An isolated seven-coordinate Ru(IV) dimer complex with [HOHOH] bridging. ligand as an intermediate for catalytic water oxidation

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1 Supporting Information An isolated seven-coordinate Ru(IV) dimer complex with [HOHOH] bridging ligand as an intermediate for catalytic water oxidation Lele Duan, Andreas Fisher, Yunhua Xu, and Licheng Sun* Department of Chemistry, School of Chemical Science and Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden. Experimental Section General Considerations: Ru(DMSO) 4 Cl 2 and 2,2 -bipyridine-6,6 -dicarboxylic acid (LH 2 ) were prepared according to the literature methods 1,2. All other chemicals are commercially available and all solvents are reagent grade. The NMR spectra were recorded with either 400 MHz or 500 MHz of Bruker Avance spectrometer. High resolution mass spectrometry measurements were performed on a Q-Tof Micro mass spectrometry. Electronic absorption spectra of solutions in CH 3 CN and kinetic measurements were measured with a PerkinElmer Lambda 750 UV-vis spectrophotometer. Cyclic voltammetric (CV) measurements were carried out with an Autolab potentiostat with an GPES electrochemical interface (Eco Chemie), using a glassy carbon disk (diameter 3 mm) as the working electrode, a platinum spiral in a compartment separated from the bulk solution by a fritted disk as counter-electrode. The reference electrode was a non-aqueous Ag/Ag + electrode (0.1 M AgNO 3 in acetonitrile). The electrolyte used was 0.1 M Bu 4 NPF 6 in dichloromethane. The oxygen evolution was recorded with a Clark-type oxygen electrode (Hansatech Instruments, Oxygraph OXYG1 and DW1/AD unit). A degassed acetonitrile solution of 1 (50 μl, 80 μm, 4 nmol) was injected using a syringe through a septum into 2 ml of aqueous CF 3 SO 3 H solution (ph 1.0) containing 30 mg of Ce(NH 4 ) 2 (NO 3 ) 6 purged with argon for 10 min. The generated O 2 was measured and recorded vs. time by this system. Synthesis: S1

2 Ru(II)L(pic) 2 (1). A mixture of 2,2 -bipyridine-6,6 -dicarboxylic acid (LH 2 ) (244 mg, 1.0 mmol), Ru(DMSO) 4 Cl 2 (484 mg, 1.0 mmol) and NEt 3 (0.8 ml) in methanol (20 ml) was degassed with N 2 and refluxed overnight. The color of this solution changed to dark red from yellow. An excess of 4-picoline (2 ml) was added and the reflux was continued for additional 4 h. The solvent was removed and the residues were washed by diethyl ether to get rid of excess 4-picoline. The rest oily part was dissolved in CH 2 Cl 2 and washed with water to remove the triethylamine hydrochloric salt. The organic layer was dried over MgSO 4 overnight and the solvent was evaporated to afford the crude product. After purification by column chromatography on Al 2 O 3 using dichloromethane-methanol (100:2, v/v) as eluents, complex 1 was obtained as a red solid (160 mg, 30%). 1 H NMR, COSY, 13 C NMR and HSQC spectra of complex 1 were presented in Figures S11 S14. 1 H NMR (500 MHz, CDCl 3 ): δ = (m, 4H), 7.66 (t, J = 7.0, 8.0 Hz, 2H), 7.59 (d, J =5.5 Hz, 4H), 6.81 (d, J = 5.0 Hz, 4H), 2.20 (s, 6H). 13 C NMR (500 MHz, CDCl 3 ): , , , , , , , and UV-vis: λ max (acetonitrile)/nm 309 (ε/dm 3 mol 1 cm ), 341 (10496), 470 (3133) and 502 (2914). HRMS (ESI): m/z + = (M + H + ), calcd: Elemental analysis: Calcd. for C 24 H 20 N 4 O 4 Ru: C 54.44, H 3.81, N 10.58%; Found: C 54.10, H 3.82, N 10.31%. μ-(hohoh)[ru(iv)l(pic) 2 ] 2 [PF 6 ] 3 2H 2 O (2). To complex 1 (7.7 mg, mmol) in a test tube was added acetonitrile (0.2 ml) and triflic acid aqueous solution (ph = 1.0, 3 ml). Then ammonium cerium nitrate (500 mg, 0.92 mmol) was gradually added under stirring. The color of the above solution changed from dark red to light yellow accompanied by evolving of large amount of bubbles. After addition of excess NH 4 PF 6 aqueous solution, the mixture was kept stationary over night to obtain dark red precipitate. The dark red single crystals of complex 2 suitable for X-ray analysis were obtained from these precipitate. Filtration and wash with water and THF gave a mixture (6.5 mg) of complexes 2 and [Ru(III)L(pic) 2 ] + species. 1 H NMR for 2 (400 MHz, CD 3 CN, 40 o C): δ = 8.84 (d, 2H), 8.56 (t, 2H), 8.13 (d, 2H), 7.46 (s, 4H), 7.10 (s, 4H), 2.28 (s, 6H). HRMS (ESI) for [Ru(IV)L(pic) 2 (OH)] + : m/z + = , calcd: References S2

3 (1) Dulière, E.; Devillers, M.; Marchand-Brynaert, J. Organometallics 2003, 22, (2) Donnici, C. L.; Filho, D. H. M.; Moreira, L. L. C.; Reis, G. T. d.; Cordeiro, E. S.; Oliveira, I. M. F. d.; Carvalho, S.; Paniago, E. B. J. Braz. Chem. Soc. 1998, 9, Crystallographic data. Crystal structure determinations: Diffraction data were collected on a Bruker-Nonius KappaCCD using MoKα. Data of 2 were collected at 173K in order to prevent decomposition of the solvate. Structure models were obtained using direct methods. Hydrogen atoms that are part of water molecules or OH were located from the Fourier map. The remaining H atoms could be located from the Fourier map. However, since the X H distances did not refine to satisfactory values, the H atoms were placed at calculated positions and refined using a riding model. The central H atom in the structure of 2 was placed at the centre of the HOHOH group, which is a special position (inversion centre, Wyckoff position 1d). The structure determination of 1 was impaired by turbostratic disorder along b. This was accounted for during data processing, However, in spite of numerous attempts to tune the integration parameters, the rejection rate remained rather high, yielding a data completeness of only 94%. 1: a=821.40(6), b=1027.3(12), c=1511(4) pm; α=74.76(13)º, β=80.9(2)º, γ=73.56(8)º; V=1169(4) 10 6 pm 3 ; triclinic, P 1, Z=2, T=299 K, 3856 independent reflections, 298 L.S. parameters, R=0.082 (all reflections), wr 2 =0.145, S=1.14. CCDC number: : a=816.8(9), b=1328.4(4), c=1451.3(4) pm; α=79.70(2)º, β=87.324(13)º, γ=83.863(15)º; V=1548.5(7) 10 6 pm 3 ; triclinic, P 1; Z=1, T=173 K; 7067 independent reflections, 448 L.S. parameters, R=0.063 (all reflections), wr 2 =0.107, S=1.01. CCDC number: S3

4 Figure S1. Cyclic voltammogram of complex 1 in dichloromethane. Figure S2. Oxygen evolution by complex 1 (2 x 10 6 M) in 2 ml of aqueous triflic acid solution (ph 1.0) using Ce(IV) (2.75 x 10 2 M) as oxidant, as well as the background curve. S4

5 Figure S3 shows that the decay of Ce(IV) is zero order with respect to Ce(IV) under catalytic condition. The reaction rates observed (k obs ) under various conditions were obtained according to the data of Figure S4. Plot of k obs vs. concentration of complex 1 gives a non-linear relationship (Figure S5). However, k obs vs. [1] 2 does lead to a linear relationship (Figure S6). Therefore, the loss of Ce(IV) is second order with respect to complex 1 with a second order rate constant of M -1 s -1. This indicates that the catalytic water oxidation by complex 1 involves a binuclear process. For details about these calculations, please see the supporting information of Meyer s paper (Concepcion, J. J.; Jurss, J. W.; Templeton, J. L.; Meyer, T. J. J. Am. Chem. Soc. 2008, 130, ) Figure S3. Absorption change of Ce(IV) monitoring at 360 nm after addition of complex 1 (4 μm) into Ce(IV) aqueous solution (1.5 mm, 1.13 mm and 0.75 mm, ph 1.0). No data was collected in the first ca. 5 seconds due to the operation for injecting catalyst and shaking the solution. S5

6 Figure S4. Absorption change of Ce(IV) monitoring at 360 nm after addition of complex 1 (1 μm, 2 μm, 4 μm and 6 μm) into Ce(IV) aqueous solution (1.5 mm, ph 1.0). No data was collected in the first ca. 5 seconds due to the operation for injecting catalyst and shaking the solution. Figure S5. Plot of k obs vs. concentration of complex 1. S6

7 Figure S6. Plot of k obs vs. [1] 2. The kinetics for Ce(IV) decay are second order with respect to the concentration of complex 1. The second order rate constant is M -1 s -1. S7

8 Figure S7. 1 H NMR spectrum (500 MHz) of the orange precipitate in CD 3 CN at room temperature. S8

9 Figure S8. 1 H NMR spectrum (500 MHz) of the dark red precipitate in CD 3 CN at room temperature. S9

10 Figure S9. Illustration of the O H O hydrogen bonding network in the crystal structure of complex 2 (Pic ligands and hydrogen atoms except the H O type are omitted for clarity). Figure S10. Oxygen evolution by the dark red precipitate (0.003 mg in 30 μl of acetonitrile) in 2 ml of triflic acid aqueous solution (ph = 1.0) using Ce(IV) ammonium nitrate (30 mg) as oxidant. The curve was recorded by Clark-type oxygen electrode. S10

11 Figure S11. 1 H NMR (CDCl 3, 500 MHz) spectrum of the complex 1. Figure S12. COSY (CDCl 3, 500 MHz) spectrum of the complex 1. S11

12 Figure S C NMR (CDCl 3, 500 MHz) spectrum of the complex 1. Figure S14. HSQC (CDCl 3, 500 MHz) spectrum of the complex 1. S12