catalysts Article Synthesis of Phenol-Tagged Ruthenium Alkylidene Olefin Metathesis Catalysts for Robust Immobilisation Inside Metal–Organic Framework Support 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 * Correspondence: mchmielewski@chem.uw.edu.pl (M.J.C.); a.kajetanowicz@uw.edu.pl (A.K.); kl.grela@uw.edu.pl (K.G.) Abstract: Two new unsymmetrical N-heterocyclic carbene ligand (uNHC)-based ruthenium com- plexes 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. Keywords: olefin metathesis; ruthenium; metal–organic framework (MOF); immobilisation Citation: Nadirova, M.; Cejas-Sánchez, J.; Sebastián, R.M.; Wiszniewski, M.; Chmielewski, M.J.; Kajetanowicz, A.; Grela, K. Synthesis 1. Introduction of Phenol-Tagged Ruthenium Olefin metathesis has emerged as one of the most powerful transformations in the Alkylidene Olefin Metathesis tool cabinet of modern organic chemistry [1,2]. The rapid growth of its popularity is Catalysts for Robust Immobilisation largely attributed to the discovery of stable, user-friendly ruthenium metathesis catalysts Inside Metal–Organic Framework that combine high activity with good tolerance to air and moisture. Its high yield, atom- Support. Catalysts 2023, 13, 297. economic, selective nature, and ease of by-product (e.g., ethylene) separation has assisted https://doi.org/10.3390/ its general acceptance in organic synthesis and process chemistry. On the other hand, catal13020297 metal complexes remaining after the olefin metathesis step may cause undesired side Academic Editors: Francis Verpoort reactions such as product isomerisation, polymerisation, or degradation during work-up [3]. and Somboon Chaemchuen Therefore, the development of efficient and economical methods to remove ruthenium Received: 31 December 2022 compounds present in the reaction mixture is crucial for the propagation of the metathesis Revised: 23 January 2023 methodology in industry. A number of efforts to remove the catalyst or the products of Accepted: 25 January 2023 its decomposition by the addition of various scavengers such as peroxides, charcoal, silica Published: 28 January 2023 gel, and other sorbents or by biphasic extraction have been carried out; however, none are universally applicable so far [3–5]. 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). Copyright: © 2023 by the authors. MOFs are crystalline and porous coordination polymers, typically constructed from rigid Licensee MDPI, Basel, Switzerland. organic ligands connected by metal ions or clusters (for a general introduction, see ref. [6], This article is an open access article and for recent reviews on catalysis in MOFs, see refs. [7–10]). In contrast to some more distributed under the terms and conventional solid supports, such as activated carbons, amorphous silicas, and polymers, conditions of the Creative Commons catalysts in MOFs are located inside well-defined nanoscopic voids in a highly porous Attribution (CC BY) license (https:// crystalline framework. In this regard, MOFs resemble crystalline mesoporous silicas and creativecommons.org/licenses/by/ zeolites, but surpass them by virtue of easy tunability, which they owe to their hybrid, 4.0/). Catalysts 2023, 13, 297. https://doi.org/10.3390/catal13020297 https://www.mdpi.com/journal/catalysts Catalysts 2023, 13, 297 2 of 12 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 immo- bilised 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 condi- tions of MOFs synthesis and, therefore, various strategies of their post-synthetic immobili- sation 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 initi- ation 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, Kaje- tanowicz et al. studied the non-covalent immobilisation of a cationic ruthenium complex in a (Cr)MIL-101-SO3 Na 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 [20–23], 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). Catalysts 2023, Catalysts 2023, 13, 13, 297 x FOR PEER REVIEW 33 of 12 of 12 Scheme 1. Structure of (Al)MIL-101-NH2 (hydrogen atoms were omitted for clarity) and the pro- Scheme 1. Structure posed mode of (Al)MIL-101-NH of immobilisation 2 (hydrogen of a phenol-tagged atoms were ruthenium omitted for clarity) and the pro- complex. posed mode of immobilisation of a phenol-tagged ruthenium complex. 2. Results 2. Results and Discussion and Discussion Synthesisof Synthesis ofcatalysts. catalysts.Synthesis Synthesisofofunsymmetrical unsymmetrical imidazolium imidazolium ligand ligand precursors precursors 3 and3 6 was accomplished using two pathways: through simple alkylation of Mes= and 6 was accomplished using two pathways: through simple alkylation of Mes (Mes 2,4,6-trimethylphenyl)-bearing (Mes = 2,4,6-trimethylphenyl)-bearing imidazole imidazolewithwith 4-(iodomethyl)phenol 4-(iodomethyl)phenol (for (for3)3)or or through through condensation of N-(2,4,6-trimethylphenyl)-1,2-diaminoethane condensation of N-(2,4,6-trimethylphenyl)-1,2-diaminoethane with 4-hydroxybenzaldehyde with 4-hydroxybenzalde- hyde in the in the presence presence of a catalytic of a catalytic amountamountof formicof acid formic acid (Scheme (Scheme 2) [29]. The2) [29]. The resulting resulting imine 4 imine 4 was reduced in situ to the corresponding diamine 5, followed was reduced in situ to the corresponding diamine 5, followed by cyclisation with triethyl by cyclisation with triethyl orthoformate to give the NHC precursor 6. The synthesis orthoformate to give the NHC precursor 6. The synthesis of uNHC Hoveyda–Grubbs-type of uNHC Hoveyda– Grubbs-type complexes II-generation II-generation complexes (uNHC (uNHC = unsymmetrical = unsymmetrical NHC) was achieved NHC)via was achieved exchange via of the exchange ofligand phosphine the phosphine ligand of the Hoveyda–Grubbs of the Hoveyda–Grubbs type I generation type I generation catalyst with an uNHC catalyst with ligand. an uNHC ligand. Treatment Treatment of of a corresponding a corresponding ligand precursor (3ligand or 6) withprecursor LiHMDS (3 orto6) with LiHMDS generate a carbene to generate a carbene in situ and reaction with the Hoveyda–Grubbs in situ and reaction with the Hoveyda–Grubbs type I generation catalyst was followed by type I generation cata- lyst was followed quenching by quenching with 5 equiv. of 4 N HCl with in 5 equiv. dioxane of to 4 N“liberate” HCl in dioxane to “liberate” the OH-group the OH- provided the desired complexes Ru1 and Ru2 in moderate yields (Scheme 2). Interestingly, in the2).case group provided the desired complexes Ru1 and Ru2 in moderate yields (Scheme In- terestingly, of in the case the Ru1 complex, theofexchange the Ru1 of complex, − Cl anions the atexchange of Cl anions the ruthenium − at the ruthenium coordination centre to a coordination labile centrefrom iodide anion to athelabile iodide anion imidazolium from ligand wasthe imidazolium observed. ligand was This so-called observed. “scrambling” This so-called resulted “scrambling” in an undefined resulted mixture in an 2undefined of [Ru](Cl) and [Ru](Cl/I) mixture 2 of [Ru](Cl) complexes (see 2 and [Ru](Cl/I) Supplementary 2 complexes (see Information, SI).Supplementary To circumvent this Information, obstacle, we SI).decided To circumvent this obstacle, to counter-exchange we decided iodide anions to chlorides to counter-exchange iodide anions through treatment to chlorides with silver chloride through treatment (1.1 equiv. with silver per [Ru](Cl/I) 2 in DCMchloride (1.1 at room equiv. per [Ru](Cl/I) temperature) 2 in to according DCM at room temperature) the previously reported method according to the [30]. This previously simple reported transformation method gave the[30]. pureThis Ru1simple complex transformation in a practicallygave the pureyield quantitative Ru1 complex (see SI). in a practically quan- titative Theyield (see SI). imidazolium ligand precursors (3, 6) and catalysts (Ru1, Ru2) were synthesised fully The synthesised characterised imidazolium using the combinationligand of precursors (3, 6) and catalysts NMR spectroscopy and HRMS (Ru1,(orRu2) were elemental 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 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]. Catalysts 2023, 13, x FOR PEER REVIEW 4 of 12 Catalysts 2023, 13, 297 4 of 12 obtained complexes ranged from 16.38 to 16.22 ppm, which is typical for this class of Hov- eyda-type catalysts [31,32]. Scheme 2. Synthesis of unsymmetrical-NHC ligand precursors 3 and 6 and Ru catalysts Ru1 and Scheme 2. Synthesis of unsymmetrical-NHC ligand precursors 3 and 6 and Ru catalysts Ru1 and Ru2 tagged with phenolic OH function. Ru2 tagged with phenolic OH function. Stability studies. Stability studies. Complexes Complexes Ru1 Ru1and Ru2 and were Ru2 dissolved were in deuterated dissolved DCMDCM in deuterated (C[Ru] = 0.02 M) in an argon atmosphere at room temperature, followed (C[Ru] = 0.02 M) in an argon atmosphere at room temperature, followed by the addi- by the addition of 1,3,5- trimethoxybenzene tion as an internal of 1,3,5-trimethoxybenzene as standard. an internalThe decomposition standard. of the catalysts The decomposition was of the quan- catalysts tified using 1H NMR spectroscopy 1 with respect to 1,3,5-trimethoxybenzene, was quantified using H NMR spectroscopy with respect to 1,3,5-trimethoxybenzene, by by measuring the decrease measuring indecrease the the intensity in theofintensity benzylidene signals in 1signals of benzylidene H NMRinspectra. 1 H NMR Unfortunately, spectra. Unfortu-the analogous experiment performed in toluene failed due to precipitate formation. nately, the analogous experiment performed in toluene failed due to precipitate formation. Both syn- thesised Both catalysts catalysts synthesised demonstrated high stability demonstrated high in deuterated stability DCM at room in deuterated DCM temperature, at room tem- being decomposed perature, in only 4% being decomposed inand only6% 4%over and106%days over(Figure 10 days 1).(Figure Comparing these results 1). Comparing to these what was results reported to what previously was reported for structurally previously related uNHC for structurally relatedcatalysts [31] shows uNHC catalysts [31] ashows posi- ative effect effect positive of the of electron-donating the electron-donating OH-substituent in the N-benzyl OH-substituent “arm”, “arm”, in the N-benzyl which visibly which stabilised the ruthenium centre against decomposition. 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 Catalysts 2023, 13, x FOR PEER REVIEW 5 of 13 Catalysts 2023, 13, 297 5 of 12 metathesis. To do so, the ring-closing metathesis (RCM) reaction of diethyl diallyl mal- onate (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 Catalysts 2023, 13, x FOR PEER REVIEW 5 offam- 13 ily [29,31,34–38], both of the studied catalysts were found to be less active under ambient conditions, but sufficiently activated at slightly elevated temperature (Figure 2). Figure 1. Results of the stability experiment for Ru1 and Ru2 in DCM-d2 at room temperature. 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 malo- nate (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 con- version of 7. As expected, similar to the other members of this uNHC catalysts family [29,31,34–38], both of the studied catalysts were found to be less active under ambient conditions, Figure Figure butofsufficiently Results 1.1.Results ofthe thestabilityactivated stability atfor experiment experiment slightly forRu1 elevated and Ru1and intemperature Ru2in Ru2 (Figure DCM-d22atatroom DCM-d room 2). temperature. temperature. 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 malo- nate (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 con- version of 7. As expected, similar to the other members of this uNHC catalysts family [29,31,34–38], both of the studied catalysts were found to be less active under ambient conditions, but sufficiently activated at slightly elevated temperature (Figure 2). Figure 2. Figure 2. Time/conversion Time/conversion plot plot for for the the RCM RCM reaction reaction of of 77 (0.1 (0.1 M) M) catalysed catalysed by by Ru1 Ru1 and and Ru2 Ru2 (1 (1 mol%) mol%) in DCM at 23 °C ◦ and in toluene at 50 °C. ◦ Conversion determined through in DCM at 23 C and in toluene at 50 C. Conversion determined through GC. GC. 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 Figure 2. Time/conversion plot for the RCM reaction of 7 (0.1 M) catalysed by Ru1 and Ru2 (1 mol%) Catalysts 2023, 13, x FOR PEER REVIEW 6 of 13 In case of Ru2, the RCM experiment at room temperature in DCM showed a maxi- Catalysts 2023, 13, 297 mum conversion of 49%, demonstrating a rather moderate activity of the catalyst under 6 of 12 ambient conditions. In the same manner, the RCM reaction of malonate 7 was also con- ducted 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 catalysts showed satisfactory results, driving the reaction to full conversion. In this case, 50 °C, both catalysts showed satisfactory results, driving the reaction to full conversion. too, we could observe higher activity of Ru1 compared to its saturated congener Ru2. In this case, too, we could observe higher activity of Ru1 compared to its saturated con- generImmobilisation Ru2. of the ruthenium complex Ru1 and desorption studies. Next, we studied the sorption Immobilisation of the of theruthenium more active Ru1 complex complex Ru1 andon a metal–organic desorption studies.framework Next, we (MOF). In search of an appropriate material, the relatively large studied the sorption of the more active Ru1 complex on a metal–organic framework size of the Hoveyda–Grubbs-type complexes (MOF). and the In search of anstability of a potential appropriate material, solid supportlarge the relatively weresizetaken intoHoveyda– of the consideration. In this manner,complexes Grubbs-type we selected and (Al)MIL-101-NH 2 , which the stability of a potential met solid the aforementioned support were taken into con- criteria [39]. sideration. Thus, the In this manner, catalyst we selected (Al)MIL-101-NH Ru1 (approximately 10 w/w%)2,was which met the aforementioned dissolved in DCM or toluene (1 criteria [39]. Thus,bythe mM) followed catalyst the additionRu1 of(approximately an appropriate 10 w/w%) amount wasofdissolved in DCM or2 (see SI). (Al)MIL-101-NH toluene (1 mM) followed by the addition of an appropriate amount After 1 h of stirring, the mixture was centrifuged and the supernatant was examined of (Al)MIL-101-NH 2 using (see SI). After 1 h of stirring, the mixture was centrifuged and the supernatant spectrophotometric methods, determining the catalyst concentration in the supernatant [12]. was exam- ined using spectrophotometric methods, determining the catalyst concentration in the su- As a result, in both DCM and toluene, an almost quantitative sorption was observed (Table 1, pernatant [12]. As a result, in both DCM and toluene, an almost quantitative sorption was 99.2% and 99.4% of the catalyst was absorbed in (Al)MIL-101-NH2 , respectively). Since the observed (Table 1, 99.2% and 99.4% of the catalyst was absorbed in (Al)MIL-101-NH2, re- catalyst was spectively). held Since theinside catalystthewasMOF heldby reversible inside the MOFnoncovalent by reversibleinteractions, the desorption noncovalent interac- was tions, the desorption was the next in line to investigate. Therefore, we investigatedthe the next in line to investigate. Therefore, we investigated the robustness of thecatalyst’s immobilisation robustness of the by washing catalyst’s the obtainedbyRu1@(Al)MIL-101-NH immobilisation 2 with toluene and DCM, washing the obtained Ru1@(Al)MIL-101- starting NH 2 withwith toluene theand less polar DCM, toluene. starting withTo thedo lessso, we toluene. polar placed Tothedomaterial on a the so, we placed G4 filtering funnel with material on a side argon inlet G4 filtering funnel(seewithSupplementary side argon inlet Material for a photo) (see Supplementary and slowly Material for a filtered photo) and slowly the solvents throughfiltered thethe solvents throughThe catalyst@MOF. the supernatants catalyst@MOF.were The supernatants were UV-Vis. monitored using monitored Interestingly, usingwe UV-Vis. did not Interestingly, observe any we did not observe significant any significant leaching leaching of of the absorbed the catalyst from absorbed catalyst from (Al)MIL-101-NH 2 (Al)MIL-101-NH under these 2 underdynamic challenging these challenging dynamic conditions—the conditions— total amount of Ru1 the total amount of Ru1 washed out with toluene (20 mL) washed out with toluene (20 mL) and DCM (20 mL) was less than 10% (Figure 3).and DCM (20 mL) was less than 10% (Figure 3). 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/Solvent Catalyst/Solvent The Amount The amount of Catalyst of catalyst adsorbedAdsorbed from [%] from solution Solution [%] Ru1/Toluene Ru1/Toluene 99.4 99.4 Ru1/DCM Ru1/DCM 99.2 99.2 Figure Figure3.3.Desorption Desorptionof of Ru1 catalyst Ru1 fromfrom catalyst (Al)MIL-101-NH 2 by subsequent (Al)MIL-101-NH washingwashing 2 by subsequent with toluene with toluene and later with DCM. and later with DCM. Powder X-ray diffraction (PXRD) studies revealed that the material remained crys- talline 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 sup- port and, therefore, the choice of toluene as a solvent was more favourable in this case. 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 tolu- ene 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 sup- Catalysts 2023, 13, 297 port and, therefore, the choice of toluene as a solvent was more favourable in this 7case. of 12 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 Comparedperformance. After 24 h ofcatalysis to the homogeneous reaction,discussed only 54%earlier of conversion was (Figure 2) achieved where under the conver- these conditions. As a matter of fact, increasing the Ru1@(Al)MIL-101-NH sion was quantitative, the heterogenised system Ru1@(Al)MIL-101-NH2 demonstrated 2 loading up toa 2poorer mol%performance. did not lead toAfter increased 24 h ofconversion. 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 Table 2 mol%2. did Results notof theto lead RCM reactionconversion. increased of DEDAM (7) with Ru1 and Ru1@(Al)MIL-101-NH2 com- plexes in toluene. (C [7] = 0.1 M). Conversion was determined through GC (tetradecane was used as an internal Table standard). 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). [Ru] Time, [h] Conversion, [%] Ru1 (1 mol%) 3 95 homogeneous [Ru] 24 Time, [h] >99 Conversion, [%] Ru1@MOF (1 mol%) Ru1 (1 mol%) 33 53 95 heterogeneous 24 54 homogeneous 24 >99 Ru1@MOF (1 Ru1@MOF (2 mol%) mol%) 33 50 53 Catalysts 2023, 13, x FOR PEER REVIEW heterogeneous 24 51 8 of 13 heterogeneous 24 54 Ru1@MOF (2 mol%) Next, we decided to test the new system 3 on a set of olefin metathesis50 substrates with the standard Table loading heterogeneous 3. Results (1 mol%) of the RCM reactionof of Ru1@MOF. selected 24 Surprisingly, dienes catalysed excellent results 51were obtained by Ru1@(Al)MIL-101-NH 22 com- in the plex RCM reaction in toluene at 80 °C.of(CDATA [7] = 0.1(11)—the [7] conversion M). Conversion reached 65% was determined in 3 hGC through and 91% in 24was (tetradecane h. It used as an internal standard). should be mentioned here that we tried to improve the catalyst performance by treating the Next, we decided to test the new system on a set of olefin metathesis substrates with MOF with dry HCl in Et2 O after sorption of the catalyst [12]. Interestingly, the conversion of the standard loading (1 mol%) Catalysts 2023, 13, x FOR PEER REVIEW of Ru1@MOF. Surprisingly, excellent resultsConversion were obtained 8 of 13 DATA (11) in the reaction catalysed with [Ru]@MOF Ru1@(Al)MIL-101-NH Substrate 2 ·HCl reached 78% in just Product in the RCM reaction of DATA (11)—the conversion reached 65% in 3 h and 91% in 24 in 24 h h. It 15 min, but, unfortunately, did not increase after 24 h. Disappointingly, the RCM reaction should be mentioned here that we tried to improve the catalyst performance by treating of the olefin metathesis substrates 9 and 13 conducted in a similar manner (1 mol% of the MOF Table with of 3. Results dry HCl the RCM in reaction Et2O after sorptiondienes of selected of thecatalysed catalyst by [12]. Interestingly, the conver- Ru1@(Al)MIL-101-NH 2 com- Ru1@(Al)MIL-101-NH 2 ) resulted in a poorer outcome, giving only 31 and 30% conversion, sion plex inof DATA toluene (11) at 80 in °C. respectively (see Table 3).the (C reaction catalysed [7] = 0.1 M). with Conversion Ru1@(Al)MIL-101-NH was determined through 2· GCHCl reached was (tetradecane 78% in just used 15internal as an min, but, unfortunately, did not increase after 24 h. Disappointingly, the RCM standard). reaction of theofolefin Table 3. Results the RCM metathesis substrates reaction of selected 9 and dienes 13 conducted catalysed in a similar manner by Ru1@(Al)MIL-101-NH 2 complex Conversion (1 mol% of Ru1@(Al)MIL-101-NH [Ru]@MOF ◦ 2) resulted Substratein a poorer outcome, Product in toluene at 80 C. (C [7] = 0.1 M). Conversion was determined through GC (tetradecane giving only 31 and was 30% used as Ru1@(Al)MIL-101-NH 22 in31 24 h conversion, respectively an internal standard). (see Table 3). Conversion [Ru]@MOF Substrate Product in 24 h Ru1@(Al)MIL-101-NH Ru1@(Al)MIL-101-NH2 2 31 31 Ru1@(Al)MIL-101-NH Ru1@(Al)MIL-101-NH2 22 9191 Ru1@(Al)MIL-101-NH2 91 Ru1@(Al)MIL-101-NH22 Ru1@(Al)MIL-101-NH 31 31 Catalysts 2023, 13, 297 8 of 12 Table 3. Cont. Conversion [Ru]@MOF Substrate Product in 24 h Catalysts 2023, Catalysts 2023, 13, 13, xx FOR FOR PEER PEER REVIEW REVIEW 99 of of 13 13 Ru1@(Al)MIL-101-NH Ru1@(Al)MIL-101-NH Ru1@(Al)MIL-101-NH2 ·HCl 22 91 91 78 Ru1@(Al)MIL-101-NH Ru1@(Al)MIL-101-NH2 22 Ru1@(Al)MIL-101-NH 30 30 30 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 Ru1@(Al)MIL-101-NH Ru1@(Al)MIL-101-NH argon 3. atmosphere Materials and Methods using22the Methods ·HCl ·HCl standard Schlenk technique. The addition of dry solvents 78 78 or 3. Materials and reagents was carried out using argon-flushed plastic syringes. General Remarks. General Remarks. All All reactions reactions requiring requiring exclusion exclusion of of oxygen oxygen and and moisture moisture were were Analytical thin layer chromatography (TLC) was performed on Merck Silica gel 60 carried carried out in dry out in dryaluminium glassware glassware sheets. with with dry dry solvents solvents (SPS (SPS MBraun) MBraun) under under a dry and oxygen-free F254 precoated Components were visualised byaobservation dry and oxygen-free under UV argon atmosphere argon atmosphere using using the the standard standard Schlenk Schlenk technique. technique. The The addition addition of of dry dry solvents solvents or or light (254 nm or 365 nm) or dyed using aqueous KMnO4 or anisaldehyde reagent. Flash reagents reagents was carried out using argon-flushed plastic syringes. column was carried out using chromatography was argon-flushed carried out using plastic syringes. silica gel 60 (230–400 mesh), purchased Analytical thin Analytical thin layer layer chromatography chromatography (TLC) (TLC) was was performed performed on on Merck Merck Silica Silica gel 60 60 from Merck. GC chromatograms were recorded using a PerkinElmer Clarus 580 gel model. F254 precoated F254 precoated aluminium aluminium sheets. sheets. Components Components were were visualised visualised by by observation observation under under UV As the capillary column, an IntertCap 5MS-Sil column was employed with helium asUV the light light (254 (254 nm nmGC or or 365365 nm) or nm) or dyed dyed using aqueous KMnO 4 or anisaldehyde reagent. Flash carrier gas. conversions wereusing aqueous determined KMnO based on4 theor anisaldehyde ratio of an internal reagent. Flash standard column chromatography column chromatography was was carried carried out out using silica silica gel 60 60 (230–400 (230–400 mesh), purchased purchased (trimethoxybenzene or tetradecane) andusingthe startinggel material. 1 H NMR mesh), spectra were from from Merck. Merck. GC chromatograms GC chromatograms were recorded using a PerkinElmer were recorded using a PerkinElmer Clarus 580 model. Clarus 580 model. recorded in DCM-d 2 , DMSO-d6 , and MeOH-d4 at room temperature on Agilent Mercury As As the capillary the capillary(400 column, column, an anThe IntertCap IntertCap 5MS-Sil 5MS-Sil column columninwas was employed employed with helium withChemical helium as as the the spectrometers MHz). data were interpreted first-order spectra. shifts carrier carrier gas. GC gas. δ are reported GC conversions conversions in parts perwere were million determined determined based on based (ppm) downfield onfromthe ratio the ratio of an of an internal trimethylsilane internal standard as standard reference (trimethoxybenzene (trimethoxybenzene to residual solvent or or tetradecane) tetradecane) signal: DCM-d2and and the [δHthe starting starting = 5.32 ppm], material. material. DMSO-d 1 1H NMR spectra were rec- H 6NMR [δH =spectra2.50 ppm],were rec-D2 O orded orded [δH =in in 4.79DCM-d DCM-dppm], 2, DMSO-d6, and MeOH-d4 at room temperature on Agilent Mercury spec- 2, DMSO-d and MeOH-d 6, and MeOH-d [δH = 3.31 4 at room ppm]. temperature The following on Agilent abbreviations Mercuryare spec- used to 4 trometers trometers indicate the (400 (400 MHz). MHz). signal The data The multiplicity: data wereswere interpreted interpreted (singlet), in first-order in d (doublet), first-order spectra. t (triplet),spectra. q (quartet), Chemical Chemical shifts δδ shifts quin (quintet), are are reported sextreported (sextet),in in parts ddparts(doublet per million per million of doublet), (ppm)dtdownfield (ppm) downfield (doublet of from from trimethylsilane trimethylsilane triplet), ddd (doublet as of as reference reference doubletto to of residual residual doublet), solvent solvent etc., br. signal: signal: s (broad DCM-d DCM-d 2 [δH = 5.32 ppm], DMSO-d6 [δH = 2.50 ppm], D2O [δH = 2 [δH signal), and = 5.32 ppm], DMSO-d m (multiplet). Coupling6 [δH constants = 2.50 ppm], D2Ogiven (J) are [δH =in 4.79 4.79 ppm], Hz ppm], and and and refer MeOH-d toMeOH-d H,H-couplings. 4 [δH = 3.31 4 [δH = 3.31 ppm]. 13 C ppm]. NMR spectraThe following The following were recorded abbreviations abbreviations at room are are used to used temperature to indi- indi- on cate Agilent cate the signal Mercury the signal multiplicity: s 101 MHz spectrometers. multiplicity: (singlet), d (doublet), s (singlet), d (doublet),The spectra t (triplet), were recorded t (triplet), q (quartet), in DCM-d q (quartet), quin (quintet), quin2 ,(quintet), DMSO-d6 , sext sext (sextet), and(sextet), MeOH-ddd dd (doublet shifts 4 . Chemical (doublet of doublet), of doublet), are reported dt (doublet dt (doublet in δ units of relative of triplet),to triplet), ddd ddd (doublet the(doublet solvent signal: of doublet of doublet DCM-d of2 of doublet), [δC = 53.84 doublet), etc.,ppm], etc., br. ss (broad br. (broad DMSO-d signal), 6 [δC and signal), and = 39.52 m (multiplet). m (multiplet). ppm], andCoupling Coupling MeOH-d4constants constants [δC = 49.00 (J) are (J) are ppm]. given given Highin in Hz and resolution refer to mass H,H-couplings. spectra (HR-MS) 13C NMR spectra were recorded at room temperature on were obtained Hz and refer to H,H-couplings. C NMR spectra were recorded at room temperature on 13 on an AutoSpec Premier spectrometer. Agilent Elemental Agilent Mercury Mercuryanalyses 101were 101 MHzcarried MHz spectrometers. out at theThe spectrometers. The spectra Polish Academy spectra were of were recorded Science,in recorded inInstitute DCM-d2of DCM-d 2, DMSO- Organic , DMSO- d , and dChemistry. 6 6, and MeOH-d MeOH-d IR spectra 4 . Chemical 4. Chemical shifts were recorded are shifts areon reported in a Perkin-Elmer reported δ units in δ units relative Spectrum relativeOne to to thethe FTIR solvent signal: spectrometer. solvent signal: DCM-d Substances DCM-d 2 [δC 2 [δC were = 53.84 = 53.84 ppm], applied ppm],asDMSO-dDMSO-d a film, solid, [δC 6 [δC or 6 = 39.52 ppm], in solution. = 39.52 ppm], The and MeOH-d and obtained MeOH-d4data 4 [δC [δC were = 49.00 = 49.00 ppm]. processed ppm]. High resolution with resolution the software mass spectra Omni32. (HR-MS) were Wavenumbers were obtained areobtained given inon on cman − 1 an.AutoSpec AutoSpec Powder X-ray Premier spectrom- diffraction: All High mass spectra (HR-MS) Premier spectrom- eter. powder Elemental X-ray analyses diffraction were (PXRD) carriedpatternsout at the were eter. Elemental analyses were carried out at the Polish Academy of Science, Institute ofPolish recorded Academy on a of Bruker Science, D8 Institute Discover of X-ray Organic diffractometerChemistry. (CuKα IR spectra radiation), were withrecorded a parallel on Organic Chemistry. IR spectra were recorded on a Perkin-Elmer Spectrum One FTIR spec- a beam Perkin-Elmer formed by Spectrum a Goebel One mirror FTIR spec- equipped trometer. with a VANTEC trometer. Substances Substances were applied applied as 1 position-sensitive were as aadetector. film, solid, film, solid, Allorormeasurements in solution. in solution. The Thewereobtained obtainedperformed data were data were in an processed aluminium with the holder. software The nitrogenOmni32. Wavenumbers adsorption isotherms processed with the software Omni32. Wavenumbers are given in cm−1. Powder X-ray dif- are given were in measuredcm −1. Powder at liquid X-ray dif- nitrogen fraction: temperature fraction: All powder All powder (77 K)X-ray X-ray diffraction usingdiffraction Quantachrome (PXRD) (PXRD) patterns were Autosorb-IQ-MP patterns were recorded recorded sorption onanalyser. on aa Bruker Bruker D8 D8 PriorDis- Dis-to cover X-ray diffractometer (CuKα radiation), cover X-ray diffractometer (CuKα radiation), with a parallel beam formed by a Goebelwith a parallel beam formed by a Goebel mirror equipped mirror equipped with with aa VANTEC VANTEC 11 position-sensitive position-sensitive detector. detector. All All measurements measurements were were performed in an aluminium holder. The nitrogen performed in an aluminium holder. The nitrogen adsorption isotherms were measured at adsorption isotherms were measured at liquid nitrogen temperature (77 K) using Quantachrome liquid nitrogen temperature (77 K) using Quantachrome Autosorb-IQ-MP sorption ana- Autosorb-IQ-MP sorption ana- lyser. Prior lyser. Prior to to measurements, measurements, all all samples samples were were dried dried for for no no less less than than 24 24 hh under under vacuum vacuum Catalysts 2023, 13, 297 9 of 12 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 1 H 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%). 1 H NMR (400 MHz, CD2 Cl2 ) 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). 13 C NMR (101 MHz, CD2 Cl2 ) 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 C29 H32 Cl2 N2 O2 Ru: 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%). 1 H NMR (400 MHz, CD2 Cl2 ) 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). 13 C NMR (101 MHz, CD2 Cl2 ) 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 Catalysts 2023, 13, 297 10 of 12 (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 frame- work 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 cata- lyst 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. 1 H NMR spectrum of (Al)MIL- 101-NH2 digested in 4 wt. % NaOD/D2 O; 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. 1 H NMR of compound 1; Figure S9. 13 C NMR of compound 1; Figure S10. 1 H NMR of compound 3; Figure S11. 13 C NMR of compound 3; Figure S12. 1 H NMR of compound 5, Figure S13. 13 C NMR of compound 5; Figure S14. 1 H NMR of compound 6; Figure S15. 13 C NMR of compound 6; Figure S16. 1 H NMR of Ru1 after the crystallization from DCM/MeOH; Figure S17. 1 H NMR of Ru1 after stirring it with AgCl; Figure S18. 13 C NMR of Ru1 after stirring it with of AgCl; Figure S19. 1 H NMR of Ru2; Figure S20. 13 C NMR of Ru2; Figure S21. 1 H NMR of compound 15; Figure S22. 13 C NMR of compound 15; Table S1. Stability studies of Ru1 and Ru2 in CD2 Cl2 ; 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 innova- tion 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. References 1. Grela, K. (Ed.) Olefin Metathesis: Theory and Practice; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2014. 2. Grubbs, R.H.; Wenzel, A.G.; O’Leary, D.J.; Khosravi, E. (Eds.) Handbook of Metathesis; Wiley-VCH: Weinheim, Germany, 2015. 3. Clavier, H.; Grela, K.; Kirschning, A.; Mauduit, M.; Nolan, S.P. Sustainable Concepts in Olefin Metathesis. Angew. Chem. Int. Ed. 2007, 46, 6786–6801. [CrossRef] [PubMed] 4. Vougioukalakis, G.C. Removing Ruthenium Residues from Olefin Metathesis Reaction Products. Chem.—A Eur. J. 2012, 18, 8868–8880. [CrossRef] [PubMed] 5. Wheeler, P.; Phillips, J.H.; Pederson, R.L. Scalable Methods for the Removal of Ruthenium Impurities from Metathesis Reaction Mixtures. Org. Process Res. Dev. 2016, 20, 1182–1190. [CrossRef] Catalysts 2023, 13, 297 11 of 12 6. Yaghi, O.M.; Kalmutzki, M.J.; Diercks, C.S. (Eds.) Introduction to Reticular Chemistry: Metal-Organic Frameworks and Covalent Organic Frameworks; Wiley-VCH: Weinheim, Germany, 2019. 7. Dybtsev, D.N.; Bryliakov, K.P. Asymmetric catalysis using metal-organic frameworks. Coord. Chem. Rev. 2021, 437, 213845. [CrossRef] 8. Wei, Y.-S.; Zhang, M.; Zou, R.; Xu, Q. Metal–Organic Framework-Based Catalysts with Single Metal Sites. Chem. Rev. 2020, 120, 12089–12174. [CrossRef] 9. Bavykina, A.; Kolobov, N.; Khan, I.S.; Bau, J.A.; Ramirez, A.; Gascon, J. Metal–Organic Frameworks in Heterogeneous Catalysis: Recent Progress, New Trends, and Future Perspectives. Chem. Rev. 2020, 120, 8468–8535. [CrossRef] 10. Yang, D.; Gates, B.C. Catalysis by Metal Organic Frameworks: Perspective and Suggestions for Future Research. ACS Catal. 2019, 9, 1779–1798. [CrossRef] 11. Rogge, S.M.J.; Bavykina, A.; Hajek, J.; Garcia, H.; Olivos-Suarez, A.I.; Sepúlveda-Escribano, A.; Vimont, A.; Clet, G.; Bazin, P.; Kapteijn, F.; et al. Metal–organic and covalent organic frameworks as single-site catalysts. Chem. Soc. Rev. 2017, 46, 3134–3184. [CrossRef] 12. Chołuj, A.; Zieliński, A.; Grela, K.; Chmielewski, M.J. Metathesis@MOF: Simple and Robust Immobilization of Olefin Metathesis Catalysts inside (Al)MIL-101-NH2. ACS Catal. 2016, 6, 6343–6349. [CrossRef] 13. Chołuj, A.; Nogaś, W.; Patrzałek, M.; Krzesiński, P.; Chmielewski, M.J.; Kajetanowicz, A.; Grela, K. Preparation of Ruthenium Olefin Metathesis Catalysts Immobilized on MOF, SBA-15, and 13X for Probing Heterogeneous Boomerang Effect. Catalysts 2020, 10, 438. [CrossRef] 14. Chołuj, A.; Karczykowski, R.; Chmielewski, M.J. Simple and Robust Immobilization of a Ruthenium Olefin Metathesis Catalyst Inside MOFs by Acid–Base Reaction. Organometallics 2019, 38, 3392–3396. [CrossRef] 15. Chołuj, A.; Krzesiński, P.; Ruszczyńska, A.; Bulska, E.; Kajetanowicz, A.; Grela, K. Noncovalent Immobilization of Cationic Ruthenium Complex in a Metal–Organic Framework by Ion Exchange Leading to a Heterogeneous Olefin Metathesis Catalyst for Use in Green Solvents. Organometallics 2019, 38, 3397–3405. [CrossRef] 16. Spekreijse, J.; Öhrström, L.; Sanders, J.P.M.; Bitter, J.H.; Scott, E.L. Mechanochemical Immobilisation of Metathesis Catalysts in a Metal–Organic Framework. Chem.—A Eur. J. 2016, 22, 15437–15443. [CrossRef] 17. Yuan, J.; Fracaroli, A.M.; Klemperer, W.G. Convergent Synthesis of a Metal–Organic Framework Supported Olefin Metathesis Catalyst. Organometallics 2016, 35, 2149–2155. [CrossRef] 18. Arnanz, A.; Pintado-Sierra, M.; Corma, A.; Iglesias, M.; Sánchez, F. Bifunctional Metal Organic Framework Catalysts for Multistep Reactions: MOF-Cu(BTC)-[Pd] Catalyst for One-Pot Heteroannulation of Acetylenic Compounds. Adv. Synth. Catal. 2012, 354, 1347–1355. [CrossRef] 19. Sivan, S.E.; Oh, K.-R.; Yoon, J.-W.; Yoo, C.; Hwang, Y.K. Immobilization of a trimeric ruthenium cluster in mesoporous chromium terephthalate and its catalytic application. Dalton Trans. 2022, 51, 13189–13194. [CrossRef] [PubMed] 20. Berijani, K.; Morsali, A.; Hupp, J.T. An effective strategy for creating asymmetric MOFs for chirality induction: A chiral Zr-based MOF for enantioselective epoxidation. Catal. Sci. Technol. 2019, 9, 3388–3397. [CrossRef] 21. Rimoldi, M.; Nakamura, A.; Vermeulen, N.A.; Henkelis, J.J.; Blackburn, A.K.; Hupp, J.T.; Stoddart, J.F.; Farha, O.K. A metal– organic framework immobilised iridium pincer complex. Chem. Sci. 2016, 7, 4980–4984. [CrossRef] 22. Baek, J.; Rungtaweevoranit, B.; Pei, X.; Park, M.; Fakra, S.C.; Liu, Y.-S.; Matheu, R.; Alshmimri, S.A.; Alshehri, S.; Trickett, C.A.; et al. Bioinspired Metal–Organic Framework Catalysts for Selective Methane Oxidation to Methanol. J. Am. Chem. Soc. 2018, 140, 18208–18216. [CrossRef] 23. Choi, S.; Jung, W.-J.; Park, K.; Kim, S.-Y.; Baeg, J.-O.; Kim, C.H.; Son, H.-J.; Pac, C.; Kang, S.O. Rapid Exciton Migration and Amplified Funneling Effects of Multi-Porphyrin Arrays in a Re(I)/Porphyrinic MOF Hybrid for Photocatalytic CO2 Reduction. ACS Appl. Mater. Interfaces 2021, 13, 2710–2722. [CrossRef] 24. Wu, P.; He, C.; Wang, J.; Peng, X.; Li, X.; An, Y.; Duan, C. Photoactive Chiral Metal–Organic Frameworks for Light-Driven Asymmetric α-Alkylation of Aldehydes. J. Am. Chem. Soc. 2012, 134, 14991–14999. [CrossRef] [PubMed] 25. Madrahimov, S.T.; Gallagher, J.R.; Zhang, G.; Meinhart, Z.; Garibay, S.J.; Delferro, M.; Miller, J.T.; Farha, O.K.; Hupp, J.T.; Nguyen, S.T. Gas-Phase Dimerization of Ethylene under Mild Conditions Catalyzed by MOF Materials Containing (bpy)NiII Complexes. ACS Catal. 2015, 5, 6713–6718. [CrossRef] 26. Zhu, W.; Xiang, G.; Shang, J.; Guo, J.; Motevalli, B.; Durfee, P.; Agola, J.O.; Coker, E.N.; Brinker, C.J. Versatile Surface Functional- ization of Metal–Organic Frameworks through Direct Metal Coordination with a Phenolic Lipid Enables Diverse Applications. Adv. Funct. Mater. 2018, 28, 1705274. [CrossRef] 27. Monsigny, L.; Kajetanowicz, A.; Grela, K. Ruthenium Complexes Featuring Unsymmetrical N-Heterocyclic Carbene Ligands– Useful Olefin Metathesis Catalysts for Special Tasks. Chem. Rec. 2021, 21, 3648–3661. [CrossRef] [PubMed] 28. Paradiso, V.; Costabile, C.; Grisi, F. Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands. Beilstein J. Org. Chem. 2018, 14, 3122–3149. [CrossRef] 29. Ablialimov, O.; K˛edziorek, M.; Torborg, C.; Malińska, M.; Woźniak, K.; Grela, K. New Ruthenium(II) Indenylidene Complexes Bearing Unsymmetrical N-Heterocyclic Carbenes. Organometallics 2012, 31, 7316–7319. [CrossRef] 30. Patrzałek, M.; Piatkowski, ˛ J.; Kajetanowicz, A.; Grela, K. Anion Metathesis in Facile Preparation of Olefin Metathesis Catalysts Bearing a Quaternary Ammonium Chloride Tag. Synlett 2019, 30, 1981–1987. [CrossRef] Catalysts 2023, 13, 297 12 of 12 31. Małecki, P.; Gajda, K.; Ablialimov, O.; Malińska, M.; Gajda, R.; Woźniak, K.; Kajetanowicz, A.; Grela, K. Hoveyda–Grubbs-Type Precatalysts with Unsymmetrical N-Heterocyclic Carbenes as Effective Catalysts in Olefin Metathesis. Organometallics 2017, 36, 2153–2166. [CrossRef] 32. Małecki, P.; Gajda, K.; Gajda, R.; Woźniak, K.; Trzaskowski, B.; Kajetanowicz, A.; Grela, K. Specialized Ruthenium Olefin Metathesis Catalysts Bearing Bulky Unsymmetrical NHC Ligands: Computations, Synthesis, and Application. ACS Catal. 2019, 9, 587–598. [CrossRef] 33. Planer, S.; Małecki, P.; Trzaskowski, B.; Kajetanowicz, A.; Grela, K. Sterically Tuned N-Heterocyclic Carbene Ligands for the Efficient Formation of Hindered Products in Ru-Catalyzed Olefin Metathesis. ACS Catal. 2020, 10, 11394–11404. [CrossRef] 34. Smoleń, M.; Kośnik, W.; Loska, R.; Gajda, R.; Malińska, M.; Wożniak, K.; Grela, K. Synthesis and catalytic activity of ruthenium indenylidene complexes bearing unsymmetrical NHC containing a heteroaromatic moiety. RSC Adv. 2016, 6, 77013–77019. [CrossRef] 35. Grudzień, K.; Trzaskowski, B.; Smoleń, M.; Gajda, R.; Woźniak, K.; Grela, K. Hoveyda-Grubbs catalyst analogues bearing the derivatives of N-phenylpyrrol in the carbene ligand-structure, stability, activity and unique ruthenium-phenyl interactions. Dalton Trans. 2017, 46, 11790–11799. [CrossRef] [PubMed] 36. Smoleń, M.; Kośnik, W.; Gajda, R.; Woźniak, K.; Skoczeń, A.; Kajetanowicz, A.; Grela, K. Ruthenium Complexes Bearing Thiophene-Based Unsymmetrical N-Heterocyclic Carbene Ligands as Selective Catalysts for Olefin Metathesis in Toluene and Environmentally Friendly 2-Methyltetrahydrofuran. Chem.—A Eur. J. 2018, 24, 15372–15379. [CrossRef] [PubMed] 37. Ablialimov, O.; K˛edziorek, M.; Malińska, M.; Woźniak, K.; Grela, K. Synthesis, Structure, and Catalytic Activity of New Ruthenium(II) Indenylidene Complexes Bearing Unsymmetrical N-Heterocyclic Carbenes. Organometallics 2014, 33, 2160–2171. [CrossRef] 38. Jolly, P.I.; Marczyk, A.; Małecki, P.; Ablialimov, O.; Trzybiński, D.; Woźniak, K.; Osella, S.; Trzaskowski, B.; Grela, K. Azoliniums, Adducts, NHCs and Azomethine Ylides: Divergence in Wanzlick Equilibrium and Olefin Metathesis Catalyst Formation. Chem.—A Eur. J. 2018, 24, 4785–4789. [CrossRef] 39. Serra-Crespo, P.; Ramos-Fernandez, E.V.; Gascon, J.; Kapteijn, F. Synthesis and Characterization of an Amino Functionalized MIL-101(Al): Separation and Catalytic Properties. Chem. Mater. 2011, 23, 2565–2572. [CrossRef] 40. Rouquerol, J.; Llewellyn, P.L.; Rouquerol, F. Is the bet equation applicable to microporous adsorbents. Stud. Surf. Sci. Catal. 2007, 160, 49–56. [CrossRef] 41. Walton, K.S.; Snurr, R.Q. Applicability of the BET Method for Determining Surface Areas of Microporous Metal−Organic Frameworks. J. Am. Chem. Soc. 2007, 129, 8552–8556. [CrossRef] 42. Zwoliński, K.M.; Nowak, P.; Chmielewski, M.J. Towards multifunctional MOFs – transforming a side reaction into a post-synthetic protection/deprotection method. Chem. Commun. 2015, 51, 10030–10033. [CrossRef] 43. Ho, T.-L.; Olah, G.A. Cleavage of Esters and Ethers with Iodotrimethylsilane. Angew. Chem. Int. Ed. 1976, 15, 774–775. [CrossRef] Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). 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