirm the structure of corrole **1b** (Figure 1). Single clear dark violet, prism-shaped crystal crystals of **1b** were isolated after recrystallization from a mixture of DCM and cyclohexane. Detailed information for the crystallographic data collection and refinement are given in the Supporting Information. The arrangement of atoms in the solid form of compound **1b** (Figure 1) is typical of -C₆F₄H-substituted corroles without a central metal atom. Three of the four pyrrole rings lie almost flat in a plane, while the remaining one bends out of plane and forms a Hydrogen bond with an oxygen atom from a nearby molecule. On average, the entire 23-atom ring system deviates by only 0.226 Å from a perfect plane, with the hydrogen-bonding pyrrole being the most out-of-plane at 0.424 Å. In Figure 2, the crystalline packing is shown along the *a* axis. The second molecule is generated via an inversion center (space group P-1). There is only one intermolecular Hydrogen bond, connecting the oxygen O2 of the phosphonate group to the proton of the nitrogen atom N2 (N2-H2···O2 = 2.812(2) Å). This nitrogen atom N2 is distinctly oriented out of the porphyrin plane (-0.424 Å), as are the carbon atoms C8 (0.548 Å) and C9 (0.515 Å) of the same pyrrole group.
<figure><img src="image_3.png" /><figcaption>**Figure 1.** ORTEP view of corrole **1b**. Thermal ellipsoids are drawn at 50% probability level. DCM solvent is omitted for clarity.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Figure 2.** View of the crystal packing of corrole **1b** along a crystallographic axis. Intermolecular Hydrogen bonds are depicted with blue dashed lines.</figcaption></figure>

**Synthesis of the PCN-222.** PCN-222 was synthesized through a modified solvothermal method similar to procedures reported in the literature.¹², ¹³ After the synthesis, PCN-222 was further activated by washing the MOF thoroughly with a solution of 0.1M HCl/Acetone in order to remove the modulator, dichloroacetic acid, present on the metal cluster. This activation releases the vacancies naturally present on the PCN-222 metal cluster and frees position for further modification.

**Synthesis of CoCorr(2a)@PCN-222 and CoCorr(2b)PCN-222.** The two studied corroles **2a** and **2b** were introduced to the activated PCN-222 by grafting on the free metal cluster vacancies of the MOF by reacting with the phosphonic acid functions. The grafting of the corroles **2a** and **2b** respectively give the materials **Corr(2a)@PCN-222** and **Corr(2b)@PCN-222**. The two obtained materials were then further metalated with cobalt (insertion of Co inside the corrole macrocycles grafted inside the MOF) to obtain **CoCorr(2a)@PCN-222** and **CoCorr(2b)PCN-222**, respectively for PCN-222 containing the cobalt complex of grafted corrole **2a** and for PCN-222 containing the cobalt complex of grafted corrole **2b**.

**Characterization of CoCorr(2a)@PCN-222 and CoCorr(2b)PCN-222 and structure stability.** The corrole grafting ratio was calculated as the ratio of corrole present in the material *per* porphyrin expected in the activated PCN-222, and it was determined using ¹H NMR by breaking down the materials using a solution of DCl and NaF in DMSO-d₆. The corrole grafting ratio were thus obtained with 0.2 corrole *per* porphyrin in **CoCorr(2a)@PCN-222** and 0.39 in **CoCorr(2b)PCN-222**. ICP measurements (**Table S5**) reveal a metalation ratio of the grafted corroles of 80 % for **CoCorr(2b)PCN-222**. For **CoCorr(2a)@PCN-222**, the cobalt ICP measurement is lower than expected, as systematically observed in all our samples with less than a certain quantity of corrole grafted (lower than 0.35).⁹ The structural stability of all the synthesized materials was studied using Powder XRD (PXRD) (**Figure 3**). All the materials present the same crystal structure, and the final materials
CoCorr(2a)@PCN-222 and CoCorr(2b)PCN-222 maintain a stable and crystalline structure after overcoming the several modification steps required for their synthesis (Table S6.).

<figure><img src="image_5.png" /><figcaption>Figure 3. Powder XRD analysis of the materials along the different modification steps.</figcaption></figure>

## Porosity measurements.

Further analysis of all the synthesized materials by BET measurements revealed the presence of both micropores and mesopores through a combination of typical adsorption type I and IV isotherms (Figure 4). Specific areas of 1893.4 m² g⁻¹ and 1880.1 m² g⁻¹ were recorded for Corr(2a)@PCN-222 and Corr(2b)@PCN-222 respectively. Both measurements are lower than those recorded for the as synthesized PCN-222, 1947.6 m² g⁻¹, and for the activated PCN-222, 2143.0 m² g⁻¹, which is coherent with the fact that corroles 2a and 2b have been grafted successfully inside the PCN-222, resulting in less space in the MOF pores (Table 1).

<figure><img src="image_6.png" /><figcaption>Figure 4. N₂ adsorption isotherms recorded at 77 K for PCN-222, activated PCN-222 and grafted PCN-222 with corroles 2a and 2b.</figcaption></figure>

<table><caption>**Table 1.** Specific area for PCN-222, activated PCN-222 (act PCN-222), and PCN-222 grafted with corroles 2a and 2b (noted Corr(2a)@PCN-222 and Corr(2b)@PCN-222. a) and b) two side views of PCN-222 MOF.</caption><thead><tr><th></th><th>PCN-222</th><th>act PCN-222</th><th>Corr(2a)@PCN-222</th><th>Corr(2b)@PCN-222</th></tr></thead><tbody><tr><td>Specific area (m² g⁻¹)</td><td>1947.6</td><td>2143.0</td><td>1893.4</td><td>1880.1</td></tr></tbody></table>

<figure><img src="image_7.png" /></figure>
Carbon Monoxide and Carbon Dioxide adsorption.

Gas sorption measurements were conducted on **CoCorr(2a)@PCN-222** and **CoCorr(2b)@PCN-222**. The DMSO ligand resulting from the cobalt metalation step was first exchanged with the more labile NH₃(g) ligands in order to allow the facile activation (removal of the axial ligands) of the corroles cobalt sites. Heating at 80 °C under vacuum removes the two NH₃(g) molecules coordinated on the cobalt centers, and make them readily available for further CO(g) coordination. Then, the adsorption isotherms of CO(g) vs. CO₂(g), O₂(g) and N₂(g) were recorded (Figure 5). For both samples, the steep slope corresponding to CO(g) adsorption at low pressure is assigned to an efficient chemisorption process involving binding to the cobalt corrole. In parallel, a significant CO₂(g) intake through physisorption is noted, while N₂(g) and O₂(g) adsorbed volumes remain low and confirm the selectivity of the material for CO(g) thanks to a chemisorption process. Indeed, the CO(g) sorption shows a strong increase at very low pressure (< 0.01 atm) that corresponds to a selective sorption of CO(g) on unsaturated sites of cobalt corroles. After saturation of the cobalt sites, physisorption takes over from chemisorption and this phenomenon results in a straight linear sorption process (Henry-type isotherm) for P/P₀ > 0.02. For **CoCorr(2a)@PCN-222**, at 1 atm, the CO(g) volumes adsorbed were 13.03 cm³ g⁻¹ and the CO₂(g) volume adsorbed were equal to 31.35 cm³ g⁻¹. **CoCorr(2b)@PCN-222** demonstrated better CO sorption, also due to a more efficient grafting of the corrole, and the volumes adsorbed at 1 atm were determined to be 15.93 cm³ g⁻¹ for CO(g) and 30.50 cm³ g⁻¹ for CO₂(g).

In order to describe more precisely the CO(g) selectivity of our materials, the isotherms were fitted with a double site Langmuir model for CO(g) adsorptions and with a single site Langmuir model for CO₂(g), O₂(g) and N₂(g). Fitting curves and fitting parameters are given in **Figure S25** and **S26**, and in **Table S7** and **S8**. Selectivity of the two materials for CO(g) over CO₂(g), O₂(g) and N₂(g) was calculated using Henry selectivity at 298 K at zero loading and are given in **Table 2**. These calculations allow to confirm the relatively high selectivity of CO(g) over CO₂(g), O₂(g) and N₂(g), especially at low pressure were selectivity values up to 215 and 1000 for selectivity of CO(g) over N₂(g) and down to 27 and 205 for selectivity of CO(g) over CO₂(g) for **CoCorr(2a)@PCN-222** and **CoCorr(2b)@PCN-222** respectively. Best results for CO(g) over N₂(g), CO₂(g) and O₂(g) was obtained for **CoCorr(2b)@PCN-222**. In addition, if we consider the selectivity, the CO uptake at low pressure (< 0.05 atm), the repeatability of the sorption measurements and the ease of the scale-up synthesis (corrole **2b** versus corrole **2a**), it turns out that **CoCorr(2b)@PCN-222** is the best candidate to functionalize PCN-222 by a corrole for further applications in capture or detection of CO. To compare with our previous work (**Table 2**), PCN-222 previously grafted with carboxylic acid corroles⁹ gives better chemisorption and selectivity than the PCN-222 grafted with phosphonic acid corroles. In order to increase grafted material selectivity, we will need to improve the grafting ratio and the cobalt metalation of the corroles inside the MOFs.

<table><caption>**Table 2.** Henry selectivity for PCN-222 grafted with corroles **2a** and **2b** for CO over N₂, O₂ and CO₂ at 298 K at zero loading compared with Henry selectivity for PCN-222 grafting with carboxylic acid cobalt corroles⁹ and cobalt corroles based POP⁸.</caption><thead><tr><th>Material</th><th>CO / N<sub>2</sub></th><th>CO / O<sub>2</sub></th><th>CO / CO<sub>2</sub></th><th>Grafting ratio</th><th>Ref</th></tr></thead><tbody><tr><td>CoCorr(2a) @PCN-222</td><td>215</td><td>98</td><td>27</td><td>0.2</td><td>tw</td></tr><tr><td>CoCorr(2b) @PCN-222</td><td>1000</td><td>831</td><td>205</td><td>0.39</td><td>tw</td></tr><tr><td>CoCorr3@PCN-222</td><td>1776</td><td>1474</td><td>317</td><td>0.35</td><td>9</td></tr><tr><td>POP-CorCo-2</td><td>15700</td><td>7380</td><td>1880</td><td>/</td><td>8</td></tr></tbody></table>

<figure><img src="image_8.png" /><figcaption>**Figure 5.** Adsorption measurements of CO, CO₂, O₂ and N₂ for a) **CoCorr(2a)@PCN-222** and b) **CoCorr(2b)@PCN-222**.</figcaption></figure>
**Conclusion.** In conclusion, we have developed the synthesis of A₂B-corrole bearing a phosphonic acid group at the 10-meso position, which allows further linking within the cavities of the PCN-222 MOF. After cobalt metalation of the corrole macrocycle, the modified MOFs display selective CO binding with high selectivity for CO vs. CO₂, N₂, and O₂. In comparison with our previous work,⁹ carboxylic acid corroles offer slightly better chemisorption, as the CO(g) gas uptake at low pressure was higher for carboxylic acid corroles. However, corroles functionalized by phosphonic groups offer a new and attractive alternative method to graft porphyrinoid-type complexes into the porous structure of a MOF.

**Methods.** Materials and methods. See Supporting Information

**Synthesis method.** See Supporting Information

**Characterization instruments.** See Supporting Information

**Acknowledgements.**

This work was supported by the Université Bourgogne Europe (UBE), the CNRS (UMR UB-CNRS 6302) and the Conseil Régional de Bourgogne through the Plan d'Actions Régional pour l'Innovation (PARI II CDEA) and the European Union through the PO FEDER-FSE Bourgogne 2014/2020. The French Research Agency (ANR) is gratefully acknowledged for financial support (ANR BioSens-Path-22-CE42-0016-02). GD thanks the ANR for a PhD Grant. ML warmly thanks the Conseil Régional de Bourgogne for an ICE PhD grant. The authors thank the "Plateforme d'Analyse Chimique et de Synthèse Moléculaire de l'Université de Bourgogne" (PACSMUB, http://www.wpcm.fr) for access to spectroscopy instrumentation. The authors also thank Dr Quentin Bonnin and Mrs Marie-José Penouilh (Université de Bourgogne, PACSMUB) for HRMS analysis. Mrs Sandrine Pacquelet is warmly acknowledged for synthetic contribution.

**Authors contributions.** Mrs. G. Divoux contributed for the synthesis and the spectroscopic characterization of the corroles. Mrs M. Loze and Dr. L. André contributed for the MOFs modification. The X-Ray structure was solved by Dr. Y. Rousselin. The writing-original draft and writing review & editing were performed by Dr. L. André, Dr. N. Desbois, Dr. S. Brandès and Prof. Dr. Claude P. Gros. The manuscript was well discussed by all of these authors.

**Conflict of interests.** There are no conflicts to declare.

**Notes and references**

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