Efficient Homogeneous Catalysis in the Reduction of CO 2 to CO

Transcription

1 Supporting Information for: Efficient Homogeneous Catalysis in the Reduction of CO 2 to CO David S. Laitar, Peter Müller, Joseph P. Sadighi* Full listing for text reference (3): Arakawa, H.; Aresta, M.; Armor, J. N.; Barteau, M. A.; Beckman, E. J.; Bell, A. T.; Bercaw, J. E.; Creutz, C.; Dinjus, E.; Dixon, D. A.; Domen, K.; DuBois, D. L.; Eckert, J.; Fujita, E.; Gibson, D. H.; Goddard, W. A.; Goodman, D. W.; Keller, J.; Kubas, G. J.; Kung, H. H.; Lyons, J. E.; Manzer, L. E.; Marks, T. J.; Morokuma, K.; Nicholas, K. M.; Periana, R.; Que, L.; Rostrup-Nielson, J.; Sachtler, W. M. H.; Schmidt, L. D.; Sen, A.; Somorjai, G. A.; Stair, P. C.; Stults, B. R.; Tumas, W. Chem. Rev. 2001, 101, Experimental: General Considerations. All synthetic manipulations were carried out using standard Schlenk techniques under an argon atmosphere, or in an Innovative Technologies glovebox under an atmosphere of purified nitrogen. Reactions were carried out in flame-dried glassware cooled under vacuum. Elemental analyses were performed by Desert Analytics, Tucson, AZ. Anhydrous toluene, hexanes, and tetrahydrofuran were purchased from Aldrich in 18 L Pure-Pac solvent delivery kegs and sparged vigorously with argon for 40 minutes prior to first use. The solvents were further purified by passing them under argon pressure through two packed columns of neutral alumina and a third column packed with activated 4 Å molecular sieves (for tetrahydrofuran) or through neutral alumina and copper(ii) oxide (for toluene and hexanes). Benzene and pentane, anhydrous, were purchased from Aldrich in S1

2 Sure-Seal bottles, and stored in a glove box over 4Å molecular sieves. All non-dried solvents used were reagent grade or better. IR spectra were recorded on a Nicolet Impact 410 spectrometer as KBr pellets. NMR solvents C 6 D 6 (Cambridge Isotope Laboratories) and C 4 D 8 O (Cambridge Isotope Laboratories) were dried over sodium/benzophenone. All NMR solvents were degassed by three freeze-pump-thaw cycles and vacuum-transferred prior to use. 1 H NMR spectra were recorded on a Varian 300 MHz instrument, with shifts reported relative to the residual solvent peak. 11 B NMR spectra were recorded on a Varian 500 MHz instrument, with shifts referenced to an external standard of 0.5 M BF 3 in diethyl ether (0 ppm). 13 C NMR spectra were recorded on a Varian 500 MHz instrument, with shifts referenced relative to the solvent peak. The starting materials copper(i) chloride (Strem) and sodium tert-butoxide (Aldrich), were used as received. Bis(pinacolato)diboron (Frontier) was recrystalized from toluene/pentane at 40 C. [1,3- Bis(2,6-diisopropylphenyl)imidazol-2-ylidene]copper(I) tert-butoxide 1 and 1,3-dicyclohexylimidazolium chloride 2 were synthesized as described previously. [1,3-Dicyclohexylimidazol-2-ylidene]copper(I) tert-butoxide was made by analogy to a published procedure. 1 [1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene]copper(I) pinacolatoboryl (1). In a glove box, [1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene]copper(I) tert-butoxide (0.204 g, mmol) and bis(pinacolato)diboron (0.099 g, mmol) were added to a vial wrapped in black electrical tape. Pentane (anhydrous, 5 ml) was added, and the mixture was stirred vigorously for 20 minutes. The resulting white suspension was filtered and dried in vacuo to afford the title compound (0.205 g, 91%) (samples typically contained ~5% (IPr)Cu(OBpin) presumably due to adventitious moisture or oxygen). 1 H NMR (C 6 D 6 ): δ 7.15 (t, J = 7.6 Hz, 2 H, para-ch), 7.05 (d, J = 7.8 Hz, 4 H, meta-ch), 6.21 (s, 2 H, NCH), 2.65 (sept., J = 6.9 Hz, 4 H, CH(CH 3 ) 2 ), 1.48 (d, J = 6.9 Hz, 12 H, CH(CH 3 ) 2 ), 1.09 (d, J = 6.9 Hz, 12 H, CH(CH 3 ) 2 ) 1.06 (s, 12 H, pinacol-ch 3 ). 13 C NMR (C 6 D 6 ): δ (NCCu), (ortho-c), S2

3 135.5 (ipso-c), (para-c), (meta-c), (NCH), 79.2 (OC(CH 3 ) 2 ), 29.4 (CH(CH 3 ) 2 ), 26.5 (OC(CH 3 ) 2 ), 25.7 (CH(CH 3 ) 2 ), 24.1 (CH(CH 3 ) 2 ). 11 B NMR (C 6 D 6 ): δ Anal. Calcd. C 33 H 48 N 2 O 2 BCu: C, 68.44; H, Found: C, 68.53; H, [1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene]copper(I) pinacolatoborate (2). In a glove box, a 100 ml round bottomed flask was charged with 1 (0.100 g, mmol) and benzene (5 ml) and sealed with a vacuum adaptor. The flask was taken out of the glove box, the solution was degassed on a vacuum line by one freeze-pump-thaw cycle and CO 2 (1.1 atm) was added. After stirring for 10 minutes, the reaction mixture was concentrated in vacuo to give the title complex as a bright white solid (0.094 g, 91%). 1 H NMR (C 6 D 6 ): δ 7.21 (t, J = 7.7 Hz, 2 H, para-ch), 7.07 (d, J = 7.7 Hz, 4 H, meta- CH), 6.27 (s, 2 H, NCH), 2.56 (sept., J = 6.9 Hz, 4 H, CH(CH 3 ) 2 ), 1.39 (d, J = 6.6 Hz, 12 H, CH(CH 3 ) 2 ), 1.10 (s, 12 H, pinacol-ch 3 ), 1.08 (d, J = 6.9 Hz, 12 H, CH(CH 3 ) 2 ). 13 C NMR (C 6 D 6 ): δ (NCCu), (ortho-c), (ipso-c), (para-c), (meta-c), (NCH), 79.2 (OC(CH 3 ) 2 ), 29.3 (CH(CH 3 ) 2 ), 25.7 (OC(CH 3 ) 2 ), 25.4 (CH(CH 3 ) 2 ), 24.2 (CH(CH 3 ) 2 ). 11 B NMR (C 6 D 6 ): δ Anal. Calcd. C 33 H 48 N 2 O 3 BCu: C, 66.60; H, Found: C, 66.71; H, General Procedure for Room Temperature Deoxygenation of Carbon Dioxide: In a glove box, a 25 ml resealable Schlenk flask was charged with bis(pinacolato)diboron (0.317 g, 1.25 mmol). The flask was sealed with a Teflon stopcock, taken out of the glove box, and connected to a Schlenk line. The flask was evacuated and backfilled with CO 2 (1.1 atm). Under a positive pressure of CO 2 the stopcock was replaced with a rubber septum, and a solution of (12.5 µmol: 2 ml of a 6.24 mm stock solution, prepared from g (IPr)Cu(Ot-Bu) and 4 ml benzene) was added via syringe. The rubber septum was quickly replaced with a stopcock, and the flask was stirred at room temperature for 20 hours. The reaction mixture was concentrated in vacuo, taken into a glove box and dissolved in S3

4 benzene (0.7 ml). 11 B NMR analysis of the crude reaction mixture showed complete consumption of bis(pinacolato)diboron. Room Temperature Deoxygenation of 13 CO 2 : In a glove box, (pin)bb(pin) (0.080 g, 0.32 mmol) and IPrCuOtBu (1.5 mg, mmol, dissolved in 0.7 ml THF) was added to a J-Young tube. The tube was sealed, taken out of the glove box, and connected to a Schlenk line. The solution was degassed by one freeze-pump-thaw cycle, and back-filled with 13 CO 2. An initial 13 C NMR spectrum was recorded at 80 C, and the solution was allowed to stand for 22 hrs at room temperature (during that time, tube was occasionally inverted to ensure mixing). The NMR tube was then inserted into an NMR probe cooled to 80 C and another spectrum was recorded. 13 C NMR showed complete consumption of 13 CO 2, and 11 B NMR showed 50 % consumption of (pin)bb(pin). General Procedure for High Temperature Deoxygenation of Carbon Dioxide: In a glove box, a 25 ml resealable Schlenk flask was charged with bis(pinacolato)diboron (0.317 g, 1.25 mmol) and THF (1 ml). The flask was sealed with a Teflon stopcock, taken out of the glove box, and connected to a Schlenk line. The solution was degassed by one freeze-pump-thaw cycle and backfilled with CO 2 (1.1 atm). Under a positive pressure of CO 2, the stopcock was replaced with a rubber septum, and a solution of (IPr)Cu(Ot-Bu) (1.25 µmol: 0.5 ml of a 2.5 mm stock solution, prepared from g (IPr)Cu(Ot-Bu) and 10 ml THF) was added via syringe. The rubber septum was quickly replaced with a stopcock, and the flask was heated at 100 C for 20 hours. The flask was then cooled to room temperature, and the solution was concentrated in vacuo. In a glove box, the crude reaction mixture was dissolved in benzene (0.7 ml). Analysis by 11 B NMR spectroscopy indicated complete consumption of bis(pinacolato)diboron. S4

5 General Procedure for Low Temperature Deoxygenation of Carbon Dioxide: In a glove box, a 25 ml resealable Schlenk flask was charged with bis(pinacolato)diboron (0.317 g, 1.25 mmol) and THF (4 ml). The flask was sealed with a Teflon stopcock, taken out of the glove box, and affixed to a Schlenk line. The solution was degassed by one freeze-pump-thaw cycle and backfilled with CO 2 (1.5 atm). Under a positive pressure of CO 2 the stopcock was replaced with a rubber septum, and the flask was cooled to 0 C. A solution of (ICy)Cu(Ot-Bu) ( mmol: 1 ml of a 12.5 mm stock solution, prepared from g (ICy)Cu(Ot-Bu) and 4 ml THF) was added via syringe. The rubber septum was quickly replaced with a stopcock, and the flask was stirred at 0 C for 30 min. The flask was taken out of the ice bath stirred for 30 minutes, and the solution was concentrated in vacuo. In a glove box, the crude reaction mixture was dissolved in benzene (0.7 ml). Analysis by 11 B NMR spectroscopy indicated complete consumption of bis(pinacolato)diboron. Low Temperature NMR experiments: In a glove box, 1 (30 mg) was added to J-Young tube, and the tube was sealed with a Teflon stopcock. Outside of the glove box, the tube was evacuated on a Schlenk line, and d 8 -THF (0.7 ml) was added via vacuum transfer from of a purple Na/benzophenone kettle pot. The tube was cooled to 78 C, and 13 CO 2 (1.5 atm) was admitted. The tube was sealed, rapidly inserted into a pre-cooled ( 80 C) NMR Spectrometer, then warmed in 10-degree increments to 40 C over a half-hour. X-ray Diffraction Studies: Experiments were performed on single crystals of 1, and 2 (both grown by the vapor diffusion of hexanes into concentrated toluene solutions at 40 C). Colorless crystals were removed from the supernatant and transferred onto a microscope slide coated with Paratone N oil. Crystals were affixed to a glass fiber or a cryoloop using the oil, frozen in a nitrogen stream, and optically centered. The data were collected on a Siemens three-circle platform goniometer equipped with a Bruker Smart Apex CCD detector with graphite-monochromated Mo Kα radiation (λ = S5

6 Å), using both phi and omega scans at 173 C. The structures were solved by direct methods (SHELXS) 3 and refined against F 2 on all data by full matrix least squares with SHELXL-97 (Sheldrick, G. M. SHELXL 97; Universität Göttingen: Göttingen, Germany, 1997). All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed at idealized positions and refined using a riding model. [1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene]copper(I) pinacolatoboryl (1). An isopropyl group was found to be disordered (C10, C11 and C12) and was refined with the help of similarity restraints on 1-2 and 1-3 distances and displacement parameters. Rigid bond restraints for anisotropic displacement parameters were also used. The occupancies for the disordered parts were refined freely and converged at a ratio of 42:58. One peak of significant residual electron density was found less than one angstrom from copper (1.62 e/å 3 ). Figure S1. X-ray crystal structure of 1. Hydrogen atoms (calculated) and solvent omitted for clarity. Shown as stick representation for clarity in labeling. S6

7 Figure S2. X-ray crystal structure of 1 shown as 50% ellipsoids with 0.5 hexane molecule included. Hydrogen atoms (calculated) omitted for clarity. Table 1. Crystal data and structure refinement for 1. Identification code Empirical formula C 36 H 55 BCuN 2 O 2 Formula weight Temperature 100(2) K Wavelength Å Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = (14) Å α= 90. b = (3) Å β= (4). c = (18) Å γ = 90. Volume (8) Å 3 S7

8 Z 4 Density (calculated) Mg/m 3 Absorption coefficient mm -1 F(000) 1340 Crystal size 0.20 x 0.12 x 0.07 mm 3 Theta range for data collection 2.06 to Index ranges -13<=h<=13, 0<=k<=30, 0<=l<=18 Reflections collected Independent reflections 7514 [R(int) = ] Completeness to theta = % Absorption correction Semi-empirical from equivalents Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 7514 / 12 / 413 Goodness-of-fit on F Final R indices [I>2sigma(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Largest diff. peak and hole and e.å -3 Table 2. Atomic coordinates ( x 10 4 ) and equivalent isotropic displacement parameters (Å 2 x 10 3 ) for 1. U(eq) is defined as one third of the trace of the orthogonalized U ij tensor. x y z U(eq) Cu(1) 2975(1) 8417(1) 3892(1) 22(1) B(1) 1625(3) 8884(1) 2989(2) 22(1) O(1) 992(2) 8853(1) 1987(1) 24(1) O(2) 1140(2) 9329(1) 3372(1) 24(1) C(1) 4152(2) 8032(1) 4974(2) 19(1) N(1) 4257(2) 7487(1) 5167(1) 19(1) N(2) 4981(2) 8255(1) 5792(1) 17(1) C(2) 5131(2) 7373(1) 6076(2) 20(1) C(3) 5586(2) 7858(1) 6467(2) 21(1) C(4) 3611(2) 7069(1) 4491(2) 21(1) C(5) 2349(2) 6932(1) 4432(2) 28(1) C(6) 1805(3) 6487(1) 3831(2) 34(1) C(7) 2480(3) 6210(1) 3315(2) 34(1) S8

9 C(8) 3710(3) 6371(1) 3359(2) 32(1) C(9) 4310(3) 6806(1) 3954(2) 27(1) C(10) 1588(3) 7246(1) 4979(2) 41(1) C(11A) 382(19) 7501(8) 4360(16) 78(5) C(12A) 1170(20) 6861(6) 5746(11) 66(5) C(11B) 157(10) 7268(6) 4375(9) 57(3) C(12B) 1840(11) 7045(4) 5965(6) 51(2) C(13) 5681(3) 6969(1) 4017(2) 34(1) C(14) 5815(4) 7090(2) 3011(2) 54(1) C(15) 6647(3) 6533(1) 4550(2) 43(1) C(16) 5274(2) 8831(1) 5920(2) 18(1) C(17) 4577(2) 9157(1) 6382(2) 20(1) C(18) 4927(2) 9707(1) 6526(2) 24(1) C(19) 5921(2) 9918(1) 6228(2) 25(1) C(20) 6589(2) 9587(1) 5771(2) 24(1) C(21) 6279(2) 9035(1) 5607(2) 21(1) C(22) 3464(2) 8928(1) 6691(2) 27(1) C(23) 2184(3) 9021(2) 5894(2) 43(1) C(24) 3388(3) 9169(1) 7653(2) 34(1) C(25) 6978(2) 8671(1) 5067(2) 26(1) C(26) 6410(3) 8761(1) 3966(2) 33(1) C(27) 8436(2) 8764(1) 5396(2) 35(1) C(28) 238(2) 9354(1) 1677(2) 22(1) C(29) 6(2) 9539(1) 2638(2) 22(1) C(30) -967(3) 9223(1) 853(2) 31(1) C(31) 1078(2) 9749(1) 1328(2) 28(1) C(32) -1154(3) 9264(1) 2822(2) 36(1) C(33) -53(3) 10151(1) 2762(2) 30(1) C(34) 4831(3) 235(2) 9654(3) 55(1) C(35) 5886(4) 375(2) 9235(3) 65(1) C(36) 5586(7) 847(4) 8588(6) 164(4) S9

10 Table 3. Bond lengths [Å] and angles [ ] for 1. Cu(1)-C(1) 1.937(2) Cu(1)-B(1) 2.002(3) B(1)-O(2) 1.399(3) B(1)-O(1) 1.401(3) O(1)-C(28) 1.470(3) O(2)-C(29) 1.455(3) C(1)-N(2) 1.363(3) C(1)-N(1) 1.363(3) N(1)-C(2) 1.395(3) N(1)-C(4) 1.442(3) N(2)-C(3) 1.393(3) N(2)-C(16) 1.448(3) C(2)-C(3) 1.343(3) C(4)-C(5) 1.396(3) C(4)-C(9) 1.401(3) C(5)-C(6) 1.406(3) C(5)-C(10) 1.519(4) C(6)-C(7) 1.377(4) C(7)-C(8) 1.383(4) C(8)-C(9) 1.401(4) C(9)-C(13) 1.524(4) C(10)-C(12B) 1.451(8) C(10)-C(11A) 1.485(18) C(10)-C(11B) 1.540(11) C(10)-C(12A) 1.623(14) C(13)-C(14) 1.532(4) C(13)-C(15) 1.534(4) C(16)-C(21) 1.401(3) C(16)-C(17) 1.403(3) C(17)-C(18) 1.400(3) C(17)-C(22) 1.523(3) C(18)-C(19) 1.385(4) C(19)-C(20) 1.385(3) C(20)-C(21) 1.397(3) C(21)-C(25) 1.532(3) S10

11 C(22)-C(23) 1.532(4) C(22)-C(24) 1.534(3) C(25)-C(27) 1.533(4) C(25)-C(26) 1.535(3) C(28)-C(30) 1.514(3) C(28)-C(31) 1.521(3) C(28)-C(29) 1.551(3) C(29)-C(33) 1.515(3) C(29)-C(32) 1.528(3) C(34)-C(35) 1.495(5) C(34)-C(34)# (8) C(35)-C(36) 1.460(9) C(1)-Cu(1)-B(1) (10) O(2)-B(1)-O(1) 108.7(2) O(2)-B(1)-Cu(1) (17) O(1)-B(1)-Cu(1) (19) B(1)-O(1)-C(28) (18) B(1)-O(2)-C(29) (17) N(2)-C(1)-N(1) (18) N(2)-C(1)-Cu(1) (16) N(1)-C(1)-Cu(1) (16) C(1)-N(1)-C(2) (18) C(1)-N(1)-C(4) (18) C(2)-N(1)-C(4) (18) C(1)-N(2)-C(3) (18) C(1)-N(2)-C(16) (18) C(3)-N(2)-C(16) (18) C(3)-C(2)-N(1) (19) C(2)-C(3)-N(2) (19) C(5)-C(4)-C(9) 123.5(2) C(5)-C(4)-N(1) 118.9(2) C(9)-C(4)-N(1) 117.6(2) C(4)-C(5)-C(6) 116.6(2) C(4)-C(5)-C(10) 122.2(2) C(6)-C(5)-C(10) 121.3(2) C(7)-C(6)-C(5) 121.4(3) S11

12 C(6)-C(7)-C(8) 120.5(2) C(7)-C(8)-C(9) 120.8(2) C(4)-C(9)-C(8) 117.2(2) C(4)-C(9)-C(13) 122.6(2) C(8)-C(9)-C(13) 120.2(2) C(12B)-C(10)-C(11A) 127.0(9) C(12B)-C(10)-C(5) 111.5(3) C(11A)-C(10)-C(5) 115.3(8) C(12B)-C(10)-C(11B) 115.0(6) C(11A)-C(10)-C(11B) 23.8(6) C(5)-C(10)-C(11B) 110.2(5) C(12B)-C(10)-C(12A) 30.9(5) C(11A)-C(10)-C(12A) 105.9(8) C(5)-C(10)-C(12A) 111.7(4) C(11B)-C(10)-C(12A) 87.6(7) C(9)-C(13)-C(14) 111.7(2) C(9)-C(13)-C(15) 111.2(2) C(14)-C(13)-C(15) 111.1(2) C(21)-C(16)-C(17) 122.9(2) C(21)-C(16)-N(2) 118.1(2) C(17)-C(16)-N(2) 119.0(2) C(18)-C(17)-C(16) 117.1(2) C(18)-C(17)-C(22) 121.2(2) C(16)-C(17)-C(22) 121.8(2) C(19)-C(18)-C(17) 121.2(2) C(20)-C(19)-C(18) 120.4(2) C(19)-C(20)-C(21) 120.8(2) C(20)-C(21)-C(16) 117.6(2) C(20)-C(21)-C(25) 121.2(2) C(16)-C(21)-C(25) 121.2(2) C(17)-C(22)-C(23) 110.6(2) C(17)-C(22)-C(24) 113.0(2) C(23)-C(22)-C(24) 109.4(2) C(21)-C(25)-C(27) 112.8(2) C(21)-C(25)-C(26) 109.6(2) C(27)-C(25)-C(26) 110.6(2) O(1)-C(28)-C(30) (19) S12

13 O(1)-C(28)-C(31) (19) C(30)-C(28)-C(31) (19) O(1)-C(28)-C(29) (17) C(30)-C(28)-C(29) 115.0(2) C(31)-C(28)-C(29) (19) O(2)-C(29)-C(33) (19) O(2)-C(29)-C(32) (19) C(33)-C(29)-C(32) 110.4(2) O(2)-C(29)-C(28) (17) C(33)-C(29)-C(28) (19) C(32)-C(29)-C(28) 113.4(2) C(35)-C(34)-C(34)# (4) C(36)-C(35)-C(34) 112.9(5) Symmetry transformations used to generate equivalent atoms: #1 -x+1,-y,-z+2 Table 4. Anisotropic displacement parameters (Å 2 x 10 3 ) for 1. The anisotropic displacement factor exponent takes the form: -2π 2 [ h 2 a* 2 U h k a* b* U 12 U 11 U 22 U 33 U 23 U 13 U 12 Cu(1) 25(1) 17(1) 19(1) 2(1) 0(1) -1(1) B(1) 23(1) 17(1) 24(1) 3(1) 4(1) -4(1) O(1) 28(1) 16(1) 26(1) -1(1) 6(1) 4(1) O(2) 25(1) 21(1) 20(1) 2(1) 1(1) 2(1) C(1) 19(1) 17(1) 19(1) -2(1) 6(1) 1(1) N(1) 23(1) 14(1) 18(1) -1(1) 4(1) 0(1) N(2) 19(1) 14(1) 18(1) -1(1) 4(1) 1(1) C(2) 25(1) 16(1) 19(1) 2(1) 5(1) 2(1) C(3) 23(1) 18(1) 19(1) 1(1) 4(1) 1(1) C(4) 28(1) 12(1) 18(1) 1(1) 1(1) 1(1) C(5) 25(1) 19(1) 34(1) -2(1) -1(1) 3(1) C(6) 27(1) 23(1) 40(2) 1(1) -9(1) -1(1) C(7) 52(2) 15(1) 20(1) -3(1) -12(1) 3(1) C(8) 54(2) 20(1) 18(1) -1(1) 6(1) 4(1) S13

14 C(9) 40(1) 18(1) 21(1) 1(1) 7(1) 2(1) C(10) 28(1) 30(2) 67(2) -13(1) 16(1) -1(1) C(11A) 49(8) 46(9) 138(12) -6(9) 27(8) 19(7) C(12A) 73(11) 62(8) 78(8) -7(6) 47(8) 22(7) C(11B) 28(4) 53(6) 88(6) -23(6) 14(3) 8(4) C(12B) 44(5) 58(5) 60(4) -15(3) 28(4) 7(4) C(13) 44(2) 30(1) 35(1) -3(1) 21(1) -1(1) C(14) 63(2) 65(2) 44(2) 11(2) 29(2) 4(2) C(15) 38(2) 46(2) 47(2) 4(1) 18(1) 7(1) C(16) 19(1) 14(1) 17(1) 1(1) 0(1) -1(1) C(17) 20(1) 18(1) 20(1) -1(1) 2(1) 1(1) C(18) 25(1) 19(1) 24(1) -2(1) 2(1) 5(1) C(19) 26(1) 13(1) 28(1) 1(1) -1(1) -2(1) C(20) 21(1) 21(1) 26(1) 3(1) 3(1) -2(1) C(21) 20(1) 20(1) 21(1) 4(1) 3(1) 4(1) C(22) 27(1) 22(1) 35(1) -5(1) 15(1) 0(1) C(23) 24(1) 73(2) 33(1) -20(1) 9(1) -11(1) C(24) 29(1) 44(2) 28(1) 3(1) 10(1) 9(1) C(25) 28(1) 22(1) 30(1) 1(1) 13(1) 1(1) C(26) 31(1) 42(2) 29(1) -7(1) 11(1) -3(1) C(27) 27(1) 48(2) 31(1) 1(1) 10(1) 8(1) C(28) 26(1) 16(1) 21(1) 2(1) 5(1) 2(1) C(29) 21(1) 23(1) 20(1) 2(1) 5(1) 1(1) C(30) 32(1) 30(1) 25(1) -1(1) 0(1) 0(1) C(31) 33(1) 26(1) 26(1) 5(1) 10(1) -1(1) C(32) 30(1) 45(2) 35(1) 7(1) 14(1) -1(1) C(33) 31(1) 25(1) 32(1) -2(1) 8(1) 7(1) C(34) 48(2) 64(2) 54(2) -25(2) 18(2) -7(2) C(35) 68(3) 68(3) 58(2) -10(2) 19(2) -2(2) C(36) 126(6) 217(10) 126(6) -47(6) 4(5) 48(6) S14

15 Table 5. Hydrogen coordinates ( x 10 4 ) and isotropic displacement parameters (Å 2 x 10 3 ) for 1. x y z U(eq) H(2) H(3) H(6) H(7) H(8) H(10A) H(10B) H(11A) H(11B) H(11C) H(12A) H(12B) H(12C) H(11D) H(11E) H(11F) H(12D) H(12E) H(12F) H(13) H(14A) H(14B) H(14C) H(15A) H(15B) H(15C) H(18) H(19) H(20) H(22) H(23A) H(23B) S15

16 H(23C) H(24A) H(24B) H(24C) H(25) H(26A) H(26B) H(26C) H(27A) H(27B) H(27C) H(30A) H(30B) H(30C) H(31A) H(31B) H(31C) H(32A) H(32B) H(32C) H(33A) H(33B) H(33C) H(34A) H(34B) H(35A) H(35B) H(36A) H(36B) H(36C) [1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene]copper(I) pinacolatoborate (2) The structure was refined as a pseudo-merohedral twin, obeying the twin law This corresponds to a 180º rotation about the crystallographic a-axis. In the monoclinic system this operation is not allowed, unless the monoclinic angle is very close to 90º, which is the case here. The twin-ratio was refined freely and converged at a value of (9), making the structure of 2 an almost perfect twin. S16

17 Figure S3. X-ray crystal structure of 2. Hydrogen atoms (calculated) and solvent omitted for clarity. Shown as stick representation for clarity in labeling. Figure S4. X-ray crystal structure of 2 shown as 50% ellipsoids with toluene molecule included. Hydrogen atoms (calculated) omitted for clarity S17

18 Table 6. Crystal data and structure refinement for 2. Identification code Empirical formula C 40 H 56 BCuN 2 O 3 Formula weight Temperature 100(2) K Wavelength Å Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = (19) Å α= 90. b = (3) Å β= (5). c = (4) Å γ = 90. Volume (12) Å 3 Z 4 Density (calculated) Mg/m 3 Absorption coefficient mm -1 F(000) 1472 Crystal size 0.20 x 0.10 x 0.10 mm 3 Theta range for data collection 0.81 to Index ranges -14<=h<=14, 0<=k<=20, 0<=l<=33 Reflections collected Independent reflections [R(int) = ] Completeness to theta = % Absorption correction Semi-empirical from equivalents Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters / 0 / 438 Goodness-of-fit on F Final R indices [I>2sigma(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Largest diff. peak and hole and e.å -3 S18

19 Table 7. Atomic coordinates ( x 10 4 ) and equivalent isotropic displacement parameters (Å 2 x 10 3 ) for 2. U(eq) is defined as one third of the trace of the orthogonalized U ij tensor. x y z U(eq) Cu(1) 6946(1) 8494(1) 1811(1) 21(1) C(1) 6974(2) 9632(1) 2102(1) 20(1) O(1) 7058(2) 7369(1) 1554(1) 34(1) O(2) 7797(2) 6250(1) 955(1) 24(1) O(3) 6502(2) 7357(1) 620(1) 24(1) B(1) 7116(3) 7034(2) 1074(1) 25(1) N(1) 6868(2) 10430(1) 1852(1) 22(1) N(2) 7200(2) 9868(1) 2619(1) 21(1) C(2) 7029(3) 11139(2) 2199(1) 25(1) C(3) 7232(2) 10788(2) 2687(1) 24(1) C(4) 6611(2) 10530(2) 1288(1) 21(1) C(5) 5359(2) 10695(2) 1136(1) 24(1) C(6) 5133(3) 10846(2) 596(1) 28(1) C(7) 6118(3) 10825(2) 228(1) 31(1) C(8) 7337(3) 10622(2) 387(1) 30(1) C(9) 7616(2) 10465(2) 924(1) 24(1) C(10) 4250(3) 10656(2) 1536(1) 34(1) C(11) 3534(4) 9775(2) 1466(2) 68(1) C(12) 3341(3) 11436(2) 1489(1) 44(1) C(13) 8966(3) 10226(2) 1084(1) 29(1) C(14) 9364(3) 9325(2) 850(1) 45(1) C(15) 9928(3) 10944(2) 932(2) 52(1) C(16) 7440(2) 9222(2) 3034(1) 21(1) C(17) 6409(2) 8884(2) 3322(1) 26(1) C(18) 6672(3) 8257(2) 3722(1) 33(1) C(19) 7901(3) 7988(2) 3822(1) 32(1) C(20) 8896(3) 8336(2) 3529(1) 33(1) C(21) 8698(2) 8969(2) 3129(1) 27(1) C(22) 5044(2) 9149(2) 3202(1) 33(1) C(23) 4349(3) 9478(2) 3701(1) 42(1) C(24) 4341(3) 8374(3) 2944(2) 67(1) C(25) 9801(3) 9329(2) 2806(1) 37(1) S19

20 C(26) 10874(3) 9659(3) 3156(2) 63(1) C(27) 10285(3) 8625(3) 2414(1) 53(1) C(28) 7390(2) 5949(2) 435(1) 22(1) C(29) 8488(3) 5477(2) 160(1) 32(1) C(30) 6300(3) 5307(2) 524(1) 31(1) C(31) 6970(3) 6844(2) 169(1) 24(1) C(32) 8070(3) 7370(2) -73(1) 34(1) C(33) 5904(3) 6736(2) -232(1) 37(1) C(1T) 2122(3) 7078(2) 848(1) 48(1) C(2T) 3342(3) 7203(2) 1053(1) 47(1) C(3T) 3564(4) 7122(3) 1589(2) 61(1) C(4T) 2582(5) 6915(3) 1936(2) 70(1) C(5T) 1378(4) 6785(3) 1734(2) 67(1) C(6T) 1141(3) 6873(2) 1200(2) 55(1) C(10T) 1886(4) 7144(3) 270(2) 66(1) Table 8. Bond lengths [Å] and angles [ ] for 2. Cu(1)-O(1) (16) Cu(1)-C(1) 1.857(2) C(1)-N(1) 1.355(3) C(1)-N(2) 1.364(3) O(1)-B(1) 1.306(3) O(2)-B(1) 1.410(3) O(2)-C(28) 1.444(3) O(3)-B(1) 1.397(3) O(3)-C(31) 1.453(3) N(1)-C(2) 1.385(3) N(1)-C(4) 1.449(3) N(2)-C(3) 1.392(3) N(2)-C(16) 1.445(3) C(2)-C(3) 1.350(3) C(4)-C(5) 1.394(3) C(4)-C(9) 1.401(3) C(5)-C(6) 1.395(3) C(5)-C(10) 1.540(3) C(6)-C(7) 1.389(4) S20

21 C(7)-C(8) 1.378(4) C(8)-C(9) 1.397(3) C(9)-C(13) 1.519(4) C(10)-C(12) 1.516(4) C(10)-C(11) 1.532(5) C(13)-C(15) 1.526(4) C(13)-C(14) 1.533(4) C(16)-C(17) 1.398(4) C(16)-C(21) 1.398(3) C(17)-C(18) 1.404(4) C(17)-C(22) 1.520(4) C(18)-C(19) 1.377(4) C(19)-C(20) 1.382(4) C(20)-C(21) 1.397(4) C(21)-C(25) 1.517(4) C(22)-C(24) 1.523(4) C(22)-C(23) 1.531(4) C(25)-C(26) 1.513(4) C(25)-C(27) 1.531(4) C(28)-C(30) 1.516(3) C(28)-C(29) 1.521(4) C(28)-C(31) 1.564(3) C(31)-C(33) 1.517(4) C(31)-C(32) 1.526(4) C(1T)-C(6T) 1.393(5) C(1T)-C(2T) 1.395(5) C(1T)-C(10T) 1.473(5) C(2T)-C(3T) 1.371(5) C(3T)-C(4T) 1.387(6) C(4T)-C(5T) 1.377(6) C(5T)-C(6T) 1.371(6) O(1)-Cu(1)-C(1) (10) N(1)-C(1)-N(2) (18) N(1)-C(1)-Cu(1) (15) N(2)-C(1)-Cu(1) (16) B(1)-O(1)-Cu(1) (16) S21

22 B(1)-O(2)-C(28) (18) B(1)-O(3)-C(31) (18) O(1)-B(1)-O(3) 126.7(2) O(1)-B(1)-O(2) 122.7(2) O(3)-B(1)-O(2) 110.5(2) C(1)-N(1)-C(2) (18) C(1)-N(1)-C(4) (18) C(2)-N(1)-C(4) (18) C(1)-N(2)-C(3) (19) C(1)-N(2)-C(16) (19) C(3)-N(2)-C(16) (19) C(3)-C(2)-N(1) 106.8(2) C(2)-C(3)-N(2) 105.8(2) C(5)-C(4)-C(9) 123.3(2) C(5)-C(4)-N(1) 117.4(2) C(9)-C(4)-N(1) 119.3(2) C(4)-C(5)-C(6) 117.0(2) C(4)-C(5)-C(10) 122.2(2) C(6)-C(5)-C(10) 120.7(2) C(7)-C(6)-C(5) 121.0(2) C(8)-C(7)-C(6) 120.5(2) C(7)-C(8)-C(9) 120.8(2) C(8)-C(9)-C(4) 117.2(2) C(8)-C(9)-C(13) 119.4(2) C(4)-C(9)-C(13) 123.4(2) C(12)-C(10)-C(11) 110.2(3) C(12)-C(10)-C(5) 113.5(2) C(11)-C(10)-C(5) 109.4(2) C(9)-C(13)-C(15) 112.8(2) C(9)-C(13)-C(14) 111.2(2) C(15)-C(13)-C(14) 110.2(2) C(17)-C(16)-C(21) 123.3(2) C(17)-C(16)-N(2) 118.7(2) C(21)-C(16)-N(2) 118.0(2) C(16)-C(17)-C(18) 117.3(2) C(16)-C(17)-C(22) 122.5(2) C(18)-C(17)-C(22) 120.1(2) S22

23 C(19)-C(18)-C(17) 120.7(2) C(18)-C(19)-C(20) 120.3(2) C(19)-C(20)-C(21) 121.7(3) C(20)-C(21)-C(16) 116.6(2) C(20)-C(21)-C(25) 120.8(2) C(16)-C(21)-C(25) 122.5(2) C(17)-C(22)-C(24) 110.1(3) C(17)-C(22)-C(23) 112.0(2) C(24)-C(22)-C(23) 111.2(3) C(26)-C(25)-C(21) 112.2(3) C(26)-C(25)-C(27) 110.5(3) C(21)-C(25)-C(27) 110.7(3) O(2)-C(28)-C(30) (19) O(2)-C(28)-C(29) 109.3(2) C(30)-C(28)-C(29) 110.3(2) O(2)-C(28)-C(31) (17) C(30)-C(28)-C(31) 113.3(2) C(29)-C(28)-C(31) 114.8(2) O(3)-C(31)-C(33) 108.8(2) O(3)-C(31)-C(32) (19) C(33)-C(31)-C(32) 110.7(2) O(3)-C(31)-C(28) (17) C(33)-C(31)-C(28) 113.6(2) C(32)-C(31)-C(28) 113.5(2) C(6T)-C(1T)-C(2T) 118.6(3) C(6T)-C(1T)-C(10T) 120.9(4) C(2T)-C(1T)-C(10T) 120.5(3) C(3T)-C(2T)-C(1T) 120.4(3) C(2T)-C(3T)-C(4T) 120.6(4) C(5T)-C(4T)-C(3T) 119.2(4) C(6T)-C(5T)-C(4T) 120.8(4) C(5T)-C(6T)-C(1T) 120.5(4) S23

24 Table 9. Anisotropic displacement parameters (Å 2 x 10 3 ) for 2. The anisotropic displacement factor exponent takes the form: -2π 2 [ h 2 a* 2 U h k a* b* U 12 ] U 11 U 22 U 33 U 23 U 13 U 12 Cu(1) 36(1) 15(1) 13(1) -1(1) 0(1) 2(1) C(1) 24(1) 20(1) 15(1) -1(1) 4(1) 1(1) O(1) 67(1) 15(1) 20(1) -1(1) 2(1) 4(1) O(2) 37(1) 20(1) 16(1) -3(1) -6(1) 4(1) O(3) 36(1) 17(1) 20(1) 1(1) -1(1) 2(1) B(1) 37(2) 17(1) 22(1) 2(1) 0(1) -3(1) N(1) 29(1) 19(1) 17(1) 0(1) 0(1) -1(1) N(2) 26(1) 20(1) 16(1) 0(1) 0(1) 1(1) C(2) 34(1) 17(1) 23(1) -2(1) 0(1) -1(1) C(3) 33(1) 17(1) 22(1) -3(1) 2(1) 1(1) C(4) 31(1) 17(1) 15(1) 0(1) 2(1) -3(1) C(5) 32(1) 21(1) 19(1) 3(1) 1(1) -3(1) C(6) 36(1) 26(1) 22(1) 3(1) -7(1) -5(1) C(7) 51(2) 28(1) 15(1) 0(1) -3(1) -8(1) C(8) 44(2) 28(1) 18(1) -2(1) 7(1) -7(1) C(9) 34(1) 20(1) 18(1) -3(1) 2(1) -5(1) C(10) 31(1) 49(2) 21(1) 6(1) 3(1) 2(1) C(11) 59(2) 36(2) 109(3) 13(2) 45(2) -3(2) C(12) 41(2) 35(2) 55(2) -6(1) 11(1) -4(1) C(13) 33(1) 30(1) 25(1) 0(1) 4(1) 1(1) C(14) 47(2) 33(2) 55(2) -4(1) 12(2) 10(1) C(15) 38(2) 41(2) 79(3) -4(2) -4(2) -7(1) C(16) 37(1) 16(1) 10(1) -2(1) -2(1) 3(1) C(17) 34(1) 28(1) 17(1) 0(1) -1(1) -4(1) C(18) 52(2) 29(1) 17(1) 1(1) 0(1) -9(1) C(19) 62(2) 20(1) 14(1) 0(1) -7(1) 5(1) C(20) 49(2) 23(1) 29(1) -4(1) -8(1) 13(1) C(21) 36(1) 22(1) 23(1) -4(1) 0(1) 6(1) C(22) 32(1) 43(2) 25(1) 6(1) -2(1) -6(1) C(23) 47(2) 47(2) 33(2) -2(1) -1(1) 8(1) C(24) 39(2) 94(3) 68(3) -39(2) -2(2) -9(2) C(25) 33(1) 44(2) 34(2) 4(1) 0(1) 8(1) S24

25 C(26) 44(2) 84(3) 60(2) -17(2) 9(2) -20(2) C(27) 47(2) 74(3) 38(2) -5(2) 8(1) 12(2) C(28) 34(1) 17(1) 16(1) -1(1) -4(1) -1(1) C(29) 44(2) 29(1) 23(1) -2(1) 4(1) 9(1) C(30) 44(2) 20(1) 31(1) 3(1) -6(1) -5(1) C(31) 34(1) 19(1) 19(1) 1(1) -1(1) -1(1) C(32) 48(2) 28(1) 26(1) 4(1) 4(1) -5(1) C(33) 56(2) 25(1) 30(1) 4(1) -17(1) -1(1) C(1T) 50(2) 30(1) 64(2) -5(1) 6(2) -4(1) C(2T) 41(2) 37(2) 61(2) -12(2) 10(1) -1(1) C(3T) 59(2) 59(2) 63(2) -19(2) -3(2) -5(2) C(4T) 95(3) 70(3) 44(2) -21(2) 10(2) -12(2) C(5T) 70(2) 53(2) 76(3) -27(2) 31(2) -17(2) C(6T) 46(2) 41(2) 79(3) -11(2) 21(2) -5(2) C(10T) 71(2) 60(2) 67(2) 13(2) -14(2) -13(2) Table 10. Hydrogen coordinates ( x 10 4 ) and isotropic displacement parameters (Å 2 x 10 3 ) for 2. x y z U(eq) H(2) H(3) H(6) H(7) H(8) H(10) H(11A) H(11B) H(11C) H(12A) H(12B) H(12C) H(13) H(14A) H(14B) S25

26 H(14C) H(15A) H(15B) H(15C) H(18) H(19) H(20) H(22) H(23A) H(23B) H(23C) H(24A) H(24B) H(24C) H(25) H(26A) H(26B) H(26C) H(27A) H(27B) H(27C) H(29A) H(29B) H(29C) H(30A) H(30B) H(30C) H(32A) H(32B) H(32C) H(33A) H(33B) H(33C) H(2T) H(3T) H(4T) H(5T) S26

27 H(6T) H(10A) H(10B) H(10C) Mankad, N. P.; Laitar, D. S.; Sadighi, J. P. Organometallics 2004, 23, Herrmann, W. A.; Koecher, C.; Goossen, L. J.; Artus, G. R. J. Chem. Eur. J. 1996, 2, Sheldrick, G. M. Acta Crystallogr. Sect. A 1990, 46, 467. S27