upporting Information ynthesis of ulfur-rich Polymers: Copolymerization of Episulfide with Carbon Disulfide by Using [PPN]/(salph)(III) ystem Koji Nakano, Go Tatsumi and Kyoko Nozaki* Department of Chemistry and Biotechnology, Graduate chool of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. e-mail: nozaki@chembio.t.u-tokyo.ac.jp Table of Contents General 2 Experimental Procedures 3 Reaction Time and Temperature Dependences of the Copolymer/Propylene Trithiocarbonate Ratio and Molecular Weight of the Copolymer 7 Proposed Polymerization Mechanism 9 1 H and 13 C NMR pectra 10 IR pectra 13 References 14 1
General Methods. All manipulations involving air- and/or moisture-sensitive compounds were carried out in a glove box under argon atmosphere or with the standard chlenk technique under argon purified by passing through a hot column packed with BAF catalyst R3-11. All the solvents used for reactions were distilled under argon after drying over an appropriate drying reagent or passed through solvent purification columns. Propylene sulfide was dried over CaH 2 and distilled. Most of other reagents were used without further purification unless otherwise specified. NMR spectra were recorded in deuteriochloroform on a 500 MHz spectrometers ( 1 H 500 MHz; 13 C 125 MHz, 31 P 202 MHz). Chemical shifts are reported in ppm relative to the residual protiated solvent peak (7.26 ppm for CH 3 ) for 1 H, deuteriochloroform (77.16 ppm) for 13 C, an external 85% H 3 PO 4 standard (0 ppm) for 31 P. Data are presented in the following space: chemical shift, multiplicity (s = singlet, d = doublet, m = multiplet and/or multiplet resonances), coupling constant in hertz (Hz), and signal area integration in natural numbers. IR spectra were recorded on a FT-IR spectrophotometer. Gel permeation chromatography (GPC) analyses were carried out using a HPLC instrument equipped with two columns (hodex KF-804L) using tetrahydrofuran as an eluent at 40 C at 1 ml/min. The molecular weight was calibrated against standard polystyrene samples. Glass-transition temperature was measured by differential scanning calorimetry (DC) apparatus. Heating rates were 10 C per minute. The refractive index was measured by Abbe refractometer. The recycling preparative GPC was performed with JAI GEL-1H and -2H columns (chloroform as an eluent). 2
Representative Procedure for the Copolymerization of Propylene ulfide with C 2. A 20 ml chlenk tube was charged with complex 3 (13 mg, 2.0 10 2 mmol), [PPN] (12 mg, 2.0 10 2 mmol), propylene sulfide (P) (0.78 ml, 10 mmol), and C 2 (1.2 ml, 20 mmol) under argon atmosphere. The reaction mixture was stirred at 25 C for 5 h. Dodecane as an internal standard was added to the reaction mixture, and an aliquot was taken from the resulting mixture to determine the yields of copolymer 1 and propylene trithiocarbonate (2), and 1/2 ratio. The rest of polymerization mixture was diluted with C 2 (10 ml), transferred into round-bottomed flask, and quenched with a mixture of methanol and 1.0 M aqueous H. To the mixture was added methanol (50 ml), affording the crude copolymer. After the supernatant was removed, the crude copolymer was dissolved in C 2 (10 ml) and precipitated from methanol (50 ml). Yellowish precipitate was collected and dried in vacuo to constant weight. The obtained copolymer was analyzed by NMR spectroscopy and GPC. IR (film) 1066, 1045 [ C(=) ], 800 ( CH and CH 2 ) cm 1, cast film); 1 H NMR (CD 3 ) δ 4.52 4.44 (m, 1H), 3.83 3.75 (m, 2H), 1.59 (d, J = 6.9 Hz, 3H); 13 C NMR (CD 3 + C 2 ) δ 221.1 221.0, 46.0 45.9, 41.8 41.7, 19.2 19.1. [Propylene trithiocarbonate (2) 1 : IR (neat) 1080, 1053, 1035, [ C(=) ], 868 ( CH and CH 2 ) cm 1, neat); 1 H NMR (CD 3 ) δ 4.52 (m, 1H), 4.01 (dd, J = 11.8, 5.4 Hz, 1H), 3.67 (dd, J = 11.9, 7.6 Hz, 1H), 1.63 (d, J = 6.6 Hz, 3H)]. Copolymerization of Propylene ulfide with C 2 by Using Pre-mixed Complex. A 20 ml chlenk tube was charged with complex 3 (13 mg, 2.0 10 2 mmol), [PPN] (12 mg, 2.0 10 2 mmol), and THF (5.0 ml) under argon atmosphere. The resulting mixture was stirred at 25 C for 1 h, and then the solvent was evaporated under reduced pressure. To the residue was added P (0.78 ml, 10 mmol) and C 2 (1.2 ml, 20 mmol) under argon atmosphere. The reaction mixture was stirred at 25 C for 5 h. According to the representative procedure, the yields of 1 and 2 (90%), and 1/2 ratio (92/8) were determined, and the copolymer was purified (1.26 g, 84% yield, M n = 42,600 g mol 1, M w /M n = 1.3). 3
cheme 1. (10 mmol) t Bu N O t Bu 3 N O t Bu t Bu + [PPN] (0.020 mmol) THF 25 C, 1 h evaporation C 2 (20 mmol) 25 C, 5 h 1 n + 2 (0.020 mmol) yield of 1 + 2 = 90% (NMR) 1/2 = 92/8 M n = 42,600 (g mol 1 ) M w M n = 1.3 Treatment of Cyclic Trithiocarbonate 2 with [PPN]/Complex 3. A 20 ml chlenk tube was charged with complex 3 (14 mg, 2.1 10 2 mmol), [PPN] (12 mg, 2.1 10 2 mmol), propylene trithiocarbonate (2) (634 mg, 4.2 mmol), and C 2 (0.50 ml, 8.4 mmol) under argon atmosphere. The reaction mixture was stirred at 25 C for 5 h. A small aliquot of the reaction mixture was picked up and analyzed by 1 H NMR spectroscopy, demonstrating no production of copolymer 1. 2 [PPN] complex 3 (2/[PPN]/3 = 200/1/1) C 2 (8.4 mmol) 25 C, 5 h No polymeric materials (1) (4.2 mmol) Copolymerization of Propylene ulfide with C 2 in the Presence of 1,2-Butene Trithiocarbonate. A 20 ml chlenk tube was charged with complex 3 (12 mg, 2.0 10 2 mmol), [PPN] (13 mg, 2.0 10 2 mmol), P (0.78 ml, 10 mmol), C 2 (1.2 ml, 20 mmol), 1,2-butene trithiocarbonate (ca. 115 mg, ca. 0.70 mmol) and dodecane (50 μl, 0.22 mmol) under argon atmosphere. After mixing for about 5 seconds, a small aliquot of the mixture was picked up and analyzed by 1 H NMR spectroscopy to determine the initial molar ratio of 1,2-butene trithiocarbonate and dodecane. The rest of the reaction mixture was stirred at 25 C for 5 h. Then, a small aliquot of the reaction mixture was picked up. 1 H NMR spectrum of the sample showed that 1,2-butene 4
trithiocarbonate was not consumed. Furthermore, purification of the polymerization mixture gave only pure copolymer 1. Et + C 2 + P (10 mmol) (20 mmol) (0.7 mmol) [PPN] complex 3 (P/[PPN]/3 = 500/1/1) dodecane (50 μl, 0.22 mmol) rt, 5 h 1 n + 2 Et + >99% recovery (2) yield of 1 + 2 = 35% (NMR) 1/2 = 82/18 M n = 21,400(g mol 1 ) M w M n = 1.6 ynthesis of Racemic 1-Diphenylphosphinopropane-2-thiol and Transformation to Its (1)-( )-Camphanate. A 80-mL chlenk tube was charged with Ph 2 PH (13.6 ml, 10wt% in hexane, 4.8 mmol) under argon atmosphere. Diethyl ether (8.0 ml) was added into the solution at 78 C, and then n BuLi (3.2 ml, 1.58 M in hexane, 5.1 mmol) were slowly added. After stirring for 30 min, rac-p (0.48 ml, 6.1 mmol) was added dropwise. The resulting yellow solution was slowly warmed to ambient temperature, and stirred for another 30 min. The reaction was quenched with water, and the diethyl ether layer was separated and concentrated. 1 H NMR spectrum of the crude product demonstrated that 1-diphenylphosphinopropane-2-thiol was obtained as major product. Purification of a part of the crude mixture by recycling preparative GPC with chloroform gave 1-diphenylphosphinopropane-2-thiol as a colorless solid. 1 H NMR (CD 3 ) δ 7.45 7.41 (m, 4H), 7.37 7.33 (m, 6H), 3.03 2.94 (m, 1H), 2.42 (dd, J = 12.1, 5.7 Hz, 1H), 2.38 (dd, J = 12.1, 6.0 Hz, 1H), 2.00 (d, J = 5.5 Hz, 1H), 2.42 (dd, J = 12.1, 5.7 Hz, 1H), 1.46 (d, J = 6.9 Hz, 1H); 31 P NMR (CD 3 ) δ 19.6. A 3 ml vial was charged with the purified 1-diphenylphosphinopropane-2-thiol (26 mg, 0.10 mmol) and (1)-( )-camphanic chloride (22 mg, 0.10 mmol) in CD 3 (2 ml). The mixture was shaken several times, and a part of the reaction mixture was transferred into a NMR sample tube. 31 P NMR 5
spectrum showed the two signals with equal integral value at 11.4 and 12.6 ppm for diastereomers. (Each signal tends to shift slightly depending on the concentration.) cheme 2. O Ph 2 PH BuLi (1.1 equiv.) Et 2 O, hexane 78 C, 30 min (1.3 equiv.) Ph 2 P H O O (1.0 equiv.) Ph 2 P O O O ynthesis of Enantio-enriched Propylene ulfide and Determination of the Enantiomeric Excess. 2 According to the literature, 2 (R)-P was synthesized. In order to determine the enantiomeric excess, the obtained (R)-P was converted into (R)-1-diphenylphosphinopropane-2-thiol and its (1)-( )-camphanate by the same procedure described above. 31 P NMR spectrum demonstrated that the integral ratio of the two signals for the diastereomers was 95 ( 13.7 ppm)/5 ( 12.6 ppm). Thus, the enantiomeric excess of the starting (R)-P was determined to be 90% ee. Effect of Molar Ratio of Propylene ulfide and C 2 on Copolymer/Cyclic Trithiocarbonate (1/2) electivity. When the copolymerization of P with C 2 was carried out under the condition of P/C 2 = 1/0.5 for 5 h (Table 1, run 4), the polymerization mixture became highly viscous. Although it was suspected that the high viscosity caused low copolymer selectivity, the copolymerization under the same P/C 2 ratio for a shorter reaction time of 2 h also gave a significant amount of cyclic trithiocarbonate (yield of 1 + 2 = 24%, 1/2 = 70/30) in spite of very low viscosity of the polymerization mixture. Furthermore, the copolymerization in the presence of excess C 2 afforded the copolymer selectively (1/2 = 92/8, Table 1, run 7), though the polymerization mixture became highly viscous. Accordingly, high concentration of C 2, that is, high concentration of the trithiocarbonate-chain end is necessary for high copolymer selectivity. 6
Thermal Decomposition of the Copolymer. When the solid copolymer (284 mg, 1.89mmol of the repeating unit) in a 80 ml chlenk tube was heated gradually at 25 200 C (30 min) and at 200 C for another ten minutes, an oily material was obtained (1.87 mmol, 99% NMR yield, phenanthrene as an internal standard). This material was identified as pure propylene carbonate 2 by 1 H NMR spectroscopy. The copolymer decomposed slowly at lower temperature (5% at 150 C for 10 min, 10% at 170 C for 10 min), and decomposed rapidly at around 200 C. Reaction Time and Tepmperature Dependences of the Molecular Weight of the Copolymer and Copolymer/Propylene Trithiocarbonate Ratio. The molecular weight of copolymer 1 increased constantly with the reaction time, while the 1/2 ratio remained constant until the shortage of monomer P. The copolymerization (P = 10 mmol, C 2 = 20 mmol, 3 = [PPN] = 2.0 10 2 mmol) was Table 1. Reaction Time Dependences of the Copolymer/Propylene Trithiocarbonate Ratio and Molecular Weight of the Copolymer 1 [PPN] complex 3 (P/[PPN]/3 = 500/1/1) + C 2 + 25 C n P (20 mmol) 1 2 (10 mmol) run time (h) yield of 1 + 2 (%) b 1/2 b M n (g mol 1 ) c c M w /M n 1 1 5 84/16 4,000 1.2 2 2 20 84/16 8,200 1.3 3 3 34 84/16 11,900 1.4 4 4 48 84/16 16,300 1.3 5 5 60 84/16 19,500 1.4 6 8 85 84/16 31,000 1.4 7 24 97 77/23 30,600 1.6 a Reaction conditions: P (10 mmol), [PPN] (0.20 mol%), complex 3 (0.20 mol%), C 2 (20 mmol) at 25 C. b Determined based on 1 H NMRspectroscopy of the crude product by using dodecane as an internal standard. c Determined by gel permeation chromatography using a polystyrene standard. 7
carried out at 25 C, and a small aliquot was picked up every hour for the initial 5 h and after 8 and 24 h. The results are summarized in Table 1. The ratio was almost constant (1/2 = 84/16) until the P conversion reached 85% in 8 h (runs 1 6). In contrast, when most of P was consumed (97% conversion of P), the ratio of cyclic propylene trithiocarbonate (2) increased (1/2 = 77/23, run 7). In addition, the copolymerization for 7 days (P = 10 mmol, C 2 = 10 mmol, 3 = [PPN] = 2.0 10 2 mmol) gave copolymer 1 and propylene trithiocarbonate (2) in 28/72 ratio (Equation 3). These results are similar to those in the copolymerization of terminal epoxides with CO 2. 3 Lowering the reaction temperature simply retard the formation of both 1 and 2 keeping the 1/2 ratio constant (Equation 4). When the copolymerization was carried out at 0 C for 5 h (P = 10 mmol, C 2 = 20 mmol, 3 = [PPN] = 2.0 10 2 mmol), the ratio at 2% conversion was almost identical (88/12) to that under 25 C. The results described above demonstrate that (1) cyclic trithiocarobnate formed from the beginning at the constant rate, regardless of polymerization temperature, and (2) the degradation of the copolymer occurs via back-biting process under the reaction condition (at least at very high conversion), giving cyclic trithiocarbonate. With these data only, we cannot conclude whether the formation of cyclic trithiocarbonate mainly occurs either via back-biting from the chain-end or via another process. However, the fact that the higher C 2 concentration suppressed the formation of 2 (see the main text) should strongly support the back-biting to be a major route for the formation of 2. [PPN] complex 3 (P/[PPN]/3 = 500/1/1) + C 2 + 25 C, 7 days n P (20 mmol) (10 mmol) 1 2 yield of 1 + 2 = 99% (NMR) 1/2 = 28/72 (eq. 3) [PPN] complex 3 (P/[PPN]/3 = 500/1/1) + C 2 + 0 C, 5 h n P (20 mmol) (10 mmol) 1 2 yield of 1 + 2 = 2% (NMR) 1/2 = 88/12 (eq. 4) 8
Plausible Reaction Mechanism (cheme 3). 3,4 A mixture of complex 3 and [PPN] is in equilibrium with ate complex 4. Chromium complex 3 should work as Lewis-acidic center to activate an episulfide. The ring-opening of the activated episulfide by the attack of chloride ion gives thiolate complex 5, which would be in equilibrium with the neutral chromium complex and the dissociated anionic thiolate-chain end (6). Complex 5 and/or the anionic chain end in 6 react(s) with C 2, giving chromium trithiocarbonate complex 7 and/or the anionic trithiocarbonate-chain end in 8. Complex 7 and its dissociated state 8 are also in equilibrium. During the chain propagation, the dissociated trithiocarbonate-chain end in 8 attacks episulfide activated by the Lewis-acidic neutral complex (9) to regenerate complex 5. Under low concentration of C 2, the anionic chain end in 6 undergo back-biting to provide cyclic trithiocarbonate 2. The anionic thiolate-chain end in 6 is effectively trapped by the chromium center as 5 to suppress the back-biting. Both of two axial chloride ligands on complex 4 would be capable to initiate the polymerization. 3b cheme 3. initiation propagation P P [PPN] [PPN] [PPN] 4 P' P' 7 8 [PPN] (= 3) C 2 P P 9 P P [PPN] [PPN] [PPN] P' P' 5 6 P P' =, polymer chain 9
CH 3 b a c a b n c TM Figure 1. 1 H NMR spectrum of the alternating copolymer of propylene sulfide with C 2 (CD 3 ). 10
d C 2 c a b d n CD 3 b a c Figure 2. 13 C NMR spectrum of the alternating copolymer of propylene sulfide with C 2 (CD 3 + C 2 ). Each carbon was assigned by DEPT technique. 11
Ph 2 P H Figure 3. 1 H NMR spectrum of 1-diphenylphosphinopropane-2-thiol (CD 3 ). 12
(a) (b) Figure 4. IR spectrum of (a) the alternating copolymer of propylene sulfide with C 2 (film) and (b) cyclic propylene carbonate (neat). 13
References 1) Taguchi, Y.; Yanagiya, K.; hibuya, I.; uhara, Y. Bull. Chem. oc. Jpn. 1987, 60, 727. 2) Hauptman, E.; Fagan, P. J.; Marshall, W. Organometallics 1999, 18, 2061. 3) (a) Cohen, C. T.; Coates, G. W. J. Polym. ci., Part A: Polym. Chem. 2006, 44, 5182. (b) Cohen, C. T.; Chu, T.; Coates, G. W. J. Am. Chem. oc. 2005, 127, 10869. 4) (a) Lu, X. B.; hi, L.; Wang, Y. M.; Zhang, R.; Zhang, Y. J.; Peng, X. J.; Zhang, Z. C.; Li, B. J. Am. Chem. oc. 2006, 128, 1664. (b) Darensbourg, D. J.; Phelps, A. L. Inorg. Chem. 2005, 44, 4622. (c) Aida, T.; Ishikawa, M.; Inoue,. Macromolecules 1986, 19, 8. 14