ionic liquids si new version 5 10 12 - pnas › content › suppl › 2012 › 06 › 07 ›...

An acidic ionic liquidwater aolution as both medium and proton source for

electrocatalytic H2 evolution by [Ni(P2N2)2]2+ complexes

Douglas H Pool Michael P Stewart Molly OrsquoHagan Wendy J Shaw John A S Roberts R

Morris Bullock and Daniel L DuBois

johnrobertspnnlgov danielduboispnnlgov

Center for Molecular Electrocatalysis Chemical and Materials Sciences Division PO Box

999 K2-57 Pacific Northwest National Laboratory Richland Washington 99352

Supporting Information

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Contents

Table S1 Electrochemical data for 5 in various solvents

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Figure S1 Cyclic voltammograms of 5 in benzonitrile and acetonitrile

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Figure S2 31P NMR spectra of 5 in [(DBF)H]NTf2 with varying mole fractions of DBF

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Figure S3 Cyclic voltammograms of [(DBF)H]NTf2 (χH2O from 0 to

075) and with 5 added (χH2O = 072)

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Text S1 Cyclic Voltammetry in [(DBF)H]NTf2 Effects of Added Water on Viscosity

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Figure S4 A Cyclic voltammograms of ferrocene in [(DBF)H]NTf2 with χH2O from 0 to 075 B Plot of ipox

2 vs χH2O for ferrocene oxidation

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Figure S5 icat vs [5] in [(DBF)H]NTf2 (χH2O = 072)

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Figure S6 icat for 6‐9 as a function of catalyst concentration in [(DBF)H]NTf2 (χH2O = 072)

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Figure S7 Cyclic voltammograms of 6‐9 in [(DBF)H]NTf2 (χH2O = 072)

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Figure S8 Cyclic voltammograms of 10 in [(DBF)H]NTf2 (χH2O from 0 to

077)

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Figure S9 31P1H NMR spectra of 5 6 and 10 in neat [(DBF)H]NTf2

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Figure S10 Chronopotentiograms showing the open circuit potential of a frit‐separated AgClAg reference electrode vs a Pt wire in [(DBF)H]NTf2 under H2 with χH2O ranging from 0 to 074

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Figure S11 Open circuit potential (OCP) vs Fc+Fc as a function of A [H2O] B ln[H2O]

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Figure S12 A Cyclic voltammograms of 11 and ferrocene in [(DBF)H]NTf2 (χH2O = 072) B Plot of ip for the Ni(III) reduction peak

current vs υ12

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Text S2 Supplementary Experimental Information

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Table S1 Electrochemical data for 5 in various solvents with 01‐02 M NBu4PF6 1 mm glassy carbon working electrode υ = 005 V sminus1

Ni(III) Ni(I0)

solvent E12 (V) ΔEp (mV) E12 (V) ΔEp (mV)

MeCN minus084 71 irrev

PhCN minus081 59 minus104 58

DBF minus082 70 minus104 66

Referenced to the Fc+Fc couple

Figure S1 Cyclic voltammograms A of 5 (1 mM) in benzonitrile (01 M NBu4PF6) and B of 5 (09 mM) in acetonitrile (01 M NBu4PF6) 1 mm glassy carbon working electrode scan rate υ = 005 V sminus1


Figure S3 Cyclic voltammograms of [(DBF)H]NTf2 (χH2O from 0 to 075) and with 5

added (051 mM χH2O = 072) 1 mm glassy

carbon working electrode υ = 01 V sminus1 Text S1 Cyclic Voltammetry in [(DBF)H]NTf2

Effects of Added Water on Viscosity Solute diffusion coefficients are roughly inversely proportional to solution viscosity(1) The viscosity of [(DBF)H]NTf2 decreases with increasing water content and cyclic voltammograms of ferrocene in [(DBF)H]NTf2 (Figure S4A) show the expected increase in Fc+Fc redox currents The plot of ipox

2 vs χH2O

(Figure S4B ipox is the ferrocene oxidation peak current) shows the dependence of viscosity on water content since ipox

2 increases in proportion to DFc the diffusion coefficient of ferrocene (equation [4] of the main text)(2)

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Similarly icat2 increases in proportion to Dcat

the catalyst diffusion coefficient (equation [3]) Changes in viscosity also affect Dcat and the increase in current with 5 as water is added (Figure 8) is due in part to this effect (3) However complex 5 is diprotic at low χH2O and

is deprotonated as water is added The state of protonation affects the shape charge and charge distribution and thus diffusion Therefore viscosity effects on the diffusion of ferrocene (ipox) and complex 5 (icat) are best compared under conditions where 5 is aprotic This is shown in Figure 8 with χH2O from 064 to 075

ipox increases from 146 to 172 μA whereas icat increases from 152 to 358 μA much more than expected due to viscosity changes so the kinetics of catalysis must also be changing possible reasons are outlined in the Discussion

Figure S4 A Cyclic voltammograms of ferrocene (initially 19 mM) in [(DBF)H]NTf2 with χH2O from 0 to 075 1 mm glassy carbon working

electrode υ = 01 V sminus1 B Plot of ipox2 vs χH2O for

ferrocene oxidation

Figure S5 Observed icat vs [5] in [(DBF)H]NTf2 (χH2O = 072) Open circles ([5] gt 1 mM) were not

used in the linear regression

Figure S6 Observed catalytic currents icat for [Ni(P2

PhN2C6H4X)2]

2+ species 6‐9 (X shown) as a

function of catalyst concentration in [(DBF)H]NTf2 (χH2O = 072) 1 mm glassy carbon

working electrode υ = 01 V sminus1

Figure S7 Cyclic voltammograms of [Ni(P2

PhN2C6H4X)2]

2+ species in [(DBF)H]NTf2 (χH2O

= 072) X = H (6 041 mM) OMe (7 042 mM) CH2P(O)(OEt)2 (8 041 mM) Br (9 039 mM) 1 mm glassy carbon working electrode υ = 01 V sminus1

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PhN2C6H4CF3)2]

2+ (10 12 mM) in

[(DBF)H]NTf2 (χH2O from 0 to 077) 1 mm glassy

carbon working electrode υ = 01 V sminus1

Figure S9 31P1H NMR spectra of 5 (scaled times 100) 6 (scaled times 100) and 10 in neat [(DBF)H]NTf2 [Ni

2+] asymp 20 mM

Figure S10 Chronopotentiograms showing the open circuit potential of a frit‐separated AgClAg reference electrode containing MeCN (01 M NBu4PF6) vs a Pt wire in [(DBF)H]NTf2 under 1 atm H2 (not referenced to Fc

+Fc) A with no added water B with χH2O = 072 C

with χH2O ranging from 0 to 074

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Figure S11 Open circuit potential (OCP) vs Fc+Fc as a function of A [H2O] B ln([H2O]) For each plot linear regressions use the data shown with solid blue circles only The regression equations given were used to interpolate OCP values appearing in Table 3 and are presented without further interpretation Solid red circles show the interpolated values using the OCP vs [H2O] linefit for [H2O] lt 5 and the OCP vs ln([H2O]) linefit for [H2O] ge 5

Figure S12 A Cyclic voltammograms of a solution of 11 (055 mM) and ferrocene (21 mM) in [(DBF)H]NTf2 (χH2O = 072) showing the

Ni(III) redox couple (blue trace) and both the Ni (III) couple and the subsequent irreversible reduction of electrode‐generated Ni(I) 1 mm glassy carbon working electrode υ = 005 V sminus1 B Plot showing the linear dependence of ip for the Ni(III) reduction peak current on υ12 demonstrating diffusion control for this reduction wave in [(DBF)H]NTf2 (χH2O = 072)


Materials and Methods Materials were handled using standard Schlenk techniques or in an inert atmosphere glove box Ether (Et2O Burdick amp Jackson) tetrahydrofuran (THF Alfa-Aesar anhydrous non-stabilized) and acetonitrile (MeCN Alfa-Aesar anhydrous amine-free) were purified by sparging with nitrogen and passage through neutral alumina and ethanol (EtOH Pharmco-Aaper absolute anhydrous) was purified by sparging with nitrogen and passage through calcium sulfate using a solvent purification system (PureSolvtrade Innovative Technologies Inc) Benzonitrile (PhCN Aldrich anhydrous) was used as received Dimethylformamide (DMF Burdick amp Jackson) was dried over activated 4Aring molecular sieves NN-di-n-butylformamide (DBF Alfa 99) was filtered through activated alumina before use Water was dispensed from a Millipore MilliQ purifier and sparged with nitrogen Hydrogen (Matheson UHP 99999) was purified by passage through a wateroxygenhydrocarbon trap

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(Restek 22464) and an indicating wateroxygen trap (Restek 22474) and fed through the glove box wall Acetonitrile-d3 (CD3CN Cambridge Isotope Laboratories 995 D) was vacuum distilled from P2O5 Chloroform-d (CDCl3 Cambridge Isotope Laboratories 995 D) was used as received Dichloromethane-d2 (CD2Cl2 Cambridge Isotope Laboratories 995 D) was distilled from calcium hydride Tetraethylammonium tetrafluoroborate (NEt4BF4 Alfa-Aesar) was recrystallized from hot EtOH and dried under vacuum Trifluoromethanesulfonic acid (HOTf Aldrich 99) was used as received and handled under nitrogen Ferrocenium tetrafluoroborate (Aldrich) was recrystallized from water and dried under vacuum Ferrocene (Aldrich) and bis(trifluoromethanesulfonyl)amine (HNTf2 Acros 99) were sublimed under vacuum before use Phenylphosphine (Strem 99) paraformaldehyde (Aldrich 95) 4-n-hexylaniline (Alfa 98) and electrochemical grade tetrabutylammonium hexafluorophosphate (NBu4PF6 Fluka ge 990) were used as received [(DMF)H]OTf(4) [Ni(dppb)2] (BF4)2(5) [Ni(PPh

2NPh

2)2][BF4]2(6) and [Ni(PPh2N

C6H4X2)2][BF4]2 (X = CH3 OMe CH2P(O)(OEt)2 Br and CF3)(7)

were prepared by literature methods

NMR Instrumentation and Methods NMR experiments were run on Varian NMR systems at 300 or 500 MHz 1H frequency operated with a VNMRS console Direct detect dual-band or OneNMR probes

were used Typical 31P 90deg pulses were sim8 μs and 31P NMR spectra were collected with 1H decoupling

The 1H chemical shifts were internally calibrated to the proton-containing impurity of the deuterated solvent CD2HCN (193 ppm) and CDHCl2 (532 ppm) or externally referenced to TMS for [(DBF)H]NTf2 solutions 31P1H NMR spectra were externally referenced to phosphoric acid 19F NMR spectra were externally referenced to 005 PhCF3 in C6D6 (minus6372 ppm) 13C1H NMR spectra were referenced to the NMR solvent CD3CN (139 ppm -CD3) CDCl3 (7723 ppm) or externally referenced to TMS for [(DBF)H]NTf2 solutions 31P1H NMR spectra with [(DBF)H] NTf2 as solvent were acquired using at least 1024 transients

NMR Diffusion Measurements A 300 MHz 1H frequency Varian NMRS system equipped with a Performa II gradient generator was used for all diffusion experiments The probe was a direct dual band probe Diffusion coefficients for 5 and 11 (both ~20 mM) in CD3CN (01 M NBu4PF6) were measured by by 31P PGSE giving D = 87 times 10minus6 and 10 times 10minus5 cm2 sminus1 respectively The diffusion coefficient for 5 was also determined by observing ligand P-CH2-N resonances using 1H PGSE giving 77 times 10minus6 cm2 sminus1 These results demonstrate good agreement between NMR and electrochemical diffusion measurements in MeCN (01 M NBu4PF6)

Elemental Analyses Elemental analysis was performed by Atlantic Microlab Inc using V2O5 as a combustion catalyst

Electrochemical Methods Cyclic voltammetry experiments were conducted using CH Instruments 620D or 660C potentiostats using a standard three-electrode cell The working electrode was a 1 mm glassy carbon disk (Cypress Systems) cleaned between scans using a polishing pad (Buehler MicroClothreg) with either an aqueous alumina slurry (Gamal grade B Fisher Scientific) followed by

rinsing with 18 MΩ water for experiments outside of the glove box or using Buehler MetaDireg II 025 m diamond paste with 18 MΩ water as lubricant followed by rinsing with MeCN for experiments inside the glovebox A 3 mm diameter glassy carbon rod from Alfa Aesar was used as an auxiliary electrode The reference electrode was a bare platinum wire (Alfa Aesar) and ferrocene was added to the analyte

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solutions as an internal standard unless otherwise noted Controlled potential coulometry experiments were performed using a CH Instruments 1100A potentiostat

Working Electrode Surface Area Determination The surface area of the working electrode (A in equations [3] and [4] of the main text) required to calculate turnover frequencies for catalysis in [(DBF)H]NTf2 was determined by chronoamperometry using a 0978 mM solution of ferrocene in MeCN (01 M NBu4PF6) with an anodic potential step traversing the Fc+Fc couple Data from t = 0038 to 02 s were plotted using the Cottrell equation Taking 24 times 10minus5 cm2sminus1 as the diffusion coefficient for ferrocene(8) the calculated surface area was 954 times 10minus3 cm2

Preparation of 15‐di(4‐n‐hexylphenyl)‐37‐diphenyl‐15‐diaza‐37‐diphosphacyclooctane

(P2PhN2

C6H4‐hex) Phenylphosphine (186 g 169 mmol) and paraformaldehyde (113 g 376 mmol) were

combined in 40 mL of EtOH under nitrogen and heated for 5 h starting at 60 degC for the first h 70 degC for

the second h and 75 degC for the remaining time during which the reaction mixture became clear 4-n-

hexylaniline (33 mL 171 mmol) was added dropwise to the stirring reaction mixture White precipitate had formed after one hour and the mixture was allowed to cool unstirred for 16 h affording a white solid having approximately the same volume as the initial reaction solution The solid was washed three times with 20 mL of EtOH and dried in vacuo The product was recovered in a glove box as a cotton-like mass of fine needles giving 4261 g (6842 mmol 81) Crystals for analysis were obtained from THFEt2O Anal Calc for C40H52N2P2 C 7714 H 842 N 450 Found C 7740 H 853 N 456 1H NMR

(CD2Cl2 500 MHz 25 degC) δ 762 (m 4 H Ph) 747 (m 6 H Ph) 702 (d J = 9 Hz 4 H Ph) 663 (d J =

9 Hz 4 H Ph) 441 (m 4 H P-CH2-N) 402 (dd J = 155 Hz 4 H P-CH2-N) 246 (t 8 Hz 4 H N-CH2-CH2-) 152 (m 4 H N-CH2-CH2-) 127 (m 12 H N-(CH2)2-(CH2)3-) 086 (t J = 7 Hz 6 H -CH3) 31P1H NMR (CD2Cl2 2023 MHz 25 degC) δ minus514

Preparation of [Ni(P2PhN2

C6H4‐hex)2](BF4)2 (5) P2PhN2

C6H4-hex (0428 g 0688 mmol) and

[Ni(NCMe)6](BF4)2frac12 MeCN (0168 g 0337 mmol) were combined in 15 mL of MeCN immediately affording a dark red solution on stirring After stirring for 2 d the solvent was removed in vacuo and 15 mL of Et2O was added Stirring for 2 d afforded a fine pink suspension The powder was collected on a frit washed with 20 mL of Et2O and dried in vacuo for 0402 g (0272 mmol 81) Anal Calc for C80H104N4B2F8NiP4 C 6501 H 709 N 379 Found C 6477 H 699 N 399 1H NMR (CD3CN

500 MHz 25 degC) δ 738 (t J = 7 Hz 4H Ph) 730 (m 8H Ph) 721 (d J = 9 Hz 8 H Ph) 714 (m 16

H Ph) 418 (d J = 14 Hz 8 H P-CH2-N) 386 (d J = 14 Hz 8 H P-CH2-N) 258 (t 8 Hz 8 H N-CH2-CH2-) 158 (m 8 H N-CH2-CH2-) 129 (m 24 H N-(CH2)2-(CH2)3-) 085 (t J = 7 Hz 12 H -CH3) 31P1H NMR (CD3CN 2023 MHz 25 degC) δ 534 31P1H NMR (DBF 2023 MHz 23 degC) δ 61

Cyclic Voltammetry of 5 in MeCN PhCN and DBF Stock solutions of ferrocene (00207 g 0111 mmol) in 50 mL of MeCN and 5 (00165 g 00112 mmol) in 10 mL of MeCN were prepared using

volumentric flasks and aliquots of each (50 and 100 L respectively) were added to four 3 mL conical vials The solvent was allowed to evaporate 10 mL of either [(DBF)H]NTf2 or a solution of NBu4PF6 (02 M) in MeCN PhCN or DBF was then added to each vial The mixtures were stirred and cyclic voltammograms were recorded using a frit-separated AgClAg reference electrode

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Electrocatalytic hydrogen production with 5 in MeCN A cyclic voltammogram was collected with a 20 mL solution of 5 (090 mM) NBu4PF6 (01 M) and ferrocene (le 3 mM) in MeCN and ip for the

Ni(III) reduction was noted (102 μA υ = 005 V sminus1) Three aliquots (2 times 200 L 450 L) of [(DMF)H]OTf (0963 M MeCN) were added and a cyclic voltammogram was obtained after each Catalytic current enhancements icatip were 404 469 and 440 respectively with ip corrected for dilution

using the ferrocene oxidation current Aliquots of H2O were added (25 L 5 times 10 L) and a cyclic voltammogram collected after each (υ = 005 V sminus1) giving icatip = 728 774 812 826 836 874 and 836

Preparation of [(DBF)H]NTf2 In the glove box DBF (25102 g 015963 mol) was weighed out in a 100 mL round bottom flask with a stirbar HNTf2 (45187 g 016073 mol) was added in six portions After the first addition heat was evolved and a white vapor formed above the reaction mixture which was then stoppered The mixture was allowed to stir until the white vapor was no longer visible before the next additon After stirring overnight DBF (0174 g 000111 mol) was added to bring the mole ratio DBFHNTf2 to 11 and the mixture was stirred for 24 h affording a pale yellow oil 1H NMR (CD3CN

300 MHz 25 degC) δ 1181 (1H C=O-H) 824 (1H C(O-H)H) 354 (t J = 74 Hz 2 H N-CH2-) 351 (t J

= 76 Hz 2 H N-CH2-) 164 (m 4 H N-CH2-CH2-) 132 (m 4 H N-CH2-CH2-CH2-) 093 (t J = 7 Hz

3 H -CH3) 092 (t J = 7 Hz 3 H -CH3) 13C1H NMR (CD3CN 75 MHz 25 degC) δ 1652 (C=O-H+)

1210 (q J = 321 Hz -CF3) 532 (N-CH2-) 476 (N-CH2-) 301 (N-CH2-CH2-) 289 (N-CH2-CH2-) 205

(N-CH2-CH2-CH2-) 201 (N-CH2-CH2-CH2-) 138 (-CH3) 19F NMR (CD3CN 282 MHz 25 degC) δ minus807

1H NMR (CDCl3 300 MHz 25 degC) δ 1255 (1H C=O-H) 841 (1H C(O-H)H) 359 (t J = 8 Hz 2 H N-

CH2-) 357 (t J = 8 Hz 2 H N-CH2-) 169 (m 4 H N-CH2-CH2-) 138 (m 4 H N-CH2-CH2-CH2-)

097 (t J = 7 Hz 6 H -CH3) 13C1H NMR (CDCl3 75 MHz 25 degC) δ 1644 (C=O-H+) 1197 (q J =

321 Hz -CF3) 527 (N-CH2-) 471 (N-CH2-) 296 (N-CH2-CH2-) 285 (N-CH2-CH2-) 199 (N-CH2-

CH2-CH2-) 194 (N-CH2-CH2-CH2-) 135 (-CH3) 134 (-CH3) 13C1H NMR (neat 75 MHz 25 degC) δ

1640 (C=O-H+) 1192 (q J = 321 Hz -CF3) 526 (N-CH2-) 470 (N-CH2-) 291 (N-CH2-CH2-) 281 (N-CH2-CH2-) 195 (N-CH2-CH2-CH2-) 190 (N-CH2-CH2-CH2-) 127 (-CH3) 126 (-CH3)

Preparation of [(DBF)H]NTf2 Solutions Due to its substantial viscosity and corrosiveness [(DBF)H]NTf2 was generally handled using pipettes and dispensed by mass Volumes were calculated from the density of [(DBF)H]NTf2 (determined for each batch for a typical batch ρ = 135 g mLminus1 averaged over six measurements with a standard deviation of 0006 g mLminus1) Solutes were weighed out in a 3 mL conical vial and [(DBF)H]NTf2 was added until the mass corresponding to the desired volume was obtained The mixtures were then stirred until no solids could be seen

Addition of H2O to 5 in [(DBF)H]NTf2 08 mL of 5 (22 mM in [(DBF)H]NTf2) was added to an NMR

tube and an initial 31P NMR spectrum was obtained H2O (20 L) was added inside the glove box the contents of the tube were mixed by repeated inversion and another spectrum was acquired This process

was repeated for seven more 20 L additions

Addition of DBF to 5 in [(DBF)H]NTf2 08 mL of an 18 mM solution of 5 in [(DBF)H]NTf2 was added

to an NMR tube and an intial 31P NMR spectrum was obtained DBF (50 L) was added inside the glove

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box the contents of the tube were mixed by repeated inversion and another spectrum was acquired This

process was repeated for three more 50 L additions

Stability of 5 in [(DBF)H]NTf2 A 53 mM solution of 5 in [(DBF)H]NTf2 was prepared in air and transferred to an NMR tube 31P NMR spectra were initially obtained daily and then every few days The initial spectrum had broad peaks at minus15 ppm (87 total integration) and at 0 and 7 ppm (65 total integration each) After 39 d the integral of the peak at minus15 ppm decayed to 70 of the total and the peaks at 0 and 7 ppm were visible but could not be integrated due overlap with new signals Small peaks at 50 37 33 32 20 16 5 minus22 minus38 and minus40 ppm were observed

Stability of 5 in [(DBF)H]NTf2 with Added Water A 13 mM solution of 5 in [(DBF)H]NTf2 was

prepared and stirred overnight 0075 mL of water was then added to 075 mL of this solution which was stirred 15 minutes and transferred to an NMR tube A 31P NMR spectrum obtained after 90 min showed a broad peak at 355 ppm (98 total integration) and a singlet at 217 ppm After 6 d the integral of the peak at 355 ppm decayed to 56 of the total and the peak at 217 ppm grew to 11 of the total Small peaks at 36 35 34 29 28 19 and 4 ppm were observed

Stability of 5 in [(DBF)H]NTf2 with Added DBF 08 mL of an 19 mM solution of 5 in [(DBF)H]NTf2 was added to an NMR tube and a 31P NMR spectrum obtained In a glove box DBF (08 mL 440 mmol) was added to the NMR tube and mixed After the initial spectrum the mixture was monitored for 34 d after which the main peak at 58 ppm remained and very small peaks grew in at 32 minus44 and minus49 ppm

Stability of 5 in DBF A 24 mM solution of 5 in DBF was added to an NMR tube The initial 31P NMR spectrum showed singlet resonances at δ 62 (5 98 of the total integral) and minus494 (free P2

PhN2C6H4-hex 2) After 12 d these peaks constituted 60 and 40 of the total integral respectively

NMR Spectroscopy of 6 and 10 in [(DBF)H]NTf2 Complex 6 (00257 g 00217 mmol) was stirred in 1 mL of [(DBF)H]NTf2 for 3 days 08 mL of this solution was added to an NMR tube 31P1H NMR

(2023 MHz 25 degC) δ minus155 minus02 72 Complex 10 (00243 g 172 times 10minus5 mol) was dissoved in 08 mL

of [(DBF)H]NTf2 with stirring overnight The solution was transfered to an NMR tube and sealed with a

septum 31P1H NMR (2023 MHz 25 degC) δ minus155 minus02 72 19F NMR (2822 MHz 25 degC) δ minus638 (-

C6H4CF3) minus807 (N(S(O)2CF3)2minus) minus1501 minus1520 minus1533 (BF4

minus) 31P NMR spectra of 5 6 and 10 in neat [(DBF)H]NTf2 are given in Figure S9 Like 5 6 exhibits a peak at minus14 ppm and two smaller peaks downfield The signal at 7 ppm is assigned to overlapping aprotic and monoprotic 6 Complex 10 shows a sharp singlet at 5 ppm consistent with aprotic Ni2+complex As expected the degree of protonation tracks the ordering in pendant amine basicity 10 lt 6 lt 5 Adding water to 10 has little effect on the 31P NMR spectrum a sample of 10 in [(DBF)H] NTf2 (χH2O = 072) was prepared by dissolving 10 (00242 g 171 times

10minus5 mol) in 07 mL of [(DBF)H]NTf2 with stirring overnight before adding 105 L of water This

solution was transfered to an NMR tube and sealed with a septum 31P1H NMR (2023 MHz 25 degC) δ

minus155 minus02 72 19F NMR (2822 MHz 25 degC) δ minus640 (-C6H4CF3) minus811 (N(S(O)2CF3)2minus) minus1500

minus1511 minus1521 (BF4minus)

Cyclic Voltammetry of Ferrocene in [(DBF)H]NTf2 Addition of H2O A cyclic voltammogram was

recorded (υ = 100 mV sminus1) with ferrocene (lt 2 mM) in 10 mL [(DBF)H]NTf2 Water was added in 25 L

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aliquots After each addition the solution was stirred briefly and a cyclic voltammogram was recorded These cyclic voltammograms show the onset of electrode-catalyzed hydrogen production at minus12 V vs Fc+Fc indicating no overlap with catalytic waves when Ni catalysts are used (Figure S3)

Cyclic Voltammetry of 5 in [(DBF)H]NTf2 (χH2O = 072) Scan Rate Effects Solutions with [5] = 25

mM scanned at 01 5 and 10 V sminus1 show ~10 increase in current between the slowest and fastest scan rates significantly smaller than expected for a diffusion-controlled process and consistent with kinetic control of the catalytic current(3)

Controlled‐Potential Coulometry of 5 in [(DBF)H]NTf2 (χH2O = 072) A controlled-potential

coulometry experiment using a 07 mM solution of 5 in [(DBF)H]NTf2 (χH2O = 072) was conducted to

confirm the catalytic production of hydrogen A sealed bulk electrolysis cell equipped with a reticulated vitreous carbon working electrode (1 cm diameter by 3 cm length Duocelreg 30 pores per inch) and two glass electrode compartments separated by Vycor frits was calibrated for volume and found to hold 320 mL Coiled nichrome wires were placed in each fritted compartment one for use as the auxiliary electrode and the other as the reference electrode The flask was filled with 14 mL of a [(DBF)H]NTf2 (χH2O = 072) solution to which 139 mg of 5 (0009 mmol) and 35 mg of ferrocene (0019 mmol) were

added Controlled potential electrolysis was performed at ndash10 V versus Fc+Fc Due to the relatively high viscosity of the medium it was necessary to periodically free small bubbles of generated H2 from the working electrode and glass wall by cautiously tapping the electrochemical cell Samples of the gas in the headspace were removed via a gastight syringe at various times during the experiment and were analyzed by gas chromatography using the detector response calibration to determine the amount of H2 generated Gas analysis for H2 was performed using an Agilent 6850 gas chromatograph fitted with a 10prime Supelco

18Prime Carbosieve 100120 column calibrated with two H2N2 gas mixtures of known composition Following the passage of 2379 coulombs these results provided a current efficiency of 92 plusmn 5 with a turnover number (mol H2mol catalyst) of 13

Cyclic voltammetry of 5 at different concentrations in [(DBF)H]NTf2 (χH2O = 072) Solutions of 5

ranging from 5μM to 63 mM in [(DBF)H]NTf2 (χH2O = 072) were prepared by serial dilution For each

set of experiments a fresh batch of [(DBF)H]NTf2 (χH2O = 072) was prepared and an initial cyclic

voltammogram was recorded Then aliquots of a stock solution of 5 in [(DBF)H]NTf2 (χH2O = 072) were

added with vigorous stirring After each addition a cyclic voltammogram of the quiescent solution was

recorded In one series of experiments six 5 L aliquots of 5 (810 mM in [(DBF)H]NTf2 χH2O = 072)

were added to an initial volume of 116 mL of [(DBF)H]NTf2 (χH2O = 072) giving [5] ranging from

0035 to 024 mM After each addition three cyclic voltammograms were recorded and the voltammogram giving the highest reproducible icat value was used to determine the turnover frequency This assumes that icat is attributable only to homogeneous electrocatalysis and that the main source of variability in icat is a reduction in effective electrode surface area due to imperfect electrode polishing Background currents attributed to capacitance and electrode-catalyzed hydrogen production were measured and subtracted from traces used to determine icat

Cyclic voltammetry of 6 7 8 and 9 at different concentrations in [(DBF)H]NTf2 (χH2O = 072) The

procedure outlined above for 5 was used 6 aliquots of a 813 mM stock solution (8 times 25 L) were added

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to a 092 mL solution (giving [6] = 021-141 mM) and a single cyclic voltammogram was recorded at each concentration The two most concentrated samples gave lower icat values than expected for a first-order dependence of icat on [6] so only the data with [6] spanning 021-111 mM was used to calculate the

turnover frequency 7 aliquots of a 694 mM stock solution (5 times 25 L) were added to a 115 mL solution (giving [7] = 014-067 mM) At each concentration two cyclic voltammograms were recorded and the higher icat value was used to determine the turnover frequency at that concentration 8 Aliquots of a 669

mM stock solution (5 L 2 times 10 L 2 times 25 L 50 L) were added to a 115 mL solution (giving [8] = 0029-066 mM) and a single cyclic voltammogram was recorded at each concentration 9 Aliquots of a

774 mM stock solution (5 times 10 L) were added to a 115 mL solution (giving [9] = 0068-039 mM) At each concentration three cyclic voltammograms were recorded using the highest reproducible value icat for determining the turnover frequency at that concentration

Supplementary Information References

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2 Randles JEB (1948) A cathode ray polarograph Part II The current-voltage curves Trans Faraday Soc 44327-338

3 Nicholson RS Shain I (1964) Theory of Stationary Electrode Polarography Single Scan and Cyclic Methods Applied to Reversible Irreversible and Kinetic Systems Anal Chem 36706-723

4 Favier I Duntildeach E (2004) New Protic Salts of Aprotic Polar Solvents Tetrahedron Lett 453393-3395

5 Miedaner A Haltiwanger RC amp DuBois DL (1991) Relationship between the bite size of diphosphine ligands and tetrahedral distortions of square-planar nickel(II) complexes stabilization of nickel(I) and palladium(I) complexes using diphosphine ligands with large bites Inorg Chem 30417-427

6 Wilson AD et al (2006) Hydrogen Oxidation and Production Using Nickel-Based Molecular Catalysts with Positioned Proton Relays J Am Chem Soc 128358-366

7 Kilgore UJ et al (2011) [Ni(PPh2N

C6H4X2]

2+ Complexes as Electrocatalysts for H2 Production

Effect of Substituents Acids and Water on Catalytic Rates J Am Chem Soc 1335861-5872

8 Kadish KM Ding JQ Malinski T (1984) Resistance of nonaqueous solvent systems containing tetraalkylammonium salts Evaluation of heterogeneous electron transfer rate constants for the ferroceneferrocenium couple Anal Chem 561741-1744

S2

Contents

Table S1 Electrochemical data for 5 in various solvents

S3

Figure S1 Cyclic voltammograms of 5 in benzonitrile and acetonitrile

S3


S3

Figure S3 Cyclic voltammograms of [(DBF)H]NTf2 (χH2O from 0 to

075) and with 5 added (χH2O = 072)

S3

Text S1 Cyclic Voltammetry in [(DBF)H]NTf2 Effects of Added Water on Viscosity

S3

Figure S4 A Cyclic voltammograms of ferrocene in [(DBF)H]NTf2 with χH2O from 0 to 075 B Plot of ipox

2 vs χH2O for ferrocene oxidation

S4

Figure S5 icat vs [5] in [(DBF)H]NTf2 (χH2O = 072)

S4

Figure S6 icat for 6‐9 as a function of catalyst concentration in [(DBF)H]NTf2 (χH2O = 072)

S4

Figure S7 Cyclic voltammograms of 6‐9 in [(DBF)H]NTf2 (χH2O = 072)

S4

Figure S8 Cyclic voltammograms of 10 in [(DBF)H]NTf2 (χH2O from 0 to

077)

S5

Figure S9 31P1H NMR spectra of 5 6 and 10 in neat [(DBF)H]NTf2

S5

Figure S10 Chronopotentiograms showing the open circuit potential of a frit‐separated AgClAg reference electrode vs a Pt wire in [(DBF)H]NTf2 under H2 with χH2O ranging from 0 to 074

S5

Figure S11 Open circuit potential (OCP) vs Fc+Fc as a function of A [H2O] B ln[H2O]

S6

Figure S12 A Cyclic voltammograms of 11 and ferrocene in [(DBF)H]NTf2 (χH2O = 072) B Plot of ip for the Ni(III) reduction peak

current vs υ12

S6


S6

S3


Ni(III) Ni(I0)












2 vs χH2O



S4







ferrocene oxidation




PhN2C6H4X)2]





PhN2C6H4X)2]



S5


PhN2C6H4CF3)2]

2+ (10 12 mM) in




2+] asymp 20 mM




S6






S7


2NPh











S8




(P2PhN2








C6H4‐hex)2](BF4)2 (5) P2PhN2







S9






















S10





















S11



















S12













C6H4X2]




S3


Ni(III) Ni(I0)












2 vs χH2O



S4







ferrocene oxidation




PhN2C6H4X)2]





PhN2C6H4X)2]



S5


PhN2C6H4CF3)2]

2+ (10 12 mM) in




2+] asymp 20 mM




S6






S7


2NPh











S8




(P2PhN2








C6H4‐hex)2](BF4)2 (5) P2PhN2







S9






















S10





















S11



















S12













C6H4X2]




S4







ferrocene oxidation




PhN2C6H4X)2]





PhN2C6H4X)2]



S5


PhN2C6H4CF3)2]

2+ (10 12 mM) in




2+] asymp 20 mM




S6






S7


2NPh











S8




(P2PhN2








C6H4‐hex)2](BF4)2 (5) P2PhN2







S9






















S10





















S11



















S12













C6H4X2]




S5


PhN2C6H4CF3)2]

2+ (10 12 mM) in




2+] asymp 20 mM




S6






S7


2NPh











S8




(P2PhN2








C6H4‐hex)2](BF4)2 (5) P2PhN2







S9






















S10





















S11



















S12













C6H4X2]




S6






S7


2NPh











S8




(P2PhN2








C6H4‐hex)2](BF4)2 (5) P2PhN2







S9






















S10





















S11



















S12













C6H4X2]




S7


2NPh











S8




(P2PhN2








C6H4‐hex)2](BF4)2 (5) P2PhN2







S9






















S10





















S11



















S12













C6H4X2]




S8




(P2PhN2








C6H4‐hex)2](BF4)2 (5) P2PhN2







S9






















S10





















S11



















S12













C6H4X2]




S9






















S10





















S11



















S12













C6H4X2]




S10





















S11



















S12













C6H4X2]




S11



















S12













C6H4X2]




S12













C6H4X2]




ionic liquids si new version 5 10 12 - pnas › content › suppl › 2012 › 06 › 07 ›...

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