ester hydrogenation catalyzed by ru-cnn pincer … · 1 esi for ester hydrogenation catalyzed by...

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ESI for

Ester hydrogenation catalyzed by Ru-CNN pincer complexes

Yunshan Sun, Christian Koehler, Runyu Tan, Vincent T. Annibale, and Datong Song*

*Davenport Chemical Research Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6. Email: [email protected] ; Fax: + 1 416 978 7013; Tel: + 1 416 978 7014. General Consideration All experiments with metal complexes were carried out under nitrogen using standard Schlenk techniques or in a nitrogen-atmosphere glovebox from MBraun. Unless otherwise stated, all liquid chemicals were purchased from commercial sources, degassed and dried over 4Å molecular sieves prior to use. CH2Cl2 was distilled over CaH2; THF was distilled over sodium/benzophenone; toluene and hexanes were purified using the solvent purification system from Innovative Technology Inc.; CDCl3 and CD2Cl2 were distilled over CaH2; RuHCl(CO)(PPh3)3 was prepared according to literature procedures.1 The ligand precursors Dipp-CNBrBr and Mesityl-CNBrBr were prepared with a modified literature procedure (Scheme 1S).2

1D NMR spectra were recorded on a Mercury 300 spectrometer working at 300 MHz for 1H or a Varian 400 spectrometer working at 400 MHz for 1H and 100 MHz for 13C. 2D NMR experiments were carried out on a Varian 400 spectrometer working at 400 MHz for 1H and 100 MHz for 13C or a Varian 500 spectrometer working at 500 MHz for 1H and 125 MHz for 13C. Both 1H and 13C NMR chemical shifts are reported in ppm and referenced relative to the solvent’s residual signals. All chemical shifts are assigned via 2D NMR experiments. IR spectra were measured on a Perkin-Elmer SpectrumOne instrument. GC analyses were carried out on an Agilent 7980A GC system (equipped with an HP-5 column) connected with a 5975C inert XL MSD. Elemental analyses were performed at our Chemistry Department using a PE 2400 C/H/N/S analyzer.

X-ray Diffraction Analysis. Single crystals of 1aHBr·CHCl3, 1bHBr, 2a and 2b suitable for X-ray crystallographic analysis were obtained as described below and mounted on the tip of a MiTeGen MicroMount. The single-crystal X-ray diffraction data were collected on a Bruker Kappa APEX II diffractometer with Mo Kα radiation (λ = 0.71073 Å) operating at 50 kV and 30 mA, at 150 K controlled by an Oxford Cryostream 700 series low temperature system. The diffraction data were processed with the Apex 2 software package.3 All structures were solved by the direct methods and refined using SHELXTL V6.10.4 All nonhydrogen atoms were refined anisotropically, except for those of the disordered portions. The hydrides are located directly from the difference Fourier map, while all other hydrogen atoms were either calculated using the riding model. The contributions of all hydrogen atoms were included in the structure factor calculations. The selected crystal data are shown in Table 1S.

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2011

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Table 1S. Selected Crystal Data.

1aHBr·CHCl3 1bHBr 2a 2b 3b·1.5(C7H8)

Formula C27H38BrCl3N4 C23H31BrN4 C27H37BrN4ORu C24H31BrN4ORu C52.5H57N4OPRu

FW 604.87 443.43 614.59 572.51 892.06

T (K) 150(2) 150(2) 150(2) 150(2) 121(2)

space group Pna21 P21/c P21/n C2/c P21/n

a (Å) 31.4131(16) 8.9717(2) 11.9037(5) 20.3638(4) 9.1370(5)

b (Å) 8.2264(4) 27.7991(8) 16.1438(7) 10.1860(2) 18.7042(10)

c (Å) 11.8449(6) 9.8235(2) 14.7255(7) 23.8259(5) 26.1341(12)

(deg) 90 90 90 90 90

(deg) 90 108.4310(10) 109.140(2) 100.6510(10) 95.801(2)

(deg) 90 90 90 90 90

V (Å3) 3060.9(3) 2324.36(10) 2673.4(2) 4856.96(17) 4443.45

Z 4 4 4 8 4

Dc (g·cm−3) 1.313 1.267 1.527 1.566 1.333

(mm−1) 1.627 1.783 2.107 2.314 0.432

no. of refln collected 22490 17718 54156 16273 37440

no. of indept refln 5200 4087 13497 4283 10188

GOF on F2 1.015 1.017 1.012 1.020 1.038

R [I > 2(I)] R1 = 0.0430 a) R1 = 0.0294 R1 = 0.0460 R1 = 0.0276 R1 = 0.0657

wR2 = 0.0682 b) wR2 = 0.0653 wR2 = 0.0913 wR2 = 0.0566 wR2 = 0.1609

R (all data) R1 = 0.0736 R1 = 0.0405 R1 = 0.0957 R1 = 0.0422 R1 = 0.1035

wR2 = 0.0759 wR2 = 0.0694 wR2 = 0.1065 wR2 = 0.0613 wR2 = 0.1786

a) R1 = (Fo − Fc)/Fo b) wR2 = [[w(Fo

2 – Fc2)2]/w(Fo

2)2]1/2


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Scheme 1S. Syntheses of ligand precursors 1aHBr and 1bHBr.

Synthesis of Dipp-CNBrBr (3-((6-(bromomethyl)pyridin-2-yl)methyl)-1-(2,6-diisopropylphenyl)-1H-imidazol-3-ium bromide). To a solution of 2,6-bis(bromomethyl)pyridine (2.32 g, 8.75 mmol) in toluene (100 mL) was added dropwise a solution of 1-(2,6-diisopropylphenyl)-1H-imidazole (1 g, 4.38 mmol) in toluene (50 mL) at room temperature over 20 min. The reaction mixture was stirred at room temperature for 0.5 h, then at 85°C for 2 d. The precipitate was collected by filtration, washed with toluene (20 mL × 1) and hexanes (20 mL × 2), then dried under vacuum to give Dipp-CNBrBr (1.97 g, 91% yield based on imdazole) as an off-white solid. 1H NMR (CDCl3, 400 MHz, 25°C) δ 10.21 (1H, s, NCHN), 8.18 (1H, s, NCHCHN), 7.92 (1H, d, J = 7.6 Hz, Hpy), 7.78 (1H, t, J = 7.6 Hz, Hpy), 7.54 (1H, t, J = 8 Hz, Harom), 7.41 (1H, d, J = 7.6 Hz, Hpy), 7.31 (2H, d, J = 7.6 Hz, Harom), 7.13 (1H, s, NCHCHN), 6.28 (2H, s, NimCH2C), 4.45 (2H, s, CCH2Br), 2.24-2.37 (2H, m, CHMe2), 1.23 (6H, d, J = 6.8 Hz, CH3), 1.14 (6H, d, J = 6.8 Hz, CH3).

Synthesis of Mesityl-CNBrBr (3-((6-(bromomethyl)pyridin-2-yl)methyl)-1-mesityl-1H-imidazol-3-ium bromide). Mesityl-CNBrBr (305 mg, 68% yield based on imdazole) was obtained from 2,6-bis(bromomethyl)pyridine (529.9 mg, 2 mmol) and 1-(2,4,6-trimethylphenyl)-1H-imidazole (186.1 mg, 1 mmol) in toluene (20 mL) according to the above experimental procedure. 1H NMR (CDCl3, 300 MHz, 25°C) δ 10.31 (1H, dd, J = 1.2, 1.5 Hz, NCHN), 8.05 (1H, dd, J = 1.5, 1.6 Hz, NCHCHN), 7.92 (1H, d, J = 7.5 Hz, Hpy), 7.77 (1H, dd, J = 7.5, 7.8 Hz, Hpy), 7.40 (1H, d, J = 7.8 Hz, Hpy), 7.10 (1H, dd, J = 1.5, 1.6 Hz, NCHCHN), 7.01 (2H, s, Harom), 6.21 (2H, s, NimCH2C), 4.46 (2H, s, CCH2Br), 2.35 (3H, s, CH3), 2.09 (6H, s, CH3).

Synthesis of 1aHBr (3-((6-((diethylamino)methyl)pyridin-2-yl)methyl)-1-(2,6-diisopropylphenyl)-1H-imidazol-3-ium bromide). To a suspension of Dipp-CNBrBr (1.96 g, 3.98 mmol) and K2CO3 (2.75 g, 20 mmol) in acetonotrile (200 mL) was added dropwise diethylamine (0.32 g, 4.38 mmol) at room temperature. The mixture was stirred at room temperature overnight. The inorganic salts were filtered off and washed with acetonitrile (20 mL × 1). The combined filtrate was concentrated to dryness in vacuo; the residue was then dissolved in CH2Cl2 and filtered. The filtrate was concentrated to dryness under vacuum to give 1aHBr (1.9 g, 98%) as a pale yellow solid. Crystals of 1aHBr·CHCl3 suitable for X-ray crystallographic analysis were grown through a bi-layer diffusion method using CHCl3 and hexanes. 1H NMR (CDCl3, 400 MHz, 25°C) δ 10.22 (1H, s, NCHN), 8.17 (1H, s, imi-H12), 7.78 (1H, d, J = 7.6 Hz, py-H9), 7.71 (1H, t, J = 7.6 Hz, py-H8),


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7.53 (1H, t, J = 8.0 Hz, Harom), 7.48 (1H, d, J = 7.6 Hz, py-H7), 7.30 (2H, d, J = 8.0 Hz, Harom), 7.11 (1H, s, imi-H13), 6.19 (2H, s, NimCH2C), 3.63 (2H, s, pyCH2NEt2), 2.52 (4H, q, J = 7.2 Hz, NCH2Me), 2.24-2.35 (2H, m, CHMe2), 1.21 (6H, d, J = 6.8 Hz, CH(CH3)2), 1.13 (6H, d, J = 6.8 Hz, CH(CH3)2), 1.01 (6H, t, J = 7.2 Hz, NCH2CH3).

13C NMR (CDCl3, 100 MHz, 25°C) δ 161.28 (s, py-C6), 151.68 (s, py-C10), 145.52 (s, Carom), 138.33 (s, NCHN), 138.08 (s, py-C8), 132.08 (s, Carom), 130.28 (s, Carom), 124.85 (s, Carom), 124.04 (s, imi-C12), 123.42 (s, imi-C13), 123.13 (s, py-C7), 122.26 (s, py-C9), 59.57 (s, C5), 54.11 (s, C11), 47.54 (s, NCH2Me), 28.77 (s, CHMe2), 24.52 (s, CH(CH3)2), 24.40 (s, CH(CH3)2), 12.13 (s, NCH2CH3). Anal. Calcd (%) for C26H37N4Br: C 64.32 H 7.68 N 11.54 Found: C 64.14 H 7.92 N 11.31.

Synthesis of 1bHBr (3-((6-((diethylamino)methyl)pyridin-2-yl)methyl)-1-mesityl-1H-imidazol-3-ium bromide). 1bHBr (486.4 mg, 98% yield) was obtained from Mesityl-CNBrBr (507.7 mg, 1.12 mmol), K2CO3 (790.3 mg, 5.73 mmol) and diethylamine (93.7 mg, 1.27 mmol) in acetonitrile (50 mL) according to the above experimental procedure. Crystals of 1bHBr suitable for X-ray crystallographic analysis were grown through a bi-layer diffusion method using CH2Cl2 and hexanes. 1H NMR (CDCl3, 400 MHz, 25°C) δ 10.14 (1H, dd, J = 1.2, 1.6 Hz, NCHN), 7.99 (1H, t, J = 1.6 Hz, imi-H12), 7.62 (1H, d, J = 5.2 Hz, py-H9), 7.62 (1H, d, J = 4.0 Hz , py-H7), 7.41 (1H, dd, J = 4.8, 4.0 Hz, py-H8), 7.15 ( 1H, dd, J = 1.6, 2.0 Hz, imi-H13), 6.93 (2H, s, Harom), 6.03 (2H, s, NimCH2C), 3.56 (2H, s, pyCH2NEt2), 2.46 (4H, q, J = 7.2 Hz, NCH2Me), 2.27 (3H, s, PhCH3), 2.01 (6H, s, PhCH3), 0.95 (6H, t, J = 7.2 Hz, NCH2CH3).

13C NMR (CDCl3, 100 MHz, 25°C) δ 161.23 (s, 1C, Py-C6), 151.49 (s, 1C, Py-C10), 141.25 (s, 1C, Carom), 138.03 (s, 1C, NCHN), 137.77 (s, Py-C8), 134.25 (s, Carom), 130.70 (s, Carom), 129.80 (s, Carom), 123.85 (s, imi-C12), 122.96 (s, py-C7), 122.61 (s, imi-C13), 121.77 (s, py-C9), 59.35 (s, C5), 53.95 (s, C11), 47.38 (s, NCH2Me), 21.08 (s, PhCH3), 17.63 (s, PhCH3), 11.99 (s, NCH2CH3). Anal. Calcd (%) for C23H31N4Br: C 62.30 H 7.05 N 12.63 Found C 62.04 H 6.87 N 12.46.

Scheme 2S. Synthesis of Ruthenium Complexes 2a and 2b

Synthesis of [RuH(1a)(CO)Br], 2a. At -78oC, to a mixture of 1aHBr (0.528 g, 1.09 mmol) and LiHMDS (0.182 g, 1.09 mmol) in a Schlenk flask was added a pre-cooled (-78°C) THF (85 mL) via a cannula. The mixture was allowed to stir at -30°C for 4 h, then transferred via a cannula into a three-neck flask charged with RuHCl(CO)(PPh3)3 (1.04 g, 1.09 mmol). The mixture was warmed to 70°C and stirred at this temperature overnight (about 12 hours). The brown solution was concentrated to dryness in vacuo and the residue was washed with hexanes (80 mL × 3). To the residue was added dichloromethane (10 mL). The inorganic salts were filtered off and the filtrate was concentrated to ~3 mL. A large amount of yellow precipitate formed immediately upon the addition of hexanes (100 mL). The concentration and precipitation were repeated twice and the precipitate was collected by filtration and subsequently dried under vacuum to


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give a mixture of [RuH(1a)(CO)Br] and [RuH(1a)(CO)Cl] (~98:2 ratio determined by 1H NMR spectroscopy) (0.59 g, 88%) as a bright yellow powder. The mixture crystallizes as disordered single crystals, in which both Br and Cl are present. The preliminary structure is shown in Figure 1S. The mixture can be directly used for the catalytic activity study. The pure [RuH(1a)(CO)Br] was obtained via salt metathesis with LiBr in THF.

A solution of the mixture of [RuH(1a)(CO)Br] and [RuH(1a)(CO)Cl] (60 mg) and LiBr (270 mg) in anhydrous THF (10 mL) was stirred under N2 at room temperature for 2 d before the removal of solvent under vacuum. The residue was extracted with CH2Cl2 (5 mL) and the inorganic salts were removed by filtration. The filtrate was concentrated to about 1~2 mL and hexanes (20 mL) was added to afford the precipitate of pure 2a (53 mg, 88%) as a yellow solid. Crystals suitable for X-ray crystallographic analysis were grown through a bi-layer diffusion method using CH2Cl2 and hexanes.

1H NMR (C6D6, 400MHz, 25°C) δ -14.21 (1H, s, Ru-H), 7.38 (1H, t, J = 7.6 Hz, Harom), 7.33 (1H, dd, J = 7.6, 1.6 Hz, Harom), 7. 23 (1H, dd, J = 7.6, 1.6 Hz, Harom), 6.97 (1H, d, J = 14.8 Hz, NimCH2C), 6.75 (1H, t, J = 7.6 Hz, py-H8), 6.46 (1H, d, J = 2.0 Hz, imi-H12), 6.44 (1H, d, J = 1.6 Hz, imi-H13), 6.37 (2H, d, J = 7.6 Hz, py-H7 and H9), 4.20 (1H, d, J = 14.8 Hz, NimCH2C), 3.79 (1H, d, J = 14 Hz, pyCH2NEt2), 3.36 (1H, d, J = 14 Hz, pyCH2NEt2), 3.46-3.22 (3H, m, CHMe2 and NCH2Me), 3.09-2.94 (2H, m, NCH2Me), 2.35-2.26 (1H, m, NCH2Me), 1.88 (3H, d, J = 6.4 Hz, C(CH3)2), 1.59 (3H, d, J = 6.4 Hz, C(CH3)2), 1.24 (3H, d, J = 6.8 Hz, C(CH3)2), 1.16 (3H, t, J = 6.8 Hz, NCH2CH3), 1.08 (3H, d, J = 6.8 Hz, C(CH3)2), 0.80 (3H, t, J = 6.8 Hz, NCH2CH3).

1H NMR (CD2Cl2, 400MHz, 25°C) δ -15.34 (1H, s, Ru-H), 7.78 (1H, t, J = 7.6, 8 Hz, py-H8), 7.43 (1H, d, J = 7.6 Hz, py-H9), 7.42 (1H, t, J = 7.6, 8 Hz, Harom), 7.37 (1H, d, J = 8 Hz, py-H7), 7.26 (1H, dd, J = 1.6, 8 Hz, Harom), 7.23 (1H, dd, J = 1.6, 7.6 Hz, Harom), 7.14 (1H, d, J = 2.0 Hz, imi-H12), 6.74 (1H, d, J = 2.0 Hz, imi-H13), 6.74 (1H, d, J = 15.2 Hz, NimCH2C), 5.00 (1H, d, J = 15.2 Hz, NimCH2C), 4.08 (1H, d, J = 14 Hz, pyCH2NEt2), 3.99 (1H, d, J = 14.4 Hz, pyCH2NEt2), 3.22-3.31 (1H, m, NCH2Me), 3.04-3.15 (2H, m, NCH2Me), 2.62-2.71 (1H, m, CHMe2), 2.55-2.62 (1H, m, CHMe2), 2.47-2.55 (1H, m, NCH2Me), 1.35 (3H, d, J = 6.8 Hz, CH(CH3)2), 1.31 (3H, d, J = 6.8 Hz, CH(CH3)2), 1.10 (3H, d, J = 6.8 Hz, CH(CH3)2), 1.07 (3H, t, J = 7.2 Hz, NCH2CH3), 1.05 (3H, t, J = 7.2 Hz, NCH2CH3), 0.97 (3H, d, J = 6.8 Hz, CH(CH3)2).

13C NMR (CD2Cl2, 100 MHz, 25°C) δ 208.57 (d, J = 7.4 Hz, CO), 193.65 (d, J = 6 Hz, NCN), 161.44 (s, py-C6), 156.49 (s, py-C10), 148.67 (s, Carom), 147.09 (s, Carom), 137.59 (s, py-C8), 137.13 (s, Carom), 129.88 (s, Carom), 124.38 (s, Carom), 123.81 (s, Carom), 122.77 (s, imi-C13), 122.31 (s, py-C9), 121.74 (s, imi-C12), 121.15 (s, py-C7), 66.22 (s, C5), 55.68 (s, C11), 55.33 (s, NCH2Me), 50.51 (s, NCH2Me), 28.58 (s, CH(CH3)2), 28.51 (s, CH(CH3)2), 25.62 (s, CH(CH3)2), 25.56 (s, CH(CH3)2), 23.46 (s, CH(CH3)2), 22.67 (s, CH(CH3)2), 11.42 (s, NCH2CH3), 9.59 (s, NCH2CH3). IR (KBr, pellet, cm-1) ν 1963 (Ru-H), 1892 (CO). Anal. Calcd (%) for C27H37N4BrORu: C 52.77 H 6.07 N 9.12 Found: C 52.31 H 5.70 N 8.79.


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Figure 1S. The disordered structure of the mixed crystal of [RuH(1a)(CO)Br] and [RuH(1a)(CO)Cl]. The ratio was refined as 95:5 for the best R-factor. Selected bond lengths (Å): Ru1-Cl1 2.556(19), Ru1-Br1 2.6849(3), Ru1-C29 1.824(2), Ru1-C1 1.989(2), Ru1-N3 2.1352(18), Ru1-N4 2.2611(18).

Synthesis of [RuH(1b)(CO)Br], 2b. The mixture of [RuH(1b)(CO)Br] and [RuH(1b)(CO)Cl] (92:8 ratio) was obtained as a bright yellow powder (451.3 mg, 85% yield) from 1bHBr (408 mg, 0.92 mmol), LiHMDS (153.14 mg, 0.92 mmol) and RuHCl(CO)PPh3)3 (875.4 mg, 0.92 mmol) in THF (70 mL) according to the above experimental procedure.

Pure 2b (22.4 mg, 90% yield) was obtained from the mixture of [RuH(1b)(CO)Br] and [RuH(1b)(CO)Cl] (25 mg) via salt metathesis with LiBr (80 mg) in THF (5 mL) according to the above experimental procedure. Crystals suitable for X-ray crystallographic analysis were grown through a bi-layer diffusion method using CH2Cl2 and hexanes. 1H NMR (CD2Cl2, 400MHz, 25°C) δ -15.35 (1H, s, Ru-H), 7.78 (1H, t, J = 7.6, 8.0 Hz, py-H8), 7.42 ( 1H, d, J = 7.6 Hz, py-H9), 7.37 (1H, d, J = 7.6 Hz, py-H7), 7,17 (1H, d, J = 2.0 Hz, imi-H12), 6.98 (1H, s, mes-Harom), 6.95 (1H, s, mes-Harom), 6.66 (1H, d, J = 2.0 Hz, imi-H13), 6.48 (1H, d, J = 15.2 Hz, NimiCH2C), 5.02 (1H, d, J = 15.2 Hz, NimiCH2C), 4.21 (1H, d, J = 14.4 Hz, pyCH2NEt2), 4.05 (1H, d, J = 14.4 Hz, pyCH2NEt2), 3.23-3.00 (3H, m, NCH2Me), 2.74-2.65 (1H, m, NCH2Me), 2.34 (3H, s, PhCH3), 2.19 (3H, s, PhCH3), 1.97 (3H, s, PhCH3), 1.10 (3H, t, J = 7.2 Hz, NCH2CH3), 1.03 (3H, t, J = 7.2 Hz, NCH2CH3). 13C NMR (CD2Cl2, 100 MHz, 25°C) δ 205.89 ( d, J = 6 Hz, CO), 189.91 (d, J = 4 Hz, NCN), 159.67 (s, Py-C6), 154.15 (s, Py-C10), 137.37 (s, Py-C8), 136.67 (s, Carom), 136.20 (s, Carom), 135.79 (s, Carom), 134.90 (s, Carom), 127.89 (s, Carom), 127.38 (s, Carom), 121.13 (s, Py-C9), 121.00 (s, imi-C13), 120.00 (s, imi-C12), 119.85 (s, Py-C7), 65.84 (s, C5), 55.61 (s, C11), 54.96 (s, NCH2CH3), 50.29 (s, NCH2CH3), 21.85 (s, mes-CH3), 19.46 (s, mes-CH3), 19.15 (s, mes-CH3), 11.37 (s, NCH2CH3), 10.75 (s, NCH2CH3). IR (KBr, pellet, cm-1) ν 1950 (Ru-H), 1897 (CO). Anal. Calcd. (%) for C24H31N4BrORu: C 50.35 H 5.46 N 9.79 Found: C 50.17 H 5.85 N 9.60.

Synthesis of Ruthenium (II) Complex 3a. To a mixture of [RuH(1a)(CO)Br] and [RuH(1a)(CO)Cl] obtained above (30 mg, 0.049 mmol) and KHMDS (9.7 mg, 0.049 mmol) was added a pre-cooled (-30°C) toluene (1 mL). The resulting purple mixture was allowed to warm to room temperature, stirred for 30 min,


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and then filtered. The filtrate was concentrated to dryness in vacuo to remove the solvent and HN(SiMe3)2. The residue was extracted with hexanes (15 mL × 3) and filtered. The combined filtrate was concentrated to dryness in vacuo to give complex 3a (23 mg, 90%) as a purple solid. The analytically pure sample was obtained after recrystallization in toluene and hexanes at -30°C (70 mg of 3a in 0.5 mL of toluene and 1.5 mL of hexanes; 65% recovery). 1H NMR (C6D6, 400 MHz, 25°C) δ -22.69 (1H, s, Ru-H), 7.38 (1H, t, J = 7.6 Hz, Harom), 7.25 (1H, dd, J = 7.6, 1.2 Hz, Harom), 7.24 (1H, dd, J = 7.6, 1.2 Hz, Harom), 6.75 (1H, d, J = 2.0 Hz, imi-H12), 6.52 (1H, d, J = 2.0 Hz, imi-H13), 6.49 (1H, dd, J = 9.2, 6.0 Hz, py-H8), 6.33 (1H, d, J = 9.2 Hz, py-H9), 6.13 (1H, s, Nimz-CH=py), 5.48 (1H, d, J = 6.4 Hz, py-H7), 3.38 (1H, d, J = 12.8 Hz, pyCH2NEt2), 2.71 (1H, d, J = 13.2 Hz, pyCH2NEt2), 2.81-2.64 (3H, m, CHMe2 and NCH2Me), 2.53-2.37 (2H, m, NCH2Me), 2.17 (1H, m, NCH2Me), 1.50 (3H, d, J = 6.8 Hz, CH(CH3)2), 1.37 (3H, d, J = 6.8 Hz, CH(CH3)2), 1.11 (3H, d, J = 6.8 Hz, CH(CH3)2), 1.03 (3H, d, J = 6.8 Hz, CH(CH3)2), 0.82 (3H, t, J = 7.2 Hz, NCH2CH3), 0.66 (3H, t, J = 7.2 Hz, NCH2CH3).

13C NMR (C6D6, 100 MHz, 25°C) δ 207.66 (s, CO), 184.93 (s, NCN), 156.02 (s, py-C6), 147.84 (s, Carom), 147.79 (s, Carom), 140.48 (s, py-C10), 137.92 (s, Carom), 130.11 (s, Carom), 127.19 (s, py-C8), 124.52 (s, Carom), 124.50 (s, Carom), 122.66 (s, imi-C13), 119.08 (s, py-C9), 118.60 (s, imi-C12), 97.99 (s, py-C7), 95.60 (s, C11), 63.48 (s, C5), 54.17 (s, NCH2CH3), 52.05 (s, NCH2CH3), 28.81 (s, CH(CH3)2), 28.56 (s, CH(CH3)2), 25.88 (s, CH(CH3)2), 25.57 (s, CH(CH3)2), 23.96 (s, CH(CH3)2), 23.07 (s, CH(CH3)2), 11.87 (s, NCH2CH3), 10.67 (s, NCH2CH3). IR (KBr, pellet, cm-1) ν 1886 (CO). Anal. Calcd. (%) for C27H36N4ORu·0.35C7H8: C 62.50 H 6.91 N 9.90 Found: C 62.23 H 7.13 N 9.43.

Synthesis of Ruthenium (II) Complex 3b. To a pre-cooled solution (-36 °C) of 2b (22.90 mg, 0.04 mmol) and triphenylphosphine (7.98 mg, 0.04 mmol) in toluene (5 mL) was added a pre-cooled solution (-36°C) of KHMDS ( 10.5 mg, 0.04 mmol) in toluene (2 mL). The reaction mixture was stirred for 1 h at ambient temperature and filtered to remove KBr. The solvent was then removed under vacuum. The residual solid was recrystallized in a toluene/hexanes mixed solvent in a -36 °C freezer to afford red crystals of 3b (23.4 mg, 86% yield). 1H NMR (C6D6, 400 MHz, 25°C) δ 7.52 (dt, 6H, PPh3, J = 1.6 Hz, J = 8.4 Hz); 7.13–7.01 (m, 16.5H, PPh3 and toluene), 6.85 (1H, s, mes-Harom), 6.84 (1H, s, mes-Harom); 6.52 ( dd, 1H, py-H8, J = 9.2 Hz, J = 6.0 Hz); 6.50 (d, 1H, imz-H12, J = 1.6 Hz ); 6.09 (d, 1H, imz-H13, J = 2.0 Hz ); 5.95 (d, 1H, py-H9, J = 9.2 Hz); 5.51 (d, 1H, py-H7, J = 6.0 Hz); 5.46 (s, 1H, Nimz-CH=py); 3.54 (d, 1H, py-CH2-NEt2, J = 12.4 Hz); 2.97 (q, 1H, NCH2Me, J = 5.6 Hz); 2.85 (d, 1H, py-CH2-NEt2, J = 12.8 Hz); 2.60 (q, 1H, NCH2Me, J = 7.2 Hz); 2.84 (q, 1H, NCH2Me, J = 6.4 Hz); 2.22 (m, 4H, mes-CH3 and NCH2Me,); 2.15 (s, 3H, mes-CH3); 2.11 (s, 4.5H, toluene-CH3); 1.65 (s, 3H, mes-CH3); 0.77 (t, 3H, C1H, J = 7.2); 0.33 (t, 3H, C1H, J = 7.2); -12.0 (br, 1H, RuH). 31P NMR (C6D6, 162 MHz, 25°C) δ 9.26 (br). Elementary analysis for C42H45N4OPRu·1.5C7H8: calculated C: 70.68; H: 6.44; N: 6.28 found C: 70.17; H: 6.91; N: 5.89. Ruthenium (II) complex 4a. The J. Young NMR tube charged with a solution of complex 3a (23 mg, 0.043 mmol) in C6D6 (0.8 mL) was evacuated under liquid N2 cooling, then H2 was introduced. The NMR tube was sealed at liquid N2 temperature and the solution was warm to room temperature, affording a clean solution of complex 4a (dark brown in solution) in C6D6 under H2. Complex 4a slowly loses H2 to regenerate complex 3a in solution under N2. Therefore, the isolation of 4a was unsuccessful. 1H NMR (C6D6, 400MHz, 25°C) δ -4.35 (2H, s, Ru-H), 7.41(1H, dd, J = 6.8, 8.4 Hz, Harom), 7.33 (1H, d, J = 7.2 Hz, Harom), 7.32 (1H, d, J = 8.4 Hz, Harom), 6.74 (1H, t, J = 7.6 Hz, py-H8), 6.50 (1H, d, J = 2.0 Hz, imi-H13), 6.47 (1H, d, J = 2.0 Hz, imi-H12), 6.41 (1H, d, J = 7.6 Hz, py-H7), 6.33 (1H, d, J = 7.6 Hz, py-H9), 4.66 (2H, s, NimCH2C), 3.81 (2H, s, pyCH2NEt2), 3.16-3.23 (2H, m, CHMe2), 2.76-2.85 (4H, m, NCH2Me), 1.71 (6H, d, J = 6.8 Hz, CH(CH3)2), 1.11 (6H, d, J = 6.8 Hz, CH(CH3)2), 0.97 (6H, t, J = 7.2 Hz, NCH2CH3).

13C NMR (C6D6, 100 MHz, 25oC) δ 213.89 (s, 1C, CO), 204.62 (s, 1C, NCN), 160.07 (s, 1C, py-C6), 154.25 (s, 1C, py-C10), 147.94 (s, 2C, Carom), 138.03 (s, 1C, Carom), 133.45 (s, 1C, py-C8), 129.77 (s, 1C, Carom), 124.24 (s, 2C, Carom), 121.75 (s, 1C, imi-C13), 119.82 (s, 1C, py-C9), 119.30 (s, 1C, py-C7), 118.80 (s, 1C, imi-C12), 66.79 (s, 1C, C5), 56.05 (s,


8

1C, C11), 53.15 (s, 2C, NCH2CH3), 28.81 (s, 2C, CH(CH3)2), 25.80 (s, 2C, CH(CH3)2), 23.39 (s, 2C, CH(CH3)2), 10.70 (s, 2C, NCH2CH3).

Figure 2S. Pov-Ray plots of the molecular structure of 4a. All H atoms are omitted for clarity except for hydrides. The dipp groups of the NHC arms are shrunk to the ipso carbon and the ethyl groups of the amine arms are omitted for clarity. Observation of Ruthenium (II) complex 5a. To a fresh solution of complex 4a (0.032 mmol) in C6D6 (0.8 mL) under N2 (prepared in situ from complex 3a (17 mg, 0.032 mmol) in C6D6 under H2 (introduced and sealed at -78°C) followed by the replacement of H2 with N2) was added acetophenone (3.9 uL, 0.034mmol) at room temperature. The resulting brown C6D6 solution contains mainly 5a. Complex 5a displays broad signals in the 1H NMR spectrum at 25°C. At 60°C, the 1H NMR signals become sharper and therefore, the 1H NMR data of 5a at 60°C are reported below. Complex 5a releases acetophenone to regenerate trans-dihydride 4a via a β-hydride elimination in the absence of excess acetophenone. 1H NMR (C6D6, 400 MHz, 60°C) δ -16.33 (1H, br, Ru-H), 7.73(1H, d, J = 7.2 Hz, Harom), 7.32 (1H, t, J = 7.6 Hz, Harom), 7. 23-7.27 (3H, m), 7.14-7.20 (2H, m), 6.99-7.11 (2H, m), 6.70 (1H, t, J = 6.4 Hz, py-H8), 6.60 (1H, br, imi-H12), 6.53 (1H, br, py-H7), 6.38 (1H, br, imi-H13), 6.21 (1H, br, py-H9), 5.47 (1H, br, NimCH2C), 4.62 (1H, q, J = 6.4 Hz, Ph(CH3)CHORu), 3.91 (1H, d, J = 12.4 Hz, pyCH2NEt2), 3.11-3.15 (3H, m, pyCH2NEt2 and NCH2Me), 2.62-2.83 (4H, m, NCH2Me and CHMe2), 1.58 (3H, d, J = 6.8 Hz, CH(CH3)2), 1.44 (3H, d, J = 6.8 Hz, CH(CH3)2), 1.32 (3H, d, J = 6.4 Hz, Ph(CH3)CHORu), 1.09 (3H, t, J = 7.2 Hz, NCH2CH3), 1.01 (3H, d, J = 7.6 Hz, CH(CH3)2), 0.88 (3H, d, J = 6.8 Hz, CH(CH3)2), 0.80 (3H, t, J = 7.2 Hz, NCH2CH3).

General Procedures for Hydrogenation of Esters. To a mixture of 2a (6.2 mg, 0.01 mmol) and KOtBu (9 mg, 0.08 mmol) in Parr high pressure reactor was added a solution of the ester (1 mmol) in toluene (2 mL). The purple solution was purged with H2 and stirred under 5.3 bar of H2 at 105°C. Samples were taken from the dark blue reaction mixture and quenched by exposure to air. The samples were analyzed by gas chromatography (GC) or 1H NMR using mesitylene as an internal standard.


9

DFT Calculations. DFT calculations were performed using Gaussian 09 software package[6] and the rmpw1pw91 method. The SDD basis set with effective core potential was used on the Ru center, while for the rest of the elements 6-31G* basis set was used. The geometry optimizations were performed with no symmetry constraint. The self-consistent reaction field (SCRF) calculations using the PCM-UFF solvation model were performed on the PCM optimized structures. Benzene was used in the PCM calculations. Vibrational frequency analysis was then performed to confirm the local minimum and to obtain thermodynamic data.

Optimized geometry of 3a in Cartesian coordinates:

(free energy -1438.943529 Hartree)

44 5.153279000 2.543579000 4.154315000 7 5.322645000 0.875967000 2.901483000 6 1.583929000 2.843508000 1.961568000 1 1.013224000 2.466369000 1.129186000 6 3.367171000 2.975616000 3.372874000 7 2.374032000 3.865994000 3.733928000 6 2.382814000 4.790577000 4.825669000 6 2.733249000 6.127149000 4.571362000 6 3.197052000 6.596318000 3.204100000 1 3.348651000 5.710539000 2.580159000 6 4.536479000 7.337233000 3.275161000 1 4.450088000 8.279744000 3.825912000 1 4.885784000 7.577712000 2.265603000 1 5.298538000 6.729769000 3.769301000 6 2.131520000 7.467921000 2.528375000 1 1.183392000 6.932708000 2.420515000 1 2.463140000 7.773434000 1.530461000 1 1.938548000 8.375750000 3.110109000 6 2.631015000 7.037127000 5.625166000 1 2.890381000 8.077897000 5.458915000 6 2.208018000 6.630347000 6.883213000 1 2.136561000 7.352518000 7.690684000 6 1.875911000 5.300688000 7.111447000 1 1.542549000 4.995760000 8.098259000 6 1.951032000 4.352941000 6.089493000 6 1.524389000 2.918439000 6.341418000 1 1.870668000 2.315220000 5.498108000 6 2.159512000 2.330852000 7.604217000 1 3.249452000 2.408967000 7.568039000 1 1.896515000 1.271862000 7.694527000 1 1.810110000 2.832848000 8.512475000 6 -0.005023000 2.815103000 6.401043000 1 -0.313761000 1.774226000 6.544297000


10

1 -0.466759000 3.180268000 5.478642000 1 -0.406446000 3.403947000 7.233136000 6 1.296564000 3.791083000 2.878633000 1 0.427891000 4.416005000 3.003339000 7 2.840979000 2.342611000 2.268869000 6 3.399029000 1.316705000 1.504802000 1 2.827502000 1.075193000 0.620397000 6 4.535120000 0.607206000 1.794362000 6 6.359777000 0.035462000 3.189209000 6 7.023179000 0.308167000 4.505320000 1 6.380813000 -0.068762000 5.309455000 1 7.984739000 -0.218290000 4.557981000 7 7.188960000 1.758620000 4.733251000 6 7.522585000 2.020898000 6.156397000 1 6.685539000 1.628602000 6.739000000 1 7.515693000 3.102318000 6.299368000 6 8.836854000 1.440443000 6.669278000 1 8.880148000 0.351404000 6.578742000 1 8.932077000 1.682644000 7.731847000 1 9.708763000 1.861941000 6.161091000 6 8.235335000 2.259235000 3.805125000 1 7.895793000 2.010447000 2.795737000 1 9.164295000 1.695248000 3.971153000 6 8.514034000 3.748335000 3.896316000 1 7.603356000 4.333413000 3.744057000 1 9.230014000 4.022069000 3.115851000 1 8.949401000 4.035459000 4.857192000 6 6.748320000 -1.003459000 2.389163000 1 7.590782000 -1.626372000 2.664641000 6 6.003509000 -1.245833000 1.199450000 1 6.288249000 -2.055230000 0.534286000 6 4.929148000 -0.467940000 0.912809000 1 4.328592000 -0.644207000 0.026214000 6 5.293064000 4.025808000 5.218260000 8 5.506581000 4.922689000 5.936952000 1 4.469373000 1.871091000 5.381134000


11

Optimized geometry of the unobserved isomer of 3a in Cartesian coordinates:

(free energy -1438.928322 Hartree)

44 5.361342000 2.826556000 3.771573000 7 5.257485000 0.976327000 2.795306000 6 1.696075000 2.981546000 1.745532000 1 1.124543000 2.591181000 0.919228000 6 3.538372000 3.259602000 3.051959000 7 2.482503000 3.992282000 3.530312000 6 2.462217000 4.823930000 4.697581000 6 2.609498000 6.211623000 4.534471000 6 2.852931000 6.850206000 3.178373000 1 3.069106000 6.050660000 2.463663000 6 4.064026000 7.788508000 3.189927000 1 3.891699000 8.664206000 3.824023000 1 4.263321000 8.152132000 2.176719000 1 4.957231000 7.277381000 3.556284000 6 1.600294000 7.587795000 2.688792000 1 0.739507000 6.916359000 2.614507000 1 1.775486000 8.023716000 1.699769000 1 1.331141000 8.401072000 3.371297000 6 2.505541000 7.010412000 5.674572000 1 2.614093000 8.086250000 5.582954000 6 2.273019000 6.450855000 6.923997000 1 2.199225000 7.089663000 7.798477000 6 2.131931000 5.075539000 7.056606000 1 1.943031000 4.649304000 8.036862000 6 2.216959000 4.231783000 5.947294000 6 2.005671000 2.738020000 6.113447000 1 2.231129000 2.254516000 5.158660000 6 2.950476000 2.139434000 7.159623000 1 3.993227000 2.375092000 6.927379000 1 2.842233000 1.050492000 7.187732000 1 2.738231000 2.519446000 8.164252000 6 0.542892000 2.429682000 6.455267000 1 0.389195000 1.348882000 6.538664000 1 -0.135223000 2.810795000 5.685702000 1 0.256995000 2.885279000 7.409265000 6 1.353946000 3.825329000 2.743116000 1 0.423434000 4.315764000 2.975064000 7 3.020310000 2.652985000 1.946820000 6 3.792837000 1.795598000 1.061724000 1 4.564040000 2.412522000 0.586111000 6 4.460541000 0.642337000 1.757138000 6 6.104623000 0.017425000 3.352663000 6 7.036319000 0.411764000 4.266015000


12

1 3.119179000 1.430928000 0.285659000 7 7.216669000 1.822865000 4.564442000 6 7.239153000 2.042901000 6.038329000 1 6.266057000 1.706517000 6.408740000 1 7.300434000 3.118771000 6.217871000 6 8.344655000 1.338603000 6.818489000 1 8.289855000 0.251947000 6.720803000 1 8.232340000 1.581218000 7.879684000 1 9.342834000 1.665485000 6.513055000 6 8.482821000 2.267636000 3.911149000 1 8.324297000 2.120820000 2.841017000 1 9.288267000 1.583034000 4.211962000 6 8.905551000 3.701755000 4.180057000 1 8.126847000 4.407023000 3.882967000 1 9.803886000 3.918702000 3.593150000 1 9.152707000 3.879721000 5.230741000 6 5.954909000 -1.351878000 2.909808000 1 6.567022000 -2.114026000 3.380891000 6 5.090119000 -1.661327000 1.909334000 1 4.991103000 -2.689979000 1.574598000 6 4.324449000 -0.636606000 1.279542000 1 3.669661000 -0.851630000 0.443897000 6 5.564678000 4.391296000 4.706697000 8 5.782120000 5.377669000 5.292130000 1 5.991268000 3.583958000 2.567743000 1 7.784641000 -0.278469000 4.639533000

References:

[1] N. Ahmad, J. J. Levison, S. D. Robinson, M. F. Uttley, E. R. Wonchoba, G. W. Parshall, Inorg. Synth. 1974, 15, 45-48.

[2] (a) M. Boronat, A. Corma, C. González-Arellano, M. Iglesias, F. Sánchez, Organometallics, 2010, 29, 134-141. (b) C. del Pozo, M. Iglesias, F. Sánchez, Organometallics, 2011, 30, 2180-2188.

[3] Apex 2 Software Package; Bruker AXS Inc., 2008.

[4] G. M. Sheldrick, Acta Crystallogr. 2008, A64, 112-122.

[5] J. Zhang, G. Leitus, Y. Ben-David, D. Milstein, Angew. Chem., Int. Ed. 2006, 45, 1113-1115.

[6] Gaussian 09, Revision B.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2010.


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