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Article

Synthesis of Phenol-Tagged Ruthenium Alkylidene Olefin Metathesis Catalysts for Robust Immobilisation Inside Metal–Organic Framework Support

by
Maryana Nadirova
1,
Joel Cejas-Sánchez
1,2,
Rosa María Sebastián
2,
Marcin Wiszniewski
1,
Michał J. Chmielewski
1,*,
Anna Kajetanowicz
1,* and
Karol Grela
1,*
1
Biological and Chemical Research Centre, Faculty of Chemistry, University of Warsaw, Żwirki i Wigury 101, 02-089 Warsaw, Poland
2
Department of Chemistry and Centro de Innovación en Química Avanzada, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Bellaterra, 08193 Barcelona, Spain
*
Authors to whom correspondence should be addressed.
Catalysts 2023, 13(2), 297; https://doi.org/10.3390/catal13020297
Submission received: 31 December 2022 / Revised: 23 January 2023 / Accepted: 25 January 2023 / Published: 28 January 2023
(This article belongs to the Special Issue Metal-Organic Framework Materials as Catalysts)
Browse Figures
Versions Notes

Abstract

:
Two new unsymmetrical N-heterocyclic carbene ligand (uNHC)-based ruthenium complexes featuring phenolic OH function were obtained and fully characterised. The more active one was then immobilised on the metal–organic framework (MOF) solid support (Al)MIL-101-NH2. The catalytic activity of such a heterogeneous system was tested, showing that, while the heterogeneous catalyst is less active than the corresponding homogeneous catalyst in solution, it can catalyse selected olefin metathesis reactions, serving as the proof-of-concept for the immobilisation of catalytically active complexes in MOFs using a phenolic tag.

1. Introduction

Olefin metathesis has emerged as one of the most powerful transformations in the tool cabinet of modern organic chemistry [1,2]. The rapid growth of its popularity is largely attributed to the discovery of stable, user-friendly ruthenium metathesis catalysts that combine high activity with good tolerance to air and moisture. Its high yield, atom-economic, selective nature, and ease of by-product (e.g., ethylene) separation has assisted its general acceptance in organic synthesis and process chemistry. On the other hand, metal complexes remaining after the olefin metathesis step may cause undesired side reactions such as product isomerisation, polymerisation, or degradation during work-up [3]. Therefore, the development of efficient and economical methods to remove ruthenium compounds present in the reaction mixture is crucial for the propagation of the metathesis methodology in industry. A number of efforts to remove the catalyst or the products of its decomposition by the addition of various scavengers such as peroxides, charcoal, silica gel, and other sorbents or by biphasic extraction have been carried out; however, none are universally applicable so far [3,4,5]. This situation has led to a tremendous interest in the supported or tagged versions of olefin metathesis catalysts.
One potentially very interesting class of supports is metal–organic frameworks (MOFs). MOFs are crystalline and porous coordination polymers, typically constructed from rigid organic ligands connected by metal ions or clusters (for a general introduction, see ref. [6], and for recent reviews on catalysis in MOFs, see refs. [7,8,9,10]). In contrast to some more conventional solid supports, such as activated carbons, amorphous silicas, and polymers, catalysts in MOFs are located inside well-defined nanoscopic voids in a highly porous crystalline framework. In this regard, MOFs resemble crystalline mesoporous silicas and zeolites, but surpass them by virtue of easy tunability, which they owe to their hybrid, organic–inorganic nature. Indeed, by an appropriate choice of linkers and clusters, the voids in MOFs can be made large enough to encompass even the most intricate homogeneous catalysts and to allow free diffusion of substrates and products. Furthermore, cavities may be tailored for specific needs by appropriate functionalisation of the MOFs’ organic ligands and/or coordination of functional moieties to the metal clusters. Therefore, catalysts immobilised in MOFs not only benefit from facile separation and potential reusability but are also site-separated from each other in a well-defined, tuneable nanoenvironment [8,11]. In the long term, the embedding framework may be envisaged to control substrate selectivity, regioselectivity, and even enantioselectivity of the immobilised catalysts, as well as confine different catalytic species for tandem or parallel catalysis.
However, robust immobilisation of active olefin metathesis catalysts inside MOFs is challenging. Such catalysts are unlikely to survive the typically harsh, solvothermal conditions of MOFs synthesis and, therefore, various strategies of their post-synthetic immobilisation have been developed. First, a small library of ammonium-tagged Ru-catalysts were non-covalently immobilised by Chmielewski et al. inside an aluminium-based MOF [12]. Quaternary ammonium cation-tagged ruthenium alkylidene complexes were supported inside (Al)MIL-101-NH2·HCl by simple impregnation, leading to solid heterogeneous catalysts stable even under continuous flow conditions. Structurally close Ru complexes featuring one or two ammonium tags were also immobilised via Coulomb interactions in the same (Al)MIL-101-NH2·HCl by Grela et al., who studied their mechanism of initiation and the propagation of Ru species during the catalytic cycle in this heterogeneous system [13]. Looking for more robust immobilisation methods, Chmielewski et al. used an acid−base neutralisation (a salt formation reaction) to immobilise Ru catalysts bearing basic nitrogen atoms (amine tags) on sulfonic acid-tagged MOFs [14]. In parallel, Kajetanowicz et al. studied the non-covalent immobilisation of a cationic ruthenium complex in a (Cr)MIL-101-SO3Na MOF by ion exchange (salt metathesis) [15]. In addition to the noncovalent immobilisation strategies described above, a mechanochemical procedure for the entrapment of a second-generation Hoveyda–Grubbs catalyst within the MOF was also elaborated [16]. Systems in which Ru catalysts were covalently bound to the MOF were disclosed by Yuan and Klemperer, who used an aldehyde-functionalised ruthenium catalyst to form an imine bond with an amine-functionalised IRMOF-74-III [17].
Unfortunately, none of the above-described strategies are universally applicable and free from disadvantages, so there is still a need to look for other modes of ruthenium olefin metathesis immobilisation in MOFs. In the present work, we have focused on using interaction between ruthenium catalysts featuring a phenolic tag and the coordinatively unsaturated sites in the aluminium-based MOF (Al)MIL-101-NH2. Despite the fact that the coordination of pyridines [18], aliphatic amines [19], carboxylates [20,21,22,23], and other donor moieties [24,25] with Lewis acidic centres in MOF clusters is well known and has already been utilised for the immobilisation of various catalytic species, to the best of our knowledge, phenols have never been utilised for this purpose (for a rare example of using phenol coordination to functionalise MOFs see ref. [26]). Because the more strongly basic donors such as amines and carboxylates are hardly compatible with olefin metathesis catalysts (and are likely to deactivate other transition metal catalysts, too), we envisaged that phenolic tags might serve as a viable alternative. Furthermore, upon coordination to the coordinatively unsaturated metal site, the phenolic OH becomes strongly acidic and is very likely to lose a proton, turning into a negatively charged ligand. Such a charge-assisted coordinate bond is clearly much stronger and might allow robust immobilisation. Therefore, we decided to check if phenol-tagged unsymmetrical-NHC-based Ru catalysts (for reviews on unsymmetrical-NHC-based Ru catalysts, see refs. [27,28]) can be immobilised inside a MOF, leading to the formation of stable heterogeneous catalysts (Scheme 1).

2. Results and Discussion

Synthesis of catalysts. Synthesis of unsymmetrical imidazolium ligand precursors 3 and 6 was accomplished using two pathways: through simple alkylation of Mes (Mes = 2,4,6-trimethylphenyl)-bearing imidazole with 4-(iodomethyl)phenol (for 3) or through condensation of N-(2,4,6-trimethylphenyl)-1,2-diaminoethane with 4-hydroxybenzaldehyde in the presence of a catalytic amount of formic acid (Scheme 2) [29]. The resulting imine 4 was reduced in situ to the corresponding diamine 5, followed by cyclisation with triethyl orthoformate to give the NHC precursor 6. The synthesis of uNHC Hoveyda–Grubbs-type II-generation complexes (uNHC = unsymmetrical NHC) was achieved via exchange of the phosphine ligand of the Hoveyda–Grubbs type I generation catalyst with an uNHC ligand. Treatment of a corresponding ligand precursor (3 or 6) with LiHMDS to generate a carbene in situ and reaction with the Hoveyda–Grubbs type I generation catalyst was followed by quenching with 5 equiv. of 4 N HCl in dioxane to “liberate” the OH-group provided the desired complexes Ru1 and Ru2 in moderate yields (Scheme 2). Interestingly, in the case of the Ru1 complex, the exchange of Cl− anions at the ruthenium coordination centre to a labile iodide anion from the imidazolium ligand was observed. This so-called “scrambling” resulted in an undefined mixture of [Ru](Cl)2 and [Ru](Cl/I)2 complexes (see Supplementary Information, SI). To circumvent this obstacle, we decided to counter-exchange iodide anions to chlorides through treatment with silver chloride (1.1 equiv. per [Ru](Cl/I)2 in DCM at room temperature) according to the previously reported method [30]. This simple transformation gave the pure Ru1 complex in a practically quantitative yield (see SI).
The synthesised imidazolium ligand precursors (3, 6) and catalysts (Ru1, Ru2) were fully characterised using the combination of NMR spectroscopy and HRMS (or elemental analysis), as well as IR spectroscopy. The chemical shifts of benzylidene protons of the obtained complexes ranged from 16.38 to 16.22 ppm, which is typical for this class of Hoveyda-type catalysts [31,32].
Stability studies. Complexes Ru1 and Ru2 were dissolved in deuterated DCM (C[Ru] = 0.02 M) in an argon atmosphere at room temperature, followed by the addition of 1,3,5-trimethoxybenzene as an internal standard. The decomposition of the catalysts was quantified using 1H NMR spectroscopy with respect to 1,3,5-trimethoxybenzene, by measuring the decrease in the intensity of benzylidene signals in 1H NMR spectra. Unfortunately, the analogous experiment performed in toluene failed due to precipitate formation. Both synthesised catalysts demonstrated high stability in deuterated DCM at room temperature, being decomposed in only 4% and 6% over 10 days (Figure 1). Comparing these results to what was reported previously for structurally related uNHC catalysts [31] shows a positive effect of the electron-donating OH-substituent in the N-benzyl “arm”, which visibly stabilised the ruthenium centre against decomposition.
Catalytic performance preliminary studies. Next, we decided to study the influence of the structural modification in the uNHC fragment on the activity of the newly obtained ruthenium complexes Ru1 and Ru2 bearing 4-hydroxybenzyl moiety in NHCs in olefin metathesis. To do so, the ring-closing metathesis (RCM) reaction of diethyl diallyl malonate (DEDAM) (7) was evaluated as a model reaction. For this purpose, malonate 7 was dissolved in DCM or toluene (C [7] = 0.1 M) and treated with 1 mol% catalyst (Ru1 or Ru2) [31,33]. The reaction was monitored through GC to determine the time-dependent conversion of 7. As expected, similar to the other members of this uNHC catalysts family [29,31,34,35,36,37,38], both of the studied catalysts were found to be less active under ambient conditions, but sufficiently activated at slightly elevated temperature (Figure 2).
In case of Ru2, the RCM experiment at room temperature in DCM showed a maximum conversion of 49%, demonstrating a rather moderate activity of the catalyst under ambient conditions. In the same manner, the RCM reaction of malonate 7 was also conducted using the unsaturated complex (Ru1). The outcome of this catalytic run was more positive—the conversion after 24 h reached 79%. When toluene was used as a solvent at 50 °C, both catalysts showed satisfactory results, driving the reaction to full conversion. In this case, too, we could observe higher activity of Ru1 compared to its saturated congener Ru2.
Immobilisation of the ruthenium complex Ru1 and desorption studies. Next, we studied the sorption of the more active Ru1 complex on a metal–organic framework (MOF). In search of an appropriate material, the relatively large size of the Hoveyda–Grubbs-type complexes and the stability of a potential solid support were taken into consideration. In this manner, we selected (Al)MIL-101-NH2, which met the aforementioned criteria [39]. Thus, the catalyst Ru1 (approximately 10 w/w%) was dissolved in DCM or toluene (1 mM) followed by the addition of an appropriate amount of (Al)MIL-101-NH2 (see SI). After 1 h of stirring, the mixture was centrifuged and the supernatant was examined using spectrophotometric methods, determining the catalyst concentration in the supernatant [12]. As a result, in both DCM and toluene, an almost quantitative sorption was observed (Table 1, 99.2% and 99.4% of the catalyst was absorbed in (Al)MIL-101-NH2, respectively). Since the catalyst was held inside the MOF by reversible noncovalent interactions, the desorption was the next in line to investigate. Therefore, we investigated the robustness of the catalyst’s immobilisation by washing the obtained Ru1@(Al)MIL-101-NH2 with toluene and DCM, starting with the less polar toluene. To do so, we placed the material on a G4 filtering funnel with side argon inlet (see Supplementary Material for a photo) and slowly filtered the solvents through the catalyst@MOF. The supernatants were monitored using UV-Vis. Interestingly, we did not observe any significant leaching of the absorbed catalyst from (Al)MIL-101-NH2 under these challenging dynamic conditions—the total amount of Ru1 washed out with toluene (20 mL) and DCM (20 mL) was less than 10% (Figure 3).
Powder X-ray diffraction (PXRD) studies revealed that the material remained crystalline after catalyst immobilisation, but its porosity, expressed as BET surface area, dropped significantly from 1753 m2/g for pristine MOF to 564 m2/g for Ru1@(Al)MIL-101-NH2.
Catalytic studies. The catalytic activity of the newly obtained Ru1@(Al)MIL-101-NH2 material was investigated in the model ring-closing metathesis reaction of 7 in toluene at 80 °C with 1 mol% of the heterogenised catalyst (see Table 2). Based on the leaching experiment, the less polar medium leads to the negligible desorption from the solid support and, therefore, the choice of toluene as a solvent was more favourable in this case. Compared to the homogeneous catalysis discussed earlier (Figure 2) where the conversion was quantitative, the heterogenised system Ru1@(Al)MIL-101-NH2 demonstrated a poorer performance. After 24 h of reaction, only 54% of conversion was achieved under these conditions. As a matter of fact, increasing the Ru1@(Al)MIL-101-NH2 loading up to 2 mol% did not lead to increased conversion.
Next, we decided to test the new system on a set of olefin metathesis substrates with the standard loading (1 mol%) of Ru1@MOF. Surprisingly, excellent results were obtained in the RCM reaction of DATA (11)—the conversion reached 65% in 3 h and 91% in 24 h. It should be mentioned here that we tried to improve the catalyst performance by treating the MOF with dry HCl in Et2O after sorption of the catalyst [12]. Interestingly, the conversion of DATA (11) in the reaction catalysed with Ru1@(Al)MIL-101-NH2·HCl reached 78% in just 15 min, but, unfortunately, did not increase after 24 h. Disappointingly, the RCM reaction of the olefin metathesis substrates 9 and 13 conducted in a similar manner (1 mol% of Ru1@(Al)MIL-101-NH2) resulted in a poorer outcome, giving only 31 and 30% conversion, respectively (see Table 3).

3. Materials and Methods

General Remarks. All reactions requiring exclusion of oxygen and moisture were carried out in dry glassware with dry solvents (SPS MBraun) under a dry and oxygen-free argon atmosphere using the standard Schlenk technique. The addition of dry solvents or reagents was carried out using argon-flushed plastic syringes.
Analytical thin layer chromatography (TLC) was performed on Merck Silica gel 60 F254 precoated aluminium sheets. Components were visualised by observation under UV light (254 nm or 365 nm) or dyed using aqueous KMnO4 or anisaldehyde reagent. Flash column chromatography was carried out using silica gel 60 (230–400 mesh), purchased from Merck. GC chromatograms were recorded using a PerkinElmer Clarus 580 model. As the capillary column, an IntertCap 5MS-Sil column was employed with helium as the carrier gas. GC conversions were determined based on the ratio of an internal standard (trimethoxybenzene or tetradecane) and the starting material. 1H NMR spectra were recorded in DCM-d2, DMSO-d6, and MeOH-d4 at room temperature on Agilent Mercury spectrometers (400 MHz). The data were interpreted in first-order spectra. Chemical shifts δ are reported in parts per million (ppm) downfield from trimethylsilane as reference to residual solvent signal: DCM-d2 [δH = 5.32 ppm], DMSO-d6 [δH = 2.50 ppm], D2O [δH = 4.79 ppm], and MeOH-d4 [δH = 3.31 ppm]. The following abbreviations are used to indicate the signal multiplicity: s (singlet), d (doublet), t (triplet), q (quartet), quin (quintet), sext (sextet), dd (doublet of doublet), dt (doublet of triplet), ddd (doublet of doublet of doublet), etc., br. s (broad signal), and m (multiplet). Coupling constants (J) are given in Hz and refer to H,H-couplings. 13C NMR spectra were recorded at room temperature on Agilent Mercury 101 MHz spectrometers. The spectra were recorded in DCM-d2, DMSO-d6, and MeOH-d4. Chemical shifts are reported in δ units relative to the solvent signal: DCM-d2 [δC = 53.84 ppm], DMSO-d6 [δC = 39.52 ppm], and MeOH-d4 [δC = 49.00 ppm]. High resolution mass spectra (HR-MS) were obtained on an AutoSpec Premier spectrometer. Elemental analyses were carried out at the Polish Academy of Science, Institute of Organic Chemistry. IR spectra were recorded on a Perkin-Elmer Spectrum One FTIR spectrometer. Substances were applied as a film, solid, or in solution. The obtained data were processed with the software Omni32. Wavenumbers are given in cm−1. Powder X-ray diffraction: All powder X-ray diffraction (PXRD) patterns were recorded on a Bruker D8 Discover X-ray diffractometer (CuKα radiation), with a parallel beam formed by a Goebel mirror equipped with a VANTEC 1 position-sensitive detector. All measurements were performed in an aluminium holder. The nitrogen adsorption isotherms were measured at liquid nitrogen temperature (77 K) using Quantachrome Autosorb-IQ-MP sorption analyser. Prior to measurements, all samples were dried for no less than 24 h under vacuum (2 × 10−2 mbar) at room temperature. The specific surface areas were calculated according to the Brunauer-Emmett-Teller (BET) method. For all isotherm analyses we ensured that the two consistency criteria described by Rouquerol et al. [40] and Walton et al. [41] were satisfied.
Reagents and Solvents: All reagents were purchased from Sigma-Aldrich, Apeiron Synthesis, and POCH and used without further purification unless stated otherwise.
General Procedure for Synthesis of Ru Complexes: In a dried 50 mL Schleck flask, the corresponding NHC ligand 3 or 6 (1.15 equiv.) was suspended in dry toluene (12 mL). To the resulting suspension, LiHDMS (3.2 equiv.) was added, and the mixture was stirred for 1 h at room temperature in an atmosphere of argon. To this suspension, 3 mL of dry THF was added and the reaction was stirred until the solution became clear and homogeneous. To this clear solution, Hoveyda–Grubbs type I generation (Hov I) was added (124 mg, 0.206 mmol, 1.0 equiv.). The resulting solution was stirred at room temperature for 2 h (the reaction was monitored by TLC, 50% AcOEt/n-hexane). After the complete disappearance of Hov I on TLC, CuCl (31 mg, 0.31 mmol, 1.5 equiv.) was added to the reaction and it was stirred for an additional 30 min, followed by the dropwise addition of 4N HCl in dioxane (0.258 mL). The reaction mixture was stirred for another 30 min, transferred to a round bottom flask, and volatiles were evaporated to dryness. The crude mixture was purified through column chromatography (20% to 50% AcOEt/n-hexane).
Synthesis of Ruthenium Complex Ru1: Ruthenium complex Ru1 was synthesised following the general procedure, using NHC ligand 3 (100 mg, 0.238 mmol, 1.15 equiv.), LiHDMS (110 mg, 0.66 mmol, 3.2 equiv.), Hov I (124 mg, 0.206 mmol, 1.0 equiv.), CuCl (31 mg, 0.31 mmol, 1.5 equiv.) and 4N HCl in dioxane (0.258 mL, 1.03 mmol). The desired product was crystallised from the mixture of DCM/MeOH (3:1) to give a fine dark-green powder (60 mg, 0.1 mmol, 48%). The ratio of Cl/I at the ruthenium coordination centre was established based on integration of benzylidene signals by 1H NMR as 88:12. An oven-dried vial was charged with AgCl (1.1 equiv. per iodide) and Ru-complex (30 mg). The vial was evacuated and flushed with argon three times, dry DCM (1 mL) was added, and the resulting mixture was stirred for 30 min at room temperature. The resulting solution was centrifuged, filtered through a Celite® pad, and washed with MeOH (20 mL). Solvents were evaporated and the residue was crystallised from the mixture of DCM/MeOH and dried under vacuum overnight to provide a pure product as a fine dark-green powder (90%). 1H NMR (400 MHz, CD2Cl2) δ 16.38 (s, 1H), 7.60 (ddd, J = 8.4, 7.2, 1.9 Hz, 1H), 7.54 (d, J = 8.5 Hz, 2H), 7.17 (m, 2H), 7.11–6.98 (m, 3H), 6.93 (dd, J = 5.4, 3.2 Hz, 3H), 6.87 (d, J = 2.1 Hz, 1H), 6.08 (s, 2H), 5.45 (s, 1H), 5.21 (hept, J = 6.2 Hz, 1H), 2.53 (s, 3H), 2.04 (d, J = 0.7 Hz, 6H), 1.76 (d, J = 6.1 Hz, 6H). 13C NMR (101 MHz, CD2Cl2) δ 287.5, 172.3, 156.2, 152.4, 144.1, 139.8, 137.2, 131.1, 129.1, 129.0, 127.9, 124.4, 122.6, 121.7, 121.2, 115.6, 112.9, 75.3, 54.8, 21.8, 21.0, 17.6. EA: calculated for C29H32Cl2N2O2Ru: C, 56.86; H, 5.27; N, 4.57; Found C, 56.59; H, 5.48; N, 4.34.
Synthesis of Ruthenium Complex Ru2: Ruthenium complex Ru2 was synthesised following the general procedure, using NHC ligand 6 (100 mg, 0.3 mmol, 1.15 equiv.), LiHDMS (110 mg, 0.66 mmol, 3.2 equiv.), Hov I (158 mg, 0.263 mmol, 1.0 equiv.), CuCl (39.4 mg, 0.39 mmol, 1.5 equiv.) and 4N HCl in dioxane (0.118 mL, 1.31 mmol). The desired product was crystallised from the mixture of DCM/MeOH (3:1) to give a fine dark-green powder (72 mg, 0.12 mmol, 56%). 1H NMR (400 MHz, CD2Cl2) δ 16.22 (s, 1H), 7.67–7.54 (m, 3H), 7.11 (s, 2H), 7.04–6.95 (m, 3H), 6.90 (d, J = 7.8 Hz, 2H), 5.53 (s, 2H), 5.18 (hept, J = 6.1 Hz, 1H), 3.92 (t, J = 10.0 Hz, 2H), 3.64 (d, J = 10.0 Hz, 2H), 2.48 (s, 3H), 2.24 (s, 6H), 2.01 (s, 1H), 1.71 (d, J = 6.1 Hz, 6H). 13C NMR (101 MHz, CD2Cl2) δ 152.2, 138.9, 138.0, 137.7, 130.6, 129.5, 129.5, 122.5, 122.1, 115.3, 112.86, 75.2, 47.7, 21.8, 20.9, 17.7.

4. Conclusions

Two new uNHC-based ruthenium complexes featuring phenolic OH function were obtained and fully characterised. The more active one was then successfully immobilised on the MOF support. Desorption studies suggest that the highly porous structure of (Al)MIL-101-NH2 offers a favourable environment for the non-covalent immobilisation of a phenol-tagged ruthenium catalyst. After immobilisation, the Lewis acidic coordinatively unsaturated centres located inside the well-defined nanoscopic voids in a crystalline framework of the MOF strongly bind the ruthenium complex, which results in negligible leaching even in polar solvent, such as DCM. The catalytic activity of such a formed heterogeneous system was unfortunately lower than the activity of the corresponding homogeneous catalyst in solution; however, it was found to catalyse selected olefin metathesis reactions. We believe that the results reported herein create a valid proof-of-concept and are the very first example of catalyst immobilisation by means of phenol–MOF interaction.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal13020297/s1. Figure S1. 1H NMR spectrum of (Al)MIL-101-NH2 digested in 4 wt. % NaOD/D2O; Figure S2. Powder X-ray diffraction (PXRD) pattern of (Al)MIL-101-NH2; Figure S3. N2 adsorption/desorption isotherm of (Al)MIL-101-NH2. Points in the range p/p0 = 0.0005–0.21 were used to calculate BET surface area; Figure S4. UV-Vis spectra of catalysts Ru1 and Ru2 and determination of their molar absorption coefficients ε; Figure S5. Powder X-ray diffraction (PXRD) pattern of Ru1@(Al)MIL-101-NH2; Figure S6. N2 adsorption/desorption of Ru1@(Al)MIL-101-NH2. Points in the range p/p0 = 0.0005-0.21 were used to calculate BET surface area; Figure S7. Glassware used in the desorption (leaching) experiments; Figure S8. 1H NMR of compound 1; Figure S9. 13C NMR of compound 1; Figure S10. 1H NMR of compound 3; Figure S11. 13C NMR of compound 3; Figure S12. 1H NMR of compound 5, Figure S13. 13C NMR of compound 5; Figure S14. 1H NMR of compound 6; Figure S15. 13C NMR of compound 6; Figure S16. 1H NMR of Ru1 after the crystallization from DCM/MeOH; Figure S17. 1H NMR of Ru1 after stirring it with AgCl; Figure S18. 13C NMR of Ru1 after stirring it with of AgCl; Figure S19. 1H NMR of Ru2; Figure S20. 13C NMR of Ru2; Figure S21. 1H NMR of compound 15; Figure S22. 13C NMR of compound 15; Table S1. Stability studies of Ru1 and Ru2 in CD2Cl2; Table S2. Conditions of the RCM reaction and conversion of diethyl diallylmalonate (7) in the presence of 1 mol% Ru1 or Ru2.; Table S3. Results of absorption experiments of Ru1 in DCM and toluene [42,43].

Author Contributions

Conceptualization, M.J.C. and K.G.; methodology, M.J.C.; investigation, M.N., J.C.-S. and M.W.; resources, M.J.C.; writing—original draft, M.N., M.J.C. and K.G.; writing—review & editing, M.N., J.C.-S., M.W., R.M.S., M.J.C., A.K. and K.G.; Visualization, M.W. and K.G.; Supervision, M.J.C., A.K. and K.G.; Funding acquisition, M.J.C. and K.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received funding from: European Union’s Horizon 2020 research and innovation programme (Marie Skłodowska-Curie grant agreement No 860322) and National Science Centre, Poland (OPUS grant 2017/27/B/ST5/00941).

Data Availability Statement

Data supporting reported results of this study are available in the supplementary material of this article and can be obtained from the corresponding author.

Acknowledgments

This work was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860322 for the ITN-EJD “Coordination Chemistry Inspires Molecular Catalysis” (CCIMC). MJC and MW thank the National Science Centre, Poland (OPUS grant 2017/27/B/ST5/00941), for funding.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 13 00297 sch001 550
Scheme 1. Structure of (Al)MIL-101-NH2 (hydrogen atoms were omitted for clarity) and the proposed mode of immobilisation of a phenol-tagged ruthenium complex.
Scheme 1. Structure of (Al)MIL-101-NH2 (hydrogen atoms were omitted for clarity) and the proposed mode of immobilisation of a phenol-tagged ruthenium complex.
Catalysts 13 00297 sch001
Catalysts 13 00297 sch002 550
Scheme 2. Synthesis of unsymmetrical-NHC ligand precursors 3 and 6 and Ru catalysts Ru1 and Ru2 tagged with phenolic OH function.
Scheme 2. Synthesis of unsymmetrical-NHC ligand precursors 3 and 6 and Ru catalysts Ru1 and Ru2 tagged with phenolic OH function.
Catalysts 13 00297 sch002
Catalysts 13 00297 g001 550
Figure 1. Results of the stability experiment for Ru1 and Ru2 in DCM-d2 at room temperature.
Figure 1. Results of the stability experiment for Ru1 and Ru2 in DCM-d2 at room temperature.
Catalysts 13 00297 g001
Catalysts 13 00297 g002 550
Figure 2. Time/conversion plot for the RCM reaction of 7 (0.1 M) catalysed by Ru1 and Ru2 (1 mol%) in DCM at 23 °C and in toluene at 50 °C. Conversion determined through GC.
Figure 2. Time/conversion plot for the RCM reaction of 7 (0.1 M) catalysed by Ru1 and Ru2 (1 mol%) in DCM at 23 °C and in toluene at 50 °C. Conversion determined through GC.
Catalysts 13 00297 g002
Catalysts 13 00297 g003 550
Figure 3. Desorption of Ru1 catalyst from (Al)MIL-101-NH2 by subsequent washing with toluene and later with DCM.
Figure 3. Desorption of Ru1 catalyst from (Al)MIL-101-NH2 by subsequent washing with toluene and later with DCM.
Catalysts 13 00297 g003
Table
Table 1. Results of absorption experiments of Ru1 from toluene and DCM.
Table 1. Results of absorption experiments of Ru1 from toluene and DCM.
Catalyst/SolventThe Amount of Catalyst Adsorbed from Solution [%]
Ru1/Toluene99.4
Ru1/DCM99.2
Table
Table 2. Results of the RCM reaction of DEDAM (7) with Ru1 and Ru1@(Al)MIL-101-NH2 complexes in toluene. (C [7] = 0.1 M). Conversion was determined through GC (tetradecane was used as an internal standard).
Table 2. Results of the RCM reaction of DEDAM (7) with Ru1 and Ru1@(Al)MIL-101-NH2 complexes in toluene. (C [7] = 0.1 M). Conversion was determined through GC (tetradecane was used as an internal standard).
Catalysts 13 00297 i001
[Ru]Time, [h]Conversion, [%]
Ru1 (1 mol%)
homogeneous		395
24>99
Ru1@MOF (1 mol%)
heterogeneous		3 53
2454
Ru1@MOF (2 mol%)
heterogeneous		3 50
24 51
Table
Table 3. Results of the RCM reaction of selected dienes catalysed by Ru1@(Al)MIL-101-NH2 complex in toluene at 80 °C. (C [7] = 0.1 M). Conversion was determined through GC (tetradecane was used as an internal standard).
Table 3. Results of the RCM reaction of selected dienes catalysed by Ru1@(Al)MIL-101-NH2 complex in toluene at 80 °C. (C [7] = 0.1 M). Conversion was determined through GC (tetradecane was used as an internal standard).
[Ru]@MOFSubstrateProductConversion
in 24 h
Ru1@(Al)MIL-101-NH2Catalysts 13 00297 i002Catalysts 13 00297 i00331
Ru1@(Al)MIL-101-NH2Catalysts 13 00297 i004Catalysts 13 00297 i00591
Ru1@(Al)MIL-101-NH2·HClCatalysts 13 00297 i004Catalysts 13 00297 i00578
Ru1@(Al)MIL-101-NH2Catalysts 13 00297 i006Catalysts 13 00297 i00730
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Nadirova, M.; Cejas-Sánchez, J.; Sebastián, R.M.; Wiszniewski, M.; Chmielewski, M.J.; Kajetanowicz, A.; Grela, K. Synthesis of Phenol-Tagged Ruthenium Alkylidene Olefin Metathesis Catalysts for Robust Immobilisation Inside Metal–Organic Framework Support. Catalysts 2023, 13, 297. https://doi.org/10.3390/catal13020297

AMA Style

Nadirova M, Cejas-Sánchez J, Sebastián RM, Wiszniewski M, Chmielewski MJ, Kajetanowicz A, Grela K. Synthesis of Phenol-Tagged Ruthenium Alkylidene Olefin Metathesis Catalysts for Robust Immobilisation Inside Metal–Organic Framework Support. Catalysts. 2023; 13(2):297. https://doi.org/10.3390/catal13020297

Chicago/Turabian Style

Nadirova, Maryana, Joel Cejas-Sánchez, Rosa María Sebastián, Marcin Wiszniewski, Michał J. Chmielewski, Anna Kajetanowicz, and Karol Grela. 2023. "Synthesis of Phenol-Tagged Ruthenium Alkylidene Olefin Metathesis Catalysts for Robust Immobilisation Inside Metal–Organic Framework Support" Catalysts 13, no. 2: 297. https://doi.org/10.3390/catal13020297

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