Formal SiH 4 chemistry using stable and easy-to-handle surrogates

Transcription

1 DOI: /NCHEM.2329 Formal SiH 4 chemistry using stable and easy-to-handle surrogates Antoine Simonneau and Martin Oestreich* Institut für Chemie, Technische Universität Berlin, Strasse des 17. Juni 115, D Berlin, Germany martin.oestreich@tu-berlin.de Supplementary Information NATURE CHEMISTRY 1

2 Table of Contents 1 General Information S3 2 Experimental Details for the Synthesis of Bis(pentafluorophenyl)(nonafluorobiphenyl)borane S4 (1c) and Measurement of Gutmann Beckett Parameters 2.1 Synthesis of Bis(pentafluorophenyl)(nonafluorobiphenyl)borane (1c) S4 2.2 Measurement of Gutmann Beckett Parameters (Table S1) S5 3 Experimental Details for the Synthesis of Cyclohexa-2,5-dienylsilanes 2a c S6 3.1 Synthesis of Tetra(cyclohexa-2,5-dien-1-yl)silane (2a) S6 3.2 Synthesis of Tri(cyclohexa-2,5-dien-1-yl)silane (2b) S7 3.3 Synthesis of Di(cyclohexa-2,5-dien-1-yl)silane (2c) S8 4 General Procedure for the Optimization of the Transfer Hydrosilylation of S9 Styrene (4a) in Table 1 5 Experimental Details for the Synthesis of Silanes by Transfer Hydrosilylation S9 5.1 General Procedure for the Reactions of Table 2 S9 5.2 Preparation of 7a Outside the Glove Box S9 5.3 Characterization Data of Compounds 6e,f,j,k,m, 7a d,f,h,i,l,o, and 8g S10 6 Experimental Details for the Hydrosilylation of Oct-1-ene (4g) Catalyzed by S16 Platinum. 6.1 Synthesis and Characterization Data of Tri(cyclohexa-2,5-dien-1-yl)(octyl)silane (9) S Synthesis and Characterization Data of Di(cyclohexa-2,5-dien-1-yl)(octyl)silane (10) S16 7 Experimental Details for the Generation of Octylsilane (5g) from Hydrosilylation S17 Compounds 9 and General Procedure S Characterization Data of Octylsilane (5g) S17 8 Time-Dependent NMR Experiments S General Procedure for Monitoring the Degradation of 2a c S Experimental Procedure for Monitoring the Degradation of 2b in an Open System S Degradation of 2a over Time, Selected Spectra (Fig. S2) S Degradation of 2b over Time, Plot (Fig. S3) S Degradation of 2b over Time, Selected Spectra (Closed System) (Fig. S4) S Degradation of 2c over Time, Plot (Fig. S5) S Degradation of 2c over Time, Selected Spectra (Fig. S6) S Experimental Procedure for Monitoring the Reaction of Table 1, Entry 1 S Monitoring of the Reaction of Table 1, Entry 1, Plots (Fig. S7 8) S Monitoring of the Reaction of Table 1, Entry 1, Selected Spectra (Fig. S9 11) S Experimental Procedure for Monitoring the Reaction of Styrene (4a) with Excess 2b S Monitoring of the Reaction of Styrene (4a) with Excess 2b, Plots (Fig. S12 13) S Monitoring of the Reaction of Styrene (4a) with Excess 2b, Selected Spectra (Fig. S33 S14 16) 8.14 Selected Characterization Data of Intermediates 2d, SiH 4, 5a, and 6a S36 9 NMR Spectra S37 10 Molecular Structure and X-Ray Data of Compound 2b (Fig. S17) S References S106 NATURE CHEMISTRY 2

3 1 General Information All reactions were performed in flame-dried glassware using an MBraun glove box (O 2 < 0.5 ppm, H 2 O < 0.5 ppm) or conventional Schlenk techniques under a static pressure of argon (glove box) or nitrogen. Liquids and solutions were transferred with syringes. CH 2 Cl 2, benzene, n-pentane, n-hexane, and THF were purified and dried using a MBraun solvent system. Toluene was distilled over sodium, degassed, and stored in glove box over 4 Å molecular sieves. C 6 D 6 (purchased from Aldrich) was dried over 4 Å molecular sieves; toluene-d 8 and CD 2 Cl 2 (purchased from Eurisotop) were distilled from the appropriate drying reagent, degassed, and stored in glove box over 4 Å molecular sieves. Technical grade solvents for extraction and chromatography (cyclohexane, n-pentane, ethyl acetate, and tert-butyl methyl ether) were distilled prior to use. All commercially available alkenes and alkynes 4a m,o were, if liquids, distilled, degassed, and stored in glove box over 4 Å molecular sieves. Alkene 4n [S1] was synthesized according to a reported procedure. B(C 6 F 5 ) 3 (1a), [S2] B(4-C 6 F 4 H) 3 (1b), [S3] B(C 12 F 9 ) 3 (1d), [S4] 2-bromononafluoro-1,1'-biphenyl, [S5] and (C 6 F 5 ) 2 BCl [S6] were synthesized according to reported procedures and stored in a glove box. Karstedt s catalyst was purchased from ABCR and dichloro(cycloocta-1,5-diene)platinum was purchased from Alfa Aesar. Analytical thin-layer chromatography (TLC) was performed on silica gel SIL G-25 glass plates from Macherey-Nagel. Flash column chromatography was performed on silica gel 60 (40 63 μm, mesh, ASTM) by Merck using the indicated solvents. Filtration of the reaction mixture prior to GLC analysis and reaction work-up were performed on MP Ecochrom neutral alumina of activity grade I by MP Biomedicals Germany GmbH. 1 H and 13 C NMR spectra were recorded in C 6 D 6 on Bruker AV 400 and Bruker AV 500 instruments. Chemical shifts are reported in parts per million (ppm) downfield from tetramethylsilane and are referenced to the residual solvent resonance as the internal standard (C 6 H 6 : δ = 7.16 ppm for 1 H NMR and C 6 D 6 : δ = ppm for 13 C NMR, CHDCl 2 δ = 5.32 ppm for 1 H NMR and CD 2 Cl 2 δ = ppm for 13 C NMR). 11 B, 19 F, 29 Si, and 31 P NMR spectra were calibrated according to the IUPAC recommendation using a unified chemical shift scale based on the proton resonance of trimethylsilane as primary reference. Data are reported as follows: chemical shift, multiplicity (br s = broad singlet, s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), coupling constant (Hz), and integration. Infrared (IR) spectra were recorded on an Agilent Technologies Cary 630 FT-IR spectrophotometer equipped with an ATR unit and are reported in wavenumbers (cm 1 ). Gas liquid chromatography mass spectrometry (GLC-MS) was performed on an Agilent Technologies GC-System 5975C with an Agilent Technologies Mass Selective Detector (EI) and a HP-5MS column. Gas liquid chromatography (GLC) was performed on an Agilent Technologies 7820A gas chromatograph equipped with a SE-54 capillary column (30 m 0.32 mm, 0.25 µm film thickness) by CS- Chromatography Service using the following programs: N 2 carrier gas, column flow 1.7 ml/min, injection temperature 280 C, detector temperature 300 C; temperature program: start temperature 40 C, heating rate 10 C/min, final temperature 280 C for 10 min. Melting points (m.p.) were determined with a Stuart Scientific SMP20 melting point apparatus and are not corrected. High resolution mass spectrometry [HRMS, Atmospheric-Pressure Chemical Ionization (APCI) or Electronic Impact (EI)] and elemental analyses were performed by the analytical facility at the Institut für Chemie, Technische Universität Berlin. NATURE CHEMISTRY 3

4 2 Experimental Details for the Synthesis of Bis(pentafluorophenyl)(nonafluorobiphenyl)borane (1c) and Measurement of Gutmann Beckett Parameters 2.1 Synthesis of Bis(pentafluorophenyl)(nonafluorobiphenyl)borane (1c) 1c C 24 BF 19 MW: g/mol Caution: This preparation involves the generation of lithiated perfluororarenes which are likely to explode if not kept at low temperature (< 30 C). At least, safety shields must be used when performing the following procedure. In our hands, the synthesis of borane 1c as reported by Li et al. [S7] led to mixtures of different boron compounds from which isolation of pure 1c could not be achieved. Instead, the following protocol was developed to obtain this compound in satisfying yields and purities: In a flamedried 50-mL Schlenk flask purged with argon was dissolved 2-bromononafluoro-1,1'-biphenyl (1.17 g, 2.96 mmol, 1.00 equiv) in n-pentane (20 ml). The solution was cooled to 78 C with a cryostat, and n-buli (3.1M in hexanes, ml, 2.96 mmol, 1.00 equiv) was added dropwise. The resulting suspension was slowly warmed to 55 C over approx. 2 h and kept at this temperature for 4 h. Chlorobis(perfluorophenyl)borane in n-pentane (7 ml) was then added, and the mixture was slowly warmed to room temperature overnight. The resulting suspension was filtered under argon atmosphere, and the filtrate was evaporated to dryness, affording a sticky, pale yellow oil. 19 F NMR analysis of this oil already showed a rather clean spectrum. In a glove box, the oil was dissolved in n-pentane (10 ml) and transferred to a flame-dried 25-mL Schlenk flask equipped with a magnetic stir bar. Outside the glove box, the solution was cooled to 78 C with a dry ice/ethanol bath while stirring. Precipitation of the targeted borane occured, and the supernatant was discarded via a filter cannula. This operation was repeated twice to afford an amorphous, off-white solid, which was further dried in vacuo, 674 mg, 35% yield. 19 F NMR (471 MHz, C 6 D 6 ) δ = (d, J = 20.0 Hz, 4F), (dt, J = 20.8 Hz, 10.2 Hz, 1F), (dq, J = 18.1 Hz, 6.0 Hz, 1F), (d, J = 20.7 Hz, 2F), (br s, 1F), (t, J = 17.5 Hz, 1F), (t, J = 21.2 Hz, 1F), (td, J = 22.3 Hz, 6.3 Hz, 1F), (td, J = 21.0 Hz, 7.1 Hz, 4F), (td, J = 21.2 Hz, 6.4 Hz, 2F). 11 B NMR (161 MHz, C 6 D 6 ) δ = The analytical and spectroscopic data are in accordance with those reported. [S7] NATURE CHEMISTRY 4

5 2.2 Measurement of Gutmann Beckett Parameters In a glove box, a 1.3-mL GLC vial was charged with triethylphosphine oxide (2.7 mg, 20 µmol, 1.0 equiv), bis(pentafluorophenyl)(nonafluorobiphenyl)borane (1c, 13.2 mg, 20.0 µmol, 1.00 equiv), and a magnetic stir bar. The two solids were covered with C 6 D 6 (1.0 ml), and the resulting solution was stirred for a few minutes before being transferred to an NMR tube. Complete conversion of the phosphine oxide to its borane adduct was observed by 31 P NMR analysis. 1 H NMR (500 MHz, C 6 D 6 ) δ = 0.95 (dq, J = 12.0 Hz, 7.8 Hz, 6H), 0.22 (dt, J = 18.7 Hz, 7.8 Hz, 9H). 19 F NMR (471 MHz, C 6 D 6 ) δ = (br s, 4F), (dd, J = 21.0 Hz, 9.7 Hz, 1F), (br s, 2F), (t, J = 20.4 Hz, 1F), (t, J = 20.4 Hz, 1F), (q, J = 20.7 Hz, 4F), (br s, 2F), (br s, 4F). 31 P NMR (203 MHz, C 6 D 6 ) δ = Table S1. Gutmann Beckett Analysis of Boranes 1a d 31 P { 1 H} NMR (δ/ppm) Borane 1 Et 3 PO 1 a Relative Lewis Acidity (%) b 1a 75.3 (Δδ = 30.0) [S8] 100 1b 74.4 (Δδ = 29.1) [S9] 97 1c 74.0 (Δδ = 28.7) 96 1d 79.3 (Δδ = 34.0) [S9] 113 Et 3 PO 45.3 [S9] a δ values relative to free Et 3 PO. b Calculated from ( δ for 1)/( δ for 1a). NATURE CHEMISTRY 5

6 3 Experimental Details for the Synthesis of Cyclohexa-2,5-dienylsilanes 2a c 3.1 Synthesis of Tetra(cyclohexa-2,5-dien-1-yl)silane (2a) 2a C 24 H 28 Si MW: g/mol In a flame-dried 250-mL Schlenk flask purged with N 2 were subsequently introduced THF (50 ml) and cyclohexa-1,4-diene (4.0 ml, 42 mmol, 4.2 equiv). The solution was cooled to 78 C with a dry ice/ethanol bath, and sec-buli (1.26M in cyclohexane, 33 ml, 41 mmol, 4.1 equiv) was added dropwise over 15 min. The mixture rapidly turned yellow. TMEDA (6.1 ml, 41 mmol, 4.1 equiv) was then added, and the resulting solution was slowly warmed to 35 C over approx. 2 h. Cooling back to 78 C was followed by dropwise addition of neat SiCl 4 (1.2 ml, 10 mmol, 1.0 equiv). The mixture was then slowly warmed to room temperature overnight, and stirred for further 3 d until the yellow coloration had vanished. The resulting cloudy solution was quenched with saturated aqueous NH 4 Cl (35 ml), and the aqueous layer was extracted with tert-butyl methyl ether (3 30 ml). The combined organic layers were washed with brine (40 ml) and water (40 ml). After removal of all volatiles, the crude off-white solid material was recrystallized from n-hexane to afford a white crystalline solid, 1.8 g, 52 % yield. M.P.: 86 C. IR (ATR): ~ /cm 1 = 3021, 2878, 2844, 2812, 1667, 1622, 1427, 1332, 1288, 1111, 1055, 942, 889, 760, H NMR (500 MHz, C 6 D 6 ) δ = (m, 8H), (m, 8H), (m, 4H), (m, 8H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (8C), (8C), 27.6 (4C), 26.5 (4C). 1 H- 29 Si HMQC NMR (99 MHz, C 6 D 6 ) δ = 5.9. HRMS (APCI) for [C 24 H 28 Si] + calcd m/z found ; for [C 24 H 28 Si H] + calcd m/z found Anal. Calcd for C 24 H 28 Si: C, 83.66; H, Found: C, 83.82; H, NATURE CHEMISTRY 6

7 3.2 Synthesis of Tri(cyclohexa-2,5-dien-1-yl)silane (2b) 2b C 18 H 22 Si MW: g/mol Method A. In a flame-dried 100-mL Schlenk flask purged with N 2 were subsequently introduced THF (30 ml) and cyclohexa-1,4-diene (3.8 ml, 40 mmol, 3.0 equiv). The solution was cooled to 78 C with a dry ice/ethanol bath, and sec-buli (1.34M in cyclohexane, 30 ml, 40 mmol, 3.0 equiv) was added dropwise over 15 min. The mixture rapidly turned yellow. TMEDA (6.0 ml, 40 mmol, 3.0 equiv) was then added, and the resulting solution was slowly warmed to 30 C over approx. 2 h. Cooling back to 78 C was followed by dropwise addition of neat HSiCl 3 (1.35 ml, 13.3 mmol, 1.00 equiv). The mixture was then slowly warmed to room temperature and stirred overnight. The resulting cloudy solution was quenched with saturated aqueous NH 4 Cl (30 ml), and the aqueous layer was extracted with tert-butyl methyl ether (3 25 ml). The combined organic layers were washed with brine (40 ml) and water (40 ml). After removal of all volatiles, the crude off-white solid material was recrystallized three times from n-pentane to afford a white crystalline solid, 0.5 g, 14 % yield. Method B. In a flame-dried 250-mL Schlenk flask purged with N 2 were subsequently introduced n-hexane (100 ml) and cyclohexa-1,4-diene (3.91 ml, 41.3 mmol, 3.10 equiv). The solution was cooled to 78 C with a cryostat, and sec-buli (1.38M in cyclohexane, 29.5 ml, 40.7 mmol, 3.05 equiv) was added dropwise over 15 min. TMEDA (6.08 ml, 40.7 mmol, 3.05 equiv) was then added, and the resulting yellow solution was slowly warmed to 35 C over approx. 2 h and kept at this temperature for 4 h. Neat HSiCl 3 (1.35 ml, 13.3 mmol, 1.00 equiv) was added dropwise at 35 C, and the mixture was slowly warmed to room temperature and stirred overnight. The resulting cloudy solution was quenched with saturated aqueous NH 4 Cl (50 ml), and the aqueous layer was extracted with tert-butyl methyl ether (3 35 ml). The combined organic layers were washed with brine (60 ml) and water (60 ml). After removal of all volatiles, the crude off-white solid material was recrystallized from n-pentane to afford a white crystalline solid, 2.95 g, 83 % yield. M.P.: 59 C. IR (ATR): ~ /cm 1 = 3024, 2814, 2116, 1664, 1619, 1429, 1619, 1429, 1330, 1290, 1106, 1050, 981, 935, 890, 833, 734, H NMR (500 MHz, C 6 D 6 ) δ = 5.78 (ddt, J = 10.1 Hz, 3.9 Hz, 1.9 Hz, 6H), (m, 6H), 3.90 (q, J = 1.6 Hz, 1H), (m, 3H), (m, 6H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (6C), (6C), 27.0 (3C), 26.4 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = Anal. Calcd for C 18 H 22 Si: C, 81.14; H, Found: C, 81.04; H, NATURE CHEMISTRY 7

8 3.3 Synthesis of Di(cyclohexa-2,5-dien-1-yl)silane (2c) 2c C 12 H 16 Si MW: g/mol In a flame-dried 250-mL Schlenk flask purged with N 2 were subsequently introduced THF (50 ml) and cyclohexa-1,4-diene (3.88 ml, 41.0 mmol, 2.03 equiv). The solution was cooled to 78 C with a dry ice/ethanol bath, and sec-buli (1.38M in cyclohexane, 29.4 ml, 40.6 mmol, 2.03 equiv) was added dropwise over 15 min. The mixture rapidly turned yellow. TMEDA (6.07 ml, 40.6 mmol, 2.03 equiv) was then added, and the resulting solution was slowly warmed to 10 C over approx. 3.5 h. Cooling back to 78 C was followed by dropwise addition of neat (EtO) 2 SiCl 2 (3.72 ml, 20.0 mmol, 1.00 equiv). The mixture was then slowly warmed to room temperature overnight, and stirred for further 3 d until the yellow coloration had vanished. The resulting cloudy solution was quenched with saturated aqueous NH 4 Cl (35 ml), and the aqueous layer was extracted with tert-butyl methyl ether (3 30 ml). The combined organic layers were washed with brine (40 ml) and water (40 ml). After removal of all volatiles, di(cyclohexa-2,5-dien-1-yl)diethoxysilane (3) was obtained as a pale brown oil and used in the next step without purification. Yield was quantitative. 1 H NMR (400 MHz, C 6 D 6 ) δ = 5.93 (ddd, J = 10.2 Hz, 3.3 Hz, 1.7 Hz, 4H), 5.56 (ddd, J = 10.1 Hz, 4.0 Hz, 2.1 Hz, 4H), 3.81 (q, J = 7.0 Hz, 4H), (m, 6H), 1.15 (t, J = 7.0 Hz, 6H). In a flame-dried 250-mL Schlenk flask purged with N 2 and equipped with a dropping funnel was dissolved di(cyclohexa-2,5-dien-1-yl)diethoxysilane (3, 5.5 g, 20 mmol, 1.0 equiv) in n-hexane (20 ml). The solution was cooled to 78 C with a dry ice/ethanol bath, and di(isobutyl)- aluminum hydride (1.1M in n-hexane, 69 ml, 76 mmol, 3.8 equiv) was added dropwise. The resulting mixture was stirred at 78 C for 30 min then rapidly brought to 0 C and stirred at this temperature for again 30 min. Under an argon counterflow, freshly ground Na 2 SO 4 10H 2 O was added in small portions at room temperature until hydrogen evolution was no longer observed. The suspension was next filtered over a large (diameter approx. 12 cm, height approx. 5 cm) plug of silica, and the filter cake was washed with cyclohexane (3 50 ml). After removal of all volatiles, a colorless oil was obtained which was distilled under reduced pressure (8 mbar, 100 C) to afford di(cyclohexa-2,5-dien-1-yl)silane (2c) as a colorless oil, 2.0 g, 53% yield over two steps. IR (ATR): ~ /cm 1 = 3022, 2852, 2819, 2127, 1621, 1429, 1291, 1105, 1051, 927, 893, 819, H NMR (400 MHz, C 6 D 6 ) δ = 5.68 (ddd, J = 8.1 Hz, 3.9 Hz, 1.9 Hz, 4H), 5.50 (dt, J = 10.0 Hz, 3.1 Hz, 4H), 3.87 (t, J = 2.5 Hz, 2H), (m, 4H), (m, 2H). 13 C NMR (101 MHz, C 6 D 6 ) δ = (4C), (4C), 26.3 (2C), 25.9 (2C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = HRMS (EI) for [C 12 H 16 Si] + calcd m/z found NATURE CHEMISTRY 8

9 4 General Procedure for the Optimization of the Transfer Hydrosilylation of Styrene (4a) in Table 1 Caution: For reactions employing equiv of the SiH 4 surrogate, a substantial amount of SiH 4 gas is released in the reaction vial, resulting in ignition upon unsealing under air. Extreme care must be applied if these reactions are run on a larger scale! In a glove box, a 1.3-mL GLC vial is charged with the SiH 4 surrogate (2b: 18.7 mg, 70.0 µmol, equiv / 29.3 mg, mmol, equiv / 58.6 mg, mmol, 1.10 equiv; 2c: 13.2 mg, mmol, equiv / 20.7 mg, mmol, equiv / 41.4 mg, mmol, 1.10 equiv), styrene (4a, 20.8 mg, mmol, 1.00 equiv), mesitylene (14 µl, 0.10 mmol, 0.50 equiv, internal standard) and a magnetic stir bar. The mixture is covered with CH 2 Cl 2 (0.1 ml), the resulting solution is briefly stirred, and an aliquot is taken to measure the t 0 GLC chromatogram. Into a separate vial is weighed the catalyst (1a: 5.1 mg; 1b: 4.6 mg; 1c: 6.6 mg; 1d: 9.6 mg, 10 µmol, 5.0 mol %) which is then dissolved in CH 2 Cl 2 (0.1 ml). The resulting solution is then transferred to the reaction vial, the latter is capped and stirred in the glove box at room temperature. The reaction is monitored by GLC analysis. 5 Experimental Details for the Synthesis of Silanes by Transfer Hydrosilylation 5.1 General Procedure for the Reactions of Table 2 In glove box, a 1.3-mL GLC vial is charged with the SiH 4 surrogate 2, the unsaturated substrate (0.2 mmol, 1.0 equiv) and a magnetic stir bar. In a separate vial is weighed B(C 6 F 5 ) 3 (1a: 5.1 mg, 10 µmol, 5.0 mol %), which is then dissolved in CH 2 Cl 2 (0.2 ml). The resulting solution is then transferred to the reaction vial, the latter is capped and stirred in glove box at room temperature. The reaction is monitored by GLC. When full conversion is noticed, the reaction mixture is filtered in glove box over a short neutral alumina column (ø ~0.5 cm, h ~1 cm), which is further eluted with CH 2 Cl 2 (3 0.5 ml). Outside glove box, the filtrate is next evaporated to dryness. If necessary, the crude target compound is purified by flash column chromatography. 5.2 Preparation of 7a Outside the Glove Box In glove box, a screw-cap Schlenck tube was charged with styrene (4a, 31.3 mg, mmol, 1.00 equiv). In two separate 1.3-mL GLC vials were weighed B(C 6 F 5 ) 3 (1a: 7.7 mg, 15 µmol, 5.0 mol %) and tri(cyclohexa-2,5-dien-1-yl)silane (2b, 28.0 mg, mmol, equiv). All the sealed containers were taken out of the glove box, and the Schlenk tube was connected to a N 2 line. Under a N 2 counterflow were subsequently added 0.3 ml of CH 2 Cl 2 (technical grade, distilled with a rotary evaporator prior to use), 2b then 1a. The tube was completely sealed and stirred at room temperature for 24 h. After this time, two drops of triethylamine were added to the solution under an N 2 counterflow, and the resulting mixture was stirred for 5 min before being filtered over a short alumina column (elution with CH 2 Cl 2 ). After evaporation of all volatiles, the crude product (cloudy oil) was purified by flash column chromatography using cyclohexane/tert-butyl methyl ether (97.5:2.5) as eluent. Pure 7a was obtained as a colorless oil (26 mg, 75% yield). NATURE CHEMISTRY 9

10 5.3 Characterization Data of Compounds 6e,f,j,k,m, 7a d,f,h,i,o, and 8g 7a C 24 H 28 Si MW: g/mol Prepared from styrene (4a, 20.8 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 20 h, and the crude product was purified by flash column chromatography using cyclohexane as eluent. Colorless oil, 63 mg, 91% yield. IR (ATR): ~ /cm 1 = 3023, 2916, 2099, 1941, 1869, 1799, 1600), 1492, 1450, 1173, 902, 840, 781, 730, H NMR (500 MHz, C 6 D 6 ) δ = (m, 6H), (m, 9H), 3.98 (sept, J = 3.1 Hz, 1H), (m, 6H), 0.86 (ddd, J = 11.5 Hz, 5.7 Hz, 3.2 Hz, 6H). 13 C NMR (126 MHz, C 6 D6) δ = (3C), (6C), (6C), (3C), 31.2 (3C), 13.5 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = 6.3. HRMS (EI) for [C 24 H 28 Si] + calcd m/z found The analytical and spectroscopic data are in accordance with those reported. [S10] 7b C 27 H 34 Si MW: g/mol Prepared from 4-methylstyrene (4b, 23.6 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 20 h. The crude material did not require purification. Colorless oil, 27 mg, 99% yield. IR (ATR): ~ /cm 1 = 3106, 2917, 2097, 1894, 1511, 1445, 1170, 1125, 994, 917, 854, H NMR (500 MHz, C 6 D 6 ) δ = 7.04 (s, 12H), 4.03 (quint, J = 3.1 Hz, 1H), (m, 6H), 2.18 (s, 9H), 0.90 (ddt, J = 8.6 Hz, 5.8 Hz, 3.2 Hz, 6H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (3C), (3C), (6C), (6C), 30.8 (3C), 21.1 (3C), 13.8 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = 6.2. HRMS (APCI) for [C 27 H 34 Si] + calcd m/z found ; for [C 27 H 34 Si H] + calcd m/z found c C 24 H 25 F 3 Si MW: g/mol Prepared from 4-fluorostyrene (4c, 24.4 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 40 h. The crude material did not require purification. Colorless oil, 23 mg, 85% yield. IR (ATR): ~ /cm 1 = 2918, 2103, 1599, 1505, 1464, 1412, 1217, 1155, 1121, 1085, 918, 819, H NMR (400 MHz, C 6 D 6 ) δ = (m, 12H), 3.88 (quint, J = 3.2 Hz, 1H), (m, 6H), 0.72 (ddd, J = 11.4 Hz, 5.6 Hz, 3.2 Hz, NATURE CHEMISTRY 10

11 6H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (d, J = Hz, 3C), (d, J = 2.9 Hz, 3C), (d, J = 7.7 Hz, 6C), (d, J = 21.1 Hz, 6C), 30.2 (3C), 13.5 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = 6.7. HRMS (APCI) for [C 24 H 25 F 3 Si] + calcd m/z found ; for [C 24 H 25 F 3 Si H] + calculated m/z found d C 36 H 34 Si MW: g/mol Prepared from 2-vinylnaphthalene (4d, 30.8 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 40 h, and the crude product was purified by flash column chromatography using cyclohexane/dichloromethane (4:1) as eluent. White solid, 21 mg, 63% yield. M.P.: 115 C. IR (ATR): ~ /cm 1 = 3050, 2922, 2848, 2079, 1627, 1597, 1506, 1439, 1397, 1362, 1311, 1271, 1176, 1110, 1003, 929, 896, 857, 814, 790, 745, H NMR (500 MHz, C 6 D 6 ) δ = 7.35 (m, 5H), 7.31 (d, J = 8.4 Hz, 3H), 6.98 (ddd, J = 8.1 Hz, 6.7 Hz, 1.3 Hz, 3H), 6.94 (ddd, J = 8.1 Hz, 6.9 Hz, 1.3 Hz, 3H), 6.84 (dd, J = 6.7 Hz, 1.7 Hz, 3H), 6.83 (br s, 4H), 3.78 (sept, J = 3.1 Hz, 1H), (m, 6H), 0.66 (ddd, J = 11.4 Hz, 5.7 Hz, 3.2 Hz, 6H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (3C), (3C), (3C), (3C), (3C), (3C), (3C), (3C), (3C), (3C), 31.4 (3C), 13.6 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = 5.8. HRMS (APCI) for [C 36 H 34 Si] + calcd m/z found e C 18 H 24 Si MW: g/mol Prepared from -methylstyrene (4e, 30.8 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 40 h, and the crude product was purified by flash column chromatography using cyclohexane as eluent. 6e was obtained as an inseparable 1:1 mixture of C 2 -symmetric and meso compounds, colorless oil, 5 mg, 26% yield. IR (ATR): ~ /cm 1 = 3026, 2975, 2921, 2126, 1601, 1451, 944, 870, 761, H NMR (500 MHz, C 6 D 6 ) δ = (m, 5H), 3.74 (quint, J = 3.6 Hz, 2H meso ), (m, 2H C2), 2.70 (tdd, J = 7.0 Hz, 7.0 Hz, 4.5 Hz, 2H), 1.19 (d, J = 6.8 Hz, 3H), 1.18 (d, J = 6.8 Hz, 3H), (m, 4H). 5 aromatic protons were not detected due to overlapping with solvent signal. 13 C NMR (126 MHz, C 6 D 6 ) δ = (2C), (4C), (4C), (2C), 37.6, {25.3, 25.2, (2C meso + 2C C2)}, 19.7 (2C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = { 33.5, 33.6 (Si meso + Si C2)}. HRMS (APCI) for [C 18 H 24 Si] + calcd m/z found ; for [C 18 H 24 Si H] + calcd m/z found NATURE CHEMISTRY 11

12 6f C 28 H 28 Si MW: g/mol Prepared from 1,1-diphenylethylene (4f, 36.1 mg, mmol, 1.00 equiv) and 2b (29.3 mg, mmol, equiv). Reaction was stopped after 20 h, and the crude product was purified by flash column chromatography using cyclohexane/dichloromethane (7:3) as eluent. Colorless oil, 31 mg, 79% yield. IR (ATR): ~ /cm 1 = 3022, 2883, 2126, 1943, 1874, 1800, 1751, 1596, 1490, 1448, 1406, 1171, 1128, 1071, 1020, 940, 882, 802, 739, H NMR (400 MHz, C 6 D 6 ) δ = (m, 16H), (m, 4H), 3.90 (t, J = 8.2 Hz, 2H), 3.67 (quint, J = 3.5 Hz, 2H), 1.19 (dt, J = 8.1 Hz, 3.5 Hz, 4H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (2C), (4C), (4C), (2C), 48.5 (2C), 17.1 (2C). HRMS (EI) for [C 28 H 28 Si] + calcd m/z found f C 42 H 40 Si MW: g/mol Prepared from 1,1-diphenylethylene (4f, 36.1 mg, mmol, 1.00 equiv) and 2c (13.2 mg, 70.0 µmol, equiv). Reaction was stopped after 70 h, and the crude product was purified by flash column chromatography using cyclohexane/dichloromethane (3:1) as eluent. Colorless oil, 29 mg, 84% yield. IR (ATR): ~ /cm 1 = 3022, 2919, 2114, 1944, 1874, 1800, 1751, 1596, 1490, 1447, 1405, 1171, 1129, 1071, 1029, 1010, 879, 795, 740, H NMR (500 MHz, C 6 D 6 ) δ = (m, 24H), (m, 6H), 3.86 (t, J = 8.1 Hz, 3H), 3.66 (sept, J = 2.9 Hz, 1H), 1.11 (dd, J = 8.1 Hz, 3.1 Hz, 6H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (3C), (6C), (6C), (3C), 47.9 (3C), 19.5 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = HRMS (EI) for [C 42 H 40 Si] + calcd m/z found g C 32 H 68 Si MW: g/mol Prepared from oct-1-ene (4g, 44.8 mg, mmol, 1.00 equiv) and 2b (26.7 mg, mmol, equiv). Reaction was stopped after 100 h. The crude material did not require purification. Colorless oil, 24 mg, 50% yield. IR (ATR): ~ /cm 1 = 2918, 2851, 1514, 1462, 1410, 1377, 1175, 1084, 970, 829, H NMR (500 MHz, C 6 D 6 ) δ = (m, 48H), 0.92 (t, J = 6.9 Hz, 12H), (m, 8H). 13 C NMR (126 MHz, C 6 D 6 ) δ = 34.5 (4C), 32.4 (4C), 29.8 (8C), 24.6 (4C), 23.1 (4C), 14.4 (4C), 13.1 (4C). 1 H- 29 Si HMQC NMR (99 MHz, C 6 D 6 ) δ = 3.0. HRMS Despite several attempts, no molecular ion could be observed with both EI and APCI ionization techniques. The analytical and spectroscopic data are in accordance with those reported. [S11] NATURE CHEMISTRY 12

13 7h C 21 H 40 Si MW: g/mol Prepared from methylenecyclohexane (4h, 19.2 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 20 h. The crude material did not require purification. Colorless oil, 23 mg, 99% yield. IR (ATR): ~ /cm 1 = 2915, 2847, 2101, 1445, 1402, 1308, 1263, 1222, 1149, 1054, 966, 890, 832, 790, H NMR (400 MHz, C 6 D 6 ) δ = 4.26 (d, J = 6.7 Hz, 1H), 1.85 (d, J = 12.4 Hz, 6H), (m, 6H), (m, 2H), (m, 3H), (m, 6H), (m, 4H), (m, 6H), 0.68 (dd, J = 7.0 Hz, 3.4 Hz, 6H). 13 C NMR (126 MHz, C 6 D 6 ) δ = 37.0 (6C), 35.4 (3C), 27.0 (6C), 26.7 (6C), 22.0 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = HRMS (APCI) for [C 21 H 40 Si] + calcd m/z found ; for [C 21 H 40 Si H] + calcd m/z found i C 30 H 64 Si MW: g/mol Prepared from 2-methylnon-1-ene (4i, 28.1 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 20 h. The crude material did not require purification. 7i was obtained as an inseparable 3:1 mixture of C 1 -symmetric and C 3 -symmetric compounds, colorless oil, 30 mg, 99% yield. IR (ATR): ~ /cm 1 = 2920, 2852, 2105, 1458, 1374, 1211, 1106, 1029, 857, H NMR (500 MHz, C 6 D 6 ) δ = 4.29 (sept, J = 6.4 Hz, 1H), (m, 3H), (m, 36H), 1.09 (d, J = 6.6 Hz, 9H), 0.92 (t, J = 7.1 Hz, 9H), 0.87 (dq, J = 13.8 Hz, 4.5 Hz, 3H), (m, 3H). 13 C NMR (126 MHz, C 6 D 6 ) δ = 40.8, 32.4, {30.5, 30.5 (3C C1 + 3C C3)}, 30.4, 29.9, {27.7, 27.7 (3C C1 + 3C C3)}, 23.1, {23.1, 23.0 (3C C1 + 3C C3)}, {21.6, 21.5 (3C C1 + 3C C3)}, 14.4 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = { 13.4, 13.5 (3Si C1 + Si C3)}. HRMS (APCI) for [C 30 H 64 Si] + calcd m/z found ; for [C 30 H 64 Si H] + calcd m/z found j C 18 H 20 Si MW: g/mol Prepared from indene (4j, 23.2 mg, mmol, 1.00 equiv) and 2b (29.3 mg, mmol, equiv). Reaction was stopped after 20 h. The crude material did not require purification. NATURE CHEMISTRY 13

14 Colorless needles, 23 mg, 83% yield. M.P.: 59 C. IR (ATR): /cm 1 = 3017, 2914, 2829, 2123, 1456, 1316, 1216, 1141, 1091, 986, 930, 820, H NMR (400 MHz, C 6 D 6 ) δ = (m, 8H), 3.94 (t, J = 3.2 Hz, 2H), 2.87 (dd, J = 15.1 Hz, 9.0 Hz, 4H), 2.73 (dd, J = 15.1 Hz, 10.0 Hz, 4H), 1.56 (ttt, J = 6.1 Hz, 6.1 Hz, 3.1 Hz, 2H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (4C), (4C), (4C), 36.8 (4C), 20.4 (2C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = HRMS (EI) for [C 18 H 20 Si] + calcd m/z found ~ 6k C 20 H 24 Si MW: g/mol Prepared from 1,2-dihydronaphthalene (4k, 26.0 mg, mmol, 1.00 equiv) and 2b (29.3 mg, mmol, equiv). Reaction was stopped after 40 h. The crude material did not require purification. 6k was obtained as an inseparable 1:1 mixture of C 2 -symmetric and meso compounds, colorless oil, 16 mg, 55% yield. IR (ATR): ~ /cm 1 = 3014, 2904, 2098, 1490, 1425, 1349, 1290, 1244, 1158, 1079, 1037, 994, 933, 837, 805, H NMR (500 MHz, C 6 D 6 ) δ = (m, 4H), (m, 4H), (m, 2H), 2.75 (dt, J = 16.7 Hz, 4.5 Hz, 2H), (m, 6H), (m, 2H), (m, 2H), (m, 2H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (2C), (2C), (2C), (2C), (2C), (2C), {32.6, 32.6 (2C meso + 2C C2)}, {30.1, 30.1 (2C meso + 2C C2)}, 26.5, Si DEPT NMR (99 MHz, C 6 D 6 ) δ = { 15.6, 15.7 (Si meso + Si C2)}. HRMS (EI) for [C 20 H 24 Si] + calcd m/z found The analytical and spectroscopic data are in accordance with those reported. [S12] 7l C 21 H 40 Si MW: g/mol Prepared from cycloheptene (4l, 38.5 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 120 h. Traces amounts of 6l were detected in the crude material by 1 H NMR and GLC-MS analysis but could not be removed from 7l using flash column chromatography purification methods. Colorless oil, 18 mg, 42% yield. IR (ATR): ~ /cm 1 = 2910, 2845, 2079, 1455, 1360, 1284, 1209, 1128, 1095, 1040, 1013, 935, H NMR (500 MHz, C 6 D 6 ) δ = 3.76 (q, J = 2.3 Hz, 1H), (m, 6H), (m, 6H), (m, 6H), (m, 18H), (m, 3H). 13 C NMR (126 MHz, C 6 D 6 ) δ = 31.2 (6C), 30.6 (6C), 28.6 (6C), 23.4 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = 9.6. HRMS (EI) for [C 21 H 40 Si] + calcd m/z found NATURE CHEMISTRY 14

15 6m C 14 H 28 Si MW: g/mol Prepared from 1-methylcyclohexene (4m, 19.2 mg, mmol, 1.00 equiv) and 2b (29.3 mg, mmol, equiv). Reaction was stopped after 80 h. The crude material did not require purification. 6m was obtained as an inseparable 1:1 mixture of C 2 -symmetric and meso compounds, colorless oil, 17 mg, 76% yield. IR (ATR): ~ /cm 1 = 2916, 2847, 2114, 1443, 1377, 1259, 1193, 1101, 1056, 1193, 941, 849, 829, H NMR (400 MHz, C 6 D 6 ) δ = 3.99 (dt, J = 4.5 Hz, 3.1 Hz, 1H meso ), 3.88 (t, J = 3.4 Hz, 2H C2), 3.77 (dt, J = 4.5 Hz, 4.5 Hz, 1H meso ), (m, 2H), (m, 16H), (m, 2H), 1.02 (d, J = 7.1 Hz, 6H). 13 C NMR (126 MHz, C 6 D 6 ) δ = {33.9, 33.8 (2C meso + 2C C2)}, {32.9, 32.8 (2C meso + 2C C2)}, 27.2 (2C), {26.5, 26.4 (2C meso + 2C C2)}, {26.1, 26.0 (2C meso + 2C C2)}, {24.1, 23.9 (2C meso + 2C C2)}, {18.8, 18.6 (2C meso + 2C C2)}. 1 H- 29 Si HMQC NMR (99 MHz, C 6 D 6 ) δ = HRMS (EI) for [C 14 H 28 Si] + calcd m/z found o C 18 H 34 Si MW: g/mol Prepared from hex-3-yne (4o, 16.4 mg, mmol, 1.00 equiv) and 2b (18.7 mg, 70.0 µmol, equiv). Reaction was stopped after 20 h, and the crude product was purified by flash column chromatography using cyclohexane as eluent. Colorless oil, 15 mg, 81% yield. IR (ATR): ~ /cm 1 = 2960, 2929, 2871, 2122, 1612, 1516, 1457, 1372, 1315, 1086, 943, 845, H NMR (500 MHz, C 6 D 6 ) δ = 6.13 (t, J = 7.3 Hz, 3H), 5.09 (s, 1H), 2.27 (q, J = 7.2 Hz, 6H), 2.25 (q, J = 7.1 Hz, 6H), 1.12 (t, J = 7.4 Hz, 9H), 0.98 (t, J = 7.4 Hz, 9H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (3C), (3C), 30.8 (3C), 25.9 (3C), 14.7 (3C), 14.2 (3C). 29 Si DEPT NMR (99 MHz, C 6 D 6 ) δ = HRMS (APCI) for [C 18 H 34 Si] + calcd m/z found ; for [C 18 H 34 Si H] + calcd m/z found NATURE CHEMISTRY 15

16 6 Experimental Details for the Hydrosilylation of Oct-1-ene (4g) Catalyzed by Platinum. 6.1 Synthesis and Characterization Data of Tri(cyclohexa-2,5-dien-1-yl)(octyl)silane (9) 9 C 26 H 38 Si MW: In a glove box, a 1.3-mL GLC vial was charged with tri(cyclohexa-2,5-dien-1-yl)silane (2b, g, mmol equiv) and a magnetic stir bar. Oct-1-ene (4g, 0.4 ml) was then added and the vial was capped. Outside the glove box, Karstedt s catalyst ( wt% Pt in xylenes, 109 mg, µmol, mol %) was added dropwise, and the reaction was stirred at room temperature for 16 h. After this time, the reaction was directly passed through a short column of silica gel (diameter approx. 2 cm, height approx. 10 cm) using cyclohexane as eluent, affording tri(cyclohexa-2,5-dien-1-yl)(octyl)silane (9) in pure form. Note that this compound was rather prone to rearomatization if exposed to air for hours. Colorless oil, 105 mg, 69% yield. IR (ATR): ~ /cm 1 = 3024, 2920, 2667, 1621, 1460, 1429, 1334, 1291, 1110, 1051, 940, 891, 770, 701, H NMR (500 MHz, C 6 D 6 ) δ = 5.82 (ddt, J = 10.3 Hz, 3.9 Hz, 2.0 Hz, 6H), (m, 6H), (m, 3H), (m, 6H), 1.50 (dt, J = 10.2 Hz, 7.8 Hz, 2H), (m, 10H), 0.92 (t, J = 7.0 Hz, 3H), (m, 2H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (6C), (6C), 34.7, 32.3, 29.8, 29.6, 27.8 (3C), 26.6 (3C), 24.3, 23.1, 14.4, H- 29 Si HMQC NMR (99 MHz, C 6 D 6 ) δ = 0.8. HRMS (APCI) for [C 26 H 38 Si] + calcd m/z found ; for [C 26 H 38 Si H] + calcd m/z found Synthesis and Characterization Data of Di(cyclohexa-2,5-dien-1-yl)(octyl)silane (10) 10 C 20 H 32 Si MW: In a glove box, a 1.3-mL GLC vial was charged with dichloro(cycloocta-1,5-diene)platinum (3.8 mg, 10 µmol, 5.0 mol %) and a magnetic stir bar. Into a separate vial was weighed di(cyclohexa- NATURE CHEMISTRY 16

17 2,5-dien-1-yl)silane (2c, 37.7 mg, mmol equiv) and dissolved in oct-1-ene (4g, 0.2 ml). The resulting solution was then added to the catalyst, and the vial was capped. The reaction was stirred at room temperature in the glove box for 18 h. After this time, the reaction was directly passed through a short column of silica gel (diameter approx. 2 cm, height approx. 10 cm) using cyclohexane as eluent, affording di(cyclohexa-2,5-dien-1-yl)(octyl)silane (10) in pure form. Note that this compound was rather prone to rearomatization if exposed to air for hours. Colorless oil, 35 mg, 58% yield. IR (ATR): ~ /cm 1 = 3024, 2922, 2852, 2361, 2110, 1622, 1460, 1293, 1110, 937, 894, 813, H NMR (500 MHz, C 6 D 6 ) δ = (m, 4H), (m, 4H), 3.95 (ddt, J = 3.1 Hz, 1.5 Hz, 1H), (m, 4H), (m, 2H), (m, 2H), (m, 10H), 0.91 (t, J = 7.0 Hz, 3H), (m, 2H). 13 C NMR (126 MHz, C 6 D 6 ) δ = (2C), (2C), (2C), (2C), 33.9, 32.3, 29.7 (2C), 27.6 (2C), 26.6 (2C), 25.3, 23.1, 14.4, Si DEPT NMR (99 MHz, C 6 D 6 ) δ = 8.2. HRMS (EI) for [C 20 H 32 Si] + calcd m/z found Experimental Details for the Generation of Octylsilane (5g) from Hydrosilylation Compounds 9 and General Procedure In a glove box, a 1.3-mL GLC vial is charged with the octylsilane precursor (9 or 10, 1.0 equiv), mesitylene (0.5 equiv, internal standard), and a magnetic stir bar. Into a separate vial is weighed B(C 6 F 5 ) 3 (1a, 5.0 mol %) and dissolved in CD 2 Cl 2. The resulting solution is then transferred to the reaction vial, the latter is capped and stirred in the glove box at room temperature for 4 h. After this time, the reaction mixture is diluted with more CD 2 Cl 2 to a volume of approx. 0.6 ml and transferred to an NMR tube. Yields are calculated based on the integrations of the mesitylene resonance signals. Octylsilane could not be isolated due to immediate formation of polysiloxane by reaction with ambient moisture catalyzed by B(C 6 F 5 ) 3 but its generation was verified by comparison with the NMR spectra of an authentic sample of octylsilane in CD 2 Cl Characterization Data of Octylsilane (5g) 5g C 8 H 20 Si MW: Prepared from di(cyclohexa-2,5-dien-1-yl)(octyl)silane (12, 48 mg, 0.16 mmol, 1.0 equiv) and B(C 6 F 5 ) 3 (1a, 4.1 mg, 8.0 µmol, 5.0 mol %) in CD 2 Cl 2 (0.3 ml). Yield was quantitative. 1 H NMR (500 MHz, CD 2 Cl 2 ) δ = 3.55 (t, J = 3.8 Hz, 3H), (m, 2H), (m, 10H), 0.95 (t, J = 6.8 Hz, 3H), 0.81 (qt, J = 7.6 Hz, 3.8 Hz, 2H). 13 C NMR (126 MHz, CD 2 Cl 2 ) δ = 33.0, 32.4, 29.8, 29.7, 26.9, 23.2, 14.4, Si DEPT NMR (99 MHz, C 6 D 6 ) δ = The analytical and spectroscopic data are in accordance with those reported. [S13] NATURE CHEMISTRY 17

18 8 Time-Dependent NMR Experiments Caution: In the experiments described below, substantial amounts of SiH 4 were generated in the NMR tube. Valved, pressure resistant NMR tubes must be used, and extreme care must be applied when opening them to air. 8.1 General Procedure for Monitoring the Degradation of 2a c In a glove box, a medium-walled valved NMR tube is charged with 2 (0.1 mmol, 1.0 equiv) and mesitylene (7.0 µl, 50 µmol, 0.5 equiv, internal standard), and CD 2 Cl 2 (0.2 ml) is added. Once capped, the tube is shaken to ensure complete solubilization, and taken out of the glove box to record the t 0 1 H NMR spectrum. Back in the glove box, B(C 6 F 5 ) 3 (1a, 5.1 mg, 10 μmol, 10 mol %) is deposited in the head of the horizontally held NMR tube, avoiding contact with the solution of 2 and mesitylene. Outside the glove box, the tube is shaken for a few seconds prior to its introduction into the NMR machine, and 1 H NMR spectra are recorded every 140 s over the course of 14 h. Concentrations are an approximation based on the integration of the Si H resonance signals and C(sp 2 ) H resonance signals of mesitylene. 8.2 Experimental Procedure for Monitoring the Degradation of 2b in an Open System In a glove box, a medium-walled valved NMR tube was charged with 2b (26.7 mg, 0.1 mmol, 1.0 equiv) and mesitylene (7.0 µl, 50 µmol, 0.5 equiv, internal standard), and CD 2 Cl 2 (0.2 ml) was added. Once capped, the tube was shaken to ensure complete solubilization, and taken out of the glove box to record the t 0 1 H NMR spectrum. Back in the glove box, B(C 6 F 5 ) 3 (1a, 5.1 mg, 10 μmol, 10 mol %) was added to the solution, and the NMR tube was kept open in the glove box. At random times over a period of 7 h, the tube was capped, taken out of the glove box and analyzed by 1 H NMR spectroscopy, then brought back inside the glove box and re-opened. NATURE CHEMISTRY 18

19 8.3 Degradation of 2a over Time, Selected Spectra Figure S2. Stacked 1 H NMR spectra (CD 2 Cl 2, 500 MHz). NATURE CHEMISTRY 19

20 8.4 Degradation of 2b over Time, Plot Si H 2b 1a cat. 2c Si H H 1a cat. 2d H Si H H 1a cat. H H Si H H 2b 2c 2d SiH 4 2c (open syst.) [C] (mmol ml 1 ) d (open syst.) SiH Time (h) Figure S3. Plot of the concentrations of hydrosilanes 2b d and SiH 4 against the time in the reaction of 2b with catalytic amounts of 1a (black: closed system; red: open system). NATURE CHEMISTRY 20

21 8.5 Degradation of 2b over Time, Selected Spectra (Closed System) Figure S4. Stacked 1 H NMR spectra (CD 2 Cl 2, 500 MHz). NATURE CHEMISTRY 21

22 8.6 Degradation of 2c over Time, Plot c 2d SiH 4 [C] (mmol ml 1 ) Time (h) Figure S5. Plot of the concentrations of hydrosilanes 2c, 2d, and SiH 4 against the time in the reaction of 2c with catalytic amounts of 1a. NATURE CHEMISTRY 22

23 8.7 Degradation of 2c over Time, Selected Spectra Figure S6. Stacked 1 H NMR spectra (CD 2 Cl 2, 500 MHz). NATURE CHEMISTRY 23

24 8.8 Experimental Procedure for Monitoring the Reaction of Table 1, Entry 1 In a glove box, a medium-walled valved NMR tube was charged with 2b (18.7 mg, 70.0 µmol, equiv), 4a (20.8 mg, mmol, 1.00 equiv), and mesitylene (14.0 µl, µmol, equiv, internal standard), and CD 2 Cl 2 (0.2 ml) was added. Once capped, the tube was shaken to ensure complete solubilization, and taken out of the glove box to record the t 0 1 H NMR spectrum. Back in the glove box, B(C 6 F 5 ) 3 (1a, 5.1 mg, 10 μmol, 5.0 mol %) was deposited in the head of the horizontally held NMR tube, avoiding contact with the solution of 2b, 4a and mesitylene. Outside the glove box, the tube was shaken for a few seconds prior to its introduction into the NMR machine. A first 1 H NMR spectrum was recorded after 3 min, and a second after 10 min, then 1 H NMR spectra were recorded every 10 min until 2 h after introduction of the catalyst. After this time, 1 H NMR spectra were recorded every 30 min over the course of 6 h, then every 60 min over the course of 16 h. From 2 h after introduction of the catalyst, 1 H- 1 H COSY and 1 H- 29 Si HMQC were alternatively recorded between two 1 H NMR measurements. Concentrations are an approximation based on the integration of the Si H resonance signals, one of the vinylic proton resonance signals of styrene (4a), and the C(sp 2 ) H resonance signals of mesitylene. NATURE CHEMISTRY 24

25 8.9 Monitoring of the Reaction of Table 1, Entry 1, Plots b 2c 2d SiH 4 [C] (mmol ml 1 ) Time (h) Figure S7. Plot of the concentrations of hydrosilanes 2b d and SiH 4 against the time in the reaction of Table 1, entry 1. NATURE CHEMISTRY 25

26 1 0.8 H Si H H H 1a cat. 1a SiH 3 SiH cat. 2 1a cat. 4a 5a 6a 7a 2 3 SiH [C] (mmol ml 1 ) a 5a 6a 7a Time (h) Figure S8. Plot of the concentrations of starting material 4a and hydrosilylation products 5a, 6a, and 7a against the time in the reaction of Table 1, entry 1. NATURE CHEMISTRY 26

27 8.10 Monitoring of the Reaction of Table 1, Entry 1, Selected Spectra Figure S9. Stacked 1 H NMR spectra (CD 2 Cl 2, 500 MHz). NATURE CHEMISTRY 27

28 Figure S10. 1 H- 29 Si HMQC 2D NMR (C 6 D 6, SFO1 500 MHz, SFO2 99 t = 2.5 h. NATURE CHEMISTRY 28

29 Figure S11. 1 H- 29 Si HMQC 2D NMR (C 6 D 6, SFO1 500 MHz, SFO2 99 t = 24 h. NATURE CHEMISTRY 29

30 8.11 Experimental Procedure for Monitoring the Reaction of Styrene (4a) with Excess 2b In a glove box, a medium-walled valved NMR tube was charged with 2b (71.9 mg, mmol, equiv), 4a (20.8 mg, mmol, 1.00 equiv), and mesitylene (14.0 µl, µmol, equiv, internal standard), and CD 2 Cl 2 (0.2 ml) was added. Once capped, the tube was shaken to ensure complete solubilization, and taken out of the glove box to record the t 0 1 H NMR spectrum. Back in the glove box, B(C 6 F 5 ) 3 (1a, 5.1 mg, 10 μmol, 5.0 mol %) was deposited in the head of the horizontally held NMR tube, avoiding contact with the solution of 2b, 4a, and mesitylene. Outside the glove box, the tube was shaken for a few seconds prior to its introduction into the NMR machine. A first 1 H NMR spectrum was recorded after 5 min, and a second after 10 min, then 1 H NMR spectra were recorded every 10 min until 2 h after introduction of the catalyst. After this time, 1 H NMR spectra were recorded every 30 min over the course of 6 h, then every 60 min over the course of 16 h. From 2 h after introduction of the catalyst, 1 H- 1 H COSY and 1 H- 29 Si HMQC were alternatively recorded between two 1 H NMR measurements. Concentrations are an approximation based on the integration of the Si H resonance signals, one of the vinylic proton resonance signals of styrene (4a), and the C(sp 2 ) H resonance signals of mesitylene. NATURE CHEMISTRY 30

31 8.12 Monitoring of the Reaction of Styrene (4a) with Excess 2b, Plots Si H 1a cat. Si H H 1a cat. H Si H H 1a cat. H H Si H H 2b 2c 2d [C] (mmol ml 1 ) b 2c 2d SiH Time (h) Figure S12. Plot of the concentrations of hydrosilanes 2b d and SiH 4 against the time in the reaction of 4a with excess 2b (1.35 equiv). NATURE CHEMISTRY 31

32 1 0.8 [C] (mmol ml 1 ) a 5a 6a 7a Time (h) Figure S13. Plot of the concentrations of starting material 4a and hydrosilylation products 5a, 6a, and 7a against the time in the reaction of 4a with excess 2b (1.35 equiv). NATURE CHEMISTRY 32

33 8.13 Monitoring of the Reaction of Styrene (4a) with Excess 2b, Selected Spectra Figure S14. Stacked 1 H NMR spectra (CD 2 Cl 2, 500 MHz). NATURE CHEMISTRY 33

34 Figure S15. 1 H- 29 Si HMQC 2D NMR (C 6 D 6, SFO1 500 MHz, SFO2 99 t = 4 h. NATURE CHEMISTRY 34

35 Figure S16. 1 H- 29 Si HMQC 2D NMR (C 6 D 6, SFO1 500 MHz, SFO2 99 t = 22 h. NATURE CHEMISTRY 35

36 8.14 Selected Characterization Data of Intermediates 2d, SiH 4, 5a, and 6a 2d C 6 H 10 Si MW: g/mol 1 H NMR (500 MHz, CD 2 Cl 2 ) δ = (m, 2H), (m, 2H), 3.63 (d, J = 2.8 Hz, 3H), (m, 2H), (m, 1H). 1 H- 29 Si HMQC NMR (99 MHz, CD 2 Cl 2 ) δ = H 4 Si MW: g/mol 1 H NMR (500 MHz, CD 2 Cl 2 ) δ = 3.50 (s, 4H). 1 H NMR (500 MHz, C 6 D 6 ) δ = 3.10 (s, 4H). 1 H- 29 Si HMQC NMR (99 MHz, CD 2 Cl 2 ) δ = Si DEPT NMR (99 MHz, C 6 D 6 ) δ = a C 8 H 12 Si MW: g/mol 1 H NMR (400 MHz, CD 2 Cl 2 ) δ = (m, 2H), (m, 3H), 3.56 (t, J = 3.8 Hz, 3H), (m, 2H), (m, 2H). 13 C NMR (101 MHz, CD 2 Cl 2 ) δ = 144.3, (2C), (2C), 32.8, 8.6. One carbon peak was not detected, probably due to overlapping with other signals. 1 H- 29 Si HMQC NMR (99 MHz, CD 2 Cl 2 ) δ = GLC-MS (EI) for (C 8 H 12 Si): m/z [M] +. The analytical and spectroscopic data are in accordance with those reported. [S13] 6a C 16 H 20 Si MW: g/mol 1 H NMR (400 MHz, CD 2 Cl 2 ) δ = (m, 4H), (m, 6H), 3.81 (quint, J = 3.5 Hz, 2H), (m, 4H), (m, 4H). 13 C NMR (101 MHz, CD 2 Cl 2 ) δ = (2C), (4C), (4C), 31.9, One carbon peak (2C) was not detected, probably due to overlapping with other signals. 1 H- 29 Si HMQC NMR (99 MHz, CD 2 Cl 2 ) δ = GLC-MS (EI) for (C 16 H 20 Si): m/z [M] +. The analytical and spectroscopic data are in accordance with those reported. [S14] NATURE CHEMISTRY 36

37 9 NMR Spectra NATURE CHEMISTRY 37

38 Bis(pentafluorophenyl)(2-nonafluorobiphenyl)borane (1c) 11 B NMR (C 6 D 6, 161 MHz) NATURE CHEMISTRY 38

39 19 F NMR (C 6 D 6, 471 MHz) NATURE CHEMISTRY 39

40 Tetra(cyclohexa-2,5-dien-1-yl)silane (2a) 1 H NMR (C 6 D 6, 500 MHz) NATURE CHEMISTRY 40

41 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 41

42 1 H- 29 Si HMQC 2D NMR (C 6 D 6, SFO1 500 MHz, SFO2 99 MHz) NATURE CHEMISTRY 42

43 Tri(cyclohexa-2,5-dien-1-yl)silane (2b) 1 H NMR (C 6 D 6, 500 MHz) NATURE CHEMISTRY 43

44 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 44

45 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 45

46 Di(cyclohexa-2,5-dien-1-yl)silane (2c) 1 H NMR (C 6 D 6, 400 MHz) NATURE CHEMISTRY 46

47 13 C NMR (C 6 D 6, 101 MHz) NATURE CHEMISTRY 47

48 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 48

49 Triphenethylsilane (7a) 1 H NMR (C 6 D 6, 500 MHz) NATURE CHEMISTRY 49

50 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 50

51 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 51

52 Tris(4-methylphenethyl)silane (7b) 1 H NMR (C 6 D 6, 500 MHz) SiH Me 3 NATURE CHEMISTRY 52

53 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 53

54 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 54

55 Tris(4-fluorophenethyl)silane (7c) 1 H NMR (C 6 D 6, 400 MHz) NATURE CHEMISTRY 55

56 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 56

57 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 57

58 Tris[2-(naphthalen-2-yl)ethyl]silane (7d) 1 H NMR (C 6 D 6, 500 MHz) NATURE CHEMISTRY 58

59 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 59

60 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 60

61 Bis(2-phenylpropyl)silane (6e) 1 H NMR (C 6 D 6, 500 MHz) NATURE CHEMISTRY 61

62 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 62

63 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 63

64 Tris(2,2-diphenylethyl)silane (7f) 1 H NMR (C 6 D 6, 500 MHz) NATURE CHEMISTRY 64

65 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 65

66 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 66

67 Bis(2,2-diphenylethyl)silane (6f) 1 H NMR (C 6 D 6, 400 MHz) NATURE CHEMISTRY 67

68 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 68

69 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 69

70 Tetraoctylsilane (8g) 1 H NMR (C 6 D 6, 500 MHz) NATURE CHEMISTRY 70

71 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 71

72 1 H- 29 Si HMQC 2D NMR (C 6 D 6, SFO1 500 MHz, SFO2 99 MHz) NATURE CHEMISTRY 72

73 Tris(cyclohexylmethyl)silane (7h) 1 H NMR (C 6 D 6, 400 MHz) NATURE CHEMISTRY 73

74 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 74

75 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 75

76 Tris(2-methylnonyl)silane (7i) 1 H NMR (C 6 D 6, 500 MHz) NATURE CHEMISTRY 76

77 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 77

78 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 78

79 Bis(2,3-dihydro-1H-inden-2-yl)silane (6j) 1 H NMR (C 6 D 6, 400 MHz) NATURE CHEMISTRY 79

80 13 C NMR (C 6 D 6, 126 MHz) NATURE CHEMISTRY 80

81 29 Si-dept NMR (C 6 D 6, 99 MHz) NATURE CHEMISTRY 81