Organoactinide-Mediated Hydrothiolation of Terminal Alkynes with Aliphatic, Aromatic, and Benzylic Thiols

Transcription

1 Organoactinide-Mediated Hydrothiolation of Terminal Alkynes with Aliphatic, Aromatic, and Benzylic Thiols Charles J. Weiss, Stephen D. Wobser, Tobin J. Marks* Department of Chemistry, Northwestern University, Evanston, Illinois Supporting Information Materials and Methods. Due to the air and moisture sensitivity of the organoactinide complexes in this study, all manipulations were carried out in oven-dried, Schlenk-type glassware interfaced to either a dual-manifold Schlenk line, high-vacuum line (10-6 Torr), or in a nitrogen-filled glove box (<2ppm O 2 ). Argon (Airgas) was further purified by passing through columns of MnO and activated 4 A Davison molecular sieves immediately before use. Toluene-d 8 and benzene-d 6 (Cambridge Isotope Laboratories, all 99+ atom % D) for NMR reactions and kinetic measurements were stored over Na/K alloy in vacuo and vacuum transferred immediately prior to use. D 2 O (Cambridge Isotope Laboratories, 99+ atom % D) was used as received. Tetraglyme was purchased from Aldrich and pumped on overnight to remove volatiles. Thiols and alkynes were purchased from Aldrich, Fisher, and Acros, and were transferred from multiple beds of activated Davison 4 A molecular sieves as solutions in benzene-d 6 or neat, followed by degassing (10-6 Torr) via freeze-pump-thaw methods. All substrates were stored under argon until use, and phenylacetylene and 1-ethynylcyclohexene were distilled just prior to use. The 1-pentanethiol-D was prepared as described below. The S1

2 catalysts were prepared by Dr. Bryan Stubbert as reported in the literature. S1 The triphenylmethylsilane internal integration standard for kinetics was purchased from Strem, sublimed under high-vacuum, and stored in the glove box until use. Products 13 S2 and 15 S3 (Table 1) agree with published NMR spectra. Physical and Analytical Measurements. NMR spectra were taken on Inova 400 (400MHz, 1 H; 100 MHz, 13 C) and Inova 500 (500 MHz, 1 H; 125 MHz, 13 C; 76.7 MHz, 2 H) NMR spectrometers. Chemical shifts (!) are referenced relative to internal solvent resonances and reported relative to Me 4 Si. Kinetics were monitored by a pre-heated Inova 400 NMR spectrometer temperature calibrated by an ethylene glycol standard (±0.3 o C). Spectra of air-sensitive reactions and materials were taken in airtight, Teflon valved J. Young NMR tubes. High resolution mass spectra were taken on a Thermo Finnigan MAT 900 and GC data was collected on a GC-MS HP6890 instrument equipped with a HP5972 detector and a HP-5MS (5% Phenyl Methyl Siloxane, 30m x 250!m x 0.25!m) capillary column. SD Preparation of 1-pentanethiol-d (2-D). An oven-dried, 200mL Schlenk flask was charged with LiH (0.72g, 91mmol) and a magnetic stir bar. While under nitrogen, 50mL of dry tetraglyme was cannulaed into the flask and stirred vigorously to form a slurry. The flask was cooled to 0 o C before drop-wise addition of dry 1-pentanethiol (8.4g, 80.6mmol). The reaction was allowed to warm to room temperature and stirred 1 h followed by recooling to 0 o C and drop-wise quenching with D 2 O (2.5mL, 140mmol). The product was vacuum-transferred from the tetraglyme and dried over 4 A molecular sieves before use (~2.5g, 30% yield). 1 H NMR (benzene-d 6, 400 MHz,!):! 2.17 (q, J = S2

3 7.2 Hz, 2H); 1.34 (m, 2H); 1.12 (m, 4H); 0.79 (t, J = 5.6 Hz, 3H). 2 H NMR (benzene-d 6, 76.7 MHz,!):! 1.09 (s). 13 C NMR (benzene-d 6, 100 MHz,!):! 33.9; 30.8; 24.9; 22.3; Typical NMR Scale Catalytic Reaction. In a glove box, 1a (3.5mg, 5.0µmol) and triphenylmethylsilane (8.0mg, 29.5µmol) were added to a J. Young NMR tube. The tube was sealed, removed from the glove box, and attached to a high-vacuum line where dry toluene-d 8 or benzene-d 6 was vacuum transferred into the tube. The catalyst and triphenylmethylsilane were completely dissolved followed by syringing in 0.1mL thiol and 0.1mL alkyne solutions (both 1.0 M in benzene-d 6 ;, 0.1mmol; 20-molar excess). The reaction mixture was then sealed, shaken well, and placed in a pre-heated oil bath. Figure S1. Typical NMR spectra of (A) combined substrates and 1a, (B) product and 1a, and (C) purified product for the reaction between 1-pentanethiol (2) and 1-hexyne (6) in C 6 D 6. S3

4 Typical NMR Scale Kinetic Experiment. The same procedure as described above was followed except mL of neat alkyne (~15-40 molar excess) was used instead of a solution. All [catalyst] 0 samples were below 7.7mM unless otherwise stated. The sample tube was maintained at -78 o C until just before the experiment whereupon it was thawed, shaken, and immediately placed in the pre-heated and temperature-calibrated probe of the Inova 400 NMR spectrometer. Single pulse 1 H NMR spectra were taken at regular intervals. General Procedure for Purification of Products. In the glove box, approximately ~10 mg of U(IV) or Th(IV) catalyst was loaded into a J. Young-valved NMR tube, sealed, and placed on a high-vacuum line. Next, 0.6 ml thiol solution (1.0 M in C 6 D 6 ) and 0.05 ml alkyne (neat) were syringed into the tube under argon flush. The tube was then sealed, shaken well, and placed in a pre-heated 120 o C oil bath overnight. The reaction mixture was cooled to room temperature and the contents eluted through a silica gel plug with ~10mL hexanes to remove catalyst. The filtrate was pumped on with a Schlenk line to remove volatiles. Further purification by flash chromatography (ether:hexanes eluent) was performed when necessary. To avoid degradation, S4 products 11 and 16 were purified by precipitating the catalyst by exposure to air whereupon the precipitated catalyst was centrifuged and the solution decanted. Volatiles were pumped off on a Schlenk line to yield pure product. Preparative Scale Procedure. In a glove box, CGCTh(NMe 2 ) 2 (140mg, 0.25 mmol) was added to an oven-dried, J. Young-valved glass tube with stir bar. The tube was sealed, placed on a high-vacuum line where toluene (30mL) was vacuum transferred from Na/K to dissolve the catalyst. Under an argon flush, 1-pentanethiol (0.60mL, S4

5 4.8mmol) and 1-hexyne (0.65mL, 5.7mmol) were syringed into the tube, degassed by freeze-pump-thaw, sealed, and placed in a pre-heated 120 o C oil bath for 24h. Next, the vessel was opened to ambient and catalyst removed by filtering through silica gel eluted by hexanes. The product was purified by flash chromatography (SiO 2, eluted with 5:1 hexanes/ethyl acetate) and pumped down on a Schlenk line to yield pure 10 as a yellow oil (0.62g, 3.3mmol, 69% yield). Compound 10: (yellow oil) 1 H NMR (benzene-d 6, 400 MHz,!):! 5.34 (s, 1H); 4.72 (s, 1H); 2.53 (t, J = 7.2 Hz, 2H); 2.25 (t, J = 8.0 Hz, 2H); (m, 4H); (m, 6H); (m, 6H). 13 C NMR (benzene-d 6, 125 MHz,!):! 147.2; 105.1; 38.2; 31.9; 31.8; 31.7; 28.6; 22.9; 22.8; 14.5; HRMS-EI (m/z): M + calcd for C 11 H 22 S, ; found, S Compound 11: (yellow oil) 1 H NMR (benzene-d 6, 500 MHz,!):! 5.07 (s, 1H); 4.85 (s, 1H); 2.94 (m, 1H); 2.22 (t, J = 7.5 Hz, 2H); 1.98 (m, 2H); 1.57 (m, 4H); 1.38 (m, 3H); 1.27 (m, 2H); 1.11 (m, 3H); 0.85 (t, J = 7.5 Hz, 3H). 13 C NMR (benzene-d 6, 125 MHz,!):! 145.8; 107.4; 50.42; 43.4; 38.4; 33.5; 31.7; 26.5; 22.8; HRMS-EI (m/z): M + calcd for C 12 H 22 S ; found, SCy S p-tol Compound 12: (dark yellow oil) 1 H NMR (benzene-d 6, 400 MHz,!):! (m, 2H); (m, 2H); 5.00 (s, 1H); 4.76 (s, 1H); 3.72 (s, 2H); 2.21 (m, 3H); 2.06 (s, S5

6 3H); 1.53 (m, 2H); 1.22 (m, 2H); 0.81 (m, 3H). 13 C NMR (benzene-d 6, 100 MHz,!):! 147.2; 137.1; 134.5; 129.8; 129.5; 106.2; 38.0; 36.6; 31.7; 22.7; 21.3; HRMS-EI (m/z): M + calcd for C 14 H 20 S, ; found, Ph S Compound 14: (dark yellow oil) 1 H NMR (benzene-d 6, 500 MHz,!):! 7.63 (d, J = 7.5 Hz, 2H); 7.12 (dd, J = 7.5 Hz, 2H); 7.07 (m, 1H); 5.41 (s, 1H); 5.14 (s, 1H); 2.48 (t, J = 7.5 Hz, 2H); 1.48 (t, J = 7.5 Hz, 2H); (m, 4H); 0.77 (t, J = 7.0 Hz, 3H). 13 C NMR (benzene-d 6, 125 MHz,!):! 140.5; 129.0; 128.9; 127.9; 110.7; 32.6; 28.9; 22.9; 21.6; HRMS-EI (m/z): M + calcd for C 13 H 18 S, ; found, S Compound 16: (dark yellow oil) 1 H NMR (benzene-d 6, 500 MHz,!):! 6.43 (s, 1H); 5.29 (s, 1H); 4.97 (s, 1H); 2.54 (t, J = 7.5, 2H); (m, 2H); (m, 2H); (m, 2H); (m, 2H); (m, 2H), (m, 2H); (m, 2H); 0.80 (t, J=7.0, 3H). 13 C NMR (benzene-d 6, 125 MHz,!):! 147.1; 136.4; 1277; 107.2; 32.5; 31.8; 29.0; 27.7; 26.3; 23.5; 23.0; 22.8; HRMS-EI (m/z): M + calcd for C 13 H 22 S, ; found S Compound 17: (yellow oil) 1 H NMR (benzene-d 6, 500 MHz,!):! 5.07 (s, 1H); 4.67 (s, 1H); 2.53 (t, J = 7.0 Hz, 2H); 2.14 (t, J = 11.5 Hz, 1H); 1.98 (d, J = 12.5 Hz, 2H); 1.68 (d, J = 12.5 Hz, 2H); 1.54 (t, 7.5, 3H); 1.40 (m, 2H); (m, 7H); 0.80 (t, J = 7.0 S6

7 Hz, 3H). 13 C NMR (benzene-d 6, 125 MHz,!):! 153.1; 102.7; 47.1; 33.9; 31.9; 31.6; 28.5; 27.3; 26.8; 23.0; HRMS-EI (m/z): M + calcd for C 13 H 24 S, ; found, S p-tol Compound 18: (dark yellow oil) 1 H NMR (benzene-d 6, 400 MHz,!):! 7.16 (d, J = 8.0 Hz, 2H); 6.92 (d, J = 8.0 Hz, 2H); 5.05 (s, 1H); 4.71 (s, 1H); 3.73 (s, 2H); 2.11 (m, 1H); 2.07 (s, 3H); 1.96 (m, 2H); 1.64 (m, 2H); 1.52 (m, 2H); 1.37 (m, 2H); 1.11 (m, 3H). 13 C NMR (benzene-d 6, 100 MHz,!):! 153.0; 137.0; 134.5; 129.7; 129.5; 103.8; 46.9; 36.6; 33.8; 27.2; 26.8; HRMS-EI (m/z): M + calcd for C 16 H 22 S, ; found, Reaction Substrates Product Ratio a 1 >1000:1 b 3 >1000:1 b 4 70:1 5 "20:1 c 6 40:1 7 1:1 c,d 8 10:1 c 9 >1000:1 b 10 70:1 a. Ratio determined by GC-MS unless otherwise stated. b. Side products undetectable by 1 H NMR and GC-MS. c. Determined by 1 H NMR d. Observed 2:1 ratio of trans to cis anti-markovnikov product Table S1. Ratio of Markovnikov to anti-markovnikov products. S7

8 Kinetics Kinetic analyses were performed by integrating thiol SH or product vinyl 1 H NMR resonances with respect to the Ph 3 SiMe internal standard. The data were plotted in Microsoft Excel 2004 and the least-squared slope (m) determined according to eq. S1 where t (hours) is the reaction time. All lines of best fit have an R 2 " N t was calculated via equation eq. S2 where [catalyst] 0 is the initial concentration of precatalyst. [product /thiol] t = mt m N t (h "1 ) = [catalyst] o (S1) (S2) A representative plot of the reaction between 2 and 6 (entry 1) is shown below with 5 mol % Me 2 SiCp 2 Th[CH 2 TMS] 2 precatalyst and excess 1-hexyne. The linear trend indicates zero-order dependence on [thiol] over three half-lives. Figure S2. Concentration of thiol as a function of time (h) for hydrothiolation of 1- pentanethiol (2) and excess 1-hexyne (6; 0.80 M) using 5 mol % Me 2 SiCp 2 Th[CH 2 TMS] 2 precatalyst at 90 o C in toluene-d 8 /benzene-d 6. The line is a least-squares fit to the data points. Kinetic studies of the effects of [catalyst] 0 were performed for the hydrothiolation of 1-pentanthiol (2) and 1-hexyne (6) mediated by Me 2 SiCp 2 Th[CH 2 TMS] 2. The S8

9 [catalyst] 0 was varied from 2.3x10-3 M to 2.6x10-2 M, revealing deviations from linearity at lower catalyst concentrations (Figure S3). A van t Hoff plot of the same data exhibits a single linear trend indicating essentially first-order dependence to [catalyst] 0 at all explored [catalyst] 0. A. B. Figure S3. (A) Plot of [catalyst] 0 vs. rate with the line through the data points drawn as a guide to the eye. (B) van t Hoff plot to determine the reaction order in [catalyst] 0. The line is the least-square fit to data points. S9

10 Eyring and Arrhenius plots for the reaction between 1-pentanethiol (2) and 1- hexyne (6) were plotted according to equations S3 and S4 respectively where k was calculated by the least-square slope (m) according to equation S1. The large, negative entropy of transition state indicates an intermolecular turnover-limiting step. " ln k % + $ ' = (H) (S ) # T & RT R * ln " h %. - $ ' 0 (S3), # k b &/ ln( k) = " E a RT + ln A (S4) A. "H # = +9.1(0.7) kcal/mol "S # = -45(2) e.u. S10

11 B. E a = 9.8(0.7) kcal/mol Figure S4. (A) Eyring plot (eq. S3) and (B) Arrhenius plot (eq. S4) with the line as the least-square fit to data points. A kinetic analysis of the same reaction, plotting [1-hexyne] (6) vs. rate yields an approximately first-order trend at concentrations below ~2x10-1 M (Figure S5), gradually changing to a zero-order trend at [1-hexyne] (6) above ~8x10-1 M. This behavior can be fit to a Michaelis-Menten model where the alkyne (A) acts as a competitive inhibitor (eq. S4) to the catalyst (C) as well as a turnover-limiting reactant (eq. S5). The reaction is concluded by rapid protonolysis (eq. S6) to generate product (P). CA k 1 C + A (S4) k -1 C + A k 2 CP (S5) RSH + CP k 3 C + P (S6) S11

12 At low [1-hexyne] (6), the reaction is first-order with respect to alkyne because catalyst inhibition is too slow to effectively compete with the insertion, while at high [1-hexyne] (6), inhibition becomes competitive with the insertion and the reaction becomes zeroorder with respect to alkyne (eqs. S7-S9). Rate = k 2K 4 [1" hexyne] K 4 + [1" hexyne] k 1 where K 4 = k "1 + k 2 (S7) Rate " k 2 [1# hexyne] when K 4 >> [1" hexyne] (S8) Rate " k 2 K 4 when K 4 << [1" hexyne] (S9) The behavior can also be fit to an alternative Michaelis-Menten model with an initial, turnover-limiting association of alkyne to Th(IV) (eq. S10) followed by slow insertion (eq. S11) and rapid protonolysis (eq. S12). As [1-hexyne] (6) becomes large, the system becomes saturated with alkyne and a maximum local concentration of alkyne around the metal is achieved (eq. S13-S15). (S10) (S11) (S12) Rate = k K 1 4 [1" hexyne] K 4 + [1" hexyne] where K 4 = k "1 + k 2 k 1 (S13) Rate " k 1 [1# hexyne] when K 4 >> [1" hexyne] (S14) Rate " k 1 K 4 when K 4 << [1" hexyne] (S15) Further experiments are necessary to distinguish between these two mechanisms. S12

13 Figure S5. Plot of [1-hexyne] vs. rate (N t, h -1 ) exhibits a first-order dependence on [1- hexyne] below ~2.7x10-1 M. Saturation of alkyne has been achieved above ~2.7x10-1 M. The line is a fit of eq. S7 with plot k 2 = 26.5h -1 and K 4 = 0.2M. Representative Thermodynamic Estimates for Thorium-Mediated Hydrothiolation of Terminal, Aliphatic Alkynes and Thiols S5 Si An[CH 2 TMS] 2 2 HSR RS R' i 2 CH 3 TMS Me 2 SiCp" 2 An(SR) 2 R' Si RS SR An RS H R' RSH iii ii Si SR An SR R' Si SR An RS R' Step i Bonds Broken Bonds Formed Th-CH 2 TMS 83 kcal/mol Th-SR 105 kcal/mol H-SR 88 kcal/mol H-CH 2 TMS 98 kcal/mol S13

14 "H protonolysis = [ ] [ ] # -32 kcal/mol Step ii Bonds Broken Bonds Formed HC$CR 206 kcal/mol C=C-S 145 kcal/mol Th-SR 105 kcal/mol Th-C=C 94 kcal/mol S-C=C 91 kcal/mol "H insertion = [ ] [ ] # -19 kcal/mol Step iii Bonds Broken Bonds Formed Th-C=C 94 kcal/mol Th-SR 105 kcal/mol H-SR 88 kcal/mol H-C=C 103 kcal/mol "H protonolysis = [ ] [ ] # -26 kcal/mol (S1) (a) Stubbert, B. D.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, (b) Stubbert, B. D.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, (c) Stubbert, B. D.; Stern, C. L.; Marks, T. J. Organometallics 2003, 22, (S2) Fiandanese, V.; Marchese, G.; Naso, F.; Ronzini, L. Synthesis 1987, (S3) Cao, C.; Fraser, L. R.; Love, J. A. J. Am. Chem. Soc. 2005, 127, (S4) Ananikov, V. P.; Orlov, N. V.; Beletskaya, I. P.; Khrustalev, V. N.; Antipin, M. Y.; Timofeeva, T. V. J. Am. Chem. Soc. 2007, 129, (S5) (a) Nolan, S. P.; Marks, T. J. J. Am. Chem. Soc. 1989, 111, (b) McMillen, D. F.; Golden, D. M. Annu. Rev. Phys. Chem. 1982, 33, (c) Griller, D.; Kanabus-Kaminska, J. M.; Maccoll, A. THEOCHEM 1988, 40, (d) Lin, Z Ph.D Thesis, Northwestern University, Evanston, Il December 1988, Appendix A. (e) Value for sulfur-vinyl bond was estimated from bond enthalpies and heats of formation. S14

15 Copies of 1 H-NMR and 13 C-NMR spectra. Compound 10: S13

16 Compound 11: S14

17 Compound 12: S15

18 Compound 14: S16

19 Compound 16: S17

20 Compound 17: S18

21 Compound 18: S19