Efficient H2 generation from formic acid using azole complexes in water

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1 Electronic Supplementary Information (ESI) Efficient H2 generation from formic acid using azole complexes in water Yuichi Manaka, a Wan-Hui Wang,* a,b Yuki Suna, a Hide Kambayashi, a James T. Muckerman, c Etsuko Fujita c and Yuichiro Himeda* a,b a National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5-2, -- Higashi, Tsukuba, Ibaraki, Japan himeda.y@aist.go.jp, ou-wanhui@aist.go.jp b JST, ACT-C, 4--8 Honcho, Kawaguchi, Saitama, Japan c Chemistry Department, Brookhaven National Laboratory, Upton, NY, 973-5, USA

2 General: All manipulations were carried out under an argon atmosphere. All aqueous solutions were degassed prior to use. H NMR spectra were recorded on a Bruker Avance 4 NMR spectrometer. 3 C NMR spectra were recorded on a Bruker Avance 5 spectrometer. Mass spectra were recorded on a Waters ZQ2 (ESI). Elemental analyses were carried out on an Eager 2 instrument. FT-IR spectra were recorded on a Perkin Elmer Spectrum One spectrometer. UV/Vis spectra were measured on a JASCO V-55. The ph values were measured on an Orion Model 3 STAR ph meter with a glass electrode after calibration to standard buffer solutions. The volume of evolved gas was determined by a gas meter (Shinagawa Corp., W-NK-5) and the generation rate was detected with a film flow meter (HORIBA STEC, SF-U). The formate concentration was monitored by a HPLC on an anion-exclusion column (Tosoh TSK gel SCX(H + )) with an aqueous phosphate solution (2 µm) as an eluent and a UV detector (λ = 2 ). The pressure in the reactor was measured by a pressure gauge (Swagelok S Model Transducer). [RhCp*Cl2]2 and [IrCp*Cl2]2 were purchased from Sterem Chemicals. Silver sulfate and ammonium chloride were purchased from JUNSEI Chemical. Glyoxal was purchased from Tokyo Chemical Industry. 2,2'-Bipyridine was purchased from Kanto Chemical. 2-(2-Pyridyl)benzimidazole was purchased from Wako. 2-(H-Imidazole-2-yl)pyridine and 2,2'-bis(4,5-dimethylimidazole) were purchased from Alderich. 2,2'-Bis(4,5-dimethylimidazole) was purified by washing with methanol, isopropanol and dichloromethane before use. 2-(H-Pyrazol-3-yl)pyridine was purchased from Alfa Aesar. [IrCp*(H2O)3][SO4] and [RhCp*(H2O)3][SO4] were prepared according to the literature procedure. 2,2'-Biimidazole was prepared according to the literature procedure. 2 Catalytic dehydrogenation of formic acid: Typically, a solution of complex ( µl, mm) was added to a deaerated ml sample of aqueous formic acid solution, and the mixture was stirred at the desired temperature. Bubbles were formed immediately after addition of the complex solution even at 4 C. While the gas generation was easily detected by a film flow meter in the early stage (i.e., less than minutes), the detection stability on a longer time scale is limited. Therefore, we used a gas meter (Shinagawa Corp., W-NK-5) for the determination of the total gas volume generated. The gas meter did not work in the early stage of gas generation because it requires an appropriate pressure change or a gas accumulation (approximately 5 ml). The induction period in Figure 2 is an artefact arising from the use of the gas meter. Dehydrogenation of formic acid in closed system: The experiments were performed in a 2 ml glass autoclave. A solution of complex 7 ( µl, µm) was added to a deaerated aqueous M formic acid solution (7 ml), and the mixture was stirred at 8 C. Procedure for catalytic hydrogenation of CO2/bicarbonate: A degassed aqueous 2 M KHCO3 solution ( ml) of the complex was put in a ml stainless steel reactor (ChemiStation, EYELA). The reactor was heated and then repressurized with MPa of CO2:H2 (:). After h, samples were removed and analyzed by HPLC. UV studies of acid base equilibrium: The ph of the solutions was adjusted by mixing the stock solutions of complex 7 (. mm) in.2 N H2SO4 and. N NaOH. The UV/Vis spectra were measured after testing the ph value. Synthesis of the complexes: Complex 3: An aqueous solution ( ml) of [IrCp*(H2O)3][SO4] (.3 mmol, 44 mg) and 2-(Himidazole-2-yl)pyridine (.3 mmol, 44 mg, eq.) was stirred at 3 C for 2 h. The solution was filtered. The filtrate was evaporated. Recrystallization from water gave yellow powder; yield (23 mg, 7 %). H

3 NMR (4 MHz, D2O): δ = 8.95 (dt, J = 5.6,. Hz, H), (m, 2H), 7.65 (ddd, J = 7.4, 5.6,.6 Hz, H), 7.56 (dd, J = 9.2,.6 Hz, 2 H),.63 (s, 5 H); 3 C NMR ( MHz, D2O): δ = 54.69, 52.37, 49.73, 44.4, 3.39, 29.9, 25.54, 24.45, 9.93,.75; IR (KBr): ῡ = 622, 474, 23, 79 cm - ; UV/Vis: λmax 272 ; ESI-MS (m/z): [M SO4 H2O H] + ; found, 472.; Elemental analysis calcd. for C8H24IrN3O5S + H2O: C, 34.83; H, 4.22; N, Found: C, 34.74; H, 4.38; N, Complex 4: This compound was prepared from [IrCp*(H2O)3][SO4] ( mmol, 478 mg) and 2-(Hpyrazol-3-yl)pyridine ( mmol, 45 mg, eq.) according to the procedure described for the preparation of complex 3 yield (469.7 mg, 8 %); H NMR (4 MHz, D2O): δ = 8.9 (d, J = 5.7 Hz, H), (m, 2 H), 8.4 (d, J = 2.9 Hz, H), 7.63 (ddd, J = 7.3, 5.7,.9 Hz, H), 7.9 (d, J = 2.9 Hz, H),.63 (s, 5 H); 3 C NMR ( MHz, D2O): δ = 55.9, 54.2, 53.75, 44.44, 39.22, 3.9, 25.62, 7.73, 9.54,.85; IR (KBr): ῡ = 65, 458, 92, 3, 782 cm - ; UV/Vis: λmax 3 (shoulder peak); ESI-MS (m/z): [M SO4 H2O H] + ; found, 472.; Elemental analysis calcd. for C8H24IrN3O5S + H2O: C, 34.83; H, 4.22; N, Found: C, 35.22; H, 4.39; N, Complex 5: This compound was prepared from [IrCp*(H2O)3][SO4] (.3 mmol, 43 mg) and 2-(2- pyridyl)benzimidazole (.3 mmol, 59 mg, eq.) according to the procedure described for the preparation of complex 3. yield (23.4 mg, 74 %); H NMR (4 MHz, D2O): δ = 9. (d, J = 5.4 Hz, H), 8.37 (d, J = 7.8 Hz, H), 8.3 (t, J = 7.9 Hz, H), (m, 3 H), (m, 2 H),.67 (s, 5 H); 3 C NMR ( MHz, D2O): δ = 56.7, 54.97, 49.74, 44.7, 4.9, 37.2, 32.7, 29.4, 28.44, 26.6, 9.22, 7.3, 9.52,.38; IR (KBr) : ῡ = 625, 459, 8, 27, 764 cm - ; UV/Vis: λmax 33 ; ESI-MS (m/z): [M SO4 H2O H] + ; found, 522.; Elemental analysis calcd. for C22H26IrN3O5S + H2O: C, 39.39; H, 4.2; N, Found: C, 39.52; H, 4.9; N, 6.. Complex 6: This compound was prepared from [IrCp*(H2O)3][SO4] (.5 mmol, 24 mg) and 2,2'- biimidazole (.5 mmol, 67 mg, eq.) according to the procedure described for the preparation of complex 3. yield (267 mg, 93 %); H NMR (4 MHz, D2O): δ = 7.52 (t, J =.6 Hz, 2 H), 7.4 (t, J =.6 Hz, 2 H),.67 (s, 5 H); 3 C NMR ( MHz, D2O): δ = 43.52, 29.77, 24.2, 9.4,.2; IR (KBr): ῡ = 633, 9, 2, 62 cm - ; UV/Vis: λmax 289 ; ESI-MS (m/z): [M SO4 H2O H] + ; found, The analogous complex [IrCp*(bis-IM)Cl] + was reported. 3 Complex 7: This compound was prepared from [IrCp*(H2O)3][SO4] (.23 mmol, 9 mg) and 2,2'- bis(4,5-dimethylimidazole) (.23 mmol, 43.3 mg, eq.) according to the procedure described for the preparation of complex 3. yield (93.3 mg, 65 %); H NMR (4 MHz, D2O): δ = 2.28 (s, 6 H), 2.8 (s, 6 H),.57 (s, 5 H); 3 C NMR ( MHz, D2O): δ = 4.86, 36., 29.6, 9.7, 4.57,.9; IR (KBr): ῡ = 593, 93, 4, 799 cm - ; UV/Vis: λmax 34 ; ESI-MS (m/z): [M SO4 H2O H] + ; found, 57.; Elemental analysis calcd. for C2H3IrN4O5S: C, 38.2; H, 4.95; N, Found: C, 38.7; H, 4.78; N, Complex 8: A aqueous solution ( ml) of [RhCp*(H2O)3][SO4] (.3 mmol, 7 mg) and 2,2'-bis(4,5- dimethylimidazole) (.3 m mol, 57 mg, eq.) was stirred at 3 C for 2 h. The solution was filtered. The filtrate was evaporated. Recrystallization from water gave orange powder; yield (4 mg, 87 %); H NMR (4 MHz, D2O): δ = 2.3 (s, 6 H), 2.8 (s, 6 H),.59 (s, 5 H); 3 C NMR ( MHz, D2O): δ = 39.23, 36.22, 29.62, 98.96, 4.62,.8; IR (KBr): ῡ = 622, 43, 4 cm - ; UV/Vis: λmax 37 ; ESI-MS (m/z): [M SO4 H2O H] + ; found, 427.; Elemental analysis calcd. for C2H3RhN4O6S: C, 43.; H, 5.6; N,.. Found: C, 42.8; H, 5.68; N, 9.65.

4 References:. W.-H. Wang, J. F. Hull, J. T. Muckerman, E. Fujita, T. Hirose and Y. Himeda, Chem.-Eur. J., 22, 8, J. R. Cho, S. G. Cho, E. M. Goh, J. K. Kim, United States Patent, Mar. 3, 24, US 6,73,63 B2 3. R. Ziessel, M.-T. Youinou, F. Balegroune and D. Grandjean, J. Organomet. Chem., 992, 44, 43-54

5 (a) Abs (b).5 pka = 8.8 pka 2 =.4 Abs ph Fig. S. (a) The UV/Vis spectrum of 7 measured with ph varied from 2.5 to 2.5. (b) Absorbance changes at 3, 35, 33 and 375 as a function of ph change.

6 Table S. Dehydrogenation of formic acid/formate at ph 3.5. Catalyst Conc. of catalyst TOF a Time Minimum Conversion (mm) (h - ) (h) TON (%) ,64 5 4, ,58 4 5, 5 8 b Reaction conditions: 6 C, ml of M aqueous sodium formate/formic acid (/). a The average value of the first min. b Used 2 M aqueous formic acid. Table S2. Dehydrogenation of formic acid using 7 under various catalyst concentrations and formic acid concentrations. Conc. of catalyst (mm) Conc. of formic acid (M) TOF a (h - ) Time (h) Minimum TON Conversion (%). 7,2 2,.2 6,2.3 5,.5 6,4.5 2,. 2 7,4 7 2,. 4 7,9 2 4, > , ,5 3, Reaction conditions: 6 C, ml of aqueous formic acid. a The average value of the first min.

7 Table S3. Hydrogenation of CO2/bicarbonate. Catalyst Conc. of catalyst Temperature TOF for h (mm) ( C) (h - ) Reaction conditions: ml of degassed 2 M KHCO3 solution (ph 8.6), MPa H2/CO2 (/).

8 UV/Vis spectrum of solution of complex 3-8 at room temperature in water:.2 Complex 3.4 Complex Complex 5 2 Complex Complex 7.2 Complex