Noncovalent Immobilization of Cationic Ruthenium Complex in a

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

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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 Artur Chołuj,† Paweł Krzesiński,† Anna Ruszczyńska, Ewa Bulska, Anna Kajetanowicz, and Karol Grela* Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Ż wirki i Wigury 101, 02-089 Warsaw, Poland Downloaded via BUFFALO STATE on July 22, 2019 at 20:47:26 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: A simple strategy for noncovalent immobilization of an olefin metathesis catalyst inside a (Cr)MIL-101SO3Na metal−organic framework (MOF) was presented. The olefin metathesis active corean alkylidene complex bearing an ammonium-tagged NHC ligand (Apeiron’s FixCat)was immobilized by ion exchange facilitated by the use of crown ether. The hybrid material thus obtained was shown with a number of model substrates to exhibit high activity and selectivity in a wide range of solvents. Next, selected polyfunctional pharmaceutically related substrates were transformed using 0.8−0.5 mol % of the Ru@MOF in polar solvents such as acetone and dimethyl carbonate, making this technology interesting in the context of green solvent utilization.

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INTRODUCTION Metal−organic frameworks (MOFs) are organic−inorganic materials which, as a result of large surface area, extra-high porosity, and easily tunable chemical functionalities, are gaining more and more importance in the field of gas storage, separation, sensing, and catalysis.1−6 MOFs are known for their Lewis7,8 and Brønsted acidity9 as well as Brønsted basicity,10 which is related to their structure: the presence of coordinatively unsaturated metal sites and functional groups in the organic linkers. The latter can be easily decorated with various functionalities, such as amines (e.g., (Al)MIL-101NH2),11 alcohols (UiO-66-OH),12 thiols (UiO-66-TCAT),13 and carboxylic (UiO-66-COOH)14 and sulfonic acids ((Cr)MIL-101-SO3H),15 which tune their properties and enable postsynthetic modification. In particular, a class of metal−organic frameworks called MIL-101, due to its thermal stability and chemical robustness,16 is one the most suitable candidates to be used in catalysis as well as in other applications.17−21 MIL-101 by itself, as a result of the presence of coordinatively unsaturated metal sites, can act as a mild Lewis acid;22 however, this effect is negligible for its premodified, sulfonic acid functionalized MIL-101-SO3H (Figure 1). Such a MOF possesses dense and regular Brønsted acidic sites and, in comparison to the postsynthetically functionalized acidic MOFs,23 exhibits increased stability and higher catalytic activity in various organic transformations such as acetalization,24 alcoholysis of epoxides,25 esterification,23,26 and Hantzsch reactions.27 What is more, preparation of premodified MIL-101-SO3H according to the methodology developed by Kitagawa28 and improved by Gascon15 is more convenient than postsynthetic modification of the parent MIL-101 with sulfuric acid.29 Additionally, © XXXX American Chemical Society

Figure 1. (A) Scaffold representation of MIL-101-SO3H. (B) Visual representation of MIL-101-SO3H.

because of the presence of free sulfonic groups which can be easily converted into corresponding salts, it can also serve as a support for homogeneous catalysts. Special Issue: Organometallic Chemistry within Metal-Organic Frameworks Received: May 1, 2019

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DOI: 10.1021/acs.organomet.9b00287 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Scheme 1. Immobilization of FixCat on (Cr)MIL-101-SO3−Na+ by Ion Exchange

deprotonated to compensate the charge of the [(−Ph− COO−)6Cr3O+] cluster. Nevertheless, such a structure allows for the introduction of new cations using simple ion metathesis, which we intended to exploit in the catalyst’s immobilization. Inside the relatively large pores of the MOF (2.6 and 3.2 nm) a few molecules of a ruthenium complex can be accommodated without a significant influence on the transport of substrates through inner structures of the (Cr)MIL. What is even more important, it has relatively wide pore windows (1.2 and 1.5 nm, respectively), which are sufficient for the unconstrained migration of the Hoveyda− Grubbs catalyst (ca. 1.6 × 1.2 × 0.9 nm) into the pores. Immobilization of Ruthenium Complex−FixCat. Prior to immobilizing FixCat inside the MOF, we obtained modified versions of (Cr)MIL, namely (Cr)MIL-101-SO3−Na+, in which all H+ was replaced with Na+ (such cation exchange has been already reported for (Cr)MIL-101-SO3H to tune up separation capability50,51 and for measurement of acid group content24). The quaternary ammonium group present in the FixCat complex allowed for immobilization of the catalyst inside the MOF as a result of cation exchange (Scheme 1). This type of immobilization seems to be more robust; thus, the leaching of the catalyst to the solution and contamination of the product with ruthenium should be minimal as long as there are no other cations in the solution that have a higher affinity to sulfonic groups than the FixCat cation. In our first approach, a solution of FixCat in DCM was mixed with (Cr)MIL-101-SO3−Na+ and stirred for a few minutes (Scheme 1), leading to quantitative sorption. Next, the solvent was evaporated and the residue was washed with water to remove sodium chloride. To check the activity of the newly obtained system we used a model ring-closing metathesis reaction (RCM) of diethyl 2,2diallylmalonate (1) (Scheme 2). The reaction was performed

The development of well-defined molybdenum and ruthenium complexes increased the importance of the olefin metathesis (OM) reaction as a useful methodology in the synthesis of carbon−carbon double bonds.30,31 Nowadays, OM is widely used in the synthesis of natural products32,33 and biologically active compounds,34,35 as well as in the production of polymers36,37 and valorization of biomass.38−40 Yet, its use is limited because of difficulties in separation of the catalyst from the reaction mixture and possible subsequent side reactions leading to contamination of products or even reduction of their yield. One possible way to circumvent these obstacles is to displace homogeneous catalysts with their heterogeneous counterparts. Noncovalent immobilization of well-defined Ru olefin metathesis catalysts on supports such as SiO2 and others is known, and these systems have found some applications in OM reactions in nonpolar solvents such as pentane and hexane41−43 or with nonpolar substrates.41,42 Use of NHCtagged catalysts can allow for more polar solvents.44,45 We reported previously on immobilization of a series of tagged Ru olefin metathesis catalysts on amino-functionalized MOF (Al)MIL-101-NH2·HCl by electrostatic interactions.46 The resulting systems were characterized by excellent catalytic properties, such as high turnover numbers46 and good selectivity in RCM macrocyclization,39 but they worked in relatively nonpolar solvents such as EtOAc, toluene, and PAO (paraffin-like polymerized α-olefins). When i-PrOH was used instead, almost complete leaching of the catalysts out of the support was observed, as apparently the electrostatic interactions were too weak to make the Ru@MOF system stable in protic media.46 In the present approach we decided to test the strategy where the positively charged Ru complex is immobilized inside a MOF possessing negatively charged groups. The planned immobilization, achieved formally by an ion metathesis reaction,47−49 should lead to a new noncovalently immobilized anion−cation system, possibly compatible with a broader scope of organic solvents. A related approach, based on immobilization of a Ru complex bearing not quaternary but a free amino group using an acid−base reaction, was independently developed by Chmielewski et al. and is published in this issue (see ref 88 for further explanation).

Scheme 2. Model RCM Reaction of Diethyl 2,2Diallylmalonate (1)

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RESULTS AND DISCUSSION (Cr)MIL-101-SO3H (Figure 1), synthesized in an aqueous solution of hydrofluoric acid, 2-sulfoterephthalic acid and chromium(III) nitrate at 180 °C, is one of the most stable MOFs containing strong acidic groups. According to the literature,15 only one-third of the sulfonic groups are acidic, one-third occur as a sodium salt, and one-third are

in toluene in the presence of 0.1 mol % (1000 ppm) of Ru complex, reaching 52% conversion after 24 h at 50 °C. Such result was a bit discouraging, as the same reaction catalyzed by the previously described hybrid system composed of FixCat immobilized on (Al)MIL-101-NH2·HCl gave 99% conversion.46 B


Article

Organometallics Scheme 3. Immobilization of FixCat on (Cr)MIL-101-SO3−(Na·15-crown-5)+ by Ion Exchange

Next, we investigated the activity of these two new catalytic systems in the RCM of diethyl 2,2-diallylmalonate (Scheme 2) and compared it with that of the initially obtained complex FixCat@(Cr)MIL-101-SO3−Na+. As the latter provided only 52% conversion, we were elated to observe a significant increase of conversion, to 96% for the Li derivative and to 99% in the case of the Na·15-crown-5 analogue (Table 1, entries 2 and 3). In the next trial we used the reduced catalyst loading500 ppmto better assess the differences between these catalysts. For the complex with sodium cations only 18% conversion was achieved (Table 1, entry 4), which in terms of previous results was not a big surprise, while for the other two systems, based on Li and (Na·15-crown-5) salts, we noted much better yields of 70 and 97%, respectively (Table 1, entries 5 and 6). Olefin Metathesis Activity Studies of the Obtained Catalysts. To the best of our knowledge, only five MOFbased catalytic systems have been developed so far for olefin metathesis reactions: one based on rhenium52 and four relying on well-defined ruthenium catalysts.46,53−55 All of these heterogeneous catalysts were used in nonpolar solvents such as benzene53 and toluene, EtOAc, and paraffin/PAO39,46 or neat.52 The new design is based on a not yet investigated immobilization method involving ion exchange, which should result in a system in which the catalyst is incorporated into the MOF structure by ionic bonding.56 Such an interaction should be much stronger than the physical sorption we used previously, which should enable making reactions in polar solvents. Considering the low activity of FixCat@(Cr)MIL101-SO3−Na+, subsequent studies were made exclusively with systems based on Li and Na·15-crown-5. To assess the practical usefulness of these hybrid catalysts, the model RCM reaction of diethyl 2,2-diallylmalonate (1) (Scheme 2) was performed in various solvents, including the currently recommended “green” substitutes (Table 2).57 For the RCM of 1 catalyzed by FixCat@(Cr)MIL-101SO3−Li+ in toluene, a significant decrease in conversion was observed upon reduction of catalyst loading from 1000 to 500

We suspected that the low activity of FixCat@(Cr)MIL-101SO3−Na+ can be attributed to the presence of traces of water used during the workup that cannot be removed even after prolonged drying. In order to eliminate the detrimental effect of this solvent, alternative methods of cation metathesis were amended, which required the use of other (Cr)MIL alkali metal salts. First, a lithium salt, (Cr)MIL-101-SO3−Li+, (for preparation see the Supporting Information) was treated with a methanol solution of FixCat, giving after 30 min almost quantitative immobilization. As a result of the good solubility of lithium chloride in methanol, the latter could be easily washed out of the MOF. Alternatively, a specially prepared MOF with sodium cations complexed by 15-crown-5 ether molecules (see the Supporting Information for preparation details) was used. This material was treated analogously to the Li derivative: namely, stirred with Ru catalysts in methanol and after adsorption of the whole amount of catalysts washed with methanol to remove the excess (Na·15-crown-5)+Cl− (Scheme 3 and Figure 2).

Figure 2. Visual representation of FixCat@(Cr)MIL-101-SO3−(Na· 15-crown-5)+.

Table 1. Influence of Differently Prepared Supports on Catalytic Activity of the Resulted Hybrid Catalystsa entry

Ru@MOF

loading (ppm)

conversion (%)

1 2 3 4 5 6

FixCat@(Cr)MIL-101-SO3−Na+b FixCat@(Cr)MIL-101-SO3−Li+ FixCat@(Cr)MIL-101-SO3−(Na·15-crown-5)+ FixCat@(Cr)MIL-101-SO3−Na+b FixCat@(Cr)MIL-101-SO3−Li+ FixCat@(Cr)MIL-101-SO3− (Na·15-crown-5)+

1000 1000 1000 500 500 500

52 96 99 18 70 97

Conditions: FixCat immobilized on different materials, 5 wt %, toluene, 50 °C; 24 h, c = 0.5 M. bMaterial washed with water.

a

C


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Organometallics

crown-5)+ system should be considered as more stable in polar solvents than the previously reported system. On the basis of the above results, we decided to focus on the FixCat@(Cr)MIL-101-SO3−(Na·15-crown-5)+ system, as it was giving the highest activity in the tested reactions. Although the preparation method utilizing the expensive crown ether was more costly, we assumed that the higher price of the system is balanced by its better catalytic properties. From Table 2, one can state that for the more active system the solvents from entries 8−11 give equally promising results. Therefore, our choice of solvent had to be based on additional aspects, such as physicochemical properties, toxicity, impact on the environment, and the green context.58−64 Current initiatives of the European Solvents Industry Group (ESIG) together with the European Chemicals Agency (ECHA) identified the need to re-evaluate chemical processes with regard to health, safety, and environmental risks related to the solvents used.65 Therefore, despite the good results reported in Table 2 for toluene, we decided to focus on solvents such as EtOAc, acetone, and dimethyl carbonate (DMC),66 as alternatives to traditional solvents. From these “greener” solvents we decided to choose DMC, due to its low toxicity, high biodegradability, and promise of reduced carbon footprint.67 Using this green solvent,68 the scope and limitations study of the developed hybrid catalytic system FixCat@(Cr)MIL-101-SO3−(Na·15-crown-5)+ was then attempted. Prior to this, however, the sustained heterogeneity of the catalytic system during the reaction in DMC was proven, utilizing the split (hot-filtration) test.69,70 For this purpose the RCM reaction of diethyl 2,2-diallylmalonate (1) (Scheme 2) was performed and after 30 min half of the reaction mixture was filtered via a Teflon filter into a new preheated flask. The filtered mixture was immediately analyzed to calculate the conversion at the split time, which was found to be 39%. After 24 h the conversion was determined in both filtered and nonfiltered reaction mixtures (the appropriate data are presented in Figure 3) and no increase in conversion in the filtered reaction mixture was observed. At the same time, the reaction proceeded further and reached almost quantitative conversion in the sample that was not filtered. This proves that

Table 2. Influence of Various Solvents on Activity and Leaching of New Heterogeneous Catalystsa entry 1

catalyst FixCat@(Cr) MIL-101SO3−Li+

2 3 4 5 6 7 8

9 10 11 12 13 14

FixCat@(Cr) MIL-101-SO3− (Na·15-crown5)+

loading (ppm)

conversion (%)

ruthenium content (ppm)b

toluene

1000

96

75

EtOAc DMC acetone 2-MeTHF i-PrOH

1000 1000 1000 1000

98 99 >99 70

30 20 64 70

1000 5000 250

57 99 95

70 152 22

250 250 250 250

93 93 96 73

13 6 13 24

250 5000

32 96

24 122

solvent

toluene

EtOAc DMC acetone 2-MeTHF i-PrOH

a Conditions: FixCat immobilized on different materials, 5 wt %, 50 °C; 24 h, c = 0.5 M. bRu context in crude unpurified product, based on ICP-MS measurement.

ppm (Table 1); therefore, in the next attempts we used 1000 ppm of catalysts to achieve higher conversions. Table 2 (entries 1−4) shows that solvents such as ethyl acetate, dimethyl carbonate (DMC), and acetone can be considered as the solvents of choice, as almost quantitative conversions were reached in each case. Moreover, in all cases the ruthenium content in the crude product, diethyl cyclopent-3-ene-1,1dicarboxylate (2), was relatively low, reaching only 75−20 ppm (the lowest was when DMC was applied). In 2-methyltetrahydrofuran the result was not as good, as only 70% conversion was observed after 24 h at 50 °C (Table 2, entry 5). In the experiment performed in the most polar solventi-PrOH only 57% conversion was achieved, but relatively low leaching, 70 ppm, was noted. After the catalyst loading was increased to 5000 ppm, almost quantitative conversion was obtained, but simultaneously the leaching reached 152 ppm, as a visible result of catalyst desorption (Table 2, entries 6 and 7). Then the same set of solvents was used with FixCat@(Cr)MIL-101SO3−(Na·15-crown-5)+, which was more active than its lithiated analogue (cf. Table 1). This fact allowed us to reduce the catalyst loading to 250 ppm. In all solvents but two, 2-MeTHF and i-PrOH, very good results were noted in terms of both conversion and limited ruthenium content (Table 2, entries 9−11). Switching to 2-methyltetrahydrofuran decreased the conversion to 73%, although the level of ruthenium in the crude product remained relatively low (24 ppm). For isopropyl alcohol, a significant drop in conversion occurred, which increased again to quantitative after an increase in catalyst loading to 5000 ppm. Also here some leaching related to the partial desorption of the catalyst was observed (24−122 ppm). It should be noted, however, that the previously studied Ru@(Al)MIL system was fully incompatible with i-PrOH, and the complete leaching of Ru was observed in this solvent.46 Therefore, the new FixCat@(Cr)MIL-101-SO3−(Na·15-

Figure 3. Conversion vs time plot for FixCat@(Cr)MIL-101SO3−(Na·15-crown-5)+ Conditions: 5 wt %, 250 ppm, DMC, 50 °C, 0.5 M, 24 h; split after 30 min. D


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Organometallics Table 3. Results of RCM Comparative Studyg

a Calculated on the basis of GC measurement. bYield calculated on the basis of GC measurement (with calibration curves). cRu content 7.1 ppm (ICP-MS). dRu content 63 ppm (ICP-MS). ec = 0.005 M. fc = 0.01 M. gConditions unless noted otherwise: FixCat@(Cr)MIL-101-SO3−(Na·15crown-5)+ 5 wt %, DMC, 50 °C, c = 0.5 M, 24 h.

(entry 7). It should be noted that the hybrid catalyst FixCat@(Cr)MIL-101-SO3−(Na·15-crown-5)+ was not only found to be active and selective in these transformations but could also be very easily separated from the reaction mixture by simple filtration, leading to practically pure products with relatively low Ru residue content. The experiments shown in Table 3 were made in dry solvent. We were interested to check if the amount of water in DMC can influence the catalyst activity. Therefore, we performed two model reactions of diethyl 2,2-diallylmalonate (1) with 250 ppm of FixCat@(Cr)MIL-101-SO3−(Na·15crown-5)+, one in dry DMC (Sigma-Aldrich Sure/Seal), which according to a Karl Fisher titration contained 19 ppm of water, while the second was made in not-anhydrous DMC containing ca. 20 times more water (490 ppm). To our delight, the reaction outcomes were fairly the same, as we obtained 93 and 92% conversions, respectively. This demonstrates that the Ru@MOF system does not require anhydrous solvents and works in commercially available DMC (for details, see the Supporting Information). Having successfully demonstrated the good properties of the immobilized Ru complex in model metathesis reactions, we decided to apply it to more sophisticated compounds with potential biological activity (Scheme 4). To do so, we attempted the RCM reaction leading to azepine derivative 16, a known intermediate in the synthesis of cathepsin K inhibitor.74 Using only 0.5 mol % of Ru in DMC, a quantitative conversion and high isolated yield of 16 was noted. Interestingly, the same homogeneous and not green

the active species are not present in solution, thus suggesting that this reaction is truly heterogeneous. Importantly, split tests for other solvents were carried out. In all cases, the reaction progress in the filtrate was fully suppressed; even for i-PrOH, where the catalyst’s leaching was quite significant, the split test confirmed that the system remained heterogeneous (for details see the Supporting Information). Anticipating future practical applications of the title hybrid catalyst, we tested it with a wider scope of substrates, including not only the standard malonate derivatives but also dienes that were polyfunctional and were sensitive to isomerization (Table 3). First, three rather simple derivatives of diethyl malonate were tested (Table 3, entries 1−3), leading to the expected products 2, 4, and 6 bearing five- to seven-membered rings in practically quantitative yield; the reactions utilized only 0.20− 0.25 mol % of heterogeneous Ru catalyst in DMC. Next, diallyl ether 7 was cyclized in good yield, leading to dihydrofuran derivative 8 as the only product. It should be noted that diallyl ethers are known to be susceptible to C−C double-bond migration during RCM.71 Similarly, the rather fragile polar proline diallylamide derivative 1172 was transformed with perfect conversion and selectivity (Table 3, entry 5). Interestingly, the Grubbs catalyst used in the homogeneous version of the same RCM reaction was reported to be not fully selective.73 Next, barbituric acid derivative 12 (entry 6) was obtained in DMC with excellent efficiency. In addition, some larger cycles such as the 16-membered macrocyclic musk 14 can be obtained in good yield under high-dilution conditions E


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Organometallics

The case of estrone derivative 23 was similar, as it underwent RCM in the same solvent, acetone, leading to the formation of 24 in an excellent isolated yield of 98%. It should be noted that, in all cases presented in Scheme 4, the RCM reactions catalyzed by FixCat@(Cr)MIL-101SO3−(Na·15-crown-5)+ in DMC and acetone were very clean, and the expected products were formed exclusively in high isolated yields and purity. The residual Ru levels in DMC, measured in crude unpurified product after the heterogeneous catalyst was filtered off, were in the range of 11−13 ppm and ca. 8 times higher in acetone (51−89 ppm, Scheme 4). Interestingly, addition of our newly developed scavenger, SnatchCat,80−82 and filtration through a short pad of silica, allowed us to decrease this value to only 12 ppm, as was shown in the case of estrone derivative 24 (Scheme 4).83

Scheme 4. Bioactive Molecule Synthesis by Olefin Metathesis with FixCat@(Cr)MIL-101-SO3−(Na·15-crown5)+ (24 h, Isolated Yields)

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CONCLUSION Noncovalent immobilization of the olefin metathesis catalyst FixCat inside the MOF (Cr)MIL-101-SO3−(Na·15-crown-5)+ has been achieved by ion exchange (cation metathesis) with the help of crown ether. Such linker-free immobilization, consisting only of mixing the 15-crown-5-saturated MOF with the catalyst solution, is experimentally simple and can be easily scaled up. This obtained hybrid Ru@MOF system is surprisingly stable even in rather polar solvents such as iPrOH, but the most optimal solvents are toluene, EtOAc, acetone, and dimethyl carbonate (DMC). A number of polyfunctional pharmaceutically related substrates were obtained in high yield and with perfect selectivity, transformed in solvents such as acetone and DMC, making this technology interesting in the context of a more broad use of green solvents in the chemical industry. Use of the MOF-immobilized catalyst is also operationally convenient, as the products can be easily separated from the metal by simple filtration.

SnatchCat (2.2 mol %) added to reaction mixture before filtration.

a

version reaction was recently reported using 1 mol % of notimmobilized FixCat catalyst in DCM.75 In addition, a substrate bearing a strongly chelating sulfoxide-amide moiety, diene 17, was tried, in the hopes of obtain an analogue of Modafinil, a drug used in the treatment of sleep disorders.76 Again, the use of 0.5 mol % of Ru in the form of the hybrid MOF-immobilized catalyst made it possible to form a substituted pyrroline ring of 18 quantitatively and isolate the target Modafinil analogue in good isolated yield (Scheme 4). As another example of an active pharmaceutical ingredient (API) formation by RCM, we selected the precursor 20 of the known cough suppressant pentoxyverine.77 In this specific case, we were afraid that the free carboxylic acid present in 20 would make the isolation of the product difficult, due to expected interactions with the polar MOF support. Despite these worries, the product was isolated after RCM in almost quantitative yield, as for all other products in Scheme 4, just by simple filtration of the solid catalyst and washing it with DMC. Previously, the pentoxyverine precursor was obtained by RCM using 3 mol % of homogeneous Grubbs catalyst in THF.78 In our experiment, only 0.5 mol % of Ru in the form of a heterogeneous catalyst was used. Next, an analogue 22 of the well-known UR-144,79 a psychoactive molecule invented in Abbott Laboratories, which acts as a selective full agonist of the peripheral cannabinoid receptor with generally weak cannabinoid-like activity, was approached. Interestingly, as substrate 21 was not sufficiently soluble in DMC, an alternative solvent, acetone, was used. Gratifyingly, also in this polar solvent the solid catalyst worked well, delivering the expected product in 97% isolated yield.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.9b00287. Materials and methods and detailed experimental procedures (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail for K.G.: [email protected]. ORCID

Karol Grela: 0000-0001-9193-3305 Author Contributions †

A.C. and P.K. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The research was supported by FNP Team Tech Grant No. TEAMTECH/2016−1/2. The authors are grateful to the “Catalysis for the Twenty-First Century Chemical Industry” project carried out within the TEAM-TECH programme of the Foundation for Polish Science cofinanced by the European Union from the European Regional Development under the Operational Programme Smart Growth. The study was carried F


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Organometallics

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out at the Biological and Chemical Research Centre, University of Warsaw, established within the project cofinanced by the European Union from the European Regional Development Fund under the Operational Programme Innovative Economy, 2007−2013.

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ABBREVIATIONS DMC dimethyl carbonate DCM dichloromethane OM olefin metathesis

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REFERENCES

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Article

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Noncovalent Immobilization of Cationic Ruthenium Complex in a

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