Polarization Mediated by a Cobalt Hydrogenation Catalyst

Transcription

1 13C NMR Signal Enhancement using Parahydrogen Induced Polarization Mediated by a Cobalt Hydrogenation Catalyst Kenan Tokmic, Rianna B. Greer, Lingyang Zhu, and Alison R. Fout Department of Chemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave. Urbana, IL Supporting Information Table of Contents: General Considerations Synthesis and NMR spectra of ( Mes CCC)Co(η 2 -H2C=CHCOOEt)2 NMR spectra of metal complexes Crystallographic parameters for metal complexes PHIP NMR Studies References S2 S2 S3-S4 S5-S6 S7-S20 S21 S1

2 General Considerations. All manipulations of air- and moisture-sensitive compounds were carried out in the absence of water and dioxygen in an MBraun inert atmosphere drybox under a dinitrogen atmosphere except where specified otherwise. All glassware was oven dried for a minimum of 8 h and cooled in an evacuated antechamber prior to use in the drybox. Solvents for sensitive manipulations were dried and deoxygenated on a Glass Contour System (SG Water USA, Nashua, NH) and stored over 4 Å molecular sieves purchased from Strem following a literature procedure prior to use. 1 Acetone-d6, and benzene-d 6 were purchased from Cambridge Isotope Labs and were degassed and stored over 3 Å molecular sieves prior to use. Celite 545 (J. T. Baker) was dried in a Schlenk flask for 24 h under dynamic vacuum while heating to at least 150 C prior to use in a glovebox. NMR Spectra were recorded at room temperature and 37 C on a Varian spectrometer operating at 500 MHz ( 1 H NMR) (UI500NB and CB500), 125 MHz ( 13 C)(CB500), 600 MHz ( 1 H NMR) (U600) and 150 MHz ( 13 C) (U600) and referenced to the residual HD2COCD3 and C6D5H resonance (δ in parts per million, and J in Hz). 2 Electrospray ionization mass spectrometry (ESI) was recorded on a Water Q-TOF Ultima ESI instrument at the University of Illinois at Urbana Champaign School of Chemical Sciences Mass Spectrometry Laboratory in Urbana, IL. Potassium graphite (KC8) 3, {(dppe)rh(cod)]bf4 4, ( Mes CCC)CoCl2py 5, and (MesCCC)Co-py 6 were prepared according to literature procedures. Synthesis of Metal Complexes Preparation of ( Mes CCC)Co(η 2 -H2C=CHCOOEt)2: A 20 ml scintillation vial was charged with ( Mes CCC)Co-py (0.036 g, mmol) and THF (10 ml). Ethyl acrylate (55 ul, 10 eq) was added and the solution was stirred for 2 h. After removing the THF was removed under reduced pressure and washing the solid was washed with Et2O (2 x 5 ml), the remaining residue was extracted with benzene (10 ml). Removal of the solvent under reduced pressure resulted in a fine yellow powder (0.034 g, mmol, 81%). NMR data (in benzene-d6, 25 C): 1 H δ = (m, 4H), 7.56 (t, J = 7.3, 1H), 7.02 (t, J = 7.8, 2H), 6.80 (t, J = 7.8, 2H), 6.70 (s, 2H), 6.60 (s, 2H), 6.34 (d, J = 7.9, 2H), (m, 4H), 3.45 (s, 6H), 2.59 (s, 6H), 1.93 (s, 6H), 1.51 (s, 6H), 0.76 (t, J = 7.4, 6H). 13 C δ = 204.3, 181.3, 176.3, 148.7, 138.9, 138.6, 138.3, 137.1, 132.6, 131.5, 130.4, 129.1, 128.6, 123.0, 122.7, 122.5, 110.8, 110.0, 108.4, 59.0, 50.3, 39.1, 20.8, 19.4, 18.5, S2

3 1 H NMR Spectrum, 500 MHz, C6D6 Figure S1. 1 H NMR (C6D6, 500 MHz) spectrum of ( Mes CCC)Co(η 2 -H2C=CHCOOEt)2. (denotes n-hexane). S3

4 13 C NMR Spectrum, 125 MHz, C6D6 Figure S2. 13 C NMR (C6D6, 125 MHz) spectrum of ( Mes CCC)Co(η 2 -H2C=CHCOOEt)2. ( denotes n-hexane). S4

5 Table S1 Crystallographic Parameters for ( Mes CCC)Co(η 2 -H2C=CHCOOCH2CH3)2. Empirical Formula C52 H59 Co N4 O5 Formula Weight Temperature 100(2) K Wavelength Å Crystal system Monoclinic Space group P 2 1/n a = (5) Å b = (12) Å Unit Cell Dimensions c = (8) Å α= 90 β= (2) γ = 90 Volume (4) Å 3 Z 4 Reflections collected Independent reflections 8220 Goodness-of-fit on F Final R indices [I>sigma(l)] R1 = wr2 = ( Mes CCC)Co(η 2 -H2C=CHCOOCH2CH3)2 dd59h S5

6 Table S2 Selected bond lengths and angles for ( Mes CCC)Co(η 2 -H2C=CHCOOCH2CH3)2. ( Mes CCC)Co(η 2 -H2C=CHCOOCH2CH3)2 Bond Distances (A ) Co C NHC 1.954(3) Co C aryl 1.902(3) Co C NHC (3) Co C C=C (3) Co C C=C (3) Bond Angles ( ) C NHC-Co-C NHC (12) C NHC-Co-C aryl 79.98(12) C NHC-Co-C aryl 79.51(12) C NHC-Co-C C=C 97.05(11) C NHC-Co-C C=C (11) C aryl-co-c C=C (11) C aryl-co-c C=C (11) C C=C-Co-C C=C (12) S6

7 PHIP NMR Studies Sample preparation using ( Mes CCC)Co-py: A 4 ml scintillation vial was charged with ( Mes CCC)Co-py (2.0 mg, mmol), ethyl acrylate (3.5 μl, mmol) and dissolved in ½ ml of acetone-d6 and transferred to a J. Young NMR tube. The NMR tube was subjected to two-freeze-pump-thaw cycles and p-h2 (1 atm) was added while the sample was frozen in liquid nitrogen on a high-vacuum line. The sample was kept in liquid nitrogen and warmed to ambient temperature in an isopropanol bath and shaken immediately for 5 seconds before inserting the sample into the NMR spectrometer. For the 13 C NMR experiments, the sample was shaken at Earth s magnetic field. Earth s magnetic field was determined using a ± 0 to 10 hand held gauss meter and was 7.2 meters from the 600 MHz spectrometer. For 1 H NMR experiments, the sample was shaken in adjacent to the NMR spectrometer. For reactions carried out at 37 C: the temperature of the NMR probe was set to 37 C. After warming the sample to ambient temperature, the sample was inserted into the NMR spectrometer and warmed for 2 minutes. The sample was then removed from the spectrometer, shaken at Earth s magnetic field for 5 seconds and inserted into the NMR spectrometer and a single 13 C NMR scan was collected (ca. 20 seconds from). Sample preparation using ( Mes CCC)CoCl2py: To a standard 4 ml scintillation vial charged with ( Mes CCC)CoCl2py (2.2 mg, mmol), a solution NaHBEt3 (1.0 M in toluene, 6.2 μl, mmol) was added resulting effervesce of the brown suspension. The brown mixture was dissolved in ½ ml of acetone-d6 and ethyl acrylate (3.5 μl mg, mmol) was added and the resulting yellow solution was transferred to a J. Young NMR tube. The addition of p- H2 and collection of 13 C and 1 H NMR data was identical to the protocol described above. Sample preparation using ( Mes CCC)CoCl2py exposed to ambient atmosphere: A standard 4 ml scintillation vial was charged with ( Mes CCC)CoCl2py (2.2 mg, mmol) and removed from the glovebox, allowed to stand under ambient atmosphere for 10 minutes. The sample was moved into the glovebox and the same procedure was followed as noted above. Sample preparation using [(dppb)rh(cod)]bf4: A 4 ml scintillation vial was charged with [(dppb)rh(cod)]bf4 (2.1 mg, mmol), ethyl acrylate (3.5 μl, mmol) and dissolved in ½ ml of acetone-d6 and transferred to a J. Young NMR tube. The addition of p- H2 and collection of 13 C and 1 H NMR data was identical to the protocol described above. S7

8 NMR Spectrometer. All PHIP 1 H NMR data were collected on a Varian UNITY INOVA 500 NB High-Resolution NMR Console with a 5mm Varian 1 H{ 13 C/ 15 N} PFG Z probe. All PHIP 13 C data presented herein were collected on a Varian UNITY INOVA 600 NB High-Resolution NMR Console with a 5mm Varian AutoTuneX 1 H/X PFG Z probe, X= 31 P- 15 N. All spectra 1 H NMR data were collected in acetone-d6 or benzene-d6 and the residual solvent resonance was referenced to 2.05 or 7.16 ppm, respectively. All 13 C NMR data were collected using acetoned6 and the residual solvent was referenced to ppm. 1 H NMR spectra were recorded using 45 o pulse angle or OPSY. 13 C NMR spectra were recorded using a standard 90 pulse. The enhanced 13 C NMR signal are anti-phase and are displayed in absolute mode, unless otherwise noted. The spectral window of 30 ppm was used in both proton and 1 H-OPSY experiments and 245 ppm in the 13 C NMR experiments. 1 H-OPSY NMR data was collected via a double quantum coherence pathway using the pulse sequence below (Figure S3). The OPSY spectra are anti-phase peaks and are displayed with absolute mode in the following spectra, unless otherwise noted. Figure S3 Double quantum OPSY pulse sequence (OPSY-d): the vertical bar at 1 H channel represents /2 pulse. Phase cycle: 1: (y)4(x)4, 2: (x)4(y)4, rec: (x)4(y)4. Z Gradient: 50 G/cm rectangular gradient was used. First gradient was applied for 1ms in the opposite direction of the second gradient which was applied for 2ms. 0.5ms gradient recovery delays were used after each gradient. The acquisition time was 4 seconds and no delay between scans was used. Generation of para-hydrogen. A parahydrogen converter was used to generate the para- H2 enriched hydrogen gas. This consisted of copper tubing filled with a hydrous ferric oxide catalyst that was cooled to 15 K using a closed-cycle 4 He cryostat. A detailed description of the converter can be found in Tom et al., which was able to consistently convert naturally occurring hydrogen gas (3:1 ortho:para) to 99.99% para-h2. 7 S8

9 1 H NMR Spectrum, 500 MHz, acetone-d6 1 H NMR spectrum (45 pulse) Figure S4. 1H NMR spectrum (acetone-d6, 500 MHz, 22 C) spectrum of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) and p-h2 (4 atm). Average of 4 scans is shown using a 45 pulse. ( denotes acetone-d6). S9

10 13 C NMR Spectrum, 150 MHz, acetone-d6 13 C NMR spectrum C β C C=O C α 13 C NMR spectrum C β C α C C=O Figure S5. 1 scan 13 C NMR (acetone-d6, 150 MHz, 22 C) spectrum of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) and p-h2 (4 atm). Top spectrum (absolute mode not applied), bottom spectrum (absolute mode phasing) ( denotes acetone). S10

11 13 C NMR Spectrum, 150 MHz, acetone-d6 13 C NMR spectrum C β C C=O C α Figure S6. 1 scan 13 C NMR (acetone-d6, 150 MHz, 37 C) spectrum of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) and p-h2 (4 atm). ( denotes acetone). Scheme S1: Proposed intermediate for the observed greater Cβ position 13 C signal enhancement over the Cα position S11

12 13 C NMR Spectrum, 150 MHz, acetone-d6 13 C NMR spectrum C α C β C C=O Figure S7. 1 scan 13 C NMR (acetone-d6, 150 MHz, 37 C) spectrum of the hydrogenation of ethyl acrylate (64 mm) using [(dppb)rh(cod)]bf4 (9 mol%, 5.9 mm) and p-h2 (4 atm). ( denotes acetone). S12

13 13 C NMR Spectrum, 150 MHz, acetone-d6 C C=O C α C β C C=O C α C β C C=O C 1 C 2 C α C β Figure S8. 13 C NMR (acetone-d6, 150 MHz, 37 C) spectra (1 scan) of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) (middle, orange) [(dppb)rh(cod)]bf4 (9 mol%, 5.9 mm) (top, blue) and p-h2 (4 atm). 13 C{ 1 H} NMR spectrum (1 scan) of ethyl propionate (500 mm) (bottom, black). ( denotes acetone). Signal Enhancement calculation: The 13 C signal enhancement was calculated as a ratio by comparing the integration of the enhanced 13 C signal using the rhodium or cobalt catalyst to the thermal signal of a standard solution of ethyl propionate (500 mm) in acetone-d6. The calculation does not take into consideration the amount of substrate that was hydrogenated and assumes that 64 mm of ethyl propionate is hyperpolarized from the hydrogenation of ethyl acrylate in 1 scan. 13 C Position Signal Signal Enhancement equation Catalytic System Enhancement Factor SE = (integration PHIP)/(64 mm) (integration thermal)/(500 mm) C C=O C α C β ( Mes CCC)Co-py [(dppb)rh(cod)]bf S13

14 13 C NMR Spectrum, 150 MHz, acetone-d6 13 C NMR spectrum C β C C=O C sα C α 13 C NMR spectrum C β C C=O C sα C α Figure S9. 1 scan 13 C NMR (acetone-d6, 150 MHz, 37 C) spectrum of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)CoCl2py (9 mol%, 5.9 mm), NaHBEt3 (18 mol%) and p-h2 (4 atm) (top, teal). The 13 C NMR (acetone-d6, 150 MHz, 37 C) spectrum of the same reaction, but using ( Mes CCC)Co(η 2 -H2C=CHCOOEt)2 as the catalyst, is depicted in red (bottom). ( denotes acetone). The doublet at ppm corresponds to the hyperpolarized vinyl 13 C position, Csα, with 1 JCH = Hz (doublet).. Scheme S2: Proposed intermediate for the observed Csα position 13 C NMR signal enhancement (1,2-insertion, polarization transfer, followed by β-hydride elimination). S14

15 1 H NMR Spectrum (45 pulse), 500 MHz, acetone-d6 Proposed Co-H ppm # # # Figure S10. 1 H NMR (acetone-d6, 500 MHz, 20 C) spectra using a 45 pulse of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) and p-h2 (4 atm). The bottom spectrum (red) is the average of 4 transients collected first; each successive spectrum (green, teal, and purple: moving toward the top) is the average of the next 4 transients of the same reaction. Inset (top-right) shows the upfield region of the stacked NMR spectra. (# = olefin resonances, = acetone-d 6) S15

16 1 H NMR Spectrum (45 pulse), 500 MHz, THF-d ppm (Co-H) # # Figure S11. 1 H NMR (THF-d8, 500 MHz, 20 C) spectra using a 45 pulse of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) and p-h2 (4 atm). The bottom spectrum (red) is the average of 4 transients collected first; the top spectrum (green) is the average of the next 4 transients of the same reaction, which shows loss of polarization in the product 1 H NMR resonances. Inset (top-right) shows the upfield region of the stacked NMR spectra. (# = olefin, = THF-d8) S16

17 1 H NMR Spectrum (45 pulse), 500 MHz, benzene-d ppm (Co-H) # # # # ^ ^ ^ Figure S12. 1 H NMR (benzene-d6, 500 MHz, 20 C) spectra using a 45 pulse of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) and p-h2 (4 atm). The bottom spectrum (red) is the average of 4 transients collected first; the top spectrum (teal) is the average of the next 4 transients of the same reaction, which shows loss polarization. Inset (top-right) shows the upfield region of the stacked NMR spectra. ( = benzene-d6, # = olefin, ^ = mesityl methyl resonances of ( Mes CCC)Co(η 2 - H2C=CHCOOEt)2) Figure S13: Proposed intermediates for the antiphase 1 H NMR resonance in the upfield region (-4.40 to ppm) in Figures S10-S12. S17

18 1 H-OPSY NMR Spectrum, 500 MHz, acetone-d6 1 H-OPSY NMR spectrum 1 H-OPSY NMR spectrum (displayed in absolute mode) Figure S14. 1 H-OPSY NMR (acetone-d6, 500 MHz, 20 C) spectrum (top) of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) and p-h2 (4 atm). The same spectrum displayed in absolute mode (bottom). 4 transients were collected with a total run time of 20 seconds. S18

19 1 H-OPSY NMR Spectrum, 500 MHz, acetone-d6 H1sb Hsa H2sb H1sb Hsa H2sb Figure S15. 1 H-OPSY NMR (acetone-d6, 500 MHz, 20 C) spectra of the hydrogenation of ethyl acrylate (64 mm) using ( Mes CCC)Co-py (9 mol%, 5.9 mm) and p-h2 (4 atm). The bottom spectrum (red) is the average of 4 transients collected first; each successive spectrum (green, middle, and teal, top) is the average of the next 4 transients of the same reaction, showing the decay in product polarization as the p-h2 is consumed in the NMR tube. The resonances from 5.86 to 6.40 ppm corresponds to the hyperpolarized olefinic protons of ethyl acrylate. S19

20 1 H-OPSY NMR Spectrum, 500 MHz, acetone-d6 1 H-OPSY NMR spectrum 1H-OPSY NMR spectrum (displayed in absolute mode) Figure S16. 1 H-OPSY NMR (acetone-d6, 500 MHz, 20 C) spectrum (top) of the hydrogenation of ethyl acrylate (64 mm) using [(dppb)rh(cod)]bf4 (9 mol%, 5.9 mm) and p-h2 (4 atm). The same spectrum displayed in absolute mode (bottom). 4 transients were collected with a total run time of 20 seconds. S20

21 References: 1. A.B. Pangborn, M.A. Giardello, R. H. Grubbs, R. K. Rosen and F. J. Timmers, Organometallics, 1996, 15, Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. Organometallics 2010, 29, Wietz, I. S.; Rabinovitz, M. J. Chem. Soc. Perkin Trans. 1993, 1, Barbazanges, M.; Caytan, E.; Lesage, D.; Aubert, C.; Fensterbank, L.; Gandon, V.; Ollivier, C. Chem. Eur. J. 2016, 22, Ibrahim, A. D.; Tokmic, K.; Brennan, M. R.; Kim, D.; Matson, E. M.; Nilges, M. J.; Bertke, J. A.; Fout, A. R. Dalton Trans. 2016, 45, Tokmic, K.; Jackson, B. J.; Salazar, A.; Woods, T. J.; Fout, A. R. J. Am. Chem. Soc. 2017, 139, Tom, B. A.; Bhasker, S.; Miyamoto, Y.; Momose, T.; McCall, B. J. Producing and quantifying enriched para-h2. Rev. Sci. Instrum. 2009, 80, S21