Dehydrogenative Coupling of Ethanol and Ester Hydrogenation

Sep 6, 2016 - aThe origin of the energies (kcal/mol, in ethanol solvent, at 298.15 K) is ... double hydrogen transfer” (BDHT) pathway discussed in t...
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Dehydrogenative Coupling of Ethanol and Ester Hydrogenation Catalyzed by Pincer-Type YNP Complexes Dmitry G. Gusev* Wilfrid Laurier University, Department of Chemistry and Biochemistry, 75 University Avenue West, Waterloo, Ontario N2L 3C5, Canada S Supporting Information *

ABSTRACT: The “Y” donor group (Y = −OMe, −SEt, −PPh2, −NH2, −NMe2, −Py, pyrrolidinyl, quinolyl) of the pincer-type ruthenium complexes RuHCl(CO)[κ3-YNP] has a dramatic influence on the catalytic activity in the dehydrogenative homocoupling and cross-coupling of ethanol and ester hydrogenation reactions. The observations are connected with the mechanisms of the catalytic reactions, and this paper provides evidence for ester C−O bond formation/cleavage assisted by the bifunctional catalysts in an outer-sphere fashion, reminiscent of the Tishchenko chemistry. KEYWORDS: alcohol dehydrogenation, ester hydrogenation, ester synthesis, amide synthesis, catalytic mechanisms

T

he seminal work of Milstein and co-workers1 in 2005− 2007 demonstrated the impressive synthetic potential of the catalytic homocoupling and cross-coupling of primary alcohols and the reverse processes, hydrogenation of esters and amides of Scheme 1.1 This area of research has grown in the

Chart 1. Ruthenium Complexes 2−12

Scheme 1

past decade, and the progress has been documented in many contemporary reviews and book chapters. 2,3 Extensive computational studies have been devoted to the elucidation of the catalytic mechanisms.3−6 Our complex, OsHCl(CO)[PiNH(CH2)2NHPtBu2] (1; Pi = picolyl group, −CH2Py), is an efficient precatalyst for the dehydrogenative coupling of alcohols and ester hydrogenation.7 Among the unique useful properties of 1 is the compatibility with alkenes that allows working with a broad range of unsaturated substrates, typically with 98−100% retention of the alkene functionalities. Furthermore, complex 1 is the only known efficient catalyst for the synthesis of amides from the volatile primary alcohols and amines with bp < 100 °C, such as N-alkylacetamides. In continuation of the recent work, we were interested in making the ruthenium analogue, RuHCl(CO)[PiNH(CH2)2NHPtBu2] (2), and exploring the related new pincertype YNP complexes 3−10 of Chart 1. Through a comparative study of 2−10 together with the known compounds 11 (Ru© 2016 American Chemical Society

MACHO)8 and 12,9 we wanted to probe the role and importance of the Y ligand group in the catalytic reactions of Scheme 1 and learn whether the catalyst efficiency could be Received: August 13, 2016 Revised: August 29, 2016 Published: September 6, 2016 6967

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ACS Catalysis usefully enhanced through the systematic modifications of the ligand structure. The results of this paper are presented and discussed below, and this study confirms the overall superior catalytic efficiency of the osmium vs ruthenium metal center of 1 and 2 in the reactions of Scheme 1, as well as the privileged role of the PiNPtBu ligand. This paper also reports several striking observations of the dramatic influence of the Y group of the catalysts of Chart 1 on the reactions of Scheme 1 that provide some guidance for future catalyst design. At the end, this paper revisits the catalytic mechanisms of the reactions of Scheme 1 (X = O) to provide experimental evidence for the ester C−O bond formation/cleavage assisted by the bifunctional catalysts in an outer-sphere fashion, reminiscent of the Tishchenko chemistry. The active form of the osmium catalyst OsH2(CO)[PiNH(CH2)2NHPtBu2] is indeed highly active (TOF > 7000 h−1) for the Tishchenko synthesis of ethyl acetate from acetaldehyde.

Table 1. Selected Spectroscopic Data for the Complexes of Chart 1a complex 2 3 4 5 6 7 8 9 10 12

δ(RuH), 2J(H−P)b −15.10, −14.44, −15.37, −15.79, −16.19, −16.31, −16.40, −16.18, −16.25, −14.33,

26.4 28.4 28.4 27.6 30.4 25.2 26.4 28.4 28.0 25.9

δ(31P)

δ(CO), 2J(C−P)b

125.8 99.5 124.6 127.4 139.6 117.3 125.6 126.4 125.6 70.8

207.70, 206.51, 206.85, 207.62, 206.87, 206.54, 207.14, 208.32, 208.40, 205.83,

18.1 19.3 19.5 20.1 21.4 19.3 18.7 18.8 19.5 16.2

ν(CO)c 1909.7 1920.9 1908.8 1908.0 1917.7 1917.4 1907.0 1903.5 1903.7 1917.4

a All measurements in dichloromethane. bTwo-bond spin coupling, in Hz. cStretching vibration, in cm−1 (broad absorption).

geometry with the hydride trans to the chloride and the carbonyl cis to the phosphorus group; thus, the κ3-YNP ligands are coordinated in a mer fashion, as shown in Chart 1. The 31P NMR shifts of the κ3-YNPtBu ligands on ruthenium are all very similar, δ 124.6−126.4, when Y is a nitrogen donor. The CO stretching frequencies suggest that, in the series of the κ3YNPtBu compounds, ruthenium is most electron rich in the dimethylamine and pyrrolidine complexes 9 and 10 and the least so in the ether and thioether complexes 6 and 7. We assessed some structural parameters of the ruthenium complexes and the relative hemilability of the Y groups with the help of DFT (M06-L) calculations; the relevant data are collected in Table 2. The Ru−Y bond dissociation enthalpies

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RESULTS The YNP ligands of 1−10 are modular by design. Thus, assembling a representative ligand library is straightforward via the alkylation and condensation reactions of Scheme 2, detailed Scheme 2

Table 2. Selected Gas-Phase DFT (M06-L) Data for Complexes 2 and 4−12 in the Experimental Section. The alkylation is solventless, and the excess ethylenediamine works as the reaction media and the base; the product diamines were isolated by distillation in typical 60−80% yields. These diamines react with bulky ClPR2 selectively at the primary nitrogen, and the products were isolated in excellent yields by distillation or (for the less volatile YNP ligands) by evaporation of the THF solutions. The amine ligand H2N(CH2)2NH(CH2)2NHPtBu2 was obtained in one step from diethylenetriamine and ClPtBu2, in an 85% yield. Two complexes of this work (3 and 8) were obtained by ligand exchange with RuHCl(CO)(AsPh3)3. However, our preferred approach to the ruthenium complexes of Chart 1 was based on heating a mixture of [RuCl2(COD)]n, a YNP ligand, and lithium in anhydrous ethanol (see Experimental Section for details), in a fashion similar to the reported synthesis of OsHCl(CO)[PiNH(CH2)2NHPtBu2] from [OsCl2(p-cymene)]2.7 This worked most successfully with PiNPtBu and afforded complex 2 as a crystalline air-stable solid (3.3 g, 82.5% product yield, see Scheme 3 and Figure S1 in the Supporting Information). Satisfactory elemental analyses were obtained for all complexes of this work. The key spectroscopic data in Table 1 suggest that complexes 1−10 adopt the same coordination

complex 2 4 5 6 7 8 9 10 12 a

Ru−Y, Å 2.159 2.271 2.216 2.304 2.478 2.235 2.302 2.319 2.153

(Ru−N1) (Ru−N1) (Ru−N1) (Ru−O) (Ru−S) (Ru−N1) (Ru−N1) (Ru−N1) (Ru−N1)

Ru−P, Å

Ru−N2, Å

BDEa

2.305 2.297 2.297 2.251 2.310 2.283 2.283 2.285 2.256

2.234 2.266 2.236 2.234 2.267 2.241 2.238 2.246 2.204

19.3 13.5 17.5 13.4 21.4 20.1 19.6 20.7 17.9

Ru−Y bond enthalpies, in kcal/mol.

(BDE) were calculated as enthalpy differences of the 6coordinate, 18-electron complexes 2−12 and the corresponding 5-coordinate, 16-electron species formed by rotation of the Y group out of the coordination sphere of the metal, as illustrated in Figure 1 for 2. Most complexes in Table 2 have similar Ru−Y

Scheme 3

Figure 1. Calculated structures of 2 (left) and the 16-electron complex formed upon breaking the Ru−N1 bond (right) (the C−H hydrogens are not shown). 6968

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ACS Catalysis bond enthalpies, in the range of 19.3−21.4 kcal/mol. Complex 6 possesses a weak Ru−O bond (13.4 kcal/mol), as expected. The Ru−N1 bond of the quinoline complex 5 is destabilized (17.5 kcal/mol vs 19.3 kcal/mol in 2), presumably due to repulsion between the quinoline and the carbonyl (note the increased angle N1−Ru−C1 = 99.7° in 5 vs N1−Ru−C1 = 96.8° in 2). The weakly bonded pyridine fragment of 4 (BDE = 13.5 kcal/mol) came as a surprise that, however, correlates with the longer Ru−N1 bond (2.271 Å) in 4 in comparison with the corresponding Ru−N1 bond in 2 (2.159 Å) and the diminished trans influence reflected in the Ru−P bond distances (2.297 Å (4) vs 2.305 Å (2)). The reason for making complexes 2−10 was to test them in the reactions of Scheme 1 to see the effect of fitting the YNP catalysts with different Y-donor groups. Three representative reactions of Scheme 4 were chosen for the comparative testing,

Figure 2. Vertical bars display conversions (percent) to ethyl acetate, N-butylacetamide, and the C11 alcohols, respectively, in the reactions of Scheme 4, observed with complexes 1−12.

Scheme 4. Reactions Tested in This Work

Table 3. Conversions and Selectivities of the Reactions of Scheme 4 with the Catalysts of Chart 1a

a b

catalyst

eq 1

eq 2

eq 3

1b 2 3 4 5 6 7 8 9 10 11 12

82 29 27 1 1 0 41 41 0 0 70 27

90 (0) 64 (3) 9 (3) 1 (3) 8 (6) 5 (2) 34 (5) 6 (6) 2 (14) 2 (7) 5 (10) 6 (4)

95 (98, 1) 84 (96, 2) 66 (75, 25) 5 (5, 100) 15 (5, 100) 0 (41, 23) 74 (37, 78) 69 (32, 100) 9 (31, 13) 11 (4, 100) 25 (86, 6) 82 (12, 100)

Conversions and selectivities (in parentheses) are given in percent. Data from ref 7.

genation) and the percentage of the C-9 alkenes, out of the total alkene content after hydrogenation (0% when no CC bond isomerization). Table 3 and Figure 2 also include data for the Takasago catalyst RuHCl(CO)[HN(CH2CH2PPh2)2] (11)8 and our RuHCl(CO)[PiNHCH2CH2PPh2] (12).9 The observations of Figure 2 and Table 3 form no trivial pattern; we shall note the following. (1) The catalytic performance is profoundly influenced by the Y group of the YNP catalysts. Among the catalysts ineffective in the reactions of Scheme 4 are complexes 4−6, possessing labile Y groups, and complexes 9 and 10, where Y is a tertiary amine. (2) The nature of the phosphorus group most affects the catalytic reaction of eq 2, while being less important in eqs 1 and 3. The results for 2 (PtBu2), 3 (PoTol2), and 12 (PPh2) suggest a need for a bulky, good donor PR2 group for the successful amide synthesis of eq 2. (3) The ester reduction of eq 3 is apparently the least challenging among the catalytic reactions of Scheme 4. Six complexes of this study afforded good to high conversions to the C11 alcohols. (4) There is no correlation between the results of the homocoupling and cross-coupling of ethanol in eqs 1 and 2. Catalysts that are reasonably successful (TON > 2000) in converting ethanol to ethyl acetate can be successful (1, 2, 7), or not (3, 8, 11, 12) in making N-butylacetamide. Ru-MACHO complex 11 is an extreme example of this disparity, affording

and we deliberately selected demanding tests where few existing catalysts would be expected to perform well. Specifically, very few catalysts can convert ethanol to ethyl acetate with 0.01 mol % catalyst (eq 1). For the direct synthesis of amides (eq 2), catalytic efficiency at T < 100 °C and employment of volatile substrates (the boiling points of ethanol and butylamine are near 78 °C) are unprecedented outside our work with 1. In test eq 3, hydrogenation of methyl undecenoate allows assessing both the efficiency and the selectivity of the catalysts in the presence of a CC bond susceptible to hydrogenation. Low catalyst loadings in all reactions of Scheme 4 make the overall complex stability and longevity a prerequisite for the successful catalytic performance. The observed conversions to the principal products (ethyl acetate in eq 1, N-butylacetamide in eq 2, and C11 alcohols in eq 3 of Scheme 4) are visualized in Figure 2. The complete results of the catalytic testing are collected in Table 3; these include the observations of the byproduct imine, BuN CHCH3, in the test of eq 2 (values in parentheses). Under eq 3, Table 3 displays two values in parentheses: the total alkene content after hydrogenation (100% when no alkene hydro6969

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the authors, that “with the weakening ruthenium−heteroatom bond the catalytic activity of these ruthenium pre-catalysts in the acceptorless dehydrogenation of primary alcohols as well as the hydrogenation of ketones is diminished”. The weakly bonded complexes 4−6 in our work are similarly inefficient. It is clear that structural changes resulting in increased ligand lability offer no benefits in the catalytic reactions of Scheme 1. At the start of this study, we did not anticipate that the catalytic behavior of complexes 2 and 4 should turn out to be so strikingly different. Yet, our observations correlate with the findings of Baratta and co-workers made while studying transfer hydrogenation of acetophenone with the related ruthenium complexes 17 and 18, possessing −CH2Py and − CH2CH2Py ligand groups, respectively (Chart 2).11 Baratta reported the turnover frequency with 17 1 order of magnitude greater than the corresponding TOF value with 18. They speculated that the “five-membered chelate ring (in 17) gives a higher stability to the six-coordinate complex with a neat increase of its catalytic efficiency”. Our DFT analysis of the Ru-Py bond enthalpies in 2 and 4 supports this explanation. It is further appropriate to address the effect of the size of the ring containing the Ru−P bond in 2−12. Figure 3 displays the DFT structure of 2 together with the DFT structures of RuHCl(CO)[PiNHCH2CH2CH2PtBu2] (2a) and RuHCl(CO)[PiNHCH2CH2PtBu2] (2b). Complex 2a possesses a six-atom ruthenacycle that is the largest (10.93 Å) in the series, followed by 2 (10.70 Å) and 2b (9.37 Å, as the sum of the bonds forming the metallacycle). The Ru−P and Ru−N2 distances and the Ru−N1 bond enthalpy follow the same trend: 2a possesses the longest Ru−P (2.317 Å) and Ru−N2 (2.246 Å) bonds and the strongest Ru−N1 bond (19.5 kcal/mol). The relatively weak Ru−N1 bond in 2b (16.3 kcal/mol) is similar to that of the related complex 12 (17.9 kcal/mol). One can attribute the deteriorated (12% vs 96%) selectivity in eq 3 (Scheme 4) with 12 vs 2 to the increased lability of the Ru−N1 bond in 12 and formation of η2-alkene ruthenium hydride intermediates, leading to the CC bond hydrogenation and isomerization. Overall, complexes possessing fused 5 + 6-atom metallacycles of the κ3-YNP group, especially 1 and 2, appear to be balanced the best in terms of stability. We should note, however, the relatively long M−N2 bonds of 2 and 2a in Figure 3. Thus, if the M−Y bond is weak (as in 4−6) the loss of both Ru−Y and Ru−N2 bonds of the κ3-YNP ligands becomes a

TON = 7000 toward ethyl acetate but only 100 turnovers toward N-butylacetamide with an additional 200 turnovers toward the imine, BuNCHCH3. (5) Complex 2 is a viable catalyst for the direct amide synthesis as well as for the reduction of esters with a good selectivity for CO vs CC bond hydrogenation. However, 2 is less efficient than the osmium analogue 1. The difference toward undec-10-enol becomes pronounced when using 0.01 mol % catalyst and 0.1 mol of the ester, without solvent. This gave TON = 9800 (1)7 and 5600 (2) in 5 h under p(H2) = 50 bar, with 2 mol % of NaOMe, with 98−97% retention of the CC bond. The conversion to N-butylacetamide was improved from 64 to 85% with 0.1 mol % of 2 and further to 94% with 0.1 mol % of 2 together with 2 mol % of NaOEt (both experiments gave 100 h−1, we believe it is best to consider the mechanism of Scheme 11 until an efficient catalyst for the amide synthesis of eq 2 is found that would possess no hemilabile group.

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CONCLUSIONS Several observations and conclusions of this paper can be summarized as follows. (1) The catalytic reactions represented by Scheme 1 superficially suggest a common mechanism. For example, it 6973

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Syntheses. Py(CH2)2NH(CH2)2NH2 (N-((2-Picolyl)methyl)ethylenediamine, PiCH2NN). A 100 mL round-bottom flask containing a stir bar was charged with ethylenediamine (33 g, 0.549 mol), and then 2-(2-chloroethyl)pyridine (13 g, 91.8 mmol) was added with stirring and the mixture was stirred overnight to give a 4/1 mixture of PiCH2NN and 2vinylpyridine (identified by NMR). A 70 mL portion of Et2O was added, and after vigorous shaking the top layer was decanted. The bottom layer was additionally extracted with 2 × 70 mL of Et2O, while decanting the top layer. The combined ether extract was evaporated under vacuum (one should be prepared to see ethylenediamine freezing, mp 8 °C). The product was isolated by vacuum distillation. First, ethylenediamine and 2-vinylpyridine were condensed into a flask immersed into an ice bath. Then the distillation apparatus was fitted with a cow-type receiver and the product boiling at 96−102 °C (p = 0.05 Torr, bath at 135 °C) was collected. Yield: 9.0 g (59%) of a viscous liquid. 1H NMR (benzene-d6): δ 8.48 (m, 1H, Py), 7.06 (td, J = 7.6, 2.0, 1H, Py), 6.80 (d, J = 7.6, 1H, Py), 6.63 (m, 1H, Py), 2.98 (m, 2H, CH2), 2.89 (m, 2H, CH2), 2.54 (m, 2H, CH2), 2.46 (m, 2H, CH2), 0.85 (br s, 3H, NH + NH2). 13C{1H} NMR (benzene-d6): δ 161.71 (s, Py), 150.02 (s, Py), 136.07 (s, Py), 123.52 (s, Py), 121.33 (s, Py), 53.41 (s, CH2), 49.99 (s, CH2), 42.75 (s, CH2), 39.50 (s, CH2). QuiCH2NH(CH2)2NH2 (N-((2-Quinolyl)methyl)ethylenediamine, QuiNN). A 250 mL round-bottom flask equipped with a stir bar was charged with ethylenediamine (33 g, 0.9 mol), and then 2-(chloromethyl)quinoline hydrochloride (25 g, 89.9 mmol) was added in four portions over a 1 h period with stirring and the mixture was stirred overnight. A 70 mL portion of Et2O was added, and after vigorous shaking the top layer was decanted. The bottom layer was additionally extracted with 2 × 70 mL of Et2O, while decanting the top layer. The combined ether extract was evaporated under vacuum (one should be prepared to see ethylenediamine freezing, mp 8 °C). The product was isolated by vacuum distillation. First, ethylenediamine was condensed into a flask immersed into an ice bath. Then the distillation apparatus was fitted with a cowtype receiver and the product boiling at 140−148 °C (p = 0.01 Torr) was collected. The distillation was complicated by decomposition, and only a small amount of the product was recovered, contaminated with 8−9 mol % of 2-methylquinoline. Yield: 4.1 g (ca. 17%) of a viscous liquid. 1H NMR (benzened6): δ 8.19 (d, J = 8.8, 1H, CH), 7.55 (d, J = 8.4, 1H, CH), 7.38 (d, J = 8.0, 1H, CH), 7.31 (m, 1H, CH), 7.17 (d, J = 8.4, 1H, CH), 7.11 (m, 1H, CH), 3.93 (s, 2H, CH2), 2.51 (m, 2H, CH2), 2.46 (m, 2H, CH2), 0.85 (br s, 3H, NH + NH2). 13 C{1H} NMR (benzene-d6): δ 162.02 (s), 148.86 (s), 136.29 (s), 130.11 (s), 129.74 (s), 128.10 (s), 127.99 (s), 126.30 (s), 121.03 (s), 56.60 (s, CH2), 53.30 (s, CH2), 42.77 (s, CH2). MeO(CH2)2NH(CH2)2NH2 (N-(2-Methoxyethyl)ethylenediamine, ONN). A 250 mL round-bottom flask equipped with a stir bar was charged with ethylenediamine (75 g, 1.248 mol), and then 2-bromoethyl methyl ether (25 g, 0.18 mol) was added in portions over 25 min with stirring (note: although the reaction solution becomes hot, it does not require external cooling). In 1.5 h (when the reaction solution cooled to room temperature), 100 mL of Et2O was added. A two-phase system formed upon stirring. The bottom layer was removed with a pipet, and the upper ether solution was evaporated under vacuum (one should be prepared to see ethylenediamine freezing, mp 8 °C). The remaining mixture of the product and ethylenediamine was separated by vacuum

may seem that the success of both the ester synthesis and the amide synthesis should depend on the ability of the catalyst to dehydrogenate the alcohol. In practice, there is a disconnect between the two reactions, and the catalytic efficiency in the ester synthesis does not correlate with the efficiency in the amide synthesis. Therefore, catalysts highly active in both homocoupling and cross-coupling of primary alcohols and the hydrogenation of the carbonyls may be rare compounds able to exploit the outer-sphere and inner-sphere pathways of Schemes 5, 8, and 11 similarly well. (2) Some practical advice can be offered for future catalyst design. Overall catalyst stability is a prime concern, and our preference is to work with thermally robust systems. The stability of metal complexes often follows the trend 5d > 4d > 3d; therefore, developing 3d metal catalysts for the reactions of Scheme 1 should be most challenging, whereas the use of 5d metals can be advantageous. (3) Related to point 2 above, the use of polydentate ligands can be recommended and weakly bonded groups should be avoided. For example, pincer ligands forming 6 + 5 metallacycles (with a phosphorus donor in the 6-atom ring) are suitable choices. It remains unclear why complexes 9 and 10, where Y = tertiary amine, proved to be inactive in our work; however, this experience suggests a certain caution toward the use of such groups. (4) All existing successful catalysts for the reactions of Scheme 1 possess at least one good donor group, typically a phosphorus group. Since the use of a bulky donor group seems advantageous for the amide synthesis, the other donor groups around the metal should be sterically less demanding (small or flat), to keep access to the metal as open as possible. (5) N−H, as part of a polydentate ligand, is an important directing group in the catalytic reactions of Scheme 1, via hydrogen bonding to the substrates. There are other strategies: e.g., the classical dearomatized Milstein catalyst does not possess an N−H group. In practice, there is no reason for not using the “N−H effect” in the catalytic reactions of Scheme 1, and designing ligands built around an N−H functionality is arguably the more simple approach that has been already exploited in a large number of existing bifunctional Noyori-type catalysts.

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EXPERIMENTAL SECTION Unless mentioned otherwise, the manipulations were performed under argon. The NMR spectra were recorded on Agilent DD2 400 MHz and Varian Unity Inova 300 MHz spectrometers. All 31P chemical shifts are indirectly referenced to external 85% H3PO4. The 1H and 13C chemical shifts are relative to the residual deuterated solvent peaks. The spin−spin coupling constants, J, are reported in Hz. RuCl3·nH2O was purchased from Pressure Chemicals, and Ru-MACHO was obtained from Strem. 1-13C-Ethyl acetate was supplied by Cambridge Isotope Laboratories. All other chemicals and anhydrous grade solvents were purchased from Aldrich. Methyl 10-undecenoate and butylamine were treated by passing them through activated basic alumina and stored under argon; anhydrous ethanol was stored over 3 Å molecular sieves under argon. [RuCl2(COD)]n and PyCH2NH(CH2)2NH2 were prepared following previously reported methods.7,18 The NMR spectra were analyzed with the help of the iNMR Reader, which also allowed deconvolution of the lines of Nbutylacetamide and N-butyl-1-13C-acetamide to quantify their contributions. 6974

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Research Article

ACS Catalysis distillation. First, ethylenediamine was collected into a flask immersed into an ice bath (bp near room temperature under 2 Torr, bath at 45 °C). Then the distillation apparatus was fitted with a cow-type receiver and the product distilled (bp ca. 50 °C, 2 Torr) as a clear colorless liquid. Yield: 11.53 g (54%). It is likely that a better yield could be obtained if the bottom layer (see above) were extracted with a second 100 mL portion of Et2O. 1H NMR (benzene-d6): δ 3.27 (t, J = 5.3, 2H, OCH2), 3.08 (s, 3H, OCH3), 2.62 (t, J = 5.3, 2H, CH2), 2.55 (m, 2H, CH2), 2.44 (m, 2H, CH2), 0.98 (br, 3H, NH + NH2). 13C{1H} NMR (benzene-d6): δ 73.06 (s, OCH2), 58.81 (s, OCH3), 53.58 (s, CH2), 50.03 (s, CH2), 42.78 (s, CH2). E t S ( C H 2 ) 2 N H ( C H 2 ) 2 N H 2 ( N - ( 2 - ( Et h y l t h i o ) e t hy l ) ethylenediamine, SNN). A 250 mL round-bottom flask equipped with a stir bar was charged with ethylenediamine (85 g, 1.414 mol), and then 2-chloroethyl ethyl sulfide (25.3 g, 0.20 mol) was added with stirring and the mixture was stirred overnight. The product was extracted twice with Et2O (2 × 100 mL), while decanting the top ether layer. The combined ether extract was evaporated under vacuum (one should be prepared to see ethylenediamine freezing, mp 8 °C). The remaining mixture of the product and ethylenediamine was separated by vacuum distillation. First, ethylenediamine was collected into a flask immersed into an ice bath (boiling near room temperature under 2 Torr, bath at 45 °C). Then the distillation apparatus was fitted with a cow-type receiver and the product boiling between 55 and 70 °C under vacuum of an oil pump (p = 0.01 Torr) was collected. Yield: 25.07 g (83%) of a clear colorless liquid. 1H NMR (benzene-d6): δ 2.62 (m, 2H), 2.54 (m, 2H, CH2), 2.47 (m, 2H, CH2), 2.40 (m, 2H, CH2), 2.27 (q, J = 7.6, 2H, SCH2), 1.06 (t, J = 7.6, 3H, CH3), 0.88 (br, 3H, NH + NH2). 13C{1H} NMR (benzene-d6): δ 53.06 (s, CH2), 49.63 (s, CH2), 42.73 (s, CH2), 32.86 (s, SCH2), 26.32 (s, CH2), 15.48 (s, CH3). Me2N(CH2)2NH(CH2)2NH2 (N-(2-(Dimethylamino)ethyl)ethylenediamine, Me2NNN). A 300 mL round-bottom flask equipped with a stir bar was charged with 2-chloro-N,Ndimethylethylamine hydrochloride (30 g, 0.208 mol), and then ethylenediamine (100 g, 1.66 mol) was added with stirring and the mixture was stirred for 2 h (note: the flask becomes hot; however no external cooling was used, as ethylenediamine apparently did not boil). Addition of ca. 70 mL of Et2O gave a two-phase system upon stirring. The top layer was decanted, and the bottom layer was additionally extracted with 2 × 70 mL of Et2O while decanting the top layer. The combined ether extract was evaporated under vacuum (one should be prepared to see ethylenediamine freezing, mp 8 °C). The remaining mixture of the product and ethylenediamine was separated by vacuum distillation. First, ethylenediamine was collected into a flask immersed into an ice bath (boiling near room temperature under 2 Torr, bath at 45 °C). Then the distillation apparatus was fitted with a cow-type receiver. After a small forerun was collected (1.58 g), the product boiling between 63 and 65 °C (p = 2 Torr) was collected. Yield: 19.55 g (71.5%) of a clear colorless liquid. 1H NMR (benzene-d6): δ 2.59, 2.56 (overlapped, 4H, 2CH2), 2.49 (m, 2H, CH2), 2.28 (t, J = 6.0, 2H, CH2), 2.05 (s, 6H, NMe), 0.98 (br, 3H, NH + NH2). 13C{1H} NMR (benzene-d6): δ 60.10 (s, CH2), 53.78 (s, CH2), 48.18 (s, CH2), 45.92 (s, NMe), 42.89 (s, CH2). c-C4H8N(CH2)2NH(CH2)2NH2 (N-(2-(Pyrrolidin-1-yl)ethyl)ethylenediamine, PyrNN). A 300 mL round-bottom flask equipped with a stir bar was charged with 1-(2-chloroethyl)pyrrolidine hydrochloride (25 g, 0.147 mol), and then

ethylenediamine (71 g, 1.18 mol) was added and the mixture was stirred for 3 h, affording a two-layer system where the upper dark layer contained the product and ethylenediamine in a 2:3 ratio, whereas the bottom yellow layer had the two species in a 1/21 ratio, respectively. The reaction appeared to be finished at that time. The mixture was stirred overnight. A 70 mL portion of Et2O was added, and after vigorous shaking the top layer was decanted. The bottom layer was additionally extracted with 2 × 70 mL of Et2O, while decanting the top layer. The combined ether extract was evaporated under vacuum (one should be prepared to see ethylenediamine freezing, mp 8 °C). The remaining mixture of the product and ethylenediamine was separated by vacuum distillation. First, ethylenediamine was collected into a flask immersed into an ice bath (boiling near room temperature under 3 Torr, bath at 45 °C). Then the distillation apparatus was fitted with a cow-type receiver and, after a small forerun was collected (10 drops), the product boiling between 58 and 60 °C (p = 0.01 Torr) was collected. Yield: 18.29 g (79%) of a clear colorless liquid. 1H NMR (benzene-d6): δ 2.65 (t, J = 6.4, 2H, CH2), 2.60 (m, 2H, CH2), 2.52 (overlapped m, 4H, 2 × CH2), 2.36 (m, 4H, 2 × CH2), 1.57 (m, 4H, 2 × CH2), 0.99 (br, 3H, NH + NH2). 13 C{1H} NMR (benzene-d6): δ 56.85 (s, CH2), 54.70 (s, 2 × CH2), 53.84 (s, CH2), 49.44 (s, CH2), 42.90 (s, CH2), 24.27 (s, 2 × CH2). PiNH(CH2)2NHP(o-Tol)2 (PiNP-oTol). (o-Tol)2PCl (5.14 g, 20.7 mmol) was added to a rapidly stirred solution of PiNH(CH2)2NH2 (6.25 g, 41.3 mmol) in THF (50 mL). The resulting mixture was rapidly stirred for 30 min. The solids were filtered, and the filtrate was evaporated and dried under vacuum to give a very viscous liquid (7.414 g, 98.7%). The isolated material was a 95/5 mixture of the product PiNP-oTol and the diphosphine PiN(P(o-Tol)2)(CH2)2NHP(o-Tol)2 (31P δ 51.1, 25.2 (s)), also containing minor impurities at 31P δ 14.7 (2.3%) and −36.9 (1.9%). Smaller chlorides, e.g. ClPPh2, react at both the NH and NH2 groups of PiNH(CH2)2NH2 with similar rates. 1H NMR (benzene-d6): δ 8.46 (ddd, J = 4.8, 1.6, 0.8, 1H, Py), 7.37 (overlapped m, 2H), 7.07 (overlapped m, 7H), 6.96 (d, J = 7.79, 1H, Py), 6.64 (m, 1H, Py), 3.75 (s, 2H, CH2), 2.89 (dq, J = 8.6, 6.0, 2H, CH2), 2.46 (t, J = 5.8, 2H, CH2), 2.44 (s, 6H, CH3), 1.96 (br m, 1H, NH), 1.75 (br s, 1H, NH). 13C{1H} NMR (benzene-d6): δ 161.36 (s, Py), 149.76 (s, Py), 141.61 (d, J = 26.0), 140.15 (d, J = 13.5), 136.16 (s, Py), 131.06 (d, J = 2.6), 130.77 (d, J = 4.0), 129.07 (s), 126.47 (d, J = 0.8), 122.21 (s, Py), 121.94 (s, Py), 55.67 (s, CH2), 51.95 (d, J = 6.4, CH2), 47.32 (d, J = 17.0, CH2), 21.25 (d, J = 20.6, CH3). 31P{1H} NMR (benzene-d6): δ 25.6 (s). PiCH2NH(CH2)2NHPtBu2 (PiCH2NP). A 200 mL roundbottom flask equipped with a stir bar was charged with N((2-picolyl)methyl)ethylenediamine (PiCH2NN; 8.96 g, 54.22 mmol), triethylamine (6.6 g, 65.22 mmol), and THF (50 mL). Then tBu2PCl (9.79 g, 54.19 mmol) was added with stirring, and the mixture was stirred rapidly for 24 h. The precipitated Et3N·HCl was vacuum-filtered and washed with 2 × 10 mL of THF. The filtrate was evaporated under vacuum. Hexane (20 mL) was added, and the mixture was filtered through 10 g of basic alumina in a 30 mL fritted funnel; the solids were washed with 10 mL of hexane and 10 mL of Et2O. The volatiles were evaporated, and the product was dried under vacuum at 70 °C for 1 h. Yield: 15.72 g (94%) of a viscous liquid. The product was ca. 98% pure according to 31P NMR. 1H NMR (benzened6): δ 8.48 (m, 1H, Py), 7.07 (td, J = 7.6, 2.0, 1H, Py), 6.79 (d, J = 7.6, 1H, Py), 6.64 (m, 1H, Py), 3.02 (overlapped m, 4H, 2 × 6975

DOI: 10.1021/acscatal.6b02324 ACS Catal. 2016, 6, 6967−6981

Research Article

ACS Catalysis

main fraction was collected (93−129 °C, p < 0.01 Torr, bath at 150−160 °C, 18.77 g (95%)) as a clear colorless, slightly viscous liquid. The product was >98% pure by 31P NMR. 1H NMR (benzene-d6): δ 3.01 (ddt, J = 8.0, 6.4, 5.9, 2H, CH2), 2.64 (t, J = 6.6, 2H, CH2), 2.54 (t, J = 5.9, 2H, CH2), 2.48 (t, J = 6.6, 2H, SCH2), 2.27 (q, J = 7.3, 2H, SCH2), 1.49 (br. m, 1H, NH), 1.25 (s, 1H, NH), 1.09 (d, J = 11.2, 18H, CH3), 1.06 (t, J = 7.3, 3H, CH3). 13C{1H} NMR (benzene-d6): δ 52.45 (d, J = 6.9, CH2), 50.81 (d, J = 28.7, CH2), 49.27 (s, CH2), 34.44 (d, J = 21.5, C), 32.93 (s, SCH2), 28.90 (d, J = 15.3, CH3), 26.28 (s, SCH2), 15.45 (s, CH3). 31P{1H} NMR (benzene-d6): δ 77.9 (s). H2N(CH2)2NH(CH2)2NHPtBu2 (H2NNP). A 200 mL roundbottom flask equipped with a stir bar was charged with diethylenetriamine (40 g, 0.388 mol), and tBu2PCl (10 g, 0.055 mmol) was added over 10 min with stirring. In 20 min, 50 mL of Et2O was added and the mixture was stirred for an additional 20 min and then moved into a freezer and left for 1 h at −12 °C. The precipitated diethylenetriamine·HCl was vacuumfiltered, and ether was evaporated under vacuum. The product was transferred into a 100 mL round-bottom flask containing boiling stones and a stirbar, and the unreacted diethylenetriamine was removed by distillation (bp 50−60 °C, p = 0.01 Torr, bath at 70−80 °C). Then the distillation apparatus was fitted with a cow-type receiver and the bath temperature was increased first to 140 °C and then to 160 °C. A small forerun was collected, and then the rest, until the source flask was dry. The product distilled as a clear colorless, slightly viscous liquid (bp 115 °C, p = 0.01 Torr). Yield: 11.65 g (85%). The product was 97−98% pure by 31P NMR, with several trace impurities observable. 1H NMR (CD2Cl2): δ 3.01 (ddt, J = 8.4, 6.4, 6, 2H, CH2), 2.70 (m, 2H, CH2), 2.64 (t, 3J = 6, 2H, CH2), 2.59 (m, 2H, CH2), 1.49 (br. m, 1H, NH), 1.09 (s, 3H, NH), 1.04 (d, 3 J(H,P) = 11.2, 18H, CH3). 13C{1H} NMR (CD2Cl2): δ 53.16 (s, CH2), 52.66 (d, J(C,P) = 6.8, CH2), 50.70 (d, J(C,P) = 27.9, CH2), 42.61 (s, CH2), 34.34 (d, J(C,P) = 20.1, C), 28.61 (d, J(C,P) = 14.9, CH3). 31P{1H} NMR (CD2Cl2): δ 78.6 (s). Me2N(CH2)2NH(CH2)2NHPtBu2 (Me2NNP). A 250 mL roundbottom flask equipped with a stir bar was charged with N-(2(dimethylamino)ethyl)ethylendiamine (Me2NNN; 10 g, 76.2 mmol), triethylamine (9.3 g, 91.9 mmol), and THF (50 mL). Then tBu2PCl (13.77 g, 76.2 mmol) was added with stirring, and the mixture was stirred rapidly over a weekend (the reaction was most likely finished within 24 h). The precipitated Et3N·HCl was vacuum-filtered and washed with 2 × 10 mL of THF. The filtered solution was evaporated under vacuum, and the product was isolated by distillation. A forerun was collected (25−36 °C, 0.79 g), followed by the main fraction (92−114 °C, p = 0.01 Torr, bath at 130 °C). Yield: 17.32 g (82.5%) of a clear colorless, slightly viscous liquid. The product was 97−98% pure by 31P NMR, with several trace impurities observable. 1H NMR (benzene-d6): δ 3.07 (dq, J = 8.3, 6.0, 2H, CH2N), 2.62 (t, J = 5.8, 2H, NCH2), 2.58 (t, J = 5.9, 2H, NCH2), 2.30 (t, J = 5.9, 2H, NCH2), 2.06 (s, 6H, CH2), 1.53 (br dt, J = 12.2, 6.0, 1H, NH), 1.45 (br s, 1H, NH), 1.09 (d, J = 11.2, 18H, CH3). 13 C{1H} NMR (benzene-d6): δ 59.97 (s, CH2), 53.09, (d, J = 7.0, CH2), 50.94 (d, J = 21.4, CH2), 48.02 (s, CH2), 45.91 (s, NCH3), 34.40 (d, J = 21.4, C), 28.88 (d, J = 15.3, CH3). c-C4H8N(CH2)2NH(CH2)2NHPtBu2 (PyrNP). A 250 mL roundbottom flask equipped with a stir bar was charged with N-(2(pyrrolidin-1-yl)ethyl)ethylenediamine (PyrNN; 10 g, 63.59 mmol), triethylamine (7.8 g, 77.08 mmol), and THF (50 mL). Then tBu2PCl (11.5 g, 63.66 mmol) was added with stirring,

CH2), 2.91 (t, J = 6.0, 2H, CH2), 2.60 (t, J = 5.8, 2H, CH2), 1.62 (br s, H, NH), 1.52 (br m, 1H, NH), 1.07 (d, J = 11.2, 18H, CH3). 13C{1H} NMR (benzene-d6): δ 161.60 (s, Py), 150.02 (s, Py), 136.09 (s, Py), 123.58 (s, Py), 121.35 (s, Py), 52.76 (d, J = 7.1, CH2), 50.77 (d, J = 29.0, CH2), 49.70 (s, CH2), 39.26 (s, CH2), 34.41 (d, J = 21.5, C), 28.90 (d, J = 15.2, CH3). 31P{1H} NMR (benzene-d6): δ 77.9 (s). QuiCH2NH(CH2)2NHPtBu2 (QuiNP). A 100 mL roundbottom flask equipped with a stir bar was charged with N((2-quinolyl)methyl)ethylenediamine (QuiNN; 3.97 g, ca. 19 mmol), triethylamine (2.4 g, 23.71 mmol), and THF (22 mL). Then tBu2PCl (3.5 g, 19.37 mmol) was added with stirring, and the mixture was stirred rapidly for 24 h. The precipitated Et3N· HCl was vacuum-filtered and washed with 3 × 3 mL of THF. The filtered solution was evaporated under vacuum. Hexane (20 mL) was added and the mixture was filtered through 10 g of basic alumina in a 30 mL fritted funnel; the solids were washed with 5 mL of hexane. The volatiles were evaporated, and the product was dried under vacuum at 70 °C for 1 h. Yield: 5.57 g of a viscous liquid. The product was obtained contaminated with ca. 12 mol % of 2-methylquinoline (the impurity in the starting material). 1H NMR (benzene-d6): δ 8.20 (d, J = 8.8, 1H, CH), 7.56 (d, J = 8.4, 1H, CH), 7.39 (d, J = 8.0, 1H, CH), 7.34 (m, 1H, CH), 7.13 (overlapped m, 2H, CH), 3.96 (s, 2H, CH2), 3.03 (ddt, J = 8.0, 6.0, 5.8, 2H, CH2), 2.62 (t, J = 6.0, 2H, CH2), 1.95 (s, 1H, NH), 1.43 (m, 1H, NH), 1.03 (d, J = 11.2, 18H, CH3). 13C{1H} NMR (benzened6): δ 161.75 (s), 148.89 (s), 136.30 (s), 130.12 (s), 129.74 (s), 128.10 (s), 127.99 (s), 126.32 (s), 121.02 (s), 56.44 (s, CH2), 52.82 (d, J = 7.1, CH2), 50.98 (d, J = 28.7, CH2), 34.44 (d, J = 21.3, C), 28.90 (d, J = 15.1, CH3). 31P NMR (benzene-d6): δ 78.1. MeO(CH2)2NH(CH2)2NHPtBu2 (ONP). A 250 mL roundbottom flask equipped with a stir bar was charged with N-(2methoxyethyl)ethane-1,2-diamine (ONN; 11.21 g, 94.9 mmol), triethylamine (11.5 g, 113.6 mmol), and THF (100 mL). Then tBu2PCl (17.2 g, 95.2 mmol) was added with stirring, and the mixture was rapidly stirred for 24 h. The precipitated Et3N·HCl was vacuum-filtered and washed with 2 × 10 mL of THF. The filtered solution was evaporated under vacuum, and the product was isolated by distillation. A forerun was collected (68−74 °C, 4.47 g, 18%), and then the main fraction (74−94 °C, p < 0.01 Torr, 18.25 g (73%)) was collected as a clear colorless, slightly viscous liquid. The forerun was 94% pure, by 31P NMR; the main product was spectroscopically pure. 1H NMR (benzened6): δ 3.29 (t, J = 5.4, 2H, OCH2), 3.10 (s, 3H, OCH3), 3.03 (ddt, J = 8.0, 6.0, 5.8, 2H, CH2), 2.66 (t, J = 5.4, 2H, CH2), 2.59 (t, J = 5.8, 2H, CH2), 1.60 (br, 1H, NH), 1.52 (br. m, 1H, NH), 1.09 (d, J = 10.8, 18H, CH3). 13C{1H} NMR (benzene-d6): δ 72.84 (s, OCH2), 58.83 (s, OCH3), 52.84 (d, J = 7.1, CH2), 50.81 (d, J = 28.9, CH2), 49.87 (s, CH2), 34.42 (d, J = 21.5, C), 28.88 (d, J = 15.3, CH3). 31P{1H} NMR (benzene-d6): δ 77.9 (s). EtS(CH2)2NH(CH2)2NHPtBu2 (SNP). A 200 mL round-bottom flask equipped with a stir bar was charged with N-(2(ethylthio)ethyl)ethane-1,2-diamine (SNN; 10.0 g, 67.4 mmol), triethylamine (8.2 g, 81.0 mmol), and THF (50 mL). Then tBu2PCl (12.2 g, 67.5 mmol) was added with stirring, and the mixture was rapidly stirred for 17 h. The precipitated Et3N· HCl was vacuum-filtered and washed with 2 × 10 mL of THF. The filtered solution was evaporated under vacuum, and the product was isolated by distillation. A small forerun was collected (60−93 °C, 0.71 g, bath at 140 °C), and then the 6976

DOI: 10.1021/acscatal.6b02324 ACS Catal. 2016, 6, 6967−6981

Research Article

ACS Catalysis

was used to rinse the glassware, to bring the total solvent volume to 60 mL. The autoclave was closed, tightened, and placed into an oil bath preheated to 170 °C on a hot plate stirrer. This temperature was maintained for 3.5 h, with stirring at 600 rpm. During this time, the pressure increased to ca. 10 bar. Then, the autoclave was removed from and left over the oil bath overnight. The next morning, the autoclave was vented (slight positive pressure) and opened in air and the crystalline product was isolated by vacuum filtration. The autoclave and the filtered solid were liberally washed with ca. 100 mL of denatured ethanol (in air), and the product was dried under vacuum of an oil pump (0.01 mmHg) for 1 h (prolonged drying was found to have no effect). Yield: 3.30 g (82.5%) of a crystalline orange solid. 1H NMR (CD2Cl2): δ 8.95 (m, 1H, Py), 7.71 (td, J = 7.7, 1.5, 1H, Py), 7.30 (m, 2H, Py), 4.25 (dd, J = 14.0, 3.0, 1H, CH2), 4.03 (dd, J = 25.1, 11.4, 1H, CH2), 3.93 (br, 1H, NH), 3.36−3.20 (m, 3H), 2.67 (m, 1H, CH2), 1.95 (br, 1H, NH), 1.39 (d, J = 13.3, 9H, CH3), 1.28 (d, J = 13.1, 9H, CH3), −15.10 (d, J = 26.4, 1H). 13C{1H} NMR (CD2Cl2): δ 207.70 (d, J = 18.1, CO), 157.33 (s, Py), 153.28 (d, J = 1.5, Py), 136.96 (s, Py), 124.58 (d, J = 2.0, Py), 121.22 (d, J = 2.1, Py), 61.67 (d, J = 2.1, CH2), 56.31 (d, J = 1.2, CH2), 45.36 (d, J = 5.0, CH2), 42.36 (d, J = 15.6, C), 38.48 (d, J = 33.6, C), 29.88 (d, J = 5.2, CH3), 29.64 (d, J = 4.2, CH3). 31P{1H} NMR (CD2Cl2): δ 125.8 (s). Anal. Calcd for C17H31ClN3OPRu: C, 44.30; H, 6.78; N, 9.12. Found: C, 44.43; H, 6.81; N, 9.03. RuHCl(CO)[κ3-PiNH(CH2)2NHP(o-Tol)2] (3). RuHCl(CO)(AsPh3)3 (3.71 g, 3.42 mmol) and PiNP-oTol (1.3 g, ca. 3.59 mmol) in 20 mL of diglyme were loaded into a 75 mL pressure bottle (heavy-walled round-bottom single-neck flask with a PTFE bushing as a seal). The vessel was sealed and placed in an oil bath preheated to 162 °C, and the mixture was stirred for 2 h, affording a brown solution. This solution was filtered through a layer of Celpure P300 filter aid (1 g) in a 30 mL fritted funnel, and the filter material was washed with 3 mL of diglyme. Addition of 43 mL of Et2O resulted in precipitation of a beige solid which was filtered, washed with 4 × 7 mL of Et2O, and dried under vacuum for 3 h. Yield: 1.13 g (62%). This crude product was further purified by recrystallization from 20 mL of ethanol heated to reflux. 1H NMR (CD2Cl2): δ 8.96 (dd, J = 3.3, 2.1, 1H, Py), 8.55 (m, 1H, Py), 7.75 (overlapped m, 2H), 7.22 (overlapped m, 8H), 4.33 (m, 1H, CH2), 4.12 (overlapped, 2H, NH+CH2), 3.46 (overlapped m, 2H, CH2), 3.32 (m, 1H, CH2), 2.94 (m, 1H, CH2), 2.61 (br m, 1H, NH), 2.26 (s, 3H, CH3), 2.13 (s, 3H, CH3), −14.44 (d, J = 28.5, 1H, RuH). 13C NMR (CD2Cl2): δ 206.51 (d, J = 19.3, CO), 157.39 (s), 153.38 (d, J = 1.5), 139.55 (d, J = 2.5), 139.50 (s), 138.73 (d, J = 39.0), 137.25 (s), 137.20 (d, J = 22.5), 134.17 (s), 132.83 (d, J = 17.1), 132.38 (d, J = 7.9), 131.54 (d, J = 6.4), 130.25 (d, J = 2.3), 130.04 (d, J = 2.3), 129.17 (s), 125.95 (d, J = 11.9), 125.71 (d, J = 13.3), 124.55 (d, J = 2.2), 121.44 (d, J = 2.3), 61.63 (d, J = 2.0, CH2), 55.85 (d, J = 1.2, CH2), 44.27 (d, J = 8.4, CH2), 22.58 (d, J = 3.8, CH3), 22.34 (d, J = 3.9, CH3). 31 P{1H} NMR (CD2Cl2): δ 99.5 (s). Anal. Calcd for C23H27ClN3ORuP: C, 52.22; H, 5.14; N, 7.94. Found: C, 52.23; H, 5.10; N, 7.91. RuHCl(CO)[κ3-PiCH2NH(CH2)2NHPtBu2]·EtOH (4). Anhydrous ethanol (40 mL) was poured into a 100 mL flask equipped with a magnetic stir bar and containing [RuCl2(COD)]n (2.35 g, 8.39 mmol of Ru), PiCH2NPtBu (2.6 g, 8.40 mmol), and lithium (58.6 mg, 8.44 mmol). Stirring this mixture for 40 min gave a dark solution that was transferred into a 300 mL steel autoclave equipped with a magnetic stir bar,

and the mixture was stirred rapidly over a weekend (the reaction was most likely finished within 24 h). The precipitated Et3N·HCl was vacuum-filtered and washed with 2 × 10 mL of THF. The filtered solution was evaporated under vacuum. The semisolid produced was dissolved in 40 mL of hexane and filtered; the solids were washed with 2 × 20 mL of hexane. The hexane was evaporated, and the product was dried under vacuum at 70 °C for 1 h. Yield: 16.88 g (88%) of a viscous colorless liquid. The product was ca. 98% pure according to 31P NMR. 1H NMR (benzene-d6): δ 3.09 (dq, J = 8.4, 6.0, 2H, CH2N), 2.68, 2.65 (overlapped, 4H, 2 × CH2), 2.55 (t, J = 6.0, CH2, NCH2), 2.36 (m, 4H, NCH2), 1.67 (br. s, 1H, NH), 1.60 (m, 4H, NCH2), 1.54 (br, 1H, NH), 1.09 (d, J = 11.2, 18H, CH3). 13C{1H} NMR (benzene-d6): δ 56.66 (s, CH2), 54.63 (s, 2 × CH2), 53.13 (d, J = 6.8, CH2), 50.92 (d, J = 28.8, CH2), 49.23 (s, CH2), 34.40 (d, J = 21.5, C), 28.90 (d, J = 15.3, CH3), 24.27 (s, 2 × CH2). 31P{1H} NMR (benzene-d6): δ 76.1 (s). RuHCl(CO)(AsPh3)3. This is a modified procedure based on the reported approach.19a,b Among the principal changes are replacements of 2-methoxyethanol (a prohibited substance in Canada) by 2-ethoxyethanol and of aqueous formaldehyde by paraformaldehyde. We further note that the procedure reported in ref 18 affords the product containing ca. 5% of a nonhydride complex exhibiting the characteristic 1H resonances at 7.77− 7.79 and 7.43−7.48 ppm, outside the region (7.03−7.35 ppm) where the phenyl protons of RuHCl(CO)(AsPh3) are observed in CD2Cl2. Another procedure, reported in ref 19c, where no base was used, possibly yielded the yellow RuCl2(CO)(AsPh3)3 described in ref 19b. A 500 mL two-neck round-bottom flask equipped with a stirbar and having one neck closed by a rubber septum was loaded in air with RuCl3·nH2O (3 g, ca. 11.47 mmol), AsPh3 (17 g, 55.51 mmol), and paraformaldehyde (6 g, 0.2 mol); then 150 mL of 2-ethoxyethanol (ReagentPlus, 99%) was added. The flask was fitted with a reflux condenser whose upper joint was connected with a vacuum/Ar line; then the flask was placed into an oil bath, on top of a hot plate stirrer. With rapid stirring established, the flask was opened to vacuum for 2−3 s and refilled with argon; this procedure was repeated six times. Heating was turned on, with the bath temperature set to 135 °C. In 20 min (after the mixture was heated for 7−10 min at 132−135 °C), NEtiPr2 (4 g, 30.95 mmol) was syringed in through the rubber septum and the dark reaction mixture gradually turned light orange. Heating and stirring was continued for 5 h. After it was cooled to room temperature in a cold water bath, the product was filtered in air, washed with 4 × 30 mL of denatured ethanol, and dried under vacuum to a constant weight. Yield: 11.11 g (89%) of an off-white solid that was stored and used in an Ar glovebox. A small amount (5−6 mol %) of 2-ethoxyethanol remained in the product even after prolonged drying. 1H NMR (CD2Cl2): δ 7.33 (overlapped m, Ph), 7.27 (t, J = 7.6, Ph), 7.17 (overlapped m, Ph), 7.05 (t, J = 7.6, Ph), −8.66 (s, RuH). RuHCl(CO)[κ3-PiNH(CH2)2NHPtBu2] (2). Anhydrous ethanol (40 mL) was poured into a 100 mL flask equipped with a magnetic stir bar and containing [RuCl2(COD)]n (2.43 g, 8.67 mmol of Ru), PiNPtBu (2.56 g, 8.67 mmol), and lithium (60.5 mg, 8.72 mmol). Stirring the resulting mixture for 50 min gave a dark brown solution that was filtered through a layer of Celpure P300 filter aid (1 g) in a 30 mL fritted funnel, and the filter material was washed with 18 mL of anhydrous ethanol. The filtered solution was transferred into a 300 mL steel autoclave equipped with a magnetic stir bar, and more ethanol 6977

DOI: 10.1021/acscatal.6b02324 ACS Catal. 2016, 6, 6967−6981

Research Article

ACS Catalysis

equipped with a magnetic stir bar, and more methanol was used to rinse the glassware, to bring the total solvent volume to 30 mL. The autoclave was closed, tightened, and placed into an oil bath preheated to 170 °C on a hot plate stirrer. This temperature was maintained for 3.5 h, with stirring at 600 rpm, and then the system was left at room temperature overnight. The product was isolated by filtration, washed with 3 × 10 mL of methanol, and dried under vacuum of an oil pump (0.01 mmHg) for 3 h. Yield: 0.65 g (32%) of a large crystalline yellow solid of 6. 1H NMR (CD2Cl2): δ 3.73 (s, 3H, OCH3), 3.72 (td, J = 10.6, 3.4, 1H, OCH2), 3.63 (br, 1H, NH), 3.34 (overlapped m, 2H, OCH2 + NCH2), 3.19 (m, 2H, NCH2), 2.84 (m, 2H, NCH2), 2.64 (m, 1H, NCH2), 1.91 (br m, 1H, NH), 1.33 (d, J = 13.5, 9H, CH3), 1.19 (d, J = 13.4, 9H, CH3), −16.19 (d, J = 30.3, 1H, RuH). 13C{1H} NMR (CD2Cl2): δ 206.87 (d, J = 21.4, CO), 70.72 (s, OCH2), 63.43 (s, OCH3), 57.60 (d, J = 1.1, CH2), 53.60 (s, CH2), 46.00 (d, J = 2.4, CH2), 42.85 (d, J = 19.1, C), 38.85 (d, J = 38.8, C), 29.87 (d, J = 3.5, CH3), 29.41 (d, J = 4.8, CH3). 31P{1H} NMR (CD2Cl2): δ 139.5 (s). Anal. Calcd for C14H32ClN2O2RuP: C, 39.30; H, 7.54; N, 6.55. Found: C, 39.09; H, 7.68; N, 6.32. RuHCl(CO)[κ3-EtS(CH2)2NH(CH2)2NHPtBu2] (7). [RuCl2(COD)]n (2.5 g, 8.92 mmol of Ru), SNP (2.65 g, 9.06 mmol), and lithium (62.2 mg, 8.96 mmol) were stirred in 21 mL of anhydrous ethanol in a 50 mL flask for 2 h. The product solution was filtered through a layer of Celpure P300 filter aid (1 g) in a 30 mL fritted funnel, and the filter material was washed with 17 mL of ethanol. The filtrate was transferred into a 300 mL steel autoclave equipped with a magnetic stir bar, and 2 mL of ethanol was used to rinse the glassware, to bring the total solvent volume to 40 mL. The autoclave was closed, tightened, and placed into an oil bath preheated to 170 °C on a hot plate stirrer. This temperature was maintained for 3.5 h, with stirring at 600 rpm, and then the system was left at room temperature overnight. The product was isolated by filtration, washed with 3 × 10 mL of ethanol, and dried under vacuum of an oil pump (0.01 mmHg) for 3 h. Yield: 2.68 g (65%) of an off-white solid of 7. In solution, 7 exists as a 3/1 mixture of two isomers with the Et group on the opposite sides of the SNP ligand plane. 1H NMR (CD2Cl2): δ 3−3.4 (overlapped m, 6H), 2.4−2.8 (overlapped m, 5H), 2.06 (br m, 1H, NH), 1.39 (d, J = 13.2, 9H, CH3), 1.37 (t, J = 7.4, 3H, CH3), 1.26 (d, J = 13.2, 9H, CH3), −16.31 (d, J = 25.2, RuH, major isomer), −16.44 (d, J = 24.4, RuH, minor isomer). 13C{1H} NMR (major isomer, CD2Cl2): δ 206.51 (d, J = 19.3, CO), 57.47 (d, J = 1.2, CH2), 54.50 (d, J = 2.5, CH2), 46.35 (d, J = 4.53, CH2), 43.41 (d, J = 12.6, C), 38.30 (d, J = 34.5, C), 36.50 (s, SCH2), 31.47 (d, J = 0.9, SCH2), 29.73, (overlapped d, CH3), 13.47 (s, CH3). 31 1 P{ H} NMR (CD2Cl2): δ 117.5 (s, major isomer, 76%), 117.8 (s, minor isomer, 24%). Anal. Calcd for C15H34ClN2OPRuS: C, 39.34; H, 7.48; N, 6.12; S, 7.00. Found: C, 39.42; H, 7.53; N, 6.06; S, 6.82. RuHCl(CO)(κ3-H2NNPtBu) (8). RuHCl(CO)(AsPh3)3 (2.63 g, 2.43 mmol) and H2N(CH2)2NH(CH2)2NHPtBu2 (0.6 g, 2.43 mmol) in 10 mL of diglyme were loaded into a pressure bottle (heavy-walled round-bottom single-neck flask with a PTFE bushing as a seal). The vessel was sealed and placed in an oil bath preheated to 160 °C, and the mixture was stirred for 2 h, affording a white suspension. The flask was placed in a cold water bath for 30 min, and the precipitate was filtered off, washed with diglyme (4 × 3 mL), and dried under vacuum for 3 h to give a pale yellow solid. Yield: 876 mg (87.5%). 1H NMR (CD2Cl2): δ 3.43 (s, 1H, NH), 3.35 (m, 1H, CH2), 3.20 (m,

and more ethanol was used to rinse the glassware, to bring the total solvent volume to 60 mL. The autoclave was closed, tightened, and placed into an oil bath preheated to 170 °C on a hot plate stirrer. This temperature was maintained for 4 h, with stirring at 600 rpm. After it was cooled to room temperature, the autoclave was vented and opened under argon. The dark yellow product solution was filtered through a layer of Celpure P300 filter aid. The product crystallized in 1 h, upon evaporation of ca. 50% of the solvent under vacuum of an oil pump. The solid was filtered, washed with 3 × 10 mL of ethanol, and dried under vacuum of an oil pump (0.01 mmHg) for 1 h. Yield: 2.59 g (59%) of a pale yellow solid of 4·EtOH. 1 H NMR (CD2Cl2): δ 9.25 (m, 1H), 7.69 (td, J = 7.6, 1.7, 1H), 7.25 (m, 2H), 3.80 (m, 2H), 3.63 (qd, J = 7.0, 5.3, 2H, EtOH), 3.6 (br s, 1H, NH), 3.14 (m, 2H), 2.99 (m, 1H), 2.91 (m, 1H), 2.60 (m, 2H), 1.96 (br m, 1H, NH), 1.51 (t, J = 5.3, 1H, OH), 1.37 (d, J = 13.2, 9H, CH3), 1.31 (d, J = 12.9, 9H, CH3), 1.18 (t, J = 7.0, 3H, EtOH), −15.37 (d, J = 28.1, 1H, RuH). 13C{1H} NMR (CD2Cl2): δ 206.81 (d, J = 19.4, CO), 161.38 (d, J = 0.5, Py), 157.17 (d, J = 1.7, Py), 137.53 (s, Py), 124.51 (d, J = 2.6, Py), 122.72 (d, J = 1.7, Py), 58.60 (s, CH2, ethanol), 57.41 (d, J = 2.4, CH2), 49.58 (s, CH2), 43.77 (d, J = 5.4, CH2), 41.34 (d, J = 20.6, C), 39.80 (s, CH2), 39.44 (d, J = 31.6, C), 30.15 (d, J = 4.9, CH3), 29.34 (d, J = 4.1, CH3), 18.83 (s, CH3). 31P{1H} NM R ( CD 2 C l 2 ) : δ 1 2 4 . 6 ( s ). An a l . C a l c d f o r C18H33ClN3ORuP·EtOH: C, 46.10; H, 7.54; N, 8.06. Found: C, 46.00; H, 7.58; N, 8.03. RuHCl(CO)[κ3-QuiCH2NH(CH2)2NHPtBu2] (5). Anhydrous ethanol (50 mL) was poured into a 100 mL flask equipped with a magnetic stir bar and containing [RuCl2(COD)]n (2.2 g, 7.85 mmol of Ru), QuiNP (3 g, ca. 7.85 mmol), and lithium (54.5 mg, 7.85 mmol). Stirring this mixture for 1 h gave a dark solution that was transferred into a 300 mL steel autoclave equipped with a magnetic stir bar, and more ethanol was used to rinse the glassware, to bring the total solvent volume to 60 mL. The autoclave was closed, tightened, and placed into an oil bath preheated to 170 °C on a hot plate stirrer. This temperature was maintained for 4 h, with stirring at 600 rpm, and then the system was left at room temperature overnight. The product was isolated by filtration, washed with 3 × 10 mL of ethanol, and dried under vacuum of an oil pump (0.01 mmHg) for 3 h. Yield: 2.72 g (68%) of a light orange crystalline solid of 5 with ca. 12.5 mol % of cocrystallized ethanol. 1H NMR (CD2Cl2): δ 9.35 (d, J = 8.7, 1H), 8.18 (d, J = 8.4, 1H), 7.88 (m, 2H), 7.62 (m, 1H), 7.34 (d, J = 8.4, 1H), 4.47 (dd, J = 15.2, 3.3, 1H, CH2), 4.37 (dd, J = 15.2, 12.4, 1H, CH2), 4.24 (br m, 1H, NH), 3.37 (overlapped m, 3H, CH2), 2.73 (q, J = 10.0, 1H, CH2), 1.96 (br m, 1H, NH), 1.47 (d, J = 13.4, 9H, CH3), 1.28 (d, J = 13.1, 9H, CH3), −15.79 (d, J = 27.6, 1H, RuH). 13C{1H} NMR (CD2Cl2): δ 207.57 (d, J = 20.3, CO), 159.80 (s), 148.15 (s), 138.12 (s), 131.94 (s), 131.06 (s), 128.95 (d, J = 1.7), 128.41 (s), 127.67 (s), 118.15 (d, J = 2.1), 63.59 (d, J = 1.5, CH2), 55.61 (d, J = 1.3, CH2), 44.62 (d, J = 5.2, CH2), 42.67 (d, J = 18.9, C), 39.29 (d, J = 33.8, C), 30.24 (d, J = 4.8, CH3), 29.60 (d, J = 3.8, CH3). 31P{1H} NMR (CD2Cl2): δ 127.4 (s). Anal. Calcd for C21H33ClN3ORuP•0.125EtOH: C, 49.38; H, 6.59; N, 8.12. Found: C, 49.40; H, 6.57; N, 8.12. RuHCl(CO)[κ 3 -MeO(CH 2 ) 2 NH(CH 2 ) 2 NHPtBu 2 ] (6). [RuCl2(COD)]n (1.31 g, 4.68 mmol of Ru), ONP (1.23 g, ca. 4.69 mmol), and lithium (32.7 mg, 4.71 mmol) were stirred in 20 mL of anhydrous methanol in a 50 mL flask for 2 h. The product mixture was transferred into a 300 mL steel autoclave 6978

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ACS Catalysis

6.2, 2.6, 1H, CH2), 2.72 (overlapped m, 2H, CH2), 2.59 (tdd, J = 11.5, 9.8, 1.7, 1H, CH2), 2.11 (m, 3H, CH2), 1.94 (br m, 1H, NH), 1.84 (m, 2H, CH2), 1.34 (d, J = 13.1, 9H, CH3), 1.21 (d, J = 12.9, 9H, CH3), −16.25 (d, J = 28.1, 1H, RuH). 13C{1H} NMR (CD2Cl2): δ 208.40 (d, J = 19.5, CO), 66.08 (d, J = 1.3, CH2), 60.77 (d, J = 1.6, CH2), 57.05 (d, J = 0.8, CH2), 56.98 (d, J = 1.3, CH2), 46.20 (d, J = 3.5, CH2), 42.93 (d, J = 13.1, C), 38.40 (d, J = 36.2, C), 29.95 (d, J = 3.8, CH3), 29.53 (d, J = 5.3, CH3), 23.57 (d, J = 0.4, CH2), 22.66 (s, CH2). 31P{1H} N M R (C D 2 Cl 2 ) : δ 1 2 5 . 6 ( s ) . A n a l . C a l c d f o r C17H37ClN3OPRu·0.18C8H14: C, 45.49; H, 8.18; N, 8.63. Found: C, 45.23; H, 8.54; N, 8.59. Details of the Catalytic Studies. All reaction solutions were analyzed with the help of 1H and 13C{1H} NMR spectroscopy. The proton spectra were collected using a 30 s relaxation (preacquisition) delay for accurate integration. Hydrogenation. The hydrogenation experiments of Scheme 4 (eq 3) were performed under initial p(H2) = 50 bar using 20 mmol of methyl undecenoate in 7 mL of THF. All chemicals were loaded in a 75 mL stainless-steel Parr reactor inside an argon glovebox. The pressurized reactor (disconnected from the hydrogen tank) was placed into an oil bath preheated to 100 °C on a hot plate stirrer. This temperature was maintained for 2.5 h with stirring at 500 rpm using a 1.3 × 0.95 cm rare-earth samarium−cobalt spinbar. Acceptorless Dehydrogenative Coupling Experiments of Scheme 4 (Eqs 1 and 2). In an argon glovebox, the required amounts of the catalysts and NaOEt were weighed into two 50 mL Schlenk tubes (also containing micro stirbars) on a calibrated analytical balance accurate to 0.1 mg. Next, the required amounts of the substrates (total volume 10−12 mL) were weighed into these tubes on a balance accurate to 1 mg. After the tubes were taken out of the box, they were connected to a vacuum/Ar manifold. Under argon, the stoppers were replaced by finger condensers connected to a circulating refrigerated bath. When the temperature in the bath reached −5 °C, the flasks were placed in an ethylene glycol bath, the argon tank was closed, and H2 produced as the bath temperature was increased to 90 °C was allowed to pass freely through a mineral oil bubbler (independently from each reaction flask). Throughout the reaction, the temperature in the cold fingers was maintained between −10 and −15 °C and in the bath at 90 °C with stirring at 1100 rpm. This experimental setup can be seen pictured in Figure S2 of ref 7. Details of the NMR Tube Studies. Tishchenko Reaction. In an argon glovebox, 5.0 mg of 22·0.25THF (9.4 μmol) was weighed into an NMR tube on a calibrated analytical balance accurate to 0.1 mg. Next, 1.43 g of benzene-d6 followed by 0.41 g of acetaldehyde (9.4 mmol, S/C = 1000) (total volume ca. 2 mL, ca. 4.7 M acetaldehyde) were weighed into the NMR tube on a balance accurate to 1 mg. The tube was capped, vigorously shaken, and removed from the box for immediate collection of the NMR spectra. Experiments with 1-13C-Ethyl Acetate. In an argon glovebox, two NMR tubes were loaded with 2.7 mg each of 22·0.25THF (5.06 μmol) on a calibrated analytical balance accurate to 0.1 mg. Next, a mixture of ethanol (0.70 g, 15.2 mmol), butylamine (1.11 g, 15.2 mmol), and 1-13C-ethyl acetate (68 mg, 0.76 mmol) was divided equally among three NMR tubes, two of which contained 22. The tubes were capped, vigorously shaken, and removed from the box. Two of the tubes were placed in a bath preheated to 80 °C, whereas the third tube (containing 22) remained at 23 °C. No significant

1H, CH2), 3.09 (overlapped m, 3H, NH2+CH2), 2.91 (overlapped m, 3H, CH2), 2.61 (m, 1H, CH2), 2.51 (qd, J = 12.1, 5.8, 1H, CH2), 1.97 (br m, 1H, NH), 1.36 (d, J = 13.1, 9H), 1.21 (d, J = 13.0 Hz, 9H, CH3), −16.40 (d, J = 26.1, 1H, RuH). 13C{1H} NMR (CD2Cl2): δ 207.12 (d, J = 18.7, CO), 57.10 (d, J = 1.0, CH2), 56.12 (d, J = 2.9, CH2), 46.42 (d, J = 4.0, CH2), 42.60 (d, J = 14.3, C), 40.29 (d, J = 1.1, CH2), 38.11 (d, J = 34.9, C), 29.79 (d, J = 4.0, CH3), 29.49 (d, J = 5.4, CH3). 31P{1H} NMR (CD2Cl2): δ 125.6 (s). Anal. Calcd for C13H31ClN3OPRu: C, 37.82; H, 7.57; N, 10.18. Found: C, 37.70; H, 7.62; N, 10.10. RuHCl(CO)[κ 3 -Me 2 N(CH 2 ) 2 NH(CH 2 ) 2 NHPtBu 2 ] (9). [RuCl2(COD)]n (2.54 g, 9.07 mmol of Ru), Me2NNP (2.6 g, 9.44 mmol), and lithium (62.9 mg, 9.06 mmol) were stirred in 40 mL of anhydrous ethanol in a 100 mL flask for 40 min. The reaction solution was transferred into a 300 mL steel autoclave equipped with a magnetic stir bar, and more ethanol was used to rinse the glassware, to bring the total solvent volume to 60 mL. The autoclave was closed, tightened, and placed into an oil bath preheated to 170 °C on a hot plate stirrer. This temperature was maintained for 3.5 h, with stirring at 600 rpm; then the system was left at room temperature overnight. The product was isolated by filtration, washed with 3 × 10 mL of ethanol, and dried under vacuum of an oil pump (0.01 mmHg) for 3 h. This yielded 1.68 g of a light yellow crystalline solid. A second crop (0.68 g) was obtained from the mother liquor left in a freezer at −18 °C. Total yield: 2.36 g (59%). Complex 9 crystallized with ca. 31 mol % of cyclooctene (on the basis of the 1H and 13C NMR data). 1H NMR (CD2Cl2): δ 3.54 (br m, 1H, NH), 3.30 (m, 1H, CH2), 3.18 (m, 1H, CH2), 3.02 (m, 3H, CH2), 2.93 (d, J = 1.6, 3H, CH3), 2.81 (s, 3H, CH3), 2.77 (dtd, J = 13.8, 12.2, 3.1, 1H, CH2), 2.58 (tdd, J = 11.6, 9.9, 1.7 Hz, 1H), 2.01 (dt, J = 12.4, 3.1 Hz, 1H, CH2), 1.93 (br m, 1H, NH), 1.33 (d, J = 13.1, 9H, CH3), 1.21 (d, J = 13.0, 9H), −16.18 (d, J = 28.3, 1H, RuH). 13C{1H} NMR (CD2Cl2): δ 208.32 (d, J = 18.8, CO), 59.54 (d, J = 1.2, CH2), 57.59 (d, J = 1.7, CH3), 57.06 (d, J = 1.2, CH2), 53.19 (d, J = 1.8, CH3), 52.20 (d, J = 1.9, CH2), 46.13 (d, J = 3.7, CH2), 42.71 (d, J = 12.6, C), 38.24 (d, J = 36.4, C), 29.78 (d, J = 3.8, CH3), 29.61 (d, J = 5.3, CH3). 31P{1H} NMR (CD2Cl2): δ 126.4 (s). Anal. Calcd for C15H35ClN3OPRu·0.315C8H14: C, 44.24; H, 8.35; N, 8.83. Found: C, 44.08; H, 8.70; N, 8.80. RuHCl(CO)[κ 3 -c-C 4 H 8 N(CH 2 ) 2 NH(CH 2 ) 2 NHPtBu 2 ] (10). [RuCl2(COD)]n (2.4 g, 8.57 mmol of Ru), PyrNP (2.68 g, 8.89 mmol), and lithium (60.3 mg, 8.69 mmol) were stirred in 40 mL of anhydrous ethanol in a 100 mL flask for 1 h. The reaction mixture was transferred into a 300 mL steel autoclave equipped with a magnetic stir bar, and more ethanol was used to rinse the glassware, to bring the total solvent volume to 60 mL. The autoclave was closed, tightened, and placed into an oil bath preheated to 170 °C on a hot plate stirrer. This temperature was maintained for 3.5 h, with stirring at 500 rpm; then the system was left at room temperature overnight. The product was isolated by filtration, washed with 3 × 10 mL of ethanol, and dried under vacuum of an oil pump (0.01 mmHg) for 1 h. This yielded 2.73 g of a light yellow crystalline solid. A second crop (0.23 g) was obtained from the mother liquor left in a freezer at −18 °C. Total yield: 2.96 g (74%). Complex 10 crystallized with ca. 18 mol % of cyclooctene (on the basis of the 1H and 13C NMR data). 1H NMR (CD2Cl2): δ 3.89 (m, 1H, CH2), 3.50 (m, 1H, CH2), 3.46 (br m, 1H, NH), 3.38−3.17 (overlapped m, 2H, CH2), 3.19 (ddd, J = 13.9, 12.6, 3.3, 1H, CH2), 3.03 (m, 2H, CH2), 2.87 (dddd, J = 11.4, 8.8, 6979

DOI: 10.1021/acscatal.6b02324 ACS Catal. 2016, 6, 6967−6981

Research Article

ACS Catalysis reaction was observed at 23 °C. The heated tubes were removed from the bath first after 30 min and second after 60 min of heating, and the NMR spectra were recorded at room temperature. Analogous experiments were conducted using normal (12C) ethyl acetate and reproduced the turnover numbers reported in this paper. Computational Details. The calculations were carried out in Gaussian 0920 using the M06-L functional21a and the ultrafine integration grid (a pruned (99,590) grid). Structures TS5, TS6, 30, and 31 were also optimized at the ωB97X-D level.21b The basis sets, listed by their G09 keywords, included QZVP22a,b (with def2 ECP) for Ru and Os, together with the W06 density fitting basis set in the M06-L calculations. For the nonmetal atoms of 2−12 we employed TZVP22c,d together with the TZVP density fitting basis set. The free energies of all species in Schemes 5−11 were calculated using def2TZVP for the nonmetal atoms (together with the W06 density fitting basis set at the M06-L level). The polarizable continuum model (IEFPCM) was used in all calculations of Schemes 5−10 in ethanol solvent, with the radii and nonelectrostatic terms of Truhlar and co-workers’ SMD solvation model (scrf = smd).23 All geometry optimizations without exception (i.e., no single points) were accompanied by frequency calculations, which also provided the enthalpies and free energies at 298.15 K, under a pressure of 419 atm for ethanol solvent, following the approach of Martin and co-workers.24 Representative examples of the input files are provided in the Supporting Information.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscatal.6b02324. NMR spectra of the reactions of EtOH, BuNH2, and 1-13C-ethyl acetate with and without 22 and all computational details (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail for D.G.G.: [email protected]. Notes

The author declares no competing financial interest.

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ACKNOWLEDGMENTS Insightful discussions of Schemes 5, 8, and 11 with Prof. Faraj Hasanayn are gratefully acknowledged. Financial support of this work by Wilfrid Laurier University, CFI, and the NSERC of Canada is greatly appreciated.

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REFERENCES

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