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Intramolecular heterolytic dihydrogen cleavage by a

bifunctional frustrated pyrazolylborane Lewis pair

Eileen Theuergarten, Danny Schlüns, Jörg Grunenberg, Constantin G. Daniliuc,

Peter G. Jones and Matthias Tamm*

* Institut für Anorganische und Analytische Chemie, Technische Universität

Carolo-Wilhelmina, Hagenring 30, D-38106 Braunschweig, .

Fax: +49 (251) 391-5309; Tel: +49 (251) 391-5387; E-mail: [email protected]

Contents:

1. Experimental Details

2. NMR Spectra

3. X-ray crystal structure determinations

4. Computational Details of all optimized structures Calculated structures and XYZ coordinates

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1. Experimental Details

Methods and materials: Reactions with air- and moisture-sensitive compounds were carried out under a dry atmosphere in a glovebox (MBraun 200B) or with standard Schlenk techniques with a high vacuum line. The glassware was flame dried prior to use. Solvents were dried and purified by a SPS-System from MBraun and stored over molecular sieve (4 Å) until they were needed. 5.0 was purchased from Westfalen AG and dried through a P4O10 column prior to use. The 1H, 13C, 11B and 19F NMR spectra were recorded on Bruker DPX 200 (200 MHz), Bruker AV-II 300 (300 MHz) and Bruker DRX 400 (400 MHz), devices. Tetramethylsilane (TMS) was used as internal standard for 1H and 13C and the internal standard 19 trichlorofuormethane (CFCl3) was used for the F NMR spectra. Chemical shifts are reported in ppm (parts per million). The coupling constants (J) are expressed in Hertz (Hz) and the splitted signals are labeled as s (singlet), d (doublet), m (multiplet) and br s (broad singlet). Elemental analyses were carried out with a Vario Micro Cube System. All starting materials were purchased from Aldrich or Acros and used without further purification. 3,5-Di-tert-butylpyrazole (3)[1], 1,3- [2] [3] [4] di-tert-butylimidazolin-2-ylidene (2) , B(C6F5)3 , and HB(C6F5)2 were prepared according to the literature procedures.

[1] Z.-X. Wang and H.-L. Qin, Green Chem. 2004, 6, 90. [2] a) A. J. Arduengo III., US Patent 5 077414, 1991; b) A. J. Arduengo III., H. Bock, H. Chen, M. Denk, D. A. Dixon, J. C. Green, W. A. Herrmann, N. L. Jones, M. Wagner, R. West, J. Am. Chem. Soc. 1994, 116, 6641 [3] C. Wang, G. Erker, G. Kehr, K. Wedeking and R. Fröhlich, Organometallics 2005, 24, 4760. [4] D. J. Parks, W. E. Piers and G. P. A. Yap, Organometallics 1998, 17, 5492-5503.

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Preparation of trans-5:

HB(C6F5)2 (0.75 g, 2.16 mmol) was suspended in toluene (10 mL) and a solution of 3,5-di-tert-butylpyrazole (3) (0.39 g, 2.16 mmol) in toluene (5 mL) was added. The suspension was stirred for 2 h at room temperature to obtain a clear colorless solution. The solvent was removed under vacuum yielding 1.035 g (91%) of a white solid. Crystals of trans-5 were 1 isolated from a saturated hexane solution at -30°C. H NMR (300 MHz, C6D6): δ = 0.83 (9H, s, 4 CH3), 1.32 (9H, s, CH3), 5.00 (1H, br s, BH), 5.82 (1H, d, JHH= 2.66 Hz, CH), 10.23 (1H, br s, ν 13 ½= 15 Hz, NH). C NMR (75 MHz, C6D6): δ = 28.8 (CH3, Me), 29.4 (CH3, Me), 31.0 (Cq, 1 CMe3), 32.9 (Cq, CMe3), 102.2 (CH, C=CHC), 135.5 (Cq, m, meta-C6F5), 140.3 (Cq, d, JCF= 179 1 Hz, para-C6F5), 148.0 (Cq, d, JCF= 224 Hz, ortho-C6F5), 156.2 (Cq, N=CCCH), 162.6 (Cq, 11 19 N=CCCH). B NMR (96 MHz, C6D6): δ = -13.6 (br s). F NMR (376 MHz, C6D6): δ = -135.0

(4F, m, ortho-C6F5 ), -157.6 (2F, m, para-C6F5), -163.2 (4F, m, meta-C6F5). Elemental analysis:

Found: C 52.31, N 5.25, H 4.12 for C23H21BF10N2: C 52.50, N 5.32, H 4.02.

Preparation of 6:

A 1:1 mixture of B(C6F5)3 (437 mg, 0.86 mmol) and 1,3-di-tert- butylimidazolin-2-ylidene (1) (154 mg, 0.86 mmol) was dissolved in toluene (10 mL) and immediately treated with a toluene solution (5 mL) of trans-5 (450 mg, 0.86 mmol). A white precipitate is formed within one minute. The mixture was stirred for an additional 2 h at room temperature. After filtration and evaporation of the solvent, 433 mg (95%) of 6 are isolated as a yellow oil. This oil is highly air- and moisture-sensitive and decomposes slowly at room temperature. 1 Colorless single crystals were isolated from hexane solution -30°C. H NMR (300 MHz, C6D6): 13 δ = 1.09 (18H, s, CH3), 6.22 (1H, s, CH). C NMR (75 MHz, C6D6): δ = 30.4 (CH3, Me), 32.7 1 (Cq, CMe3), 110.9 (CH, C=CHC), 136.2 (Cq, m, meta- C6F5), 140.2 (Cq, d, JCF= 168 Hz, para- 1 11 C6F5), 147.6 (Cq, d, JCF= 247 Hz, ortho-C6F5), 165.8 (Cq, N=CCCH). B NMR (96 MHz, C6D6): 19 δ = 43.1 (br s). F NMR (376 MHz, C6D6): δ = -130.9 (4F, m, ortho-C6F5), -148.7 (2F, m, para-

C6F5), -161.5 (4F, m, meta-C6F5) Elemental analysis: Found: C 52.70, N 5.34, H 3.65 for

C23H19BF10N2: C 52.67, N: 5.34, H: 4.07

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Dihydrogen Activation:

On NMR scale: 182 mg (0.35 mmol)of 6 were dissolved in 0.6 mL of toluene-d8 and transferred into an NMR tube. The light yellow solution is purged with H2 via a cannula for 20 min. After sealing the NMR tube the spectra were recorded. The spectra immediately recorded after the 1 reaction shows a trans-5/cis-5 ratio of 1.00:0.24. H NMR (200 MHz, toluene-d8) for trans-5: δ = 4 0.81 (9H, s, CH3), 1.29 (9H, s, CH3), 5.80 (1H, d, JHH= 2.52 Hz, CH), 10.20 (1H, br s, ν ½= 4 11.63 Hz, NH) for cis-5: δ =0.76 (9H, s, CH3), 0.84 (9H, s, CH3), 5.95 (1H, d, JHH= 2.77 Hz, 13 CH), 10.00 (1H, br s, ν ½= 6.95 Hz, NH),. C NMR (50 MHz, toluene-d8): δ = 28.8 (CH3, Me),

29.3 (CH3, Me), 31.0 (Cq, CMe3), 32.9 (Cq, CMe3), 102.1 (CH, C=CHC), 135.2 (Cq, br s, meta-

C6F5), 140.0 (Cq, br s, para-C6F5), 150.7 (Cq, br s, ortho-C6F5), 156.2 (Cq, N=CCCH), 162.7 (Cq, 11 19 N=CCCH). B NMR (96 MHz, toluene-d8): δ = -13.74 (br s). F NMR (376 MHz, toluene-d8) trans-5: δ = -135.1 (4F, m, ortho-C6F5), -157.6 (2F, m, para-C6F5), -163.3 (4F, m, meta-C6F5), for cis-5: δ = -139.29 (4F, m, ortho-C6F5), -159.38 (2F, m, para-C6F5), -166.49 (4F, m, meta-

C6F5).

Catalytic of N-(benzylidene)benzylamine: N-(Benzylidene)benzylamine (519 mg, 2.6 mmol) and 8 mol% (0.21 mmol) trans-5 were dissolved in toluene (35 mL) and transferred into an autoclave. The reaction mixture was heated to 110°C under 2 bar of dihydrogen for 14 h. After cooling the reaction mixture to ambient temperature, the solvent was evaporated, and the conversion was determined by 1H NMR 1 spectroscopy in CDCl3. The H NMR spectrum showed 63% conversion of N- (benzylidene)benzylamine to bis(benzyl)amine.

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2. Selected NMR Spectra

1 H NMR (C6D6)

13 1 C{ H} NMR (C6D6)

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19 1 F{ H} NMR (C6D6)

11 1 B{ H} NMR (C6D6)

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1 H NMR (C6D6)

13 1 C{ H}NMR (C6D6)

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19 1 F{ H} NMR (C6D6)

11 1 B{ H} NMR (C6D6)

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1 H NMR (toluene-d8)

13 1 C{ H} NMR (toluene-d8)

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19 1 F{ H} NMR (toluene-d8)

11 1 B{ H} NMR (toluene-d8)

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3. X-ray crystal structure determinations

X-Ray structure determination of trans-5:

Crystal data: C23H21BF10N2, M = 526.23, triclinic, P1 , a = 10.1307(4), b = 10.1737(6), c =

3 12.0636(6) Å, α = 87.644(4),  = 75.184(4), γ = 71.958(6)°, Z = 2, V = 1141.93(10) Å , Dx =

1.530 Mg m–3,  = 1.30 mm–1, T = 100(2) K. Data collection: A crystal 0.21 × 0.15 × 0.12 mm was used to record 18717 intensities to 2 145° on an Oxford Diffraction Xcalibur diffractometer using mirror-focussed Cu K radiation. An absorption correction was performed on the basis of multi-scans. Structure refinement: The structure was refined anisotropically on F2 using the program SHELXL-97 (G.M. Sheldrick, University of Göttingen, Germany). Hydrogen atoms were included using rigid methyl groups or a riding model. The hydrogen atoms at N2 and B were refined freely. The final wR2 was 0.0829 for 339 parameters and all 4716 unique reflections, with conventional R1 (F > 4(F)) 0.0317; max.  0.30 e Å–3; S 1.02.

X-Ray structure determination of 60.5 hexane:

Crystal data: C26H26BF10N2, M = 567.30, triclinic, P , a = 9.6918(2), b = 10.6951(2), c =

3 13.4413(4) Å, α = 70.662(2),  = 88.369(2), γ = 84.317(2)°, Z = 2, V = 1308.17(5) Å , Dx = 1.440

Mg m–3,  = 0.13 mm–1, T = 100(2) K. Data collection: A crystal 0.26 × 0.25 × 0.18 mm was used to record 46023 intensities to 2 54.9° on an Oxford Diffraction Xcalibur E diffractometer using monochromated Mo K radiation. An absorption correction was performed on the basis of multi-scans. Structure refinement: The structure was refined anisotropically on F2 using the program SHELXL-97 (G.M. Sheldrick, University of Göttingen, Germany). Hydrogen atoms were included using rigid methyl groups or a riding model. The hydrogen atom at N2 was refined Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010 freely. The final wR2 was 0.0731 for 363 parameters and all 5970 unique reflections, with conventional R1 (F > 4(F)) 0.0305; max.  0.30 e Å–3; S 0.91. Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010

4. Computational Details

All computations were performed using the hybrid density functional method M06-2X implemented in the Gaussian09 program.[1] For all main-group elements (C, H, N, B, F) the all- electron triple-ζ basis set (6-311++G**) was used.[2] [1] Gaussian 09, Revision A.1, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2009. [2] X. Cao and M. Dolg, J. Chem. Phys. 2001, 115, 7348

Energies for all optimized structures:

E(0 K)a H(298 K)b G(298 K)b Compound [Ha] [Ha] [Ha]

3,5-di-tert-butyl-1H-pyrazole (3) -540,303608 -540,302664 -540,362048

bis(pentafluorophenyl)borane, -1480,875349 -1480,874404 -1480,942344 HB(C6F5)2

pyrazolium-borate trans-5 -2021,239574 -2021,238630 -2021,340157

pyrazolium-borate cis-5 -2021,234911 -2021,233967 -2021,335435

pyrazolylborane 6 -2020,049878 -2020,048934 -2020,152469

2 C2v-symmetric ( -pyrazolyl)borane -2020,046512 -2020,045568 -2020,148462 of 6

transition state (TS) associated with the -2021,185825 -2021,184880 -2021,285555 H2 cleavage by 6

H2 -1,155757 -1,154812 -1,169598 aDFT incl. ZPE. bstandard conditions T = 298.15 K and p = 1 atm. Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010

Calculated structures and XYZ coordinates (in Å)

Calculated structure of 3,5-di-tert-butyl-1H-pyrazole (3)

N 0.618800 -1.382300 0.000000 N -0.722700 -1.443100 -0.023400 C 1.104400 -0.117200 -0.003200 C -0.008000 0.698600 -0.025100 C -1.122700 -0.181500 -0.037500 C -2.594800 0.164900 -0.003900 C -3.058900 0.186700 1.461800 C -3.398000 -0.887000 -0.776300 C -2.823100 1.545500 -0.628400 C 2.583200 0.180100 0.001300 C 3.236000 -0.454000 1.239800 C 3.227700 -0.391700 -1.271800 C 2.793400 1.695600 0.038000 H 1.143100 -2.242100 -0.001500 H -0.014400 1.775600 -0.037400 H -4.120300 0.446200 1.520200 H -2.913900 -0.793800 1.920900 H -2.491700 0.922400 2.038100 H -4.464200 -0.647300 -0.731600 H -3.091200 -0.915100 -1.824800 H -3.241700 -1.880100 -0.353200 H -2.314900 2.330300 -0.062100 H -2.460100 1.574500 -1.659000 H -3.891100 1.778800 -0.633600 H 3.124800 -1.541700 1.241400 H 4.305700 -0.228700 1.256400 H 2.784800 -0.066700 2.156000 H 2.770300 0.041700 -2.163900 H 4.297600 -0.166800 -1.284700 H 3.113200 -1.477600 -1.326400 H 2.343900 2.174100 -0.835500 H 2.350100 2.130400 0.937100 H 3.862200 1.922900 0.039200

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Calculated structure of bis(pentafluorophenyl)borane, HB(C6F5)2

B 0.000000 1.401600 0.000100 F -2.417300 2.501300 1.010700 F -4.828900 1.347100 0.895900 F -5.109800 -1.083200 -0.257900 F -2.970800 -2.356700 -1.310400 F -0.551000 -1.231000 -1.199300 F 0.551200 -1.230300 1.200300 F 2.971000 -2.356600 1.310400 F 5.109600 -1.083500 0.257000 F 4.828800 1.346900 -0.896600 F 2.417400 2.501500 -1.010600 C 1.372500 0.673400 0.059500 C 2.513900 1.304900 -0.438800 C 1.571900 -0.577000 0.649100 C 3.770800 0.727200 -0.392100 C 2.816100 -1.174500 0.730500 C 3.917700 -0.519400 0.197500 C -1.372400 0.673000 -0.058900 C -1.571800 -0.577400 -0.648500 C -2.513900 1.304600 0.438900 C -2.816100 -1.174700 -0.730500 C -3.770900 0.727200 0.391800 C -3.917800 -0.519400 -0.198000 H -0.000400 2.584400 -0.000500

Calculated structure of the pyrazolium-borate trans-5

B -0.235400 0.080400 0.988100 N 0.981400 -0.867000 0.620200 N 1.125900 -1.213200 -0.674700 Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010

F 2.279600 1.261900 -0.329500 F 2.518800 3.767900 -1.136700 F 0.469100 5.530300 -0.847200 F -1.859800 4.704700 0.282500 F -2.137700 2.178800 1.106800 F -1.174400 0.122700 -1.851800 F -3.501200 -0.841100 -2.738100 F -5.199600 -2.114100 -1.036800 F -4.527500 -2.394900 1.574400 F -2.224000 -1.427500 2.491700 C 2.279800 -1.858000 -0.892300 C 2.898300 -1.961000 0.342300 C 2.062400 -1.317000 1.271700 C 2.686100 -2.300100 -2.274600 C 1.642000 -3.285000 -2.824300 C 2.772000 -1.063600 -3.185300 C 4.054200 -2.981700 -2.203400 C 2.322100 -1.112300 2.749900 C 2.409600 0.392900 3.058200 C 1.231000 -1.798200 3.588200 C 3.672600 -1.749500 3.104800 C 0.038300 1.584100 0.413900 C 1.208900 2.063400 -0.158100 C 1.371200 3.373100 -0.589000 C 0.330800 4.272100 -0.445600 C -0.855600 3.846600 0.131000 C -0.973600 2.530700 0.544500 C -1.599800 -0.577400 0.372600 C -1.996800 -0.473300 -0.951500 C -3.188100 -0.970400 -1.452000 C -4.053100 -1.620500 -0.588200 C -3.703700 -1.763300 0.744700 C -2.496600 -1.248600 1.195400 H 0.468500 -0.853900 -1.356500 H -0.338800 0.128000 2.171600 H 3.840500 -2.437600 0.546400 H 1.555000 -4.162200 -2.179200 H 1.940200 -3.616900 -3.821600 H 0.655200 -2.821900 -2.907400 H 1.800800 -0.572800 -3.294600 H 3.105200 -1.363800 -4.181500 H 3.478400 -0.333100 -2.785300 H 4.814800 -2.297000 -1.820500 H 4.356600 -3.298900 -3.203500 H 4.024200 -3.866100 -1.562300 H 3.176800 0.865100 2.438900 H 2.683400 0.528800 4.107600 H 1.464000 0.904200 2.884500 H 0.238700 -1.399600 3.384300 H 1.449400 -1.652700 4.649200 H 1.218000 -2.872800 3.388400 H 3.676700 -2.822900 2.899300 H 3.861100 -1.612000 4.171400 H 4.493300 -1.281000 2.555700

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Calculated structure of the pyrazolium-borate cis-5

B -0.138000 0.072100 -0.777600 N 2.274100 -0.441000 -0.898000 N 1.206600 -0.446200 -0.076200 F 1.545100 2.081500 0.793800 F 0.955900 4.646000 1.072900 F -1.290900 5.690200 -0.047100 F -2.947800 4.082000 -1.479400 F -2.376600 1.486600 -1.779700 F -2.846300 0.398100 0.652700 F -4.641200 -1.540400 0.905600 F -4.149300 -4.021200 -0.076300 F -1.804400 -4.525000 -1.356100 F 0.019500 -2.588300 -1.629600 C 1.650800 -0.821300 1.135100 C 3.034100 -1.059700 1.037200 C 3.399700 -0.808300 -0.273300 C 4.727600 -0.868500 -0.984400 C 0.818700 -0.984100 2.395500 C 0.051900 -2.318500 2.345000 C -0.148800 0.185500 2.609500 C 1.770200 -1.033300 3.602000 C 5.119300 0.550300 -1.429700 C 4.613800 -1.790700 -2.208300 C 5.785900 -1.415600 -0.023600 C -1.327900 -0.998200 -0.519200 C -1.133300 -2.285000 -1.011000 C -2.542400 -0.792600 0.119300 C -2.053500 -3.309800 -0.875600 C -3.496500 -1.789400 0.276800 C -3.249400 -3.056600 -0.221700 C -0.426600 1.638700 -0.465500 C -1.543900 2.233300 -1.043400 C 0.399000 2.510400 0.229900 C -1.858000 3.574200 -0.911500 C 0.125100 3.862400 0.387500 C -1.013900 4.398600 -0.184000 H 3.689500 -1.368900 1.831500 H 0.731400 -3.149500 2.139700 H -0.421300 -2.493500 3.314700 H -0.727800 -2.312700 1.584800 H 0.397300 1.120000 2.753600 H -0.842800 0.317700 1.783400 H -0.739600 -0.007900 3.508400 H 2.407500 -1.920500 3.581300 H 2.402200 -0.143100 3.646000 H 1.176700 -1.075200 4.517600 H 4.396300 0.962400 -2.138200 H 5.176700 1.224900 -0.572800 H 6.095300 0.526500 -1.920400 H 5.583700 -1.861300 -2.706300 H 4.301200 -2.794900 -1.914300 H 3.894800 -1.409700 -2.938700 Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010

H 5.530500 -2.423300 0.312800 H 6.751900 -1.460700 -0.530600 H 5.893200 -0.771100 0.852200 H 0.129800 0.000400 -1.955200 H 2.110200 -0.226900 -1.871900

Calculated structure of the pyrazolylborane 6

B 0.117000 0.009200 0.089500 N -2.068500 -0.637200 -0.509600 N -0.894500 -1.004200 0.124800 F 1.222100 2.127900 -1.568800 F 0.438900 4.682900 -1.517300 F -1.538800 5.466700 0.162300 F -2.727900 3.670900 1.799000 F -1.956000 1.114900 1.778600 F 1.285500 -1.663500 -1.929100 F 3.922300 -1.925700 -2.377100 F 5.700800 -0.721700 -0.730700 F 4.838500 0.771400 1.356900 F 2.196800 1.076100 1.788200 C -0.978100 -2.322800 0.577700 C -2.201100 -2.776300 0.176800 C -2.834900 -1.690900 -0.507900 C -4.207800 -1.687400 -1.133200 C -0.013000 -3.010200 1.531300 C 0.347300 -2.060800 2.685900 C 1.263500 -3.531300 0.846900 C -0.733400 -4.229300 2.131200 C -4.520900 -0.313300 -1.727400 C -5.240100 -2.027900 -0.047000 C -4.250300 -2.756100 -2.235500 C 1.652700 -0.289700 -0.049700 C 2.599100 0.328600 0.756900 C 2.135900 -1.046400 -1.110100 C 3.960500 0.185700 0.554100 C 3.490300 -1.195200 -1.357800 C 4.403900 -0.578600 -0.515900 C -0.346700 1.507900 0.088700 C -1.362000 1.953600 0.933000 C 0.249600 2.470500 -0.718800 C -1.768600 3.275800 0.970700 C -0.142800 3.798500 -0.716700 C -1.157000 4.200300 0.137300 H -2.631000 -3.741600 0.386900 H -0.554000 -1.712500 3.196300 H 0.973000 -2.588800 3.410200 H 0.906700 -1.186200 2.349200 H 1.027200 -4.049500 -0.085200 H 1.973700 -2.734700 0.636500 H 1.761600 -4.238800 1.514700 Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010

H -1.666100 -3.941300 2.620200 H -0.953000 -4.976300 1.364500 H -0.084900 -4.697000 2.875000 H -4.481800 0.461700 -0.959200 H -3.800900 -0.049800 -2.504200 H -5.522400 -0.323600 -2.164800 H -6.244700 -2.034700 -0.478400 H -5.053100 -3.013000 0.388300 H -5.213800 -1.288000 0.756400 H -4.039500 -3.750000 -1.831900 H -5.242200 -2.780100 -2.694700 H -3.514200 -2.540800 -3.013600

2 Calculated structure of the C2v-symmetric ( -pyrazolyl)borane isomer of 6

B 0.163300 -0.155100 -0.000100 N -0.472800 -1.403300 0.683400 N -0.472900 -1.403300 -0.683400 F 1.833900 -0.189400 -2.352000 F 4.527800 -0.326900 -2.350000 F 5.879500 -0.389900 0.000300 F 4.527400 -0.325500 2.350300 F 1.833600 -0.188000 2.351800 F -2.736300 0.301300 0.000200 F -3.946400 2.664500 0.000300 F -2.485700 4.953500 -0.000100 F 0.221800 4.824800 -0.000600 F 1.461500 2.492900 -0.000700 C -1.561200 -2.051400 1.121900 C -2.230100 -2.555400 0.000200 C -1.561300 -2.051500 -1.121700 C -1.865300 -2.141700 -2.593900 C -1.865000 -2.141500 2.594100 C 1.753000 -0.200000 -0.000100 C 2.477900 -0.232100 1.177600 C 2.478100 -0.232800 -1.177700 C 3.861500 -0.295500 1.200700 C 3.861700 -0.296200 -1.200500 C 4.554400 -0.326700 0.000200 C -0.573600 1.262500 -0.000200 C 0.127200 2.468500 -0.000400 C -1.961200 1.390900 0.000000 C -0.495200 3.708000 -0.000400 C -2.619000 2.608400 0.000100 C -1.877400 3.778600 -0.000200 C -1.875700 -0.718100 -3.172700 C -3.229100 -2.802500 -2.801400 Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010

C -0.768300 -2.969100 -3.282200 C -3.228700 -2.802500 2.801900 C -1.875500 -0.717900 3.172800 C -0.767800 -2.968700 3.282400 H -3.117500 -3.166900 0.000200 H -2.643400 -0.108500 -2.689200 H -0.905300 -0.234300 -3.034900 H -2.088500 -0.755500 -4.243900 H -3.456600 -2.847900 -3.868800 H -3.236700 -3.823900 -2.412000 H -4.022200 -2.235100 -2.307600 H -0.727200 -3.980800 -2.871500 H -0.975200 -3.038700 -4.353300 H 0.208500 -2.500300 -3.146400 H -3.236200 -3.823900 2.412600 H -3.456100 -2.847800 3.869300 H -4.021900 -2.235200 2.308100 H -0.905200 -0.234000 3.034800 H -2.643500 -0.108500 2.689500 H -2.088100 -0.755200 4.244100 H -0.974600 -3.038300 4.353500 H -0.726600 -3.980500 2.871800 H 0.208900 -2.499800 3.146500

Calculated structure of the transition state (TS) associated with the H2 cleavage by 6

B -0.126800 0.045100 -0.490200 N 1.981100 -0.937000 -0.939700 N 1.012900 -0.831400 0.010000 F 2.019000 1.492700 0.990300 F 2.231000 4.127300 1.177000 F 0.444700 5.748400 -0.057800 F -1.581700 4.673800 -1.509200 F -1.825300 2.015200 -1.707700 F -2.580900 1.124100 0.843800 F -4.921300 -0.142100 0.955600 F -5.239600 -2.548500 -0.245300 F -3.167900 -3.687800 -1.574800 F -0.799400 -2.438600 -1.688300 C 1.439800 -1.375600 1.180500 C 2.721000 -1.848200 0.950100 C 3.017000 -1.553800 -0.397500 C -1.586600 -0.603800 -0.435600 C -1.799000 -1.843100 -1.033000 C -2.680300 -0.054800 0.222800 C -3.011700 -2.508800 -0.986100 C -3.907000 -0.695100 0.302700 C -4.072300 -1.928300 -0.307600 C 0.051600 1.628800 -0.334000 C -0.825100 2.505800 -0.966000 C 1.091400 2.226000 0.371300 Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2010

C -0.716600 3.881800 -0.887800 C 1.229400 3.602600 0.480000 C 0.320200 4.433600 -0.150200 C 4.274400 -1.862500 -1.172300 C 0.627700 -1.448000 2.457200 C -0.480600 -2.506200 2.315800 C 0.013400 -0.086100 2.807600 C 1.552500 -1.869200 3.606800 C 5.457100 -1.162700 -0.485100 C 4.150600 -1.367800 -2.615100 C 4.502200 -3.381600 -1.166000 H 3.360500 -2.346000 1.660000 H -0.058400 -3.468600 2.017400 H -0.988700 -2.633300 3.275600 H -1.227100 -2.213900 1.576100 H 0.791900 0.658900 2.983300 H -0.649500 0.289100 2.025800 H -0.584400 -0.180300 3.718000 H 1.956400 -2.871600 3.446800 H 2.384100 -1.169800 3.719000 H 0.986100 -1.882100 4.540700 H 5.309100 -0.080500 -0.466800 H 5.573800 -1.507700 0.545000 H 6.383400 -1.378400 -1.024500 H 5.069100 -1.596400 -3.161200 H 3.315900 -1.852800 -3.126100 H 3.989400 -0.288100 -2.648300 H 3.667600 -3.900300 -1.643800 H 5.418300 -3.624600 -1.711000 H 4.601600 -3.762300 -0.146600 H 0.080800 -0.065100 -1.951800 H 0.872200 -0.352400 -1.869800

Calculated structure of dihydrogen, H2

H 0.000000 0.000000 0.370100 H 0.000000 0.000000 -0.370100