Complex Promoted by Electron-Deficient Alkenes. Brian V. Popp and Shannon S. Stahl*

Transcription

1 Oxidatively-Induced Reductive Elimination of Dioxygen from an η 2 -Peroxopalladium(II) Complex Promoted by Electron-Deficient Alkenes Brian V. Popp and Shannon S. Stahl* Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI Table of Contents Pages General Considerations Dioxygen Gas Trapping Experiment Details Dioxygen Evolution and Trapping Data S2 S3 S4 1 H-NMR Spectroscopic Kinetic Study Details S4 1 H NMR Spectral Timecourse of the Dioxygen Substitution Reaction S5 Kinetic Fitting of 1 H NMR Spectroscopic Kinetic Study UV-visible Spectroscopic Kinetic Study Details Eyring Plots for Dioxygen Substitution Activation Parameters for Dioxygen Substitution S5 S6 S7 S7 S1

2 General Considerations. All syntheses and subsequent handling of palladium complexes was performed under a nitrogen atmosphere using either a glovebox (MBraun) or standard Schlenk techniques. Dichloromethane (Fisher) was purified by passing it over a column of activated alumina (A-2, Purifry). Dichloromethane-d 2 was obtained from Cambridge Isotope Laboratories, Inc. and was dried over CaH 2 and vacuum distilled into a Schlenk tube for storage in the glovebox. (bc)pd(dba) and (bc)pd(o 2 ), 1, were synthesized according to previously published methods 1 and (bc)pd(ns X ) complexes, 2 X, have been previously characterized. 2 All β-nitrostyrene derivatives (ns X ) were obtained from Aldrich or Fluka and were used as received. NMR spectroscopic data were obtained at 25.0 C using a Varian INOVA 500 MHz or a Bruker AC 300 MHz spectrometer. S2

3 Dioxygen Gas Trapping Experiment. This experiment was designed to quantify and characterize the dioxygen evolved during the reaction of (bc)pd(o 2 ) (1) with alkene (ns NO 2 ) via a chemical trap. The reaction apparatus used for this reaction is depicted in Figure S1. The experiment was carried out under an N 2 atmosphere inside of a glovebox in order to prevent exposure of the solutions to exogenous dioxygen. In reaction A, 8(2) µmol of 1 and 240 µmol of ns NO 2 were dissolved in 1 ml of CD 2Cl 2. In reaction B, 26(2) µmol of (bc)pd(dba) was dissolved in 1 ml of CD 2 Cl 2. The reactions were vigorously stirred for six hours in the sealed reaction apparatus, and subsequently, the reaction mixtures were transferred under N 2 to NMR tubes equipped with Teflon screw caps. 1 H NMR spectroscopic analysis using 1,3,5-tri-tertbutylbenzene as an internal standard revealed quantitative conversion of 1 to 2 NO 2 and (bc)pd(dba) to 1 within experimental error (Table S1). 6 cm Reaction A Reaction B Figure S1. Dioxygen Evolution and Trapping Reaction Apparatus. S3

4 Table S1. Dioxygen Evolution and Trapping Reaction Analysis. Reaction A a Reaction B a 1 2 NO 2 (bc)pd(dba) 1 Before Rxn 8(2) 0 26(2) 0 After Rxn 0 8(2) 16(2) 10(2) a Values reported in µmol. 1 H-NMR Spectoscopic Kinetic Studies. All data were acquired using a Varian Inova 500 MHz spectrometer. Experimental samples were prepared from stock solutions prepared in dried and degassed dichloromethane-d 2. A representative experiment for the substitution reaction between 1 and ns CF 3 follows. Using gas tight syringes, the stock solutions were transferred to an NMR tube with a J-Young valve to obtain a final sample concentration of 1.5 mm for 1 and 22.5 mm for ns CF 3. Immediately upon addition of the reagents, the tube was immersed in liquid N 2 and the head space of the tube was evacuated to ensure complete removal of gaseous O 2. Samples were thawed prior to insertion into the NMR probe and kinetic data acquisition was initiated after an equilibration time of approximately 5 minutes. The bathocuproine methylgroups for 1 and 2 CF 3 were integrated over the kinetic time-course (Figure S2). The kinetic decay of 1 and the concomitant rise of 2 CF 3 were found to fit a simple exponential equation (Figure S3). Absolute concentrations of 1, 2 CF 3 and nscf 3 were obtained by using 1,3,5-tri-tert-butylbenzene as an internal standard. S4

5 1 H NMR Spectral Timecourse of the Dioxygen Substitution Reaction Figure S2. 1 H NMR Spectra of the Reaction Timecourse for Dioxygen Substitution with ns CF 3. [Pd] (M) k = M -1 sec -1 for k = M -1 sec -1 for time (sec) Figure S3. Kinetic Analysis of the Reaction Timecourse Monitored by 1 H-NMR Spectroscopy. S5

6 UV-visible Spectroscopic Kinetic Studies. All UV-visible kinetics data were acquired on a PC-controlled Cary 3E spectrophotometer using WinUV 2.01 software. A Cary 1x1 peltier temperature controller was used to regulate the sample temperature between 10 C and 40 C. Solutions of known concentration were used to determine extinction coefficients for the reactants and products by the method of Beer s Law. A representative experiment for the substitution reaction between 1 and ns NO 2 follows. Stock solutions of (bc)pd(o 2) (10.2 mm) and ns NO 2 (75.9 mm) in dichloromethane were prepared in the glovebox and removed from the glovebox in a schlenk tube equipped with a 4 mm Kontes Teflon valve. The (bc)pd(o 2 ) stock solution was maintained at -78 C to minimize decomposition of the palladium complex. A gas-tight UVvisible cell equipped with a side-arm reservoir was used to allow both stock solutions to be added to the cell under a nitrogen atmosphere prior to initiating the reaction. The palladium stock solution (150µl) and dichloromethane (2.35 ml) were added via gas-tight syringe to the UV-visible cell, and the ns NO 2 solution (500 µl) was added to the side-arm. The total volume of the reaction was maintained at 3 ml for all experiments. After obtaining the initial absorbance reading of the (bc)pd(o 2 ) solutions, the contents of the cell and side-arm were mixed rapidly and single-wavelength (425 nm) data collection was initiated. The reactions were typically monitored for >4 half-lives. A text file of the reaction time-course was imported into Microsoft Excel for fitting. The pseudo-first order integrated rate law was used to fit the data. Three parameters (k obs, A 0, A inf ) were varied in order to minimize the sum of the squared deviations between the experimental data and the non-linear least squares fit (eq 1). A representative data set and fit is shown in Figure 1A. A t = (A " + (A 0 # A " )exp(#k obs * t)) (1) S6

7 Eyring Plots for Dioxygen Substitution NO2 CF3 Br F ln(k for /T) /T (K -1 ) Figure S4. Eyring plots showing the temperature dependent behavior of the exchange of olefin for dioxygen between 1 and ns X between 10 40ºC measured by UV-visible spectroscopy. Activation parameters were determined by a non-linear least squares solution of the Erying equation. Table S2. Activation Parameters for the Dioxygen Exchange Reaction between 1 and ns X. Entry Olefin k for (M -1 sec -1 ) a H (kcal/mol) S (e.u.) G (kcal/mol) b 1 ns NO (7) -36(2) 18.0±1.3 2 ns CF (8) -31(2) 18.6±1.4 3 ns Br (5) -31(2) 19.2±1.1 4 ns F (4) -30(1) 19.2±0.7 a. Observed at 298 K. b. Calculated at 298 K. 1 Stahl, S. S.; Thorman, J. L.; Nelson, R. C.; Kozee, M. A. J. Am. Chem. Soc. 2001, 123, (a) Stahl, S. S.; Thorman, J. L.; de Silva, N.; Guzei, I. A.; Clark, R. W. J. Am. Chem. Soc. 2003, 125, (b) Popp, B. V.; Thorman, J. L.; Morales, C. M.; Landis, C. R.; Stahl, S. S. J. Am. Chem. Soc. 2004, 126, S7