Azaphosphatranes as Structurally Tunable Organocatalysts for Carbonate Synthesis from CO 2 and Epoxides

Transcription

1 Azaphosphatranes as Structurally Tunable Organocatalysts for Carbonate Synthesis from CO 2 and Epoxides Bastien Chatelet, Lionel Joucla, Jean-Pierre Dutasta, Alexandre Martinez *, Kai C. Szeto and Véronique Dufaud *, École Normale Supérieure de Lyon, CNRS, Université de Lyon, Laboratoire de Chimie, 46 allée d Italie, Lyon, France Université de Lyon, Laboratoire de Chimie, Catalyse, Polymère, Procédés (C2P2), CNRS, Université Claude Bernard Lyon1, CPE Lyon, 43 Bd du 11 novembre 1918, Villeurbanne cedex, France Supporting Information General remarks Commercial reagents were used without further purifications. The toluene was synthesis grade and dried over 4Å molecular sieves prior to use. The stirring in the reaction vessel was performed at a stirring speed of 1000 rounds min -1. Yields were estimated from the 1 H NMR spectra using 2,4-dibromo-mesitylene as an internal standard. The 1 H and 31 P NMR spectra were recorded with a Bruker Avance 300 spectrometer at 300 and 120 MHz respectively. Catalytic procedures Reactions were carried out in a 5 ml Schlenk tube equipped with a rubber septum. In a typical run, the reactor was charged with the required quantity of styrene oxide, 0.05 mmol of catalyst (2a, 2b or 2c), toluene (if required, 1 ml) and 2,4-dibromo-mesitylene (internal standard). Carbon dioxide was first bubbled into the solution for five minutes to saturate the liquid phase. A balloon filled with carbon dioxide was then connected to the Schlenk through a needle to maintain a constant atmosphere of carbon dioxide during the course of the reaction. The mixture was placed in a thermostatic oil bath at the required temperature. Aliquots were withdrawn through the septum port, dissolved in CDCl 3 and analyzed by 1 H NMR. In the case of the long period stability studies, after each 24 hour period, after analysis of an aliquot by 1 H NMR, the reaction mixture was cooled to room temperature. Based on the SO integrated intensity in the NMR spectrum, additional substrate was added to the mixture to reestablish the initial substrate to catalyst ratio. Carbon dioxide was bubbled through the solution for fifteen minutes at room temperature, the CO 2 reservoir was connected to the reaction vessel, and it was returned to the thermostatic bath. S1

2 Procedure for the determination of isolated yields The reactions were performed with catalysts 2b and 2c following typical catalytic procedure as described above starting with 5 mmol of styrene oxide over a period of 24 h and without any solvent or internal standard. After cooling to room temperature, pentane and diethyl ether were poured on the reaction mixture until a precipitate formed. The mixture was filtered and the solid washed three times with diethyl ether. Solvents were removed from the filtrate leading to cyclic carbonate. The styrene carbonate product was isolated from batch reactions in yields of 73% for 2b and 75% for 2c. Scheme S1. Synthesis strategy for azaphosphatrane derivatives (R = methyl (2a), p- methoxybenzyl (2b), neo-pentyl (2c)). S2

3 Figure S1. 31 P{ 1 H} NMR spectrum of 2a (CDCl 3 ). Figure S2. 31 P{ 1 H} NMR spectrum of 2b (CDCl 3 ). S3

4 Figure S3. 31 P{ 1 H} NMR spectrum of 2c (CDCl 3 ). Figure S4. 31 P{ 1 H} NMR spectrum of 2a (1mol%) after cycloaddition of CO 2 to styrene oxide (7 hours). S4

5 Figure S5. 31 P{ 1 H} NMR spectrum of 2b (1mol%) after cycloaddition of CO 2 to styrene oxide (7 hours). Figure S6. 31 P{ 1 H} NMR spectrum of 2c (1mol%) after cycloaddition of CO 2 to styrene oxide (7 hours). S5

6 Figure S7. 31 P{ 1 H} NMR spectrum of 2b (0.1mol%) after cycloaddition of CO 2 to styrene oxide (96 hours). Figure S8. 31 P{ 1 H} NMR spectrum of 2c (0.1mol%) after cycloaddition of CO 2 to styrene oxide (96 hours). S6

7 Kinetic analysis showing the reaction is first order in catalyst 2b and epoxide First order kinetics plot at four catalyst concentrations of catalyst 2b. Assume reaction is first order in epoxide, then a plot of ln(n(styrene oxide)) against time should be a straight line with slope kobs = k[2b] a [CO 2 ] b 1,7 ln (n(styrene oxide)) 1,5 1,3 1,1 y = -0,0285x + 1,6121 R² = 0,9965 y = -0,0536x + 1,5959 R² = 0,9921 y = -0,1305x + 1,6014 R² = 0,9983 0,9 0,7 y = -0,1499x + 1,6117 R² = 0, Time (h) Figure S9. Catalyst loading: 0.25 mol% (squares), 0.5 mol% (crosses), 1 mol% (diamonds), 1.5 mol% (triangles). All reactions were performed at 100 C with n(styrene oxide) = 5mmol in the presence of excess of CO 2, without any additional solvent using 2,4-dibromomesitylene as an internal standard. S7

8 log (k obs ) Double logarithmic plot to determine the order with respect to catalyst 2b log [catalyst] ,8-1,6-1,4-1,2-1 -0,8-0,5 y = 0,9815x + 0,3243 R² = 0, ,5-2 Figure S10. Kobs = k[2b] a [CO 2 ] b, so log(kobs) = a log[2b] + b log[co 2 ] + log k and a plot of log(kobs) against log[2b] will have slope equal to a. Experimental procedure to determine reaction order with respect to carbon dioxide Styrene oxide (5 mmol), catalyst 2b (0.05 mmol), 2,4-dibromesitylene (as internal standard) were stirred in a Schlenk tube. A stream of a known % of CO 2 in N 2 was bubbled through the solution for fifteen minutes at atmospheric pressure. The mixture was placed in a thermostatic oil bath at 100 C. The method of initial rates was then used to determine the order with respect to carbon dioxide. The yield in carbonate was determined after 15 minutes of reaction. The rate of the reaction is: r = k CO 2 b 2b epoxide Table S1 % CO 2 Rate (mmol.l -1.s -1 ) The initial concentrations of catalyst and epoxide are the same for all reactions. S8

9 Table S2 [CO 2 ] 1 /[CO 2 ] 2 b 50/ / / / / / average 0.90 Thus, b = 0.90, an indication that the reaction is first order in CO 2. S9