Research Article pubs.acs.org/acscatalysis
Rethinking the Dehydrogenative Amide Synthesis Dmitry G. Gusev* Department of Chemistry and Biochemistry, Wilfird Laurier University, Waterloo, Ontario N2L 3C5, Canada S Supporting Information *
ABSTRACT: This paper is concerned with the mechanism of the catalytic dehydrogenative coupling of primary alcohols with amines; it addresses the question on what happens to the aldehyde produced in the catalytic solution upon dehydrogenation of an alcohol substrate. Here we demonstrate a rapid catalytic reaction of acetaldehyde with primary amines, leading to acetamides. The facile amide bond formation is a low-energy, outer-sphere catalytic process elucidated with the help of DFT calculations. Overall, the dehydrogenative amide synthesis comprises two metal-catalyzed cycles: the first producing the aldehyde and H2, and the second where the hemiaminal is formed and is dehydrogenated. The results call into question the existing mechanistic ideas (reviewed by Li and Hall) that invoke the uncatalyzed formation of a free hemiaminal intermediate and assume that the hemiaminal dehydrogenation requires a 16-electron catalyst. KEYWORDS: amide synthesis, alcohol dehydrogenation, bifunctional catalysts, pincer complexes, metal−ligand cooperation
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INTRODUCTION Catalytic dehydrogenative coupling of primary alcohols with amines in Scheme 1a is an attractive synthetic approach to
Scheme 2. Bifunctional Double Hydrogen Transfer
Scheme 1. Dehydrogenative Coupling of Alcohols and Amines Leading to Amides metal species of Scheme 3 are regarded as the dehydrogenation catalysts of the reactions of Scheme 1. Scheme 3. Alcohol Dehydrogenation According to Milstein2 (Top) and Grützmacher3 (Bottom)
amides that has received much attention in the past decade because of the excellent atom efficiency and avoidance of aggressive and toxic chemicals such as acid chlorides and anhydrides.1 Some of the best turnover numbers, up to 103, were achieved in refluxing toluene in the seminal study by Milstein and co-workers.2 Alternatively, the amide synthesis can be operated at room temperature with TON values of up to 500 in the presence of a sacrificial hydrogen acceptor according to Scheme 1b, following the transfer-dehydrogenative coupling approach developed in the group of Grützmacher.3 Reactions of Scheme 1 have been the subject of several detailed computational studies4 that presented strong arguments in support of the so-called bifunctional double hydrogen transfer (BDHT)4d,g,i mechanism for the catalytic alcohol dehydrogenation. The BDHT mechanism is related to (and can be viewed as the reverse of) the mechanism originally proposed for the bifunctional hydrogenation of carbonyls in Scheme 2, familiar from the classic work of Noyori.5 Naturally, the 16electron amido (Grützmacher) or dearomatized (Milstein) © XXXX American Chemical Society
The dominant view of the dehydrogenative amide formation,4a which can be traced to the original ideas of Milstein,2 is that the mechanism comprises three principal events: (i) Catalytic alcohol dehydrogenation affords the corresponding aldehyde according to Scheme 3. (ii) Uncatalyzed hemiaminal forms from the aldehyde and amine according to Scheme 4, the selectivity to amide Received: July 20, 2017 Revised: August 21, 2017 Published: August 22, 2017 6656
DOI: 10.1021/acscatal.7b02415 ACS Catal. 2017, 7, 6656−6662
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ACS Catalysis being explained by the slower formation of the competing hemiacetal. Scheme 4. Hemiaminal vs Hemiacetal Formation
(iii) Dehydrogenation of the hemiaminal of Scheme 4 by the 16-electron metal catalysts occurs in a fashion analogous to Scheme 3, affording the final amide product. H2 extrusion (or transfer) from the 18-electron hydrides of Scheme 3 should regenerate the 16-electron catalysts. We have recently reported the bifunctional complexes OsHX(CO)[PyCH2NHCH2CH2NHPtBu2] (1, X = Cl; 2, X = H) and their use for the solventless synthesis of amides from primary alcohols and amines with TON values of up to 1900.6 This present report outlines experimental and computational evidence for a dehydrogenative coupling mechanism with 2 where steps ii and iii of the amide synthesis are parts of one catalytic cycle. The central event, C−N bond formation, is catalyzed in an outer-sphere fashion, via a low-energy transition structure. The competing C−O bond formation, leading to ester,7 appears to be a higher-energy process, according to the DFT calculations. The results reported here call into question the existing ideas (reviewed by Li and Hall in ref 4a) that invoke uncatalyzed formation of a free hemiaminal in step ii and assume that the hemiaminal dehydrogenation requires a 16-electron catalyst in step iii.
Figure 1. Partial 1H{13C} NMR spectra of N-allylacetamide and ethanol produced by reacting acetaldehyde (7.5 mmol) with allylamine (37.5 mmol) and 2 in methanol-d4 (1.5 mL) and toluene-d8 (4.0 mL). For full proton and carbon NMR spectra with detailed assignments, see Figures S1 and S4 in the Supporting Information.
mixture with unreacted allylamine in a ca. 1/1/1 ratio, as seen in Figure S5 in the Supporting Information. Thus, the catalytic reaction required 2 equiv of the aldehyde for every 1 equiv of the amine reacted according to the equation of Figure 1. Attempts at reacting allylamine with more than 1 equiv of acetaldehyde, in toluene and at −80 °C, led to the formation of mixtures mostly containing N-allylethanimine and water, the products of the conventional condensation reaction. Although this work was not concerned with the development of a practical catalytic method for producing amides from amines and aldehydes, this useful process might be feasible if a controlled slow addition of the aldehyde into the catalytic solution was used. Efficient cooling should also be employed, since the amide formation is highly exothermic. For example, the standard enthalpies of formation of methylamine, acetaldehyde, ethanol, and N-methylacetamide indicate ΔH° = −38.1 kcal/mol of N-methylacetamide, for the reaction CH3NH2 + 2CH3CHO → CH3NHCOCH3 + CH3CH2OH.8 Further mechanistic experiments provided consistent observations. Thus, reacting acetaldehyde with benzylamine (1/4) afforded N-benzylacetamide and ethanol in a 1/1 ratio, as confirmed by the NMR spectra of Figure S6 in the Supporting Information, whereas acetaldehyde with propane-1,2-diamine (1/5) selectively afforded N-(2-aminopropyl)acetamide with ethanol (see Figure S7 in the Supporting Information). Catalyst concentration was low in the experiments of Figure 1 (ca. 2.6 mM, 1.4 mg/mL in toluene-d8). Nevertheless, the toluene-d8 solution displayed distinct resonances in the hydride region of the 1H NMR spectrum and in the 31P{1H} NMR spectrum, shown in Figure 2. The proton spectrum of this sample changed little even after 2 weeks under argon, at room temperature (see Figure S2 in the Supporting Information). The interpretation of Figure 2 is conveniently guided by the 1H NMR spectrum of 2 from our past work (top trace), exhibiting the characteristic Os−H resonances of the mer and fac isomers of 2 in the hydride region of the spectrum.6 Clearly, 2 is mostly retained at the end of the catalytic reaction (EtOH/2 = 200) and is the catalyst resting state. This observation is somewhat adventitious, as 2 is not fully stable with ethanol. Thus, the dihydride is a minor species in a 1/1 mixture of allylamine with
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RESULTS AND DISCUSSION Dehydrogenation of primary alcohols is thermodynamically unfavorable (e.g., ΔH = 19.4 kcal/mol for the dehydrogenation of ethanol to acetaldehyde);8 nevertheless, one can reasonably assume that a trace aldehyde is reversibly produced in a catalytic fashion at the start of the reactions of Scheme 1. This work addresses the question of what happens next between the aldehyde and an amine in the catalytic solution. For this purpose, acetaldehyde, allylamine, benzylamine, and propane1,2-diamine were selected as the substrates, and NMR reaction monitoring was chosen as an investigative technique, augmented by DFT modeling of the proposed catalytic intermediates. The dihydride 2 is active in the reaction of Scheme 1a at 0.05 mol % loading in amine/ethanol (1/1) mixtures.6 For consistency, the present mechanistic study also employed 0.05 mol % of 2 vs the amine; an equivalent molar amount of methanol-d4, or toluene-d8, was used in place of the ethanol. Acetaldehyde was added as a solution in the deuterated solvents to a solution of 2 in the amine, with rapid stirring. All materials were kept at −30 °C in an argon glovebox, where they were manipulated and reacted expediently while cold. Reacting acetaldehyde with allylamine (1/5) led to a rapid consumption of the aldehyde and formation of N-allylacetamide and ethanol in a 1/1 ratio, as seen in Figure 1. Heat accompanied this reaction, with the temperature rapidly rising from subzero to 40 °C, registered on the surface of the vials by an IR thermometer. The reaction solutions were yellow (typical of 2) and retained the color throughout the experiments. Reacting allylamine with 1 equiv of acetaldehyde in toluene at −80 °C similarly produced N-allylacetamide and ethanol as a 6657
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Figure 2. Hydride resonances of 2 in THF (top trace) and the hydride region of the 1H NMR spectrum of the toluene-d8 solution of Figure 1 together (bottom trace) with the corresponding 31P{1H} NMR spectrum.
Scheme 6. Catalytic Amide Synthesisa
ethanol with 0.05 mol % of 2 (EtOH/2 = 2000, see Figure S3 in the Supporting Information). In this solution, the main metal species (74%) exhibits a hydride resonance at δ −15.2 (d, 2 J(H−P) = 21 Hz) and a 31P{1H} peak at δ 79.2 that can be tentatively assigned to OsH(OEt)(CO)[PyCH2NHCH2CH2NHPtBu2] (3); however, this unstable ethoxide could not be isolated and fully characterized.9 The experimental observations suggest that 2 is stable toward amines, and it reasonably tolerates ethanol at room temperature. We know that aldehydes rapidly react with 2 in toluene. In the absence of an amine, this reaction affords the corresponding symmetrical esters, e.g. ethyl acetate from acetaldehyde, according to Scheme 5.4b,7 The role of the Scheme 5. Reactivity of 2 with Aldehydes in Toluene
alkoxide of Scheme 5 as a key catalytic intermediate facilitating the C−O bond formation has been discussed by us7 and others.10 It is reasonable to assume that 3 is also formed from 2 and acetaldehyde in the presence of an amine. Elucidation of the following reaction steps was guided by DFT calculations in toluene, using acetaldehyde with methylamine as the substrates (R = R′ = Me). Scheme 6 captures the key events of the amide formation in toluene; the computational details are included in the Supporting Information. The calculations suggest that the product of aldehyde insertion with 2, the alkoxide Int 1, is favorably hydrogen bonded by the amine in Int 2. This adds aldehyde in step III to give Int 3, further triggering the two lowenergy proton transfer steps IV and V, leading to the hemiaminal Int 5. The reaction is downhill from Int 3 to 5,
The origin of the Gibbs energies (M06L-D3, followed by ωB97X-D values, kcal/mol, in toluene at 298.15 K) is the ethoxide 3 (Int 1) with methylamine and acetaldehyde (R = R′ = Me); mass balance is ensured throughout. a
and the C−N coupling process is entropy-controlled (with the principal contribution of step III where −TΔS = 8.5 kcal/mol), as steps III−V all have negative reaction enthalpies: e.g., ΔH = −7.3 (Int 3), −7.0 (TS1), −6.5 (Int 4), −7.7 (TS2), −9.8 kcal/ mol (Int 5) at the M06L-D3 level of theory. In other words, the hemiaminal Int 5 should form nearly instantaneously upon an encounter between acetaldehyde and Int 2. Ethanol elimination 6658
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When the energies of the transition structures leading to the amide vs ester product in Chart 1 are compared, the DFT data consistently indicate that the latter is a higher energy process, apparently responsible for the selectivity of the dehydrogenative coupling of primary alcohols leading to amides or esters, with and without amine, respectively. When the energies of Chart 1 are compared with the corresponding barrier heights of the reactions of Scheme 4, ΔG⧧ ≥ 21 kcal/mol,4a,i it is apparent that the uncatalyzed formation of hemiaminals and hemiacetals must be too slow in comparison to the catalytic coupling. Thus, formation of free hemiaminals is rather unlikely with efficient dehydrogenative coupling catalysts. The trimolecular intermediates Int 3− Int 5 and the connecting transition states TS1 and TS2 must be unfavorable with sterically hindered amines. To probe this effect, acetaldehyde was reacted with propane-1,2-diamine (1/5) in toluene-d8. As expected, the reaction proceeded at the less hindered NH2 group and produced N-(2-aminopropyl)acetamide, readily identified from the spectra of Figure 3. Overall, the dehydrogenative amide synthesis of Scheme 1a with 2 involves two catalytic cycles: A, producing aldehyde and H2 according to Scheme 7, and B, comprising the catalytic cycle of Scheme 6 where the aldehyde reacts with the amine. Protonation of the hydride catalyst by alcohol in Scheme 7, leading to H2 elimination, has been discussed elsewhere.13 Two complete A cycles are necessary for one B cycle to produce one molecule of the product amide. These cycles are “independent” in the sense that they can be operated by different molecules of the catalyst; however, cycle A may branch into B via the alkoxide Int 1. With R = Me, the net reaction of Scheme 7 is EtOH → CH3CHO + H2 (ΔH1). This is a combination of two reactions of the metal complexes: [M]-H + EtOH → [M]-OEt + H2 (ΔH2) and [M]-OEt → [M]-H + CH3CHO (ΔH3), therefore, ΔH1 = ΔH2 + ΔH3. Since ΔH1 = 19.4 kcal/mol,14 a positive value of ΔH2 should make the aldehyde formation from [M]OEt thermodynamically more favorable. A positive ΔH2 value is expected when the hydride catalyst [M]-H is relatively stable but the corresponding alkoxide [M]-OEt is not. This
from Int 5 leads to the relatively stable hemiaminal complex Int 6.11 The latter undergoes rotation about the C−O bond of the hemiaminal via TS4, reminiscent of the “slip” process advocated by Hasanayn.4c The hemiaminal of Int 7 is prepared for outer-sphere dehydrogenation, familiar from the previous studies,4 affording the amide product and regenerating the dihydride 2. Step VIII is the highest energy part of the catalytic cycle, at the highest point reaching 12.8 and 7.2 kcal/mol at the M06L-D3 and ωB97X-D levels of theory, respectively (for details see Figure S10 in the Supporting Information). Some special features of Scheme 6 should be highlighted. The reaction proceeds with net retention of the N−H bond of the catalyst. Only one metal coordination site is used throughout the reaction; thus, there is no need for ancillary ligand elimination and the classical β-H elimination. The alkoxide Int 1 plays a key role in the amide synthesis of Scheme 6 as well as in the recently discussed ester synthesis catalyzed by 2;7 however, the roles are different.12 Whereas the alkoxide is directly incorporated into the ester via the transition structure of Chart 1 (right),7 the RCH2O− ligand acts as a base in the amide synthesis. This allows the catalyst to combine the hemiaminal formation and dehydrogenation into one catalytic cycle. Chart 1. C−N vs C−O Bond Formationa
a
The origin of Gibbs energies (in toluene, at 298.15 K) is the ethoxide 3 with CH3CHO and CH3NH2 (R = R′ = Me).
Figure 3. Partial 13C{1H} and 1H{13C} NMR spectra of N-(2-aminopropyl)acetamide and ethanol produced by reacting acetaldehyde (5 mmol) with propane-1,2-diamine (26 mmol, 5 M) and 2 (0.05 mol % vs amine), in toluene-d8 (2.56 mL). For full proton and carbon NMR spectra with detailed assignments, see Figure S7 in the Supporting Information. 6659
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of the existing views, free 16-electron species exemplified by the unsaturated complexes of Scheme 3 are thus demoted from being considered “the dehydrogenation catalysts” to the status of off-cycle species. Their formation together with the free hemiaminal may lead to the imine and water side products detrimental to the amide synthesis. The amide bond formation is undoubtedly one of the most important transformations in organic chemistry, biochemistry, and medicinal chemistry. The dehydrogenative coupling of Scheme 1 is a nearly ideal safe, atom-efficient approach. The detailed understanding of the chemistry of Scheme 1, presented in this paper, lays out the much-needed mechanistic foundation that should guide the continuing development of catalytic amide synthesis in the industry and academic research.
Scheme 7. Catalytic Alcohol Dehydrogenation
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observation suggests that less oxophilic (i.e., softer) d metal centers should possibly make better dehydrogenation catalysts. When the sterically sensitive nature of the amide-bond forming transition state TS1 is taken into consideration, it is further obvious that the coordination sphere of the catalyst should not be sterically congested. Although the dehydrogenative amide synthesis requires heat for the heterolytic C−H cleavage of the alkoxide intermediate of Scheme 7, the noted (vide supra) persistence of 2 in the catalytic solutions suggests that the slow extrusion of H2 in Scheme 7 may hinder the amide formation at room temperature. To test this experimentally, we reacted allylamine with ethanol in toluene-d8 under the conditions of the Grützmacher amide synthesis of Scheme 1b, using acetone-d6 as the hydrogen acceptor. Hydrogen transfer from 2 to acetone should be facile. Indeed, formation of N-allylacetamide proceeded smoothly with TON = 340 (1 h), 425 (2 h), and 460 (3 h). The reaction reached 99% conversion of ethanol in 6 h, as shown in Figure 4. The spectrum of Figure 4 displays the familiar resonances of N-allylacetamide and the remaining allylamine, together with the −CHOH signal of the byproduct secondary alcohol at δ 3.9; the trace amount of ethanol is seen at δ 3.6.
EXPERIMENTAL DETAILS All chemicals were purchased from Sigma-Aldrich. Anhydrousgrade acetaldehyde was redistilled under argon. Allylamine was used as received, with added 3 Å molecular sieves. Benzylamine and 1,2-propanediamine were filtered through activated basic alumina under argon. Toluene-d8 and methanol-d4 (Cambridge Isotope Laboratories) were used as received, with added 3 Å molecular sieves. All chemicals and solvents (except benzylamine) were stored in the freezer of the glovebox, at −30 °C. In catalytic experiments, the reactions were performed under argon, in 20 mL vials equipped with micro stir bars. All reagents were taken from the freezer (at −30 °C) immediately prior to the preparation of the reaction solutions. First, 7−10 mg of complex 2 was taken in a vial on a calibrated analytical balance accurate to 0.1 mg. Next, the calculated mass of the amine was added and the vial was placed on a magnetic stirrer. A separate 20 mL vial was filled with the calculated masses of toluene-d8 (or methanol-d4), followed by acetaldehyde. This mixture was transferred via a Pasteur pipet into the catalyst solution in the amine, with rapid stirring. After 1 min of stirring, a ca. 0.8 mL sample of the reaction solution was taken into an NMR tube. The NMR spectra were collected on a Agilent DD2 400 MHz spectrometer. For reliable integration, the 1H{13C} NMR spectra were obtained using a single 1H scan and a preset receiver gain.
CONCLUSIONS This and our recent work7 advance a view of the catalytic dehydrogenative coupling reactions of alcohols proceeding with all steps facilitated by the catalyst. Arguably a dramatic reversal
COMPUTATIONAL DETAILS The DFT calculations were carried out with Gaussian 1615 (with G09Defaults) using the M06-L functional16 together with the D3 version of Grimme’s dispersion with the original D3
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Figure 4. 1H{13C} NMR spectrum of N-allylacetamide produced by reacting ethanol (1.4 mmol, 0.5 M) with allylamine (2 mmol), acetone-d6 (2.9 mmol), and 2 (0.2 mol % vs EtOH) in toluene-d8 (2.23 mL), after 6 h at room temperature. 6660
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ACS Catalysis damping function,17 added with the “EmpiricalDispersion=GD3” keyword. Additional calculations were performed using MN15-L18 and ωB97X-D19 functionals. The basis sets, listed by their G16 keywords, included Def2QZVP (with def2 ECP) for Os and Def2TZVP for all other atoms (together with the W06 density fitting basis set when M06-L and MN15-L functionals were used).20,21 The polarizable continuum model (IEFPCM) was used in all calculations (solvent = toluene), with the radii and nonelectrostatic terms of Truhlar and coworkers’ SMD solvation model (scrf = smd).22 Every geometry optimization was accompanied by a frequency calculation that provided the enthalpies listed in Table S1 in the Supporting Information. The free energies of Scheme 6 and Chart 1 were calculated at 298.15 K while corrected molar entropies were used (for details see pages S9 and S10 in the Supporting Information). This work did not employ gas-phase optimizations or single-point calculations.
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G.; Li, S. Inorg. Chem. 2011, 50, 10572−10580. (k) Nova, A.; Balcells, D.; Schley, N. D.; Dobereiner, G. E.; Crabtree, R. H.; Eisenstein, O. Organometallics 2010, 29, 6548−6558. (5) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40, 40−73. (6) Spasyuk, D.; Vicent, C.; Gusev, D. G. J. Am. Chem. Soc. 2015, 137, 3743−3746. (7) Morris, S. A.; Gusev, D. G. Angew. Chem., Int. Ed. 2017, 56, 6228−6231. (8) Standard Thermodynamic Properties of Chemical Substances. In CRC Handbook of Chemistry and Physics, 96th ed.; Haynes, W. M., Ed.; CRC Press/Taylor and Francis: Boca Raton, FL, 2016. (9) (a) DFT calculations of this work suggest that 2 and 3 might be in equilibrium at 25 °C. The reaction enthalpy for 2 + EtOH → 3 + H2, ΔH, is 1.6 (M06L-D3) and 4.7 kcal/mol (ωB97X-D) in toluene. The calculated TΔS term is 3.5 kcal/mol under 1 bar of H2 (S° = 31.2 cal mol−1 K−1) that predicts a reaction Gibbs energy of near 0. For H2 dissolved in toluene, the absolute partial molal entropy is 19.6 cal mol−1 K−1;9b this gives TΔS = 0.0 kcal/mol and ΔG > 1.6 kcal/mol while H2 remains in solution. Assuming that the species at δ(31P) 79.4 in Figure 2 is 3 and using the known solubility of hydrogen in toluene under the standard conditions, [H2] = 3 mM,9b a rough estimate for ΔG is 5 kcal/mol. (b) Cook, M. W.; Hanson, D. N.; Alder, B. J. J. Chem. Phys. 1957, 26, 748−751. (10) (a) Chakraborty, S.; Lagaditis, P. O.; Förster, M.; Bielinski, E. A.; Hazari, N.; Holthausen, M. C.; Jones, W. D.; Schneider, S. ACS Catal. 2014, 4, 3994−4003. (b) Hasanayn, F.; Baroudi, A. Organometallics 2013, 32, 2493−2496. (11) An intermediate of this type, assigned a hemiaminal oxide structure, was detected in an ESI-MS study of the dehydrogenative coupling of benzylamine with ethanol, catalyzed by 1 under basic conditions. Collision-induced dissociation (CID) experiments demonstrated formation of N-benzylacetamide from this intermediate in the gas phase: Vicent, C.; Gusev, D. G. ACS Catal. 2016, 6, 3301− 3309. (12) Interestingly, a recent study suggested that a secondary alkoxide intermediate plays a key role in the catalytic hydrosilylation of ketones: Bleith, T.; Gade, L. H. J. Am. Chem. Soc. 2016, 138, 4972−4983. (13) (a) Hasanayn, F.; Morris, R. H. Inorg. Chem. 2012, 51, 10808− 10818. (b) Dub, P. A.; Henson, N. J.; Martin, R. L.; Gordon, J. C. J. Am. Chem. Soc. 2014, 136, 3505−3521. (c) Dub, P. A.; Gordon, J. C. Dalton Trans. 2016, 45, 6756−6781. (14) (a) Wiberg, K. B.; Crocker, L. S.; Morgan, K. M. J. Am. Chem. Soc. 1991, 113, 3447−3450. (b) The calculated values of this work are ΔH1 = 19.4 (M06L-D3) and 22.5 kcal/mol (ωB97X-D). Both DFT methods give the same ΔH2 = 17.8 kcal/mol; see also ref 9a. (15) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A. V.; Bloino, J.; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 16, Revision A.03; Gaussian, Inc., Wallingford, CT, 2016. (16) Zhao, Y.; Truhlar, D. G. J. Chem. Phys. 2006, 125, 194101− 194118. (17) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. J. Chem. Phys. 2010, 132, 154104. (18) Yu, H. S.; He, H.; Truhlar, D. G. J. Chem. Theory Comput. 2016, 12, 1280−1293. (19) Chai, J.-D.; Head-Gordon, M. Phys. Chem. Chem. Phys. 2008, 10, 6615−6620.
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscatal.7b02415. NMR spectra of the catalytic reaction solutions and additional computational details (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail for D.G.G.:
[email protected]. ORCID
Dmitry G. Gusev: 0000-0003-3302-356X Notes
The author declares no competing financial interest.
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ACKNOWLEDGMENTS The author is grateful to the Natural Sciences and Engineering Research Council of Canada-Discovery grant program, CFI LOF program, SHARCNET, and Wilfrid Laurier University for support.
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REFERENCES
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