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Alkane Cross-Metathesis Reaction Between Light And Heavy Linear Alkanes, On A Silica Supported Well-Defined Single-Site Catalyst Natalia Morlanes, Santosh Kavitake, Devon C. Rosenfeld, and Jean-Marie Basset ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b02472 • Publication Date (Web): 28 Dec 2018 Downloaded from http://pubs.acs.org on January 1, 2019
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Alkane Cross-Metathesis Reaction Between Light And Heavy Linear Alkanes, On A Silica Supported Well-Defined Single-Site Catalyst Natalia Morlanés,§ Santosh G. Kavitake,§ Devon C. Rosenfeld,‡ Jean-Marie Basset*§ §
KAUST Catalysis Center and Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Kingdom of Saudi Arabia. ‡ Feedstocks,
Energy Research and Development, Hydrocarbons Division, The Dow Chemical Company, 2301 N. Brazosport Blvd. B-251, Freeport, TX 77541 USA. ABSTRACT: Alkane cross-metathesis of light and heavy paraffins is a compelling way to upgrade two low cost streams into more valuable products, in only one step and using a single catalyst. Herein we report the cross-metathesis reaction between light and heavy paraffins occurs under mild conditions on a well-defined catalyst precursor [(≡SiO)W(Me)5] treated under hydrogen at 150°C. Experiments with isotopic labelled alkanes (13C 1-propane + n decane or n-propane + C10D22) allow us to unambiguously prove the occurrence of the cross-metathesis reaction and to elucidate the plausible reaction mechanism. In order to optimize the percent crossmetathesis between propane and n-decane, we varied several parameters; in particular the influence of the C3/C10 ratio was found to be the most important one due to the difference in the reactivity of the two components in the alkane mixtures. KEYWORDS: alkane C-H activation, cross-metathesis of linear paraffin, single-site catalyst, hydrocarbon upgrading, reaction mechanism analysis, kinetic analysis, catalyst lifetime and recyclability.
Introduction The catalytic activation of alkanes remains one of the most important challenges in chemistry due to their inertness and considerable potential application, and is a major area of research in the petrochemical industry in order to upgrade low value hydrocarbons.1-3 Alkane metathesis represents a method to upgrade low cost alkanes to value-added chemicals in a clean and efficient way via C-H activation under mild conditions on well-defined silica-supported single-site catalytic systems.4 In the literature is reported the metathesis reaction of alkanes such as ethane, propane, butane,5-8 and also for heavier feedstocks, such as hexane, cyclo-octane, or n-decane.9-11 However, to our knowledge, the intentional cross-metathesis of two linear alkanes has never been truly demonstrated in a single catalyst. Other cross-metathesis examples could be found, as the reaction between ethane and toluene yielding ethylbenzene.12-14 And separately, in another approach,15 using a tandem system with the combination of two different catalysts,16 like the reaction between light paraffin and polyethylene.17 In contrast, the cross-metathesis of olefin is more widely explored.18, 19 The aim of this work is to explore the possibility of achieving cross metathesis between light paraffins (ethane, propane and butane) and heavier linear alkanes (carbon chain length C10 and greater) to obtain valuable mid-range alkanes (preferably C5C7) following the cross-metathesis route. Herein we report the results of the cross-metathesis reaction between propane (as an example of a light paraffin) and n-decane (as an example of a heavy paraffin), selected as model system. Our main challenge is to corroborate the cross-metathesis reaction between two
different linear alkanes is occurring rather than self-metathesis of each component. Scheme 1 shows the cross-metathesis reaction between propane (red) and n-decane (blue) with the cross-metathesis products keeping part of both substrates. Considering the three elementary steps for this process on well-defined single site catalysts: 1) alkane dehydrogenation to generate olefins, 2) olefin metathesis to form new olefins and 3) olefin hydrogenation to finally produce the new alkanes.20
Scheme 1. Cross-metathesis between propane and n-decane via alkane dehydrogenation to olefin, olefin metathesis and hydrogenation of the resulting olefins into new alkanes.
Herein, we report the experimental evidence to prove the concept of cross-metathesis between light and heavy linear paraffin in the presence of well-defined silica-supported singlesite catalytic system. We studied the catalytic performance for the self-metathesis of each alkane, and also for mixtures of propane and n-decane, in order to find the reaction conditions to achieve the cross-metathesis reaction. We also designed
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under these reaction conditions. The cross-metathesis process is probably limited by the lower reaction rate of propane under these reaction conditions. 70
n-decane metathesis
60
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[(≡SiO)W(CH3)2(H)3]
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The catalytic system [(≡SiO)W(CH3)2(H)3] (Scheme 2) was used to explore the feasibility of the alkane cross-metathesis reaction. The catalyst was synthesized according to reported protocols.21, 22 The synthesis procedure (Schemes S1-S3) and the characterization of the WMe6 molecular complex (Figures S1-S3), silica supported catalyst (Figures S4-S7) and the corresponding hydride (Figure S4) have been detailed in the Supporting Information (S.I.). Results and discussion Metathesis reaction of single components and mixtures The alkane cross-metathesis reaction was explored in a fixedbed reactor (microactivity reference, PID Eng&Tech) shown in the Scheme S6, with continuous alkanes gas flow under dynamic conditions. The reaction was explored at 150°C in the presence of [(≡SiO)W(CH3)2(H)3], according to the experimental procedure described in the S.I. A chromatograph (GC) is online connected to the outlet of this reactor for a careful analysis and quantification of the reaction products, in order to calculate alkane conversions, product distribution and the mass and carbon balances. First, we analysed the selfmetathesis of each component of the mixture to establish the product distributions under specific reaction conditions. Next, we studied the metathesis reaction of propane and n-decane mixtures at different propane/n-decane molar ratios (C3/C10, = 2 - 100, Table S1), and compared the product distributions to establish the effect of varying the alkane molar ratio on crossmetathesis and where cross-metathesis is maximized. First, two important differences observed from the analysis of the metathesis of the single components: 1) n-decane yields a very a broad product distribution, alkanes in the range C2-C19 (Figure 1), in contrast with propane, which selectively forms ethane and butane, mainly Cn+1, Cn-1 products; and 2) n-decane is a more reactive substrate compared to propane (Figure 2), ndecane metathesis is around eight times faster than propane metathesis, (rate constant of propane is 0.3 versus 2.4 for ndecane, in mol of alkane converted per mol of W and per h). From the experiments carried out with mixtures of propane and n-decane at different C3/C10 molar ratios (Figure S8-S9), we observe that the cross-metathesis reaction is occurring as a nonselective process giving a broad product distribution, mainly dominated by the product distribution observed for n-decane metathesis since decane activation is dominant over propane
0
C1 C2 C3 C4 C5 C6 C7 C8 C9 C11 C12 C13 C14 C15 C16 C17 C18 C19
Scheme 2. Synthesis [(≡SiO)WMe5].20
Selectivity (%)
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n-alkanes
Figure 1. Selectivity for self-metathesis of n-decane and selfmetathesis of propane metathesis on [(≡SiO)W(CH3)2(H)3] at 150°C and atmospheric pressure.
From the kinetic analysis of the single components (Figures S10-S12), the alkane conversion rate is found to be proportional to alkane pressure with a first order dependence with the alkane partial pressure, consistent with a kinetically relevant step that could be the -bond metathesis for the initial alkane C-H activation20, 23 involved in the first alkane dehydrogenation step.24, 25
Figure 2. Reaction rate for single n-decane and propane metathesis on [(≡SiO)W(CH3)2(H)3] at 150°C and atmospheric pressure.
The product distribution could be explained by the primary products, olefin and hydrogen, detected at high space velocity and low contact time, in agreement with a dehydrogenation of the alkane as the first elementary step.26 In the case of propane (Figure S13), propylene is formed, with only the higher and the lower homologues observed after olefin metathesis, resulting in a more selective process.27 In contrast, for n-decane (Figures S14), in the case that 1-decene was the first product of dehydrogenation, this would fast isomerizes into a mixture of internal decenes,24 and after metathesis would form a mixture of new olefins of variable chain length; resulting in a final
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reaction mixture with the broad product distribution. (See the chain-walking process via double bond migration in the Scheme 3). Since the isomerization (by double bond migration) and olefin metathesis are occurring very fast after the first dehydrogenation step, these reactions might be affecting the cross-metathesis between propane and n-decane. Therefore, it is very difficult to identify cross-metathesis products among the broad product distribution observed (C1-C19), especially to distinguish from those products coming from the selfmetathesis of n-decane, which occur as a non-selective process. The optimization of the desired cross-metathesis reaction between light paraffin and n-decane, is very difficult due to the main differences in the reactivity observed for both components of interest, n-decane versus light paraffin; while n-decane is a more reactive substrate, compared to the less reactive light paraffin, is giving a wide product distribution, in high contrast with propane, which selectively forms mainly Cn+1, Cn-1.
(M+1) ion peaks. (Figure S20, enlarged NIST mass spectrum of standard alkanes). Figure 3 shows the enrichment in 13C for the alkanes in the range C4-C19 formed in the experiment between 13C 1-propane and n-decane, represented by the relative intensity of the (M+1) and M peaks (in blue, standard alkanes; in red, cross-metathesis products between 13C 1-propane and n-decane). A clear enrichment in 13C is observed for all the hydrocarbons in the range C4-C19, indicating the fragments of the 13C 1-propane starting material are in all the alkanes formed, and definitively proving the occurrence of the cross-metathesis reaction between propane and n-decane under our testing conditions catalysed by silica-supported tungsten hydride catalyst, [(≡SiO)W(CH3)2(H)3].
Proof of concept for alkane cross-metathesis reaction To confirm the occurrence of the cross-metathesis reaction between propane and n-decane, it was necessary the use of labelled alkanes. Our strategy was to run the experiments with reaction mixtures containing one labelled and one non-labelled alkane; alkane cross-metathesis will be proven through products containing labelled and non-labelled parts identified by mass spectrometry. In the case of using 13C 1-propane and n-decane, the proof will be the formation of 13C labelled hydrocarbons with the carbon number higher than 5, because in the self-metathesis of propane alkanes higher than pentane are not observed under these experimental reaction conditions. A mixture of 13C 1-propane and n-decane (non-labelled) with a molar ratio C3/C10 = 2.25, was explored using a batch reactor, (Q-Tube ractor shown in Scheme S7) in the presence of [(≡SiO)W(CH3)2(H)3] at 150°C for 5 days. The procedure is described in the S.I. Reaction products are collected in dichloromethane and analyzed by GC-MS after the reaction. The mass spectrum of the linear alkanes (C3-C19) formed in this experiment are shown in Figure S16 and helped determine whether fragments of both starting materials are incorporated into the final products. As a control experiment, the mass spectrum of the alkanes formed in the reaction of non-labelled propane with non-labelled n-decane were also analysed (Figure S17) and compared to the mass spectrum of the standard alkanes, obtained from the National Institute of Standards and Technology (NIST) database (Figure S18). In order to understand the 13C enrichment observed in the alkanes formed in the experiment 13C 1-propane and n-decane, it is first necessary to consider that standard alkanes are naturally enriched with 13C carbon atoms, and this enrichment increases with the number of carbon atoms in the molecule (See S.I. for details). The 13C enrichment is given by the ratio (M+1)/M. In the mass spectrum, we expect a higher relative intensity of the (M+1) ion peak, with respect to the intensity of the M ion peak in the experiment using 13C1-propane due to the cross-metathesis process, compared to this ratio in the mass spectrum for the non-labelled standard alkanes which only has natural 13C enrichment. In Figure S19, the mass spectrum of each alkane has been enlarged in the area of the mass for the whole molecule, in order to see the amplitude of the M and
Figure 3. Enrichment in 13C for the alkanes with increasing carbon number, reaction products in the experiment of 13C 1propane and n-decane on [(≡SiO)W(CH3)2(H)3] at 150°C (in red); and for the standard alkanes (in blue).
Percentage of cross-metathesis products Once the occurrence of the cross-metathesis reaction was confirmed, the percentage of the cross-metathesis products was next examined. The influence of the reaction conditions was explored in order to find the optimal conditions to maximize the percentage of cross-metathesis rather than the self-metathesis of the single components of the mixture. To analyse the influence of the reaction conditions, the experiments were conducted with mixtures of fully-deuterated n-decane and not-labelled propane in the fixed-bed reactor, (microactivity reference, PID Eng&Tech) shown in the Scheme S4. Dynamic conditions with continuous alkanes gas flow, were used to prevent the preferential adsorption of n-decane, since the alkane feed mixture is in the gas phase and well mixed (see S.I. for further details). A chromatograph is online connected to the outlet of this reactor for the analysis and quantification of the reaction products, to calculate alkane conversion, product distribution and the mass and carbon balances. The reaction mixture is further analyzed by GC-MS, in order to obtain the mass spectrum of the linear alkanes (C3-C19) formed in this experiment. In an experiment with a mixture of fully-deuterated n-decane and not-labelled propane, the cross-metathesis products are expected to be partially deuterated. While the products from the
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self-metathesis of fully-deuterated n-decane would be totally deuterated, and the products from the propane self-metathesis (mainly C2 and C4 with small of C5, less than 1%) would be nondeuterated compounds. First, the influence of the C3/C10 molar ratio in the range 2100 was analysed (Figures S21-S36). Figure 4 shows the product distribution produced for each molar ratio explored, (cross-metathesis products in green, n-decane self-metathesis products in blue and propane self-metathesis in red), obtained
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from the percentage of partially labelled, fully labelled and nonlabelled compounds, respectively (Figure S37-S38). In all experiments, we observe linear alkanes from C3-C19 partially labelled containing a fragment of each starting alkane, corroborating the cross-metathesis reaction is occurring. The quantitative analysis of the mass spectra is detailed in the S.I. Figures S39 shows n-decane and propane conversion into crossmetathesis or self-metathesis products.
C3/C10 = 2
C3/C10 = 5
C3/C10 = 10
C3/C10 = 25
C3/C10 = 50
C3/C10 = 100
Figure 4. Influence of the C3/C10 molar ratio on the product distribution in the cross-metathesis reaction between fully-deuterated ndecane (C10D22) and not-labelled propane, in the range C3/C10= 2-100, with [(≡SiO)W(CH3)2(H)3] at T = 150 ℃. (green: crossmetathesis products, blue: n-decane metathesis products, red: propane metathesis products)
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Figure 5 shows the percentage of cross-metathesis products and the percentage of the self-metathesis of each single component of the mixture, as a function of the C3/C10 molar ratio. The molar ratio between the components has enormous influence in the percentage cross-metathesis products formed. At low C3/C10 molar ratios, the process is dominated by the selfmetathesis of n-decane. The percentage of cross-metathesis products is increasing with the C3/C10 ratio from 1 to 10. A maximum around 50% of cross-metathesis is observed at C3/C10= 10. Further increase in the C3/C10 ratio does not lead to an increase in the percentage of cross-metathesis instead tipping the balance in favour of propane self-metathesis.
Figure 5. Influence of the C3/C10 molar ratio on the percentage of cross-metathesis products. Results from fully deuterated ndecane and propane with [(≡SiO)W(CH3)2(H)3] at T = 150 ℃.
The influence of the reaction temperature and of the catalytic system on the percentage of cross-metathesis products was further investigated in order to optimize the conditions to achieve a higher percentage of cross-metathesis rather than the self-metathesis of each single component. The percentage of cross-metathesis reaction was found to increase with the reaction temperature from 100 to 175 °C (Figures S42-46). The maximum is observed in the range of 150-175 °C. Further increase of the temperature results in catalyst deactivation. Finally, the percentage of cross-metathesis products was found to be very similar in [(≡SiO)W(CH3)2(H)3], ≡SiOTa(H)x28 and ≡SiOW-Zr(H)x25 (Figures S47-S50), due to the similar levels of alkane conversion observed. Cross-metathesis reaction mechanism From the present study of the alkane metathesis reaction carried out with mixtures of propane and n-decane, we conclude that under the reaction conditions explored here three reactions occur: the self-metathesis of propane, the self-metathesis of ndecane and the cross-metathesis reaction between propane and n-decane, demonstrated using labelled alkanes as starting materials. A general scheme for the cross-metathesis reaction is proposed in Scheme 3 for the reaction between propane and ndecane. This scheme shows the self-metathesis of propane (red cycle) and n-decane (blue cycle) and several possibilities of the cross-metathesis reaction between the alkylidene species from one alkane with the olefin intermediates from the other alkane
(species in the dashed green circles), occurring during the olefin metathesis step.29-31 Fragments of both starting materials are incorporated into the cross-metathesis products, with one, two or three methylene group from the starting propane, in agreement with the experimental observation using labelled alkanes. From known elementary steps of organometallic chemistry,20, 26 the proposed mechanism for this process involves a first step of C-H activation by -bond metathesis followed by -H elimination, with the liberation of hydrogen and the olefin, respectively, as the primary products, in agreement with the experimental observation for both single components, propane and n-decane. In the second olefin metathesis step, the olefins generated from the activation of each single component, could react with either of the hydridemetallocarbene species available in this complex system (formed by -H transfer from the metallo-alkyl species obtained from each single component) to form the most favourable (the less sterically constrained) metallocycle which undergoes metathetical cleavage giving new olefins and hydride-metallocarbene species. Schemes S8-S9 describe all these possibilities for the catalytic cycles for propane and for ndecane metathesis, respectively; including the isomerization, chain walking or double bond migration process occurring during the metathesis of n-decane, in order to explain the broad product distribution observed experimentally for this component. In the olefin metathesis step, the cross-metathesis reaction is competing with the self-metathesis of each component. The feasibility of the cross-metathesis reaction will depend on the availability of the species of interest, which is definitively controlled by the rate of activation of each single component, and can be tuned by the molar ratio between the two components. The availability of the species from propane activation are more limited for the desired process, since ndecane metathesis is~ 8 times faster than propane metathesis. Therefore, in order to have the best conditions to maximize the percentage of the cross metathesis, it is necessary a ratio of propane to n-decane of at least 8, close to the optimum C3/C10=10 observed experimentally. The catalytic cycle ends with the insertion of the olefin into the metallo-hydride or the migration of the hydride into the carbene ligands. The resulting alkyl groups can be cleaved by the H2 (primary product), which is a known step already observed during the hydrogenolysis of alkanes. Finally, there was a major concern related to the exchange of hydrogen (H) by deuterium (D) along the hydrocarbon chain that could occur under the reaction conditions explored here in the presence of the catalyst during the experiments using deuterated starting alkanes.32 Since the catalyst is able to activate alkanes under mild condition by C-H activation, and considering deuterium might be formed from deuterated alkanes during the first dehydrogenation step; there was the concern that this deuterium could be introduced in the products by this exchange process, giving the mixture of partially deuterated hydrocarbons observed in the experiment, which are considered here as the cross-metathesis products. Therefore, in order to discard the possibility of H/D exchange mechanism, several control experiments were conducted.
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C9 C10
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H W
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Scheme 3. Alkane Cross-Metathesis proposed mechanism between n-decane and propane.
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In a control experiment deuterium was intentionally introduced in a n-decane metathesis in the presence of [(≡SiO)W(CH3)2(H)3] at 150°C for 5 days experiment under batch conditions. The alkanes produced in this experiment were not partially deuterated (Figure S51), with their mass spectrum being exactly like the mass spectrum for the standard alkanes, suggesting the H/D exchange is not occurring under these reaction conditions. Due to the activation of deuterated alkanes on the original WH sites, this can form W-D intermediates, especially after the H elimination steps, and also release D2 after -bond metathesis. Later, after the cycloreversion of the metallocycle, during the steps of reinsertion and hydrogenation the deuterium from the W-D or from the D2 liberated, would be incorporated on the final products, giving partially deuterated compounds. In the experiments with fully-deuterated n-decane and not-labelled propane, this H/D exchange mechanism would give propane metathesis products with 1 or 2 D; also, it would give n-decane (C10D22) metathesis products with 1 or 2 H, compared to the totally deuterated alkanes. These species are observed experimentally and they could be formed by this H/D exchange, as well as by the cross-metathesis process, being difficult to completely ruled out the H/D exchange. However, and more importantly, this H/D exchange mechanism fails to explain long chain alkanes observed with 8 H (i.e. loss/exchange of 8 D for H) compared to the fully deuterated alkanes (total mass is decreased up to 8 units), in the experiments with fully-deuterated n-decane and not-labelled propane (Figures S23-S36). In this case, the presence of compounds with up to 8 H compared to the fully deuterated alkanes, is best explained by the transfer of 1, 2 or 3 methylene groups from the non-deuterated propane that are incorporated on the chain of the n-decane metathesis products. This process indicates that the products contain fragment of both starting substrates, corroborating the alkane cross-metathesis reaction, which was also demonstrated by the experiment with 13Cpropane and n-decane. Another control experiment, with hydrogen introduced intentionally during the metathesis of fully deuterated n-decane in the presence of [(≡SiO)W(CH3)2(H)3] at 150°C for 5 days under batch conditions. Only fully deuterated alkanes were observed in this experiment (Figure S52). The small number of moles of deuterium produced in the dehydrogenation of deuterated n-decane (C10D22), might remain in the surface of the catalyst retained by the multiple layers of liquid molecules adsorbed on the catalyst. This would facilitate the incorporation of this D2, instead of the H2, during the steps of reinsertion and hydrogenation. This observation suggests the idea that maybe, hydrogen/deuterium is not exchanged with the bulk gas, but rather stays local to the catalytic site. Similarly, in an experiment using fully deuterated propane and not-labelled n-decane, in the presence of [(≡SiO)W(CH3)2(H)3] at 150°C for 5 days experiment under batch conditions. In the mass spectrum of the products formed in this experiment, Figure S52-S56, we observed that the total mass increased up to 8 units, again suggesting 1, 2 or 3 methylene groups from the deuterated propane are transferred in the longer chain alkane products, incorporating up to 8 deuterium atoms.
Catalyst lifetime and recyclability The alkane cross-metathesis route, opens a new approach to upgrade both, low value light paraffins and heavy hydrocarbon feedstocks, producing mid-range linear alkanes in the presence of silica-supported well-defined precatalyst. In order to finish this work, the catalyst lifetime and recyclability was explored. In the Figure 6 The catalyst lifetime is about 5 days. The catalysts could be regenerated by a hydrogen treatment at 150 °C for 16 hours,33 with a recovery of the 65% of the original catalytic performance. After the second regeneration cycle, the catalyst recovers up to 25% of the initial performance. And finally, a third regeneration recovers only the 10 % of the activity. 100 80
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Figure 6. Lifetime and recyclability of [(≡SiO)W(CH3)2(H)3] catalyst in the reaction of n-decane metathesis at 150°C for 5 days.
Conclusion In conclusion, the present study proves the concept of alkane cross-metathesis between light and heavy linear paraffins, occurring under mild conditions in the presence of silicasupported catalytic system such as [(≡SiO)W(CH3)2(H)3] prepared from a single-site well-defined [(≡SiO)W(Me)5]. From the study carried out using starting labelled materials and the mass spectrometry analysis of the reaction products, when using 13C-propane and n-decane, we observed 13C enrichment in all the reaction products, linear alkanes in the range from C4 to C19 which is far above the natural enrichment observed in the standard alkanes. This 13C enrichment corroborates the occurrence of cross-metathesis between propane and n-decane. Experiments suggested the cross-metathesis reaction occurs during the olefin metathesis step, by the interaction of the alkylidene species formed from one of the starting alkanes with the olefin coming from the second alkane. The molar ratio between the light and heavy components has an enormous influence in the percentage of the cross-metathesis reaction. The percentage of cross-metathesis is increasing with the C3/C10 ratio from 1 to 10. A maximum around 50% of cross-metathesis is observed at C3/C10= 10. Increasing the C3/C10 molar ratio further, the process becomes dominated by the self-metathesis of propane.
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ASSOCIATED CONTENT Supporting Information All the experimental procedures, synthesis and characterization of the catalysts, catalytic studies, activity results and kinetic analysis, mass spectrometry analysis, and other figures are included in the Supporting Information. The Supporting Information is available free of charge on the ACS Publications website.
AUTHOR INFORMATION Corresponding Author * Prof. Jean Marie Basset, e-mail:
[email protected].
Author Contributions Natalia Morlanés performed the catalytic tests described in this work and wrote the main draft for this manuscript; Santosh G. Kavitake synthesized and characterized the catalysts used in this study; Devon C. Rosenfeld and Jean-Marie Basset supervised this work and contribute to the discussion of the results. All authors have given approval to the final version of the manuscript.
Funding Sources This research project has been funded by The Dow Chemical Company.
Notes The authors declare no competing financial interest.
ACKNOWLEDGMENT This research was supported by The Dow Chemical Company. Authors acknowledge the resources and facilities provided by the King Abdullah University of Science and Technology.
REFERENCES 1. Labinger, J. A.; Bercaw, J. E., Understanding and Exploiting CH Bond Activation. Nature 2002, 417, 507–514. 2. Crabtree, R. H.; Lei, A., Introduction: CH Activation. Chem. Rev., 2017, 117, 8481–8482. 3. Crabtree, R. H., Organometallic alkane CH activation. Journal of Organometallic Chemistry 2004, 689, 4083–4091. 4. Vidal, V.; Theolier, A.; Thivolle-Cazat, J.; Basset, J. M., Metathesis of Alkanes Catalyzed by Silica-Supported Transition Metal Hydrides. Science 1997, 276, 99–102. 5. Coperet, C.; Maury, O.; Thivolle-Cazat, J.; Basset, J. M., s-Bond Metathesis of Alkanes on a Silica-Supported Tantalum(V) Alkyl Alkylidene Complex: First Evidence for Alkane Cross-Metathesis. Angew. Chem., Int. Ed. 2001, 40, 2331–2334. 6. Le Roux, E.; Taoufik, M.; Coperet, C.; de Mallmann, A.; Thivolle-Cazat, J.; Basset, J. M.; Maunders, B. M.; Sunley, G. J., Development of Tungsten-Based Heterogeneous Alkane Metathesis Catalysts Through a Structure-Activity Relationship. Angew. Chem., Int. Ed. 2005, 44, 6755–6758. 7. Basset, J. M.; Coperet, C.; Soulivong, D.; Taoufik, M.; ThivolleCazat, J., From Olefin to Alkane Metathesis: A Historical Point of View. Angew. Chem., Int. Ed. 2006, 45, 6082–6085. 8. Blanc, F.; Coperet, C.; Thivolle-Cazat, J.; Basset, J. M., Alkane Metathesis Catalyzed by a Well-Defined Silica-Supported Mo Imido Alkylidene Complex: [(SiO)Mo(=NAr)(=CHtBu)(CH2tBu)]. Angew. Chem., Int. Ed. 2006, 45, 6201–6203. 9. Riache, N.; Callens, E.; Espinas, J.; Dery, A.; Samantaray, M. K.; Dey, R.; Basset, J. M., Striking Difference Between Alkane and Olefin Metathesis Using the Well-Defined Precursor [ Si-OWMe5]: Indirect Evidence in Favour of a Bifunctional Catalyst W Alkylidene-Hydride. Catal. Sci. Technol. 2015, 5, 280–285.
Page 8 of 10
10. Riache, N.; Callens, E.; Samantaray, M. K.; Kharbatia, N. M.; Atiqullah, M.; Basset, J. M., Cyclooctane Metathesis Catalyzed by Silica-Supported Tungsten Pentamethyl [(SiO)W(Me)(5)]: Distribution of Macrocyclic Alkanes. Chem. Eur. J. 2014, 20, 15089–15094. 11. Samantaray, M. K.; Dey, R.; Abou-Hamad, E.; Hamieh, A.; Basset, J. M., Effect of Support on Metathesis of n-Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to SilicaAlumina. Chem. Eur. J. 2015, 21, 6100–6106. 12. Soulivong, D.; Coperet, C.; Thivolle-Cazat, J.; Basset, J. M.; Maunders, B. M.; Pardy, R. B. A.; Sunley, G. J., Cross-Metathesis of Propane and Methane: A Catalytic Reaction of C-C Bond Cleavage of a Higher Alkane by Methane. Angew. Chem., Int Ed. 2004, 43, 5366–5369. 13. Taoufik, M.; Schwab, E.; Schultz, M.; Vanoppen, D.; Walter, M.; Thivolle-Cazat, J.; Basset, J. M., Cross-Metathesis Between Ethane and Toluene Catalyzed by [( SiO)(2)TaH]: the First Example of a Cross-Metathesis Reaction Between an Alkane and an Aromatic. Chem. Commun. 2004,1434–1435. 14. Merle, N.; Stoffelbach, F.; Taoufik, M.; Le Roux, E.; ThivolleCazat, J.; Basset, J. M., Selective and Unexpected Transformations of 2-Methylpropane to 2,3-Dimethylbutane and 2-Methylpropene to 2,3-Dimethylbutene Catalyzed by an Alumina-Supported Tungsten Hydride. Chem. Commun. 2009, 46, 2523–2525. 15. Goldman, A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski, W.; Brookhart, M., Catalytic Alkane Metathesis by Tandem Alkane Dehydrogenation–Olefin Metathesis. Science 2006, 312, 257–261. 16. Dobereiner, G. E.; Yuan, J.; Schrock, R. R.; Goldman, A. S.; Hackenberg, J. D., Catalytic Synthesis of n-Alkyl Arenes through Alkyl Group Cross-Metathesis. J. Am. Chem. Soc. 2013, 135, 12572–12575. 17. Jia, X.; Qin, C.; Friedberger, T.; Guan, Z.; Huang, Z., Efficient and Selective Degradation of Polyethylenes Into Liquid Fuels and Waxes Under Mild Conditions. Sci. Adv. 2016, 2, e1501591. 18. Koh, M. J.; Nguyen, T. T.; Zhang, H.; Schrock, R. R.; Hoveyda, A. H., Direct Synthesis of Z-Alkenyl Halides Through Catalytic Cross-Metathesis. Nature 2016, 531, 459–465. 19. Nguyen, T. T.; Koh, M. J.; Mann, T. J.; Schrock, R. R.; Hoveyda, A. H., Synthesis of E- and Z-Trisubstituted Alkenes by Catalytic Cross-Metathesis. Nature 2017, 552, 347–356. 20. Basset, J. M.; Coperet, C.; Soulivong, D.; Taoufik, M.; Cazat, J. T., Metathesis of Alkanes and Related Reactions. Acc. Chem. Res. 2010, 43, 323–334. 21. Samantaray, M. K.; Callens, E.; Abou-Hamad, E.; Rossini, A. J.; Widdifield, C. M.; Dey, R.; Emsley, L.; Basset, J. M., WMe6 Tamed by Silica: Si-O-WMe5 as an Efficient, Well-Defined Species for Alkane Metathesis, Leading to the Observation of a Supported W-Methyl/Methylidyne Species. J. Am. Chem. Soc. 2014, 136, 1054−1061. 22. Maity, N.; Barman, S.; Callens, E.; Samantaray, M. K.; AbouHamad, E., Minenkov, Y.; D'Elia, V.; Hoffman, A. S.; Widdifield, C. M.; Cavallo, L.; C. Gates, B. C.; Basset, J. M., Controlling the Hydrogenolysis of Silica-Supported Tungsten Pentamethyl Leads to a Class of Highly Electron Deficient Partially Alkylated Metal Hydrides. Chem. Sci., 2016, 7, 1558–1568. 23. Waterman, R., σ‑Bond Metathesis: A 30-Year Retrospective. Organometallics 2013, 32, 7249−7263. 24. Haibach, M. C.; Kundu, S.; Brookhart, M.; Goldman, A.S., Alkane Metathesis by Tandem Alkane-Dehydrogenation OlefinMetathesis Catalysis and Related Chemistry. Acc. Chem. Res. 2012, 45, 947–958. 25. Samantaray, M. K.; Dey, R.; Kavitake, S.; Abou-Hamad, E.; Bendjeriou-Sedjerari, A.; Hamieh, A.; Basset, J. M., Synergy Between Two Metal Catalysts: A Highly Active Silica-Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane. J. Am. Chem. Soc. 2016, 138, 8595–8602.
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26. Basset, J. M.; Coperet, C.; Lefort, L.; Maunders, B. M.; Maury, O.; Le Roux, E.; Saggio, G.; Soignier, S.; Soulivong, D.; Sunley, G. J., Primary Products and Mechanistic Considerations in Alkane Metathesis J. Am. Chem. Soc. 2005, 127, 8604–8605. 27. Jesper, J. H.; Sattler, B.; Ruiz-Martinez, J.; Santillana-Jimenez, E.; Weckhuysen, B. M., Catalytic Dehydrogenation of Light Alkanes on Metals and Metal Oxides. Chem. Rev. 2014, 114, 10613−10653. 28. Maury, O.; Lefort, L.; Vidal, V.; Thivolle-Cazat, J.; Basset, J. M., Metathesis of alkanes: Evidence for degenerate metathesis of ethane over a silica-supported tantalum hydride prepared by surface organometallic chemistry. Angew. Chem., Int. Ed. 1999, 38, 1952−1956. 29. Núñez-Zarur, F.; Solans-Monfort, X.; Restrepo, A., Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-
Supported Tantalum Hydrides: A DFT Study. Inorg. Chem. 2, C.C.; Gong, J., Molecular understandings on the activation of ligh hydrocarbons over heterogeneous catalysts. Chem. Sci., 2015, 6, 4403–4425. 32. Martin, D.; Duprez, D. J., Mobility of Surface Species on Oxides. 2. Isotopic Exchange of D2 with H of SiO2, Al2O3, ZrO2, MgO, and CeO2: Activation by Rhodium and Effect of Chlorine. J. Phys. Chem. B 1997, 101, 4428−4436. 33. Soignier, S.; Saggio, G.; Taoufik, M.; Basset, J.M.; ThivolleCazat, J., Dynamic behaviour of tantalum hydride supported on silica or MCM-41 in the metathesis of alkanes. Catal. Sci. Technol., 2014, 4, 233–244.
SYNOPSIS TOC
≡SiOW(H)x T = 150 ℃
53% Cross-Metathesis products
C1 C2 C4 C5 C6 C7 C8 C9 C11 C12 C13 C14 C15 C16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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TOC ≡SiOW(H)x T = 150 ℃
Cx
Cn-2-x
53% Cross-Metathesis products Cx W H Cn-2-x
C1 C2 C4 C5 C6 C7 C8 C9 C11 C12 C13 C14 C15 C16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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