ultra stable self-assembled monolayers of n nheterocyclic … · synthesis of n-heterocyclic...

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SUPPLEMENTARY INFORMATIONDOI: 10.1038/NCHEM.1891

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Ultra Stable Self-Assembled Monolayers of N-Heterocyclic Carbenes on

Gold

Cathleen M. Crudden1,2*, J. Hugh Horton1*, Iraklii I. Ebralidze1, Olena V. Zenkina1,

Alastair B. McLean3, Benedict Drevniok3, Zhe She4, Heinz-Bernhard Kraatz,4 Nicholas J.

Mosey,1 Tomohiro Seki1, Eric C. Keske1, Joanna D. Leake1, Alexander Rousina-Webb1,

Gang Wu1

1Queen's University, Department of Chemistry, Chernoff Hall, Kingston, Ontario,

Canada

2Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa,

Nagoya, Japan

3Queen's University, Department of Physics, Engineering Physics and Astronomy,

Stirling Hall, Kingston, Ontario, Canada.

4Department of Physical and Environmental Sciences, University of Toronto

Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4 and Department of Chemistry,

80. St. George Street, Toronto, M5S 3H6, Canada

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Ultra Stable Self-Assembled Monolayers of N-Heterocyclic Carbenes on

Gold

Cathleen M. Crudden1,2*, J. Hugh Horton1*, Iraklii I. Ebralidze1, Olena V. Zenkina1,

Alastair B. McLean3, Benedict Drevniok3, Zhe She4, Heinz-Bernhard Kraatz,4 Nicholas J.

Mosey,1 Tomohiro Seki1, Eric C. Keske1, Joanna D. Leake1, Alexander Rousina-Webb1,

Gang Wu1

1Queen's University, Department of Chemistry, Chernoff Hall, Kingston, Ontario,

Canada

2Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa,

Nagoya, Japan

3Queen's University, Department of Physics, Engineering Physics and Astronomy,

Stirling Hall, Kingston, Ontario, Canada.

4Department of Physical and Environmental Sciences, University of Toronto

Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4 and Department of Chemistry,

80. St. George Street, Toronto, M5S 3H6, Canada

© 2014 Macmillan Publishers Limited. All rights reserved.



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Supplementary Materials Materials and Methods S-5 General considerations S-5 Instrumentation S-5 Abbreviations S-6 Synthetic Studies S-6 Synthesis of N-heterocyclic carbenes S-6 Preparation of gold nanoparticles S-11 Surface reactions S-11 Deposition of carbenes on gold surfaces S-11 Dodecyl sulfide exchange by carbenes on gold nanoparticles S-12 Dodecyl sulfide and thiols exchange by carbenes on gold surfaces S-12 Click reaction on the surfaces S-12 Blank click reaction on NHC-terminated Au/Si S-12 Chemical Stability tests S-12 pH stability test S-12 THF stability tests S-13 Decalin stability tests S-13 Water stability tests (room temperature and elevated temperature) S-13 Peroxide stability tests S-13 Electrochemical Studies S-13 Electrode preparation and SAM preparation S-13 Electrochemical testing S-14 Testing of redox-active molecules in solution using alkylated films S-14 Computational details S-15 Figures: Fig. S1. Representative XPS data for treatment of iPr2bimy (1)-terminated Au(111) surfaces with dodecylsulfide S-17 Fig. S2a. Representative XPS data for treatment of dodecanethiol–protected Au(111) surfaces with solutions of iPr2bimy (1) for 24h at room temperature S-17 Fig. S2b. Representative XPS data for treatment of dodecanethiol–protected Au(111) surfaces with solutions of IMes (3) for 24h at room temperature S-17 Fig. S3a. Representative XPS data for treatment of benzenethiol–protected Au(111) surfaces with solutions of iPr2bimy (1) for 24h at room temperature. S-18 Fig. S3b. Representative XPS data for treatment of benzene-1,2-dithiol–protected Au(111) surfaces with solutions of iPr2bimy (1) for 24h at room temperature S-18 Fig. S3c. Representative XPS data for treatment of propane-1,3-dithiol–protected Au(111) surfaces with solutions of iPr2bimy (1) for 24h at room temperature S-18 Fig. S4a. Representative XPS data for treatment of benzenethiol–protected Au(111) surfaces with solutions of IMes (3) for 24h at room temperature S-19 Fig. S4b. Representative XPS data for treatment of benzene-1,2-dithiol–protected Au(111) surfaces with solutions of IMes (3) for 24h at room temperature S-19 Fig. S4c. Representative XPS data for treatment of propane-1,3-dithiol –protected Au(111) surfaces with solutions of IMes (3) for 24h at room temperature S-19 Fig. S5. Various bonding modes calculated for iPr2bimy (1) with Au(111) and




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Au–C bond energies calculated by DFT S-20 Fig. S6. High magnification image of IMes (3) on Au(111) showing the presence of disorganized IMes molecules rather than stacks as observed in 1–modified surfaces S-21 Fig. S7. 13C CP/MAS NMR spectra of IMes (3)-protected Au nanoparticles immediately upon ligand exchange and following exposure to ambient conditions for 15 weeks S-22 Fig. S8a. Films of iPr2bimy (1) on Au(111) before (red) and after (green) treatment with decalin at 100°C for 24h S-22 Fig. S8b. Films of iPr2bimy (1) on Au(111) before (red) and after (green) exposure to pH 2 (left) and pH 12 (right) at room temperature for 24 h S-23 Fig. S8c. Films of iPr2bimy (1) on Au(111) before (red) and after (green) exposure to pH 2 (left) and pH 12 (right) at 100°C for 24 h S-23 Fig. S8d. Films of iPr2bimy (1) on Au(111) before (red) and after (green) exposure to water at room temperature for 1 month S-23 Fig. S8e. Films of iPr2bimy (1) on Au(111) before (red) and after (green) exposure to 3% H2O2 for 24 h showing decomposition S-23 Fig. S9a. Films of IMes (3) on Au(111) before (red) and after (green) treatment with decalin at 100°C for 24h. S-24 Fig. S9b. Films of IMes (3) on Au(111) before (red) and after (green) exposure to pH 2 (left) and pH 12 (right) at 100°C for 24 h. S-24 Fig. S9c. Films of IMes (3) on Au(111) before (red) and after (green) exposure to water at room temperature for 1 month. S-24 Fig. S10a. Representative XPS data for the product of reaction of azide-terminated NHC (7) with Au/Si and subsequent conversion into a triazole by a Cu- catalyzed click reaction with ethynylferrocene. S-25 Fig. S10b. XPS spectra for the treatment of alkylated NHC (6) terminated Au(111) surface with ethynlferrocene and Cu. S-25 Fig. S11a. Electrochemical cell configurations for measurement with (a) Au/Si and (b) Au ultramicroelectrode. S-26 Fig. S11b. Determination of the electron transfer rate constants through SAMs using Laviron plots. S-26 Fig. S12. Cyclic voltammogram of (a) C12SH–Au/Si, (b) 6(C12)–Au/Si and (c) 1–Au/Si. S-27 Fig. S13. Cyclic votlammogram of (a) C12SH–Au/Si, (b) 6–Au/Si and (c) Electrochemical desorption of C12SH–Au/Si and 6–Au/Si S–28 Fig. S14. Representative XPS data for iPr2bimy (1) on gold surface S-29 Fig. S15. Representative XPS data for Enders' carbene (2) on gold suface S-30 Fig. S16. Representative XPS data for IMes (3) on gold surface S-31 Fig. S17. Representative XPS data for SIMes (4) on gold surface S-32 Fig. S18. Representative XPS data for IPr (5) on gold surface S-33 Fig. S19. 1H and 13C{1H} NMR spectra of 4-(12-bromododecyloxy)- 2-nitroaniline. S-34 Fig. S20. 2D 1H–1H COSY map of 4-(12-bromododecyloxy)-2-nitroaniline S-35 Fig. S21. 2D 1H–13C HSQC map of 4-(12-bromododecyloxy)-2-nitroaniline S-36 Fig. S22. 1H and 13C{1H} NMR spectra of 5-(12-bromododecyloxy)-1H-benzo[d]imidazole S-37




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Fig. S23. 2D 1H–1H COSY map of 5-(12-bromododecyloxy)-1H-benzo[d] imidazole S-38 Fig. S24. 2D 1H–13C HSQC map of 5-(12-bromododecyloxy)-1H-benzo[d] imidazole S-39 Fig. S25. 1H and 13C{1H} NMR spectra of 5-(12-azidododecyloxy)-1H-benzo[d]imidazole S-40 Fig. S26. 2D 1H–1H COSY map of 5-(12-azidododecyloxy)-1H-benzo[d] imidazole S-41 Fig. S27. 2D 1H–13C HSQC map of 5-(12-azidododecyloxy)-1H-benzo[d] imidazole S-42 Fig. S28. 1H and 13C{1H} NMR spectra of 1,3-diisopropyl-5-(12-(azido) dodecyloxy)-benzo[d]imidazole-1-ium iodide S-43 Fig. S29. 2D 1H–1H COSY map of 1,3-diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazole-1-ium iodide S-44 Fig. S30. 2D 1H–13C HSQC map of 1,3-diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazole-1-ium iodide S-45 Fig. S31. 1H and 13C{1H} NMR spectra of 5-(12-(4-(ferrocenyl)-1H-1,2,3- triazol-1-yl)dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide S-46 Fig. S32. 2D 1H–1H COSY map of 5-(12-(4-(ferrocenyl)-1H-1,2,3-triazol-1-yl)dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide S-47 Fig. S33. 2D 1H–13C HSQC map of of 5-(12-(4-(ferrocenyl)-1H-1,2,3-triazol-1-yl)dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide S-48 Fig. S34. 1H and 13C{1H} NMR spectra of 4-(dodecyloxy)-2-nitroaniline. S-49 Fig. S35. 2D 1H–1H COSY map of 4-(dodecyloxy)-2-nitroaniline. S-50 Fig. S36. 2D 1H–13C HSQC map of 4-(dodecyloxy)-2-nitroaniline. S-51 Fig. S37. 1H and 13C{1H} NMR spectra of 5-(dodecyloxy)-1H-benzo[d]imidazole S52 Fig. S38. 2D 1H–1H COSY map of 5-(dodecyloxy)-1H-benzo[d]imidazole S-53 Fig. S39. 2D 1H–13C HSQC map of 5-(dodecyloxy)-1H-benzo[d]imidazole S-54 Fig. S40. 1H and 13C{1H} NMR spectra of 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide. S-55 Fig. S41. 2D 1H–1H COSY map of 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide S-56 Fig. S42. 2D 1H–13C HMQC map of 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide. S-57 References S-58




S-5

Materials and Methods General considerations

Synthesis and deposition of carbenes were carried out in a nitrogen atmosphere in a glovebox (M. Braun) with oxygen and water levels ≤2 ppm. Solvents were purified on a PureSolv Solvent Purification system, distilled, degassed and stored over 4 Å molecular sieves prior to use. Hydrogen tetrachloroaurate [HAuCl4] was synthesized by the oxidation of gold metal through dissolution in aqua regia followed by evaporation of the solution after 24 hours yielded chloroauric acid tetrahydrate as a yellow solid. Instrumentation

1H and 13C{1H} NMR, spectra were recorded on a Bruker Avance-400 or 500 MHz spectrometer. Chemical shifts are reported in delta (δ) units, expressed in parts per million (ppm) downfield from tetramethylsilane using residual protonated solvent as an internal standard (C6D6, 7.15 ppm; CDCl3, 7.24, CD2Cl2, 5.32 ppm). Chemical shifts are reported as above using the solvent as an internal standard (C6D6, 128.0 ppm; CDCl3, 77.23, CD2Cl2, 53.8 ppm). All 2D spectra (gs-COSY, gs-HSQC, gs-HMBC) were acquired in the phase-sensitive mode. All data were acquired, processed, and displayed using Bruker XWinNMR and ACD Labs software and a standard pulse-sequence library. All measurements were carried out at 298 K unless otherwise stated.

Solid-state 13C NMR spectra were recorded under cross polarization (CP) magic-angle spinning (MAS) conditions on a Bruker Avance-600 NMR spectrometer (14.1 T) operating at the 1H and 13C Larmor frequencies of 600.17 and 150.93 MHz, respectively. The Hartmann-Hahn matching condition was established with a solid glycine sample. High-power 1H decoupling was applied during data acquisition. A 4-mm Bruker MAS probe was used with a sample spinning frequency of 12.5 kHz. Typically, 2-5 mg of carbene-protected gold nanoparticles were packed into a ZrO2 rotor (4-mm o.d.). To maximize detection sensitivity, solid KBr was used as inert filling materials so that the gold nanoparticles were located at the central region of the rotor. All 13C chemical shifts were referenced to that of TMS using a solid glycine as a secondary 13C chemical shift reference.

Mass-spectrometry was carried out using a Micromass Platform LCZ 4000 system. Elemental analyses were performed using Flash 2000 CHNS-O analyzer. XPS measurements were performed using a Thermo Microlab 310F ultrahigh

vacuum (UHV) surface analysis instrument using Al Kα X-rays (1486.6 eV) at 15 kV anode potential and 20 mA emission current with a surface/detector take off angle of 75°. The binding energies of all spectra were calibrated to the Au 4f line at 84.0 eV. A Shirley algorithm was used as the background subtraction method for all peaks. The Powell peak-fitting algorithm was used, with peak areas normalized between different elements using the relative XPS sensitivity factors of Scofield (S1). In cases where absolute peak intensities for a single element were compared between different samples we took care to ensure a standard sample size and orientation with respect to X-ray source and detector within the analysis chamber. Calibration of our system using Au thiol SAMs of known surface concentration gave peak areas reproducible within ± 5% between sample runs.




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Overlayer thicknesses of 1 and 3 on Au(111) were calculated from the XPS spectra using the Au 4f signal attenuation (Is/I0) using the following relationship:

𝑡𝑡 = (−𝝀𝝀𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐)𝑙𝑙𝑙𝑙𝐼𝐼!𝐼𝐼!

where t is the thickness of the overlayer, θ is the takeoff angle (here 15°), Is is the substrate signal intensity after modification, and I0 is the substrate signal intensity before modification. The parameter λ is the inelastic mean free path that was calculated for each layer using the NIST Standard Reference Database 82. Using this approach, the average overlayer thicknesses of 1, and 3 on Au(111) were determined to be 0.5 and 0.3 nm, respectively.

Scanning tunneling microscope measurements were performed in ultra-high vacuum at room temperature using a home-built Pan-style STM. Mechanically-formed platinum-iridium tips were used for all experiments. GXSM (S2) was used as control software using the Signal Ranger A810 DSP and Nanonis HVA4 high-voltage amplifier.

Abbreviations iPr2bimy (1, 1,3-dihydro-1,3-bisisopropylbenzimidazol-2-ylidene), Enders' carbene

(2, 2,4-dihydro-2,4,5-triphenyl-1,2,4-triazol-3-ylidene), IMes (3, 1,3-dihydro-1,3-bis (2,4,6-trimethylphenyl)imidazol-2-ylidene), SIMes (4, 1,3-bis(2,4,6-trimethylphenyl) imidazolin-2-ylidene) and IPr (5, 1,3-dihydro-1,3-bis(2,6-diisopropylphenyl) imidazol-2-ylidene)

Synthetic Studies Synthesis of N-heterocyclic carbenes 1,3-Dihydro-1,3-bisisopropyl-2H-benzimidazol-2-ylidene, (iPr2bimy), 1. 1,3-Diisopropyl-1H-benzo[d]imidazole-3-ium iodide (317 mg, 0.960 mmol) (S3) was dissolved in 10 mL of anhydrous THF in a glove box. A solution of KOtBu (108 mg, 0.962 mmol) in THF (20 mL) was added dropwise over an hour. The reaction was stirred for an additional hour. The THF was then evaporated under vacuum, and the resulting solid was dissolved in toluene and filtered through celite. Evaporation of the filtrate gave the desired free carbene as a yellow oil in 68 % yield.

1H NMR (C6D6): δ 7.3-7.2 (br, 4H, PhH), 4.52 (sept, JHH = 6.6 Hz, 2H, CH-(CH3)3), 1.63 (d, JHH = 6.65 Hz, 12H, CH3). That is consistent with the literature (S3).

N-heterocyclic carbenes 2-5 were were prepared using a similar method as described in the literature procedures (S4-S7).




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Synthesis of 1,3-diisopropyl-5-(dodecyloxy)-1H-benzo[d]imidazole-2-ylidene, (6)

4-(dodecyloxy)-2-nitroaniline. To a solution of 4-amino-3-nitrophenol

(1.540 g, 10 mmol) and 1-bromododecane (2.739 g, 2.633 mL, 11 mmol) in anhydrous acetonitrile (50 mL), potassium carbonate (1.380 g, 10 mmol) was added. The mixture was stirred at 80°C for 8 h under argon. Then the solvent was evaporated and the crude product was separated by flash-chromatography using hexane-chloroform gradient mixtures. Yield: 2.444 g (76%). Anal. Calc. for C18H30N2O3: C, 67.05; H, 9.38; N, 8.69. Found: C, 66.44; H, 9.42; N, 8.61. TOF MS (m/z) for C18H30N2O3: 322.2247, Calc.: 322.2256.

1H NMR (d6-DMSO): δ 7.35 (d, 1H, JHH = 2.8 Hz), 7.23 (s, 2H, NH2), 7.13(dd, 1H, JHH = 9.3, 2.8 Hz), 6.97 (d, 1H, JHH =9.3 Hz), 3.89 (t, 2H, JHH = 6.6 Hz, -O-CH2-), 1.67 (tt, 2H, JHH =6.8 Hz), 1.38 (m, 2H), 1.24 (m, 16H), 0.85 (t, 3H, JHH = 6.8 Hz).

13C{1H} NMR (d6-DMSO): δ 148.99 (s, Cq, CAr-O-CH2-), 142.29 (s, Cq, CAr-NH2), 129.59 (s, Cq, CAr-NO2), 127.90 (s, CAr), 121.15 (s, CAr), 106.28(s, CAr,), 68.50 (s, -CH2-O-), 31.75, 29.47, 29.45, 29.41, 29.17, 29.15, 29.00, 25.89, 22.54, 14.38.

5-(dodecyloxy)-1H-benzo[d]imidazole.

Formic acid (35 mL) was added to a mixture of 4-(dodecyloxy)-2-nitroaniline, (2.257 g, 7 mmol), iron powder (3.906 g, 70 mmol), and ammonium chloride (3.738 g, 70 mmol) in isopropyl alcohol (49 mL). The resulting mixture was stirred at 80°C for 3 h, then cooled to room temperature and filtered through sintered glass filter. The solid was washed with isopropyl alcohol (3 x 5 mL). The filtrate was evaporated to dryness and 30 mL of saturated sodium bicarbonate solution was added carefully to avoid significant foaming. Then sodium bicarbonate (powder) was added portion-wise until pH 6 was achieved. Then the suspension was extracted with chloroform (5 x 30 mL). The combined organic layers were dried over anhydrous magnesium sulfate, filtered and evaporated to give 1.715 g of product. Yield 81%. Anal. Calc. for C19H30N2O: C, 75.45; H, 10.00; N, 9.26. Found: C, 75.09; H, 10.03; N, 9.08. TOF MS (m/z) for C19H30N2O: 302.2348, Calc.: 302.2358.

1H NMR (CDCl3): δ 8.00 (s, 1H), 7.55 (d, 1H, JHH = 8.6 Hz), 7.09 (s, 1H), 6.95 (d, 1H, JHH =7.4 Hz), 3.89 (t, 2H, JHH = 6.5 Hz, -O-CH2-), 1.81 (m, 2H, JHH =7.3 Hz), 1.46 (m, 2H), 1.35 (m, 2H), 1.27 (m, 14H), 0.89 (t, 3H, JHH = 6.9 Hz).

13C{1H} NMR (CDCl3): δ 155.84 (s, Cq, CAr-O-CH2-), 140.34 (s, CAr, N=CH-NH), 133.64 (s, Cq), 130.76 (s, Cq), 116.32 (br s, CAr), 112.64 (br s, CAr), 97.86 (s, CAr), 68.52 (s, 1C, -CH2-O-), 31.74, 29.44, 29.27, 29.17, 25.96, 22.49, 13.88.

H2NNO2

O

HNN

O




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5-(dodecyloxy)-1,3-diisopropyl-1H-

benzo[d]imidazol-3-ium iodide. To a suspension of 5-(dodecyloxy)-

1H-benzo[d]imidazole (302.4 mg, 1 mmol) and Cs2CO3 (325.8 mg, 1mmol) in acetonitrile (50 mL), 2-iodopropane (4.25 g, 2.5 mL, 25 mmol) was slowly added. The mixture was stirred at 90°C in a round bottomed flask attached to a reflux condenser under a nitrogen atmosphere for 24 h. Then excess 2-iodopropane, solvent and volatiles were evaporated in vacuo. The residual solid was triturated and sonicated in diethyl ether (2 × 4 mL), which was then decanted off. Subsequent drying under vacuum afforded the desired product as an off-white powder (342 mg, 66% yield). Anal. Calc. for C25H43N2OI: C, 58.36; H, 8.42; N, 5.44. Found: C, 56.80; H, 8.39; N, 5.52. TOF MS (m/z) for C25H43N2O: 387.3389, Calc.: 387.3375.

1H NMR (CDCl3): δ 10.59 (s, 1H, N-CH=N), 7.67 (d, 1H, JHH = 9.0 Hz), 7.21 (d, 1H, JHH = 9.0 Hz), 7.13 (s, 1H), 5.15 (sept, JHH=6.8 Hz, 2H, CH-(CH3)2), 4.06 (t, 2H, JHH = 6.3 Hz, -O-CH2-), 1.84 (m, 14H), 1.48 (m, 2H), 1.25 (m, 16H), 0.86 (t, 3H, JHH = 6.6 Hz).

13C{1H} NMR (CDCl3): δ 158.88 (s, Cq, CAr-O-CH2-), 138.45 (s, CAr, N=CH-NH), 132.10 (s, Cq), 124.79 (s, Cq), 117.41 (s, CAr), 114.58(s, CAr), 96.79(s, CAr), 69.45 (s, 1C, -CH2-O-), 52.42 (s, CH-(CH3)2), 52.0 (s, CH-(CH3)2), 31.88, 29.62, 29.59, 29.55, 29.51, 29.34, 29.30, 29.03, 25.98, 22.64, 22.35 (s, CH-(CH3)2), 22.27 (s, CH-(CH3)2), 14.06 (s. CH3).

1,3-diisopropyl-5-(dodecyloxy)-1H-benzo[d]imidazole-2-ylidene (6). The free carbene was obtained by dissolving 1,3-diisopropyl-5-(dodecyloxy)-benzo[d]imidazole-1-ium iodide (5.1 mg, 0.01 mmol) in 2 mL of anhydrous THF in a RBF with stirring in a glove box. Separately, KOtBu (1.1 mg, 0.01 mmol) was dissolved in 0.7 mL of anhydrous THF. Both solutions were cooled to -40°C. The base solution was then added dropwise over 30 min. The reaction was stirred for an additional hour. The THF was then evaporated under vacuum, and the resulting solid was dissolved in toluene and filtered through celite and used directly for surface functionalization.

Synthesis of 1,3-diisopropyl-5-(12-(azido)dodecyloxy)-1H-benzo[d]imidazole-2-ylidene, (7).

4-(12-bromododecyloxy)-2-

nitroaniline. To a solution of 4-amino-3-nitrophenol (616 mg, 4 mmol) and 1,12-dibromo-dodecane (2.624 g, 8 mmol) in anhydrous acetonitrile (40 mL), potassium carbonate (552 mg, 4 mmol) was added. The mixture was stirred at 80°C for 8 h under argon. The solvent was then evaporated and the crude product was separated by flash-

NN

O

I–

NN

O

H2NNO2

OBr




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chromatography using hexane-ethyl acetate gradient mixtures. Yield: 1.130 g (70%). Anal. Calc. for C18H29BrN2O3: C, 53.87; H, 7.28; N, 6.98. Found: C, 53.31; H, 7.12;

N, 7.10. 1H NMR (CDCl3): δ 7.54 (d, 1H, JHH = 2.7 Hz, ArH), 7.07 (dd, 1H, JHH = 9.0 Hz,

JHH =2.7 Hz, ArH), 6.76 (d, 1H, JHH = 9.1 Hz, ArH), 5.88 (s, 2H, NH2), 3.92 (t, 2H, JHH = 6.5 Hz, O-CH2), 3.41 (t, 2H, JHH = 6.8 Hz, Br-CH2), 1.86 (tt, 2H, JHH = 7.3 Hz, JHH =7.0 Hz), 1.77 (tt, 2H, JHH =7.6 Hz, JHH =6.6 Hz), 1.43 (m, br, 4H), 1.29 (m, br, 12H).

13C{1H} NMR (CDCl3): δ 150.27 (s, Cq, C-O-CH2), 139.74 (s, Cq, C-NO2), 131.54 (s, Cq, C-NH2), 127.06 (s, Ar), 119.96 (s, Ar), 107.11(s, Ar), 68.76 (s, -CH2-O), 34.04 (s), 32.80 (s), 29.47 (m), 29.39 (s), 29.30 (s), 29.07 (s), 28.72 (s), 28.14 (s), 25.94 (s).

5-(12-bromododecyloxy)-1H-

benzo[d]imidazole. This synthetic procedure was adapted from the previously published method (S8). Formic acid (25 mL) was added to a mixture of 4-(12-bromododecyloxy)-2-nitroaniline (2.005 g, 5 mmol), iron powder (2.790 g, 50 mmol), and ammonium chloride (2.670 g, 50 mmol) in isopropanol (35 mL). The resulting mixture was stirred at 80°C for 3 h under argon, then cooled to room temperature and filtered. The solid material was washed with isopropanol (3 x 5 mL). The filtrate was evaporated to dryness and the residue was partitioned between saturated NaHCO3 (20 mL) and CHCl3 (20 mL). The water phase was additionally extracted with chloroform (3 x 20 mL). The combined organic layers were evaporated in vacuo to give the product that was used in the next step without further purification. Yield 1.735 g (91%).

Anal. Calc. for C19H29BrN2O: C, 59.84; H, 7.66; N, 7.35. Found: C, 58.07; H, 7.85; N, 7.34. ES-MS (m/z) for C19H29N2OBr: 380.1475 , Calc.: 380.1463

1H NMR (DMSO-d6): δ 8.14 (s, 1H, NH), 8.08 (s, 1H, N-CH=N), 7.44 (d, 1H, JHH = 8.8 Hz, ArH), 7.04 (s, 1H, ArH), 6.79 (d, 1H, JHH = 8.8 Hz, ArH), 3.95 (t, 2H, JHH = 6.3 Hz, O-CH2), 3.50(t, 2H, JHH = 6.6 Hz, Br-CH2), 1.77 (m, 2H), 1.71 (m, 2H), 1.42-1.33 (m, br, 4H), 1.25 (m, br, 12H).

13C{1H} NMR (CDCl3): δ 156.63 (s, N-CH=N), 139.71 (s, Cq), 136.37 (s, Cq), 131.18 (s, Cq), 116.11 (s, Ar), 114.07 (s, Ar), 97.96 (s, Ar), 68.69 (s, CH2-O), 34.03 (s), 32.80 (s), 29.50 (m), 29.39 (s), 28.72 (s), 28.14 (s), 26.04 (s).

5-(12-azidododecyloxy)-1H-

benzo[d]imidazole. 5-(12-bromododecyloxy)-1H-benzo[d]imidazole (381 mg, 1 mmol) was stirred with sodium azide (78 mg, 1.2 mmol) in DMSO (5 mL) for 4 h. Then reaction mixture was poured into 25 mL of a saturated solution of NaHCO3 in water and centrifuged. The product was extracted from precipitate with CHCl3 (3 x 25 mL). Yield 237 mg (69%).

ES-MS (m/z) for C19H29N5O: 343.2387, Calc.: 343.2372 1H NMR (DMSO-d6): δ 8.06 (s, 1H, N-CH=N), 7.44 (d, 1H, JHH = 8.5 Hz, ArH),

7.05 (s, 1H, ArH), 6.78 (d, 1H, JHH = 7.9 Hz, ArH), 3.95 (t, 2H, JHH = 6.5 Hz, -O-CH2),

HNN

ON3

HNN

OBr




S-10

3.28(m, 2H, JHH = 6.8 Hz, N3-CH2), 1.70 (m, 2H), 1.50 (m, 2H), 1.41 (m, br, 2H), 1.23 (m, br, 14H).

13C{1H} NMR (CDCl3): δ 154.88 (s, N-CH=N), 141.39 (s, Cq), 137.78 (s, Cq), 133.45 (s, Cq), 116.27 (s, Ar), 111.75 (s, Ar), 98.19 (s, Ar), 67.89 (s, CH2-O), 50.61 (s, CH2-N3), 28.98 (s), 28.89 (s), 28.78 (m), 28.50 (s), 28.21 (s), 26.11 (s), 25.58 (s).

1,3-diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazolium iodide To a suspension of 5-(12-azidododecyloxy)-

1H-benzo[d]imidazole (34.4 mg, 0.1 mmol) and Cs2CO3 (39 mg, 0.11 mmol) in acetonitrile (4 mL), 2-iodopropane (250 µL, 2.5 mmol) was slowly added. The mixture was stirred at 90 °C in a sealed pressure tube under a nitrogen atmosphere for 24 h. Then the excess of 2-iodopropane, solvent and volatiles were evaporated in vacuo. The resulting oil was triturated with ether (2 mL) to give the product as a gray powder. Yield 36 mg (65 %).

ES-MS (m/z) for C25H42N5O: 428.3397 , Calc.: 428.3389 1H NMR (CDCl3): δ 10.67 (s, 1H, N-CH=N), 7.65 (d, 1H, JHH = 9.2 Hz, ArH), 7.22

(d, 1H, JHH = 9.3 Hz, ArH), 7.11(s, 1H, ArH), 5.12 (sept, JHH=6.6 Hz, 2H, CH-(CH3)3), 4.06 (t, 2H, JHH = 6.1 Hz, O-CH2), 3.24 (t, 2H, JHH = 6.6 Hz, N3-CH2), 1.84 (m, 12H), 1.59 (m, 2H), 1.49 (m, 2H), 1.28 (m, br, 16H).

13C{1H} NMR (CDCl3): δ 158.76 (s, Cq), 138.52 (s, N-CH=N), 132.01(s, Cq), 124.70 (s, Cq), 117.29 (s, Ar), 114.46 (s, Ar), 96.62 (s, Ar), 69.30 (s, CH2-O), 52.37(s, CH3-CH-CH3), 51.94 (s, CH3-CH-CH3), 51.41 (s, CH2-N3), 29.43 (s), 29.27 (s), 29.04 (s), 28.97 (s), 28.74 (s), 26.61 (s), 25.91 (s), 22.26 (s, CH3), 22.18 (s, CH3).

1,3-diisopropyl-5-(12-(azido)dodecyloxy)-1H-benzo[d]imidazole-2-ylidene, (7). The free carbene was obtained by dissolving 1,3-diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d] imidazolium iodide (5.5 mg, 0.01 mmol) in 2 mL of anhydrous THF in a round bottomed flask with stirring in a glove box. Separately, KOtBu (1.1 mg, 0.01 mmol) was dissolved in 0.7 mL of anhydrous THF. Both solutions were cooled to -40°C. The base solution was then added dropwise over 30 min. The reaction was stirred for an additional hour. The THF was then evaporated under vacuum, and the resulting solid was dissolved in toluene and filtered through celite and used directly for surface functionalization. 5-(12-(4-(ferrocenyl)-1H-1,2,3-triazol-1-yl)dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide (7–Fc+I–) 1,3-Diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazolium iodide (55 mg, 0.1 mmol) and ethynylferrocene (28 mg, 0.14 mmol) were dissolved in THF (3 mL), and water was added (3 mL). CuSO4 (1.M aqueous solution, 0.1 mL) was added followed by freshly prepared sodium ascorbate solution (1 M aqueous solution, 0.2 mL) dropwise. The

NN

ON3

NN

O

I–

NNN

Fc

NN

O

I–

N3




S-11

solution was allowed to stir at room temperature for 1 h. After removal of the THF under vacuum, dichloromethane (5.5 mL) and conc. NH3 (1.8 mL) were added to the solution, which was allowed to stir for a further 30 min at room temperature to remove all the CuI derivative trapped inside the product as [Cu(NH3)6]. The organic phase was washed twice with water (3 mL) and once with brine (3 mL) and then dried with MgSO4. The solvent was removed under vacuum, then the reaction mixture was washed with 50 mL of pentane to remove excess of ethynylferrocene and the product was precipitated from dichloromethane and hexane to yield an orange solid (44 mg, 58%). HRMS (ESI): [M - I]+. HRMS: calcd. for C37H52FeN5) [M - I]+ 638.3522; found 638.3536.

1H NMR (CD2Cl2): δ 10.94 (s, 1H, N-CH=N), 7.64 (d, 1H, JHH = 8.6 Hz, ArH), 7.50 (s, 1H, triazole) 7.20 (d, 1H, JHH = 7.6 Hz, ArH), 7.11(s, 1H, ArH), 5.03 (m, 2H, CH-(CH3)3), 4.67 (s, 2H, ferrocene), 4.31(t, 2H, JHH = 6.5 Hz, ferrocene), 4.26 (m, 2H), 4.02 (m, 7H, ferrocene and CH2–X), 1.89 (m, 2H), 1.78 (m, 12H, -CH2-), 1.46 (m, 2H), 1.27 (m, br, 16H).

13C{1H} NMR (CDCl3): δ 159.27 (s, Cq), 146.77 (s, Cq), 139.94 (s, N-CH=N), 132.66 (s, Cq), 125.47 (s, Cq), 119.42 (s, triazole), 117.62 (s, Ar), 114.91 (s, Ar), 97.11 (s, Ar), 76.43(s, Cq), 69.98 (s, ferrocene), 69.89 (s, CH2-O), 69.03 (s, ferrocene), 67.04 (s, ferrocene), 52.62 (s, CH3-CH-CH3), 52.21 (s, CH3-CH-CH3), 50.73 (s, CH2-triazole), 30.78 (s), 30.00 (s), 29.97 (s), 29.91 (s), 29.83 (s), 29.57(s), 29.50 (s), 26.98(s), 26.46 (s), 22.60 (s, CH3), 22.50 (s, CH3).

Preparation of gold nanoparticles

Chloroauric acid tetrahydrate 52 mg, 0.126 mmol of in water (5.1 mL) was added to a solution of tetraoctylammonium bromide (167 mg, 0.306 mmol) in toluene (3.06 mL). The solution was stirred vigorously until the aqueous layer became colourless. Following this, a solution of dodecyl sulfide (170 mg, 0.459 mmol) in toluene (11.5 mL) was added and allowed to stir for another 5 minutes. A solution of sodium borohydride (69.5 mg, 1.837 mmol) in water (18 mL) was added to the mixture while stirring in one aliquot. A fast colour change from red-orange to dark purple-brown was observed, indicating colloid formation. The solution was allowed to stir for another hour before the organic layer was collected. The organic layer was reduced to a minimum amount through rotary evaporation at room temperature to prevent nanoparticle decomposition. The colloids were then suspended in anhydrous ethanol and left at room temperature overnight to precipitate. The resulting solution was then centrifuged (2500 rpm, 1 hour), decanted and dried in vacuo. The nanoparticles were then suspended in ethanol (3 x 10 mL), centrifuged, dried and stored at -40°C in solid form.

Surface reactions Deposition of carbenes on gold surfaces

Self-assembled monolayers were prepared by immersion of the gold substrates in a 1 mM solution of the corresponding carbene in anhydrous toluene for 24 h at room temperature in a glove box. Substrates then were rinsed in anhydrous THF (5 x 2 mL) and dried under a nitrogen gas stream.




S-12

Dodecylsulfide exchange by carbenes on gold nanoparticles Gold nanoparticles stabilized by dodecyl sulfide (3 mg) were dissolved in anhydrous

toluene (5 mL) under inert atmosphere in a glove box and then a 20-fold molar excess of carbene relative to gold was added. The mixture was allowed to react overnight at room temperature. Nanoparticles (except benzimidazole carbene-stabilized) were collected by centrifugation, washed with toluene (3 x 0.5 mL) and dried in vacuo. Benzimidazolylidene –stabilized nanoparticles in toluene were mixed with hexane (2 mL) collected by centrifugation, washed with hexane (3 x 0.5 mL), centrifuged, and dried in vacuo.

Dodecylsulfide and thiol exchange by carbenes on gold surfaces

Gold surfaces protected with dodecyl sulfide or dodecanethiol were immersed into a freshly prepared 1 mM solution of the corresponding carbene in anhydrous THF for 12 h in a glove box. After this time, the solution was removed by pipette, a new portion of freshly-prepared 1 mM solution of the corresponding carbene in anhydrous THF was added, and for left for an additional 12 h. After this time, the gold was removed, rinsed in THF (15 x 3 mL), and dried under a nitrogen gas stream.

Click reaction on surfaces

The appropriate alkyne, either ethynylferrocene (21 mg, 0.1 mmol) or propargyl alcohol (5.8 uL, 0.1 mmol) was dissolved in DMF (1 mL), and water (1.5 mL) was added. Then CuSO4 (1.M aqueous solution, 0.1 mL) was added followed by a freshly prepared sodium ascorbate solution (1 M aqueous solution, 0.2 mL). The mixture was allowed to stir at room temperature for 3 min. Then the stirring bar was taken out and the azide-terminated carbene surface on gold was submerged in the solution. The deposition was performed at room temperature in air for 24 h. After this time, the wafer was taken out, sonicated for 15 minutes and rinsed in the following solvents in this order: DMF, pentane, DCM, conc. NH3 water solution, DI water (3 times), ethyl acetate, and hexane.

Blank click reaction on NHC-terminated Au (polycrystalline on silicon)

Ethynylferrocene (3 mg, 0.014 mmol) was dissolved in DMF (1 mL), and water (1.5 mL) was added. Then CuSO4 (0.1M aqueous solution, 0.1 mL) was added followed by a freshly prepared sodium ascorbate solution (0.1 M aqueous solution, 0.2 mL). The mixture was allowed to stir at room temperature for 3 min. Then the stirring bar was taken out and gold-coated silicon wafer (2 x 2 cm) functionalized by the C12-terminated carbene (NHC 6) was submerged in the solution. The deposition was performed at room temperature under air for 24 h. After this time, the wafer was taken out, sonicated for 15 minutes and rinsed in the following solvents: DMF, pentane, DCM, conc. NH3 water solution, DI water (3 times), ethyl acetate, and hexane.

Chemical Stability tests

pH stability tests iPr2bimy (1)- and IMes (3)-functionalized surfaces were submerged in freshly

prepared unbuffered solutions of certain pHs (pH 2 or pH 12) in Ace Glass pressure tubes




S-13

at 25°C or 100°C for 24 h. Experiments were conducted under N2 gas to minimize the possibility of pH change due to adsorption of atmospheric CO2. After this time, functionalized surfaces were rinsed in DI water (3 x 2 mL) and dried in an N2 gas stream. The pH values were adjusted using NaOH and HCl solutions. Unbuffered solutions were employed in order to avoid potential adsorption effects of buffer ions from solution.

THF stability tests iPr2bimy (1)- and IMes (3)- functionalized surfaces were placed in Ace Glass pressure tubes and 3 mL of THF were added to each sample. The tubes were purged with nitrogen gas, sealed and heated to 68°C for 24 h. After this time, the samples were cooled to rt, rinsed in THF (2 x 5 mL), and dried under a nitrogen gas stream. Decalin stability tests iPr2bimy (1)- and IMes (3)-functionalized surfaces were placed in Ace Glass pressure tubes and 2 mL of decalin were added to each sample. The tubes were purged with nitrogen gas, sealed and heated to 100°C for 24 h. After this time, the samples were cooled to rt, rinsed hexane (2 x 5 mL), ether (2 x 5 mL), and ethanol (2 x 5 mL), and dried under a nitrogen gas stream. Water stability tests (room temperature and elevated temperature) iPr2bimy (1)- and IMes (3)-functionalized surfaces were placed in freshly deionized (resistivity 18.2 MΩ·cm) water (3 mL) in Ace Glass pressure tubes at left at 25°C or heated to 100°C for 24 h. Experiments were conducted under N2 gas. After this time, functionalized surfaces were rinsed in DI water (3 x 3 mL) and dried in an N2 gas stream. Peroxide stability tests iPr2bimy (1)-functionalized surfaces were placed in a freshly prepared 1% solution of hydrogen peroxide and left at rt for 24 h. After this time, the surfaces were rinsed in DI water (3 x 3 mL) and dried in an N2 gas stream. Electrochemical Studies Electrode preparation and SAM preparation All electrochemical experiments were carried out using a CHI-900b (CH Instruments, Austin, TX) at room temperature and three-electrode configurations. Two home-made electrochemical cells, as shown in Fig. S11a, were employed to accommodate Au/Si substrate and Au ultramicroelectrode experiments. Pt wires and Ag/AgCl/KCl(saturated) were used to serve as counter and reference electrodes respectively. All the measurements were conducted within an N2 protected atmosphere and all the electrolyte solutions were always purged with N2 for at least for 45 minutes prior to the measurement. Au/Si substrates were prepared by electron-beam deposition of 200 nm thickness Au on Si wafer with 20 nm of Ti as the adhesion layer (Western University’s Nanofab). All Au ultramicroelectrodes were home-made by inserting Au microwires (radius~12.5 µm) into a pulled glass capillary tubes and the capillary tubes




S-14

were annealed to seal the wire inside. The tip of the capillary tube was polished with 3-micron lapping films to expose the cross-section of Au wire and then the Au surface was polished down with 0.3-micron and 0.05-micron Al2O3 lapping films. The Au/Si substrates and ultramicroelectrodes were modified by immersion in 1 mM solutions of the corresponding carbene in anhydrous toluene for 24 h at room temperature in a glove box. The substrates and electrodes were rinsed in anhydrous THF (5 x 2mL) and dried under a nitrogen gas stream. Azide-functionalized substrates and electrodes were modified by reaction with ethynylferrocene using CuSO4 and sodium ascorbate solutions as catalyst (vide supra). SAMs of dodecanethiol were prepared by immersing Au/Si substrates in 1 mM ethanol solution overnight at room temperature. After immersion, the substrates were removed from the solution, rinsed with ethanol and blown dry with a nitrogen gas stream. Electrochemical testing (1) Incorporation of redox-active molecules on the surface of the electrode. The properties of SAMs were electrochemically tested by chemically attaching ferrocene to the surface (7(Fc)-Au) and monitoring the oxidation and reduction. Measurements were made in 0.1 M NaClO4 aqueous solutions. The 1st cycle of the CV is not used, since it is usually not a complete cycle. The scanning rate is stated along with figures. Oxidation and reduction peaks are observed at 0.6 V to 0.65 V and 0.45 V respectively, as shown in Fig. 3c. The oxidation current from cycle 5 and 20 show broadened peak tops. This broadening has been demonstrated to be related to the molecular configuration of the SAM molecules (S9). After 20 cycles of scanning, the oxidation peak sizes were analysed by integration of the current density over time. The oxidation electron charges transferred through SAMs were 5.35×10-5 C/cm2, 5.85×10-5 C/cm2 and 4.49×10-5 C/cm2 for the 2nd, the 5th and the 20th cycles. The results show that after 20 cycles of scanning between 0 V and 1 V, a 16% decrease was observed. This decrease is like attributed to decomposition by nucelophilic attack on ferricenium, rather than a decomposition of the film (S10). The number of electrons transferred is evaluated by using the value of the charge transferred in the 2nd cycle, which indicates a density of 3.5±0.5 electrons/ nm2 which therefore corresponds to 3.5±0.5 Fc-carbene molecules /nm2. Laviron plots, as illustrated in Fig. S11b, have been constructed to evaluate the electron charge transfer rates. The electron transfer rate constant through the carbene SAM is estimated to be 26 s-1. The evaluation methods used here have been introduced by Laviron (S11) and further discussed in literature (S12, S13). The values measured belong to the slow side of electron charge transfer rates when compared with a series of thiol SAMs6. An example (S14) with similar electron charge transfer rate is the SAMs formed by Fc(CH2)16SH, which is 28 s-1. This is understandable, as the structure of the molecule at both head and tail groups is significantly more complex than Fc(CH2)16SH. The complexity of the molecule may be responsible for more resistance towards electron charge transfer leading to slightly lower charge transferred rate constants. (2) Testing of redox-active molecules in solution using alkylated films. The electrochemical stability of carbene (6–Au and 1–Au) and thiol (C12S–Au) SAMs were tested respectively by using Fe2+/Fe3+ as a redox probe to monitor the current changes. 5 mM/5 mM K4Fe(CN)6/K3Fe(CN)6 aqueous solutions with 1 M of NaClO4 as the




S-15

supporting electrolyte were employed. Dodecanethiol SAMs on Au were measured under the same condition as a comparison to the two types of carbene SAMs. The CVs of C12S–Au in Fig. S12a show that the 2nd cycle current curve is quite flat and as more CV cycles are scanned, increased current density is observed. The CVs of carbene films (6–Au and 1–Au) in Figs. S12b and S12c show that current due to redox of Fe2+/Fe3+ changed significantly less over 150 cycles of scanning when compared with (C12S–Au). The alkylated carbene film 6–Au demonstrates the best stability among the three SAMs. As shown in Fig. 3d and Fig. S12a/b, the current observed during the 2nd cycle is a few magnitudes larger than C12S–Au, and the curves remain the same with almost no change in current density during 150 cycles of scanning. The relative change in current density relative to the 1st cycle is shown in Fig. 3d in the main text. The C12S–Au current densities are observed to increase along with more cycles of CV scanning and much more significantly than 6–Au or 1–Au. Comparison between 6–Au and C12S–Au in Figs. S12a and S12b shows that 6–Au has less change in current densities than C12S–Au regardless if it is relative current change or the absolute current change that is compared. The results indicate that 6–Au has significant better electrochemical stability than C12S–Au under the conditions tested. Additional experiments were performed as described above, except that the CV measurements were carried out between 0.6 V and -1.4 V. Measurements were started with open-circuit potentials, negative initial scan polarities were used and the scan rate was 0.1 V/s. In this case the 6–Au film showed decomposition after the first cycle (Fig. S13b) which was related to reductive stripping occuring at a higher voltage than in the case of the thiol film (Fig. S13c). Computational details

Density functional theory (DFT) calculations were performed to examine the

structural features and binding energies of 1 on the gold slabs presenting the (111) surface. To construct the slabs, the fcc unit cell of gold was optimized according the method described below. The resulting lattice constant was 4.107 Å, which is in good agreement with literature values of 4.080 Å (S15). A (111) surface was cleaved from the bulk structure and the resulting hexagonal cell was repeated twice in the lateral directions. The slabs used in the calculations were four layers thick, which tests showed was sufficient to converge surface energies to better than 1 mJ/m2. The monomer was then added to the upper surface of the slab at positions corresponding to a-top, bridging, and three-fold sites. These structures were relaxed while keeping the positions of the gold atoms in the bottom two layers of the slab fixed at their bulk positions. Analogous calculations were performed on the bare slab, i.e. the atoms in the upper two layers were relaxed while keeping those in the bottom two layers at fixed positions, and on the monomer, where all atoms were allowed to relax. The heights of the cells used in the calculations with the slab models were selected to ensure that at least 10 Å of vacuum space was present between periodic images. In addition, dipole correction techniques (S16) were employed to eliminate spurious electrostatic interactions between periodic images along the direction normal to the slabs.

All DFT calculations were performed using the PBEsol exchange correlation




S-16

functional (S17). Core electrons were treated with projector augmented wavefunction potentials (S18) including scalar relativistic effects on all atoms. The valence states were represented with a planewave basis set expanded up to a kinetic energy cutoff of 40 Ry, and a kinetic energy cutoff of 400 Ry was used to represent the augmentation charges. This level of theory reproduces experimental Au-C bond lengths of selected compounds (S19) to within 0.012 Å. A 3×3×1 set of k-points was used in the calculations involving slabs. These details were sufficient to converge the total energies of the systems examined to better than 1 meV/atom. All calculations were performed with the Quantum-Espresso simulation package (S20).




S-17

Fig. S1. Representative XPS data for treatment of 1–Au(111) surfaces with 1 mM solutions of dodecylsulfide in toluene for 24 h at room temperature. The XPS of the resulting samples show no sulfur S(2p) peak, (C), and they demonstrate retention of the NHC in the correct C/N ratio (A, B). [A, N(1s), B, C(1s), C, S(2p)]

Fig. S2a. Representative XPS data for treatment of dodecanethiol–protected Au(111) surfaces with solutions of iPr2bimy (1) for 24 h at room temperature. Integration of XPS data shows that approximately 40% of the S(2p) signal remains (C, the two signals are due to S(2p3/2 and 2p1/2)). Additionally, an N(1s) signal observed indicating displacement of ca. 60% of the thiol by the NHC. (Note that The C(1s) signal (B) simply shifts since the dodecane thiol on the original nanoparticle also contains carbon) [A, N(1s), B, C(1s), C, S(2p)]

Fig. S2b. Representative XPS data for treatment of dodecanethiol–protected

Au(111) surfaces with solutions of IMes (3) for 24h at room temperature. Integration of XPS data shows that approximately 45% of the S(2p) signal remains (C) and an N(1s) signal (A) is observed indicating displacement of ca. 55% of the thiol by the NHC. (Note the two signals in C are due to S(2p3/2 and 2p1/2) and note also that the C(1s) signal (B) simply shifts upon replacement with the carbene since the dodecane thiol on the original nanoparticle also contains carbon). [A, N(1s), B, C(1s), C, S(2p)]




S-18

Fig. S3a. Representative XPS data for treatment of benzenethiol–protected Au(111)

surfaces with solutions of iPr2bimy (1) for 24h at room temperature. Red is before, and green after. [A, N(1s), B, C(1s), C, S(2p)]

Fig. S3b. Representative XPS data for treatment of benzene-1,2-dithiol–protected

Au(111) surfaces with solutions of iPr2bimy (1) for 24h at room temperature. Red is before, and green after. [A, N(1s), B, C(1s), C, S(2p)]

Fig. S3c. Representative XPS data for treatment of propane-1,3-dithiol–protected

Au(111) surfaces with solutions of iPr2bimy (1) for 24h at room temperature. Red is before, and green after. [A, N(1s), B, C(1s), C, S(2p)]




S-19

Fig. S4a. Representative XPS data for treatment of benzenethiol–protected Au(111)

surfaces with solutions of IMes (3) for 24 h at room temperature. Red is before, and green after. [A, N(1s), B, C(1s), C, S(2p)]

Fig. S4b. Representative XPS data for treatment of benzene-1,2-dithiol–protected

Au(111) surfaces with solutions of IMes (3) for 24 h at room temperature. Red is before, and green after. [A, N(1s), B, C(1s), C, S(2p)]

Fig. S4c. Representative XPS data for treatment of propane-1,3-dithiol–protected

Au(111) surfaces with solutions of IMes (3) for 24 h at room temperature. Red is before, and green after. [A, N(1s), B, C(1s), C, S(2p)]




S-20

Fig. S5. Various bonding modes calculated for iPr2bimy (1) with Au(111) and Au–C

bond energies calculated by DFT. Bonding of the NHC to the surface via an on-top site provides the most stable complex with a bond length in the region expected for molecular NHC–Au complexes. Note that any stabilizing effect of stacking of the benzimidazolylidene units was not factored into these calculations which feature isolated NHCs on Au(111).




S-21

Fig. S6. High magnification image of IMes (3) on Au(111).

0 Å

3 Å

20 nm




S-22

Fig. S7. 13C CP/MAS NMR spectra of IMes (3)-protected Au nanoparticles immediately upon ligand exchange and following exposure to ambient conditions for 15 weeks. The carbene C atom at 183.5 ppm is indicated in blue. Small peaks labeled “ssb” are spinning side bands associated with the aromatic C atoms between 123.9 and 140.9 ppm (shown in red). The signals from the methyl carbons of IMes are shown in green. Note that nanoparticles were vigorously rinsed prior to analysis and although the presence of molecular species is unlikely, this cannot be completely ruled out at this time.

Fig. S8a. Films of iPr2bimy (1) on Au(111) before (red) and after (green) treatment

with decalin at 100°C for 24 h.




S-23

Fig. S8b. Films of iPr2bimy (1) on Au(111) before (red) and after (green) exposure

to pH 2 (left) and pH 12 (right) at room temperature for 24 h.

Fig. S8c. Films of iPr2bimy (1) on Au(111) before (red) and after (green) exposure

to pH 2 (left) and pH 12 (right) at 100°C for 24 h.

Fig. S8d. Films of iPr2bimy (1) on Au(111) before (red) and after (green) exposure

to water at room temperature for 1 month.

Fig. S8e. Films of iPr2bimy (1) on Au(111) before (red) and after (green) exposure

to 3% H2O2 for 24 h showing decomposition.




S-24

Fig. S9a. Films of IMes (3) on Au(111) before (red) and after (green) exposure to

water at room temperature for 1 month.

Fig. S9b. Films of IMes (3) on Au(111) before (red) and after (green) treatment with decalin at 100°C for 24 h.

Fig. S9c. Films of IMes (3) on Au(111) before (red) and after (green) exposure to

pH 2 (left) and pH 12 (right) at 100°C for 24 h.




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Fig. S10a. Representative XPS data for the product of reaction of azide-terminated NHC (7) with Au/Si and subsequent conversion into a triazole by a Cu-catalyzed click reaction with ethynylferrocene. Red and blue lines indicate the fits to the XPS data.

Fig. S10b. Representative XPS data for methyl-terminated NHC 6 anchored on Au/Si surfaces (black) and the same surfaces treated with ethynylferrocene under click conditions (red). The XPS of the resulting samples show neither copper Cu(2p) (C), nor iron Fe(2p) (D) peaks, and demonstrate retention of the NHC in the correct C/N ratio (A, B). [A, N(1s), B, C(1s)], suggesting no physabsorption of ethynylferrocene on the alkyl-terminated NHC 6.




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Fig. S11a. Electrochemical cell configurations for measurement with (a) Au/Si and (b) Au ultramicroelectrode.

Fig. S11b. Determination of the electron transfer rate constants through 7(Fc)-Au SAMs using Laviron plots.(S12) The plot was constructed from cyclic voltammograms, obtained with using same conditions to those in Fig. 3 in the main text and varied scanning rates: 0.25 V/s, 0.5 V/s, 1 V/s and 2 V/s.

Reference electrode (Ag/AgCl/KCl (sat))

Working electrodeFc-‐carbene on AuSi

Counter electrodePt wire

Nitrogen gas

Salt bridge

Reference electrode (Ag/AgCl/KCl (sat))

Working electrodeFc-‐carbene on AuSi

Counter electrodePt wire

Nitrogen gas

Salt bridge

a) b)

0.5 1.0 1.5 2.0 2.5 3.0 3.5

-150

-100

-50

0

50

100

150

E p-E1/

2 /m

V

log (v /mV s-1)




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Fig. S12. Cyclic voltammograms of (a) C12SH–Au/Si, (b) 6–Au/Si and (c) 1–Au/Si. The CVs were obtained in 5 mM/5 mM K4Fe(CN)6/K3Fe(CN)6 aqueous solution with 1 M of NaClO4 as the supporting electrolyte. Scanning rates: 0.1 V/s.

0.0 0.2 0.4 0.6-750

-500

-250

0

250

500

E / V (vs.Ag/AgCl)

I / µ

A/cm

2

The 2nd cycles The 10th cycles The 20th cycles The 40th cycles The 80th cycles The 150th cycles

0.0 0.2 0.4 0.6-2000

-1000

0

1000

2000

E / V (vs.Ag/AgCl)

I / µ

A/cm

2


0.0 0.2 0.4 0.6-200

-100

0

100

200


E / V (vs.Ag/AgCl)

I / µ

A/cm

2

a)

c)b)




S-28

a)

c)

Fig. S13. Cyclic voltammograms of (a) C12SH–Au/Si and (b) 6–Au/Si between 0.6 V and –1.4V vs Ag/AgCl begining with open circuit potential and negative initial scan polarities. (c) Electrochemical desorption of C12SH–Au/Si and 6–Au/Si. The CVs were obtained in 5 mM/5 mM K4Fe(CN)6/K3Fe(CN)6 aqueous solution with 1 M of NaClO4 as the supporting electrolyte. Scanning rates: 0.1 V/s.

-0.6 -0.3 0.0 0.3 0.6-450

-300

-150

0

150

E / V (vs.Ag/AgCl)

I / µ

A/cm

2

The 1st cycle The 2nd cycle The 3rd cycle The 4th cycle The 5th cycle

-1.2 -0.9 -0.6 -0.3 0.0

-80

-60

-40

-20

0

I / µ

A/cm

2

E / V (vs.Ag/AgCl)

Carbene-C12 Thiol-C12

-0.6 -0.3 0.0 0.3 0.6-1500

-1000

-500

0

500

1000

1500 The 1st cycle The 2nd cycle The 3rd cycle The 4th cycle The 5th cycle

E / V (vs.Ag/AgCl)

I / µ

A/cm

2

b)




S-29

Fig. S14. Representative XPS data for iPr2bimy (1) on gold surfaces. The black line shows the experimental data. The red line is the overall fitted spectra for 1 on flat Au(111): (A) N(1s) and (B) C(1s); while the blue line is the overall fitted spectra for 1 on gold nanoparticles: (C) N(1s), (D) C(1s), and (E) S(2p). (Fig. 1A, entry 1)




S-30

Fig. S15. Representative XPS data for Enders carbene (2) on gold surfaces. The black line shows the experimental data. The red line is the overall fitted spectra for 2 on flat Au(111): (A) N(1s) and (B) C(1s). The blue line is the overall fitted spectra for 2 on gold nanoparticles: (C) N(1s), (D) C(1s), and (E) S(2p). (Fig. 1A, entry 2)




S-31

Fig. S16. Representative XPS data for IMes (3) on gold surfaces. The black line shows the experimental data. The red line is the overall fitted spectra for 3 on flat gold Au(111) (A) N(1s) and (B) C(1s). The blue line is the overall fitted spectra for 3 on gold nanoparticles: (C) N(1s), (D) C(1s), and (E) S(2p). (Fig. 1A, entry 3)




S-32

Fig. S17. Representative XPS data for SIMes carbene (4) on gold surfaces. The black line shows the experimental data. The red line is the overall fitted spectra for 4 on flat Au (111) (A) N(1s) and (B) C(1s). The blue line is the overall fitted spectra for 4 on gold nanoparticles: (C) N(1s), (D) C(1s), and (E) S(2p). (Fig. 1A, entry 4)




S-33

Fig. S18. Representative XPS data for IPr (5) on gold surfaces. The black line shows the experimental data. The red line is the overall fitted spectra for 5 on flat gold Au(111) (A) N(1s) and (B) C(1s). The blue line is the overall fitted spectra for 5 on gold nanoparticles: (C) N(1s), (D) C(1s), and (E) S(2p). (Fig. 1A, entry 5)




S-34

C :\1-‐Work\NMR \Developed data\IE r-‐29-‐8.001.001.1r.esp

23

14

65

O7

N+21

O-24

O22

NH2 23 89

1011

1213

1415

1617

1819

Br20

IEr-29-8.001.001.1r.esp

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0Chemical Shift (ppm)

12.634.292.042.092.002.082.030.990.970.97

CHLOROFORM-d

9

11,12,13,14,15,16

56

10,17

18198

2 23

1.29

1.43

1.44

1.77

1.781.841.

861.

873.40

3.41

3.43

3.91

3.92

3.945.

88

6.756.77

7.06

7.06

7.08

7.087.

547.

54

IEr-29-8.002.001.1r.esp

170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0Chemical Shift (ppm)

CHLOROFORM-d

5 26 198

31 4

25.9

428

.14

28.7

229

.07

29.3

029

.47

32.8

034

.04

68.7

676

.74

77.0

077

.25

107.

11

119.

96

127.

06

131.

54

139.

74

150.

27

Fig. S19. 1H and 13C{1H} NMR spectra of 4-(12-bromododecyloxy)-2-nitroaniline.




S-35

Fig. S20. 2D 1H–1H COSY map of 4-(12-bromododecyloxy)-2-nitroaniline.




S-36

Fig. S21. 2D 1H–13C HSQC map of 4-(12-bromododecyloxy)-2-nitroaniline.




S-37

IEr-30.002.001.1r.esp


CHLOROFORM-d

22

12

9

11

82

7

5

6

4

26.0

428.1

428

.72

29.2

729

.39

29.5

032

.80

34.0

3

68.6

9

97.9

6

114.

0711

6.11

131.

18

136.

3713

9.71

156.

63

89

7

4

65

N3

2

NH1

O10 11

1213

1415

1617

1819

2021

22Br23

IEr-30DMSO.001.001.1r.esp

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0Chemical Shift (ppm)

12.344.262.142.201.952.011.030.920.960.920.52

DMSO-d691

13,20

211

6

14,15,16,17,18,19

217

22

12

1.25

1.33

1.35

1.401.71

1.77

3.50

3.95

6.786.807.

04

7.43

7.458.

088.

14

Fig. S22. 1H and 13C{1H} NMR spectra of 5-(12-bromododecyloxy)-1H-benzo[d]imidazole.




S-38

Fig. S23. 2D 1H–1H COSY map of 5-(12-bromododecyloxy)-1H-benzo[d]imidazole.




S-39

Fig. S24. 2D 1H–13C HSQC map of 5-(12-bromododecyloxy)-1H-benzo[d]imidazole.




S-40

89

7

4

65

N3

2

NH1

O10 11

1213

1415

1617

1819

2021 N

N+N-

IEr-37.001.001.1r.esp

10 9 8 7 6 5 4 3 2 1 0Chemical Shift (ppm)

14.262.141.822.042.002.091.040.961.010.93

DMSO-d6

13

2 7 2111

922

12

14,15,16,17,18,19,20

6

8.06

7.45

7.43 7.05

6.79

6.77 3.96 3.

953.

933.

30 3.28

3.27 2.

501.

72 1.70

1.69

1.51 1.

501.

24

IEr-37.002.001.1r.esp


DMSO-d6

12

2

5 4

9

227

6

11

8

154.

88

141.

3913

7.78

133.

45 116.

2711

1.75

98.1

9

67.8

9

50.6

1

28.9

828

.89

28.7

828

.50

28.2

126

.11

25.5

8

Fig. S25. 1H and 13C{1H} NMR spectra of 5-(12-azidododecyloxy)-1H-benzo[d]imidazole.




S-41

Fig. S26. 2D 1H–1H COSY map of 5-(12-azidododecyloxy)-1H-benzo[d]imidazole.




S-42

Fig. S27. 2D 1H–13C HSQC map of 5-(12-azidododecyloxy)-1H-benzo[d]imidazole.




S-43

94

8

5

76

O14 15

1617

1819

2021

2223

2425

26

N+3

2

N1

10

12

11

30

13

31

N27

N+28

N-29

IEr-85.001.001.1r.esp

11 10 9 8 7 6 5 4 3 2 1 0Chemical Shift (ppm)

16.274.0612.242.002.072.000.920.940.940.89

CHLOROFORM

9

25

167

2

6

15 26

17,18,19,20,21,22,23,24

11,13,30,31

10,12

10.6

7

7.67

7.64

7.23 7.

11

5.12

4.06 3.24

2.00

1.84

1.59

1.49

1.28

IEr-85.003.001.1r.esp

170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10Chemical Shift (ppm)

CHLOROFORM

13,31

11,30

10

26

4

12

9765 1528

158.

76

138.

52

132.

01

124.

70 117.

2911

4.46

96.6

2

69.3

0

52.3

751

.94

51.4

1

29.4

329

.27

29.0

4 22.2

622

.18

Fig. S28. 1H and 13C{1H} NMR spectra of 1,3-diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazolium iodide




S-44

Fig. S29. 2D 1H–1H COSY map of 1,3-diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazolium iodide




S-45

Fig. S30. 2D 1H–13C HSQC map of 1,3-diisopropyl-5-(12-(azido)dodecyloxy)-benzo[d]imidazolium iodide




S-46

ol-ferrocene click500.002.001.1r.esp

11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0Chemical Shift (ppm)

16.192.6413.121.996.851.742.041.832.081.040.901.010.80

H2ODCM5

629,32

30,31

26

2027

16

24

7

34,36,37,38

33,35

8,9,10,11,12,13,14,15

17,39,40,41,42,43

1.27

1.31

1.46

1.78

1.89

4.02

4.26

4.314.

67

5.035.

32

7.11

7.19

7.217.

507.

64

10.9

420

21

19

22

2627

O18 17

1615

1413

1211

109

87

6

N+25

24

N23

33

35

34

37

36

38

N1

N2 N

35 428 29

303231

39 404143 42

Fe

ol-ferrocene click500.001.001.1r.esp

176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8 0Chemical Shift (ppm)

DCM

35

6

33

30,31

29,32

17

39,40,41,42,43

16 34,36,37,38

27

2228

26214

5

24 2019

159.

27

146.

77

139.

94

132.

68

125.

47

119.

4211

7.62

114.

91

97.1

1

76.4

3

69.9

869

.03

67.0

4

54.4

354

.21 54

.00

53.7

853

.56

52.6

252

.21

50.7

3

30.7

830

.00

29.9

129

.50

22.6

022

.50

ol-ferrocene click500-rep.001.001.1r.esp

74 73 72 71 70 69 68 67 66Chemical Shift (ppm)

30,31 29,32

17

67.0

4

69.0

3

69.8

969

.98

Fig. S31. 1H and 13C{1H} NMR spectra of 5-(12-(4-(ferrocenyl)-1H-1,2,3-triazol-1-yl)dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide




S-47

Fig. S32. 2D 1H–1H COSY map of 5-(12-(4-(ferrocenyl)-1H-1,2,3-triazol-1-yl)dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide




S-48

Fig. S33. 2D 1H–13C HSQC map of of 5-(12-(4-(ferrocenyl)-1H-1,2,3-triazol-1-yl)dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide




S-49

1

2

6

3

5

4NH2 22

O7

N+20O-

23O21

89

1011

1213

1415

1617

1819

IR3-6-11-30-NMR400.001.001.1R.esp

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0Chemical Shift (ppm)

3.0716.192.142.012.030.981.011.901.00

2DMSO

225

68

10

19

9

11,12,13,14,15,16,17,18Water

0.85

1.24

1.381.673.

89

6.977.00

7.13

7.23

7.34

7.35

IR3-6-11-30-NMR400.002.001.1r.esp

152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8Chemical Shift (ppm)

9

11,12,13

16

6198 1817

12

10

43

5

14.3

8

22.5

425

.89

29.0

029

.15

29.4

129

.47

31.7

5

68.5

0

106.

28121.

15

127.

9012

9.59

142.

29

148.

99

Fig. S34. 1H and 13C{1H} NMR spectra of 4-(dodecyloxy)-2-nitroaniline.




S-50

Fig. S35. 2D 1H–1H COSY map of 4-(dodecyloxy)-2-nitroaniline.




S-51

Fig. S36. 2D 1H–13C HSQC map of 4-(dodecyloxy)-2-nitroaniline.




S-52

8

9

7

4

6

5

NH1

O10

N3

1112

1314

1516

1718

1920

2122

2

Ir3-7-600-CDCl3.001.001.1r.esp

8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0Chemical Shift (ppm)

3.3314.172.102.002.002.041.030.970.990.98

CHLOROFORM-d

14

2

226

7

9

13

15,16,17,18,19,20,21

1211

0.87

0.89

0.90

1.27

1.35

1.46

1.481.791.80

1.813.963.

973.

98

6.93

6.957.09

7.54

7.558.

00

Ir3-7-CDCl3-NMR400.002.001.1r.esp


5 48

7

26

9

13.8

8

22.4

925

.96

29.1

729

.27

29.4

431

.74

68.5

2

97.8

8

112.

6411

6.32

130.

7613

3.64

140.

34

155.

84

Fig. S37. 1H and 13C{1H} NMR spectra of 5-(dodecyloxy)-1H-benzo[d]imidazole




S-53

Fig. S38. 2D 1H–1H COSY map of 5-(dodecyloxy)-1H-benzo[d]imidazole




S-54

Fig. S39. 2D 1H–13C HSQC map of 5-(dodecyloxy)-1H-benzo[d]imidazole




S-55

10

12

8

9

7

4

6

5

N1

O14

N+3

1516

1718

1920

2122

2324

2526

2

13

28

11

27

Ir-8b.001.001.1r.esp

10 9 8 7 6 5 4 3 2 1Chemical Shift (ppm)

3.0316.712.2414.412.201.910.961.001.030.87

CHLOROFORM

9

7

26

2

6

17

10,12

16,11,13,27,28

15

18,19,20,21,22,23,24,25

0.84

0.86

0.87

1.25

1.48

1.82

1.83

1.84

1.84

4.06

5.157.

13

7.227.66

7.6910

.59

Ir-8b.003.001.1r.esp

160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10Chemical Shift (ppm)

19

17

18

20

22

25

244

7 65 2692 15 10,128

14.0

622.2

722

.35

29.0

329

.34

29.5

529

.62

31.8

8

52.0

052

.42

69.4

576.7

777

.08

77.4

0

96.7

9

114.

5811

7.41

124.

79

132.

10

138.

45

158.

88

Fig. S40. 1H and 13C{1H} NMR spectra of 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide.




S-56

Fig. S41. 2D 1H–1H COSY map of 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide




S-57

Fig. S42. 2D 1H–13C HMQC map of 5-(dodecyloxy)-1,3-diisopropyl-1H-benzo[d]imidazol-3-ium iodide.




S-58

References: S1. Scofield, J. H. Hartree-Slater subshell photoionization cross-sections at 1254 and

1487 eV. J. Electron Spectrosc. Relat. Phenom. 8, 129-137 (1976). S2. Zahl, P., Wagner, T., Moller, R., & Klust, A. Open source scanning probe

microscopy control software package GXSM. J. Vac. Sci. Tech. B 28, C4E39-C34E47 (2010).

S3. Huynh, H. V., Han, Y., Ho, J. H. H., & Tan, G. K. Palladium(II) Complexes of a Sterically Bulky, Benzannulated N-Heterocyclic Carbene with Unusual Intramolecular C-H···Pd and Ccarbene···Br Interactions and Their Catalytic Activities. Organometallics 25, 3267-3274 (2006).

S4. Enders, D., Breuer, K., Raabe, G., Runsink, J., Teles, J. H., Melder, J.-P., Ebel, K., & Brode, S. Preparation, Structure, and Reactivity of 1,3,4-Triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene, a New Stable Carbene. Angew. Chem. Int. Ed. 34, 1021-1023 (1995).

S5. Arduengo, A. J.,. Dias, H. V. R, Harlow, R. L., & Kline, M. Electronic stabilization of nucleophilic carbenes. J. Am. Chem. Soc. 114, 5530-5534 (1992).

S6. Arduengo, A. J., Krafczyk, R., Schmutzler, R., Craig, H. A., Goerlich, J. R., Marshall, W. J., & Unverzagt, M. Imidazolylidenes, imidazolinylidenes and imidazolidines. Tetrahedron 55, 14523-14534 (1999).

S7. Jafarpour, L., Stevens, E. D., & Nolan, S. P. A sterically demanding nucleophilic carbene: 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Thermochemistry and catalytic application in olefin metathesis. J. Organomet. Chem. 606, 49-54 (2000).

S8. Hanan, E. J., Chan, B. K., Estrada, A. A., Shore, D. G., & Lyssikatos, J. P. Mild and General One-Pot Reduction and Cyclization of Aromatic and Heteroaromatic 2-Nitroamines to Bicyclic 2H-Imidazoles. Synlett, 2759-2764 (2010).

S9 Orlowski, G. A., Chowdhury, S., Long, Y. T., Sutherland, T. C. & Kraatz, H. B. Electrodeposition of ferrocenoyl peptide disulfides. Chem. Comm., 1330-1332 (2005).

S10 Prins, R., Korswagen, A. R. & Kortbeek, A. G. T. G. Decomposition of the ferricenium cation by nucleophilic reagents. J. Organomet. Chem. 39, 335-344 (1972).

S11 Laviron, E. General expression of the linear potential sweep voltammogram in the case of diffusionless electrochemical systems. J. Electroanal. Chem. Interfacial Electrochem. 101, 19-28 (1979).

S12 Chahma, M., Lee, J. S. & Kraatz, H.-B. Fc-ssDNA conjugate: electrochemical properties in a borate buffer and adsorption on gold electrode surfaces. J. Electroanal. Chem. 567, 283-287 (2004).

S13 Eckermann, A. L., Feld, D. J., Shaw, J. A. & Meade, T. J. Electrochemistry of redox-active self-assembled monolayers. Coord. Chem. Rev. 254, 1769-1802 (2010).

S14 Smalley, J. F. et al. Heterogeneous Electron-Transfer Kinetics for Ruthenium and Ferrocene Redox Moieties through Alkanethiol Monolayers on Gold. J. Am. Chem. Soc. 125, 2004-2013 (2003).

S15. Kittel, C. Introduction to Solid State Physics, 7th ed. (John Wiley & Sons, New




S-59

York, 1996). S16. Bengtsson, L. Dipole correction for surface supercell calculations, Phys. Rev. B,

59, 12301-12304 (1999). S17. Perdew, J. P., Ruzsinszky, A., Csonka, G. I., Vydrov, O. A., Scuseria, G. E.,

Constantin, L. A., Zhou, X., & Burke, K. Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces, Phys. Rev. Lett., 100, 136406, (2008).

S18. Blöchl, P. E. Projectory augmented-wave method Phys. Rev. B, 50 17953-17979 (1994).

S19. Xu, X., Kim, S. H., Zhang, X., Das, A. K., Hirao, H., & Hong S. H. Abnormal N-Heterocyclic Carbene Gold(I) Complexes: Synthesis, Structure, and Catalysis in Hydration of Alkynes Organometallics, 32 164-171 (2013).

S20. Giannozzi, P., et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials J. Phys.: Condens. Matter, 21 395502 (2009).


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