Hydrogen Atom Transfer (HAT) Processes Promoted by the Quinolinimide-N-Oxyl. Radical. A Kinetic and Theoretical Study

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1 SUPPORTING INFORMATION Hydrogen Atom Transfer (HAT) Processes Promoted by the Quinolinimide-N-Oxyl Radical. A Kinetic and Theoretical Study Gino A. DiLabio, a Paola Franchi, c Osvaldo Lanzalunga, b * Andrea Lapi, b Fiorella Lucarini, d Marco Lucarini, c Marco Mazzonna, b Viki Kumar Prasad, a and Barbara Ticconi b a Department of Chemistry, University of British Columbia, Okanagan, 3333 University Way, Kelowna, British Columbia, Canada V1V 1V7 b Dipartimento di Chimica, Sapienza Università di Roma and Istituto CNR di Metodologie Chimiche (IMC-CNR), Sezione Meccanismi di Reazione, c/o Dipartimento di Chimica, Sapienza Università di Roma, P.le A. Moro, 5 I Rome, Italy c Dipartimento di Chimica G. Ciamician, Università di Bologna, Via San Giacomo 11, I Bologna, Italy d Département de Chimie, Université de Fribourg, Chemin du Musée 9, 1700 Fribourg, Switzerland Instrumentation Determination of the O-H BDE values by EPR measurements Figure S1. UV-vis spectroscopic characterization of QINO Figure S2. EPR spectrum of QINO obtained by oxidation of NHQI with cerium(iv) ammonium nitrate (CAN) in CH 3 CN at 25 C Figure S3. EPR spectrum observed under continuous irradiation of a CH 3 CN solution containing di-tert-butyl peroxide (10% v/v), NHQI and 4-CH 3 OCO-NHPI Figures S4-S18. Dependence of for the decay of QINO on the concentration of alkylaromatics S3 S3 S5 S6 S6 S7 S1

2 Figures S19-S24. Dependence of for the decay of PINO on the concentration of alkylaromatics S15 Figures S25-S32. Dependence of for the decay of QINO on the concentration of aliphatic hydrocarbons, alcohols, aldehydes, ethers and amides S18 Figures S33-S39. Dependence of for the decay of PINO on the concentration of aliphatic hydrocarbons, alcohols, aldehydes, ethers and amides S22 Figure S40. UV-vis spectra of QINO in MeCN/[HClO 4 ] (0-0.2 M) Figure S41. Hammett plot for the reaction of substituted toluenes with PINO in CH 3 CN at 25 C S26 S26 Figure S42. Hammett plot for the reaction of substituted toluenes with QINO in CH 3 CN/HClO M at 25 C S27 Table S1. Gas phase computational results for HAT reaction of QINO with toluene Table S2. Gas phase computational results for HAT reaction of PINO with toluene Table S3. Solvent phase computational results for HAT reaction of QINO with toluene in acetonitrile solvent Table S4. Solvent phase computational results for HAT reaction of PINO with toluene in acetonitrile solvent Figure S43. Optimized structures of the transition states for the reaction of QINO and PINO with toluene Cartesian coordinates of the optimized structures of the reaction steps S28 S28 S29 S29 S30 S31 S2

3 Instrumentation 1 H NMR and 13 C NMR spectra were recorded on a spectrometer operating at 300 MHz and 75 MHz, respectively. Spectrophotometric analyses for the HAT reactions promoted by PINO and QINO were performed with a diode array spectrophotometer thermostated by a circulating water bath. For reactions with > 0.1 s -1 the instrument was equipped with a rapid mixing accessory. EPR spectra were obtained using a X-band spectrometer. Laser flash photolysis experiments were carried out with an laser kinetic spectrometer providing 8 ns pulses, using the third armonic (355 nm) of a Nd:YAG laser. The laser energy was adjusted to 10 mj/pulse by the use of the appropriate filter. The transient spectrum was obtained by a point-to-point technique, monitoring the change of absorbance ( A) after the laser flash at intervals of 10 nm over the spectral range nm. Determination of the O-H BDE values by EPR measurements These determinations were done by using the EPR radical equilibration technique that has been largely used to measure BDE values of X-H bonds in many antioxidants. O O O O N OH MeOOC K eq + N O N O + MeOOC N OH (1S) N N O O O O NHQI 4-CH 3 OCO-PINO QINO 4-CH 3 OCO-NHPI This consists in measuring the equilibrium constant, K eq, for the hydrogen atom transfer reaction (Equation 1S) between NHQI and an appropriate reference hydroxylamine, that in the present case was represented by 4-CH 3 OCO-NHPI (see Eq 1S). The equilibrating radicals were produced by photolyzing deoxygenated CH 3 CN solution containing NHPI, the reference compound (in the range M) S3

4 and di-tertbutyl peroxide (10% v/v). The molar ratio of the two radicals was obtained from the EPR spectra and used to determine the equilibrium constant, K eq (eq 2S). The equilibrium constant was found to be independent on the initial product concentrations and on the rate of initiation. The initial concentrations of the two reactants were used for this purpose since these were high enough to avoid significant consumption during the course of the experiment. Relative radical concentrations were determined by comparison of the digitized experimental spectra with computer simulated ones. In these cases an iterative least squares fitting procedure based on the systematic application of the Monte Carlo method was performed in order to obtain the experimental spectral parameters of the two species including their relative intensities. S4

5 A λ (nm) Figure S1. UV-vis spectrum of QINO generated by oxidation of NHQI (1 mm) with cerium(iv) ammonium nitrate (0.5 mm) in MeCN at T = 25 C. S5

6 Figure S2. 1 st (top) and 2 nd derivative (bottom) EPR spectrum of QINO obtained by oxidation of NHQI 1 mm with cerium(iv) ammonium nitrate (CAN) 2 mm in CH 3 CN at 25 C. The 2 nd derivative spectrum clearly shows unresolved hyperfine structure due to small coupling of the unpaired electron with the nitrogen and hydrogen aromatic nuclei. Figure S3. EPR spectrum observed under continuous irradiation of a CH 3 CN solution containing ditert-butyl peroxide (10% v/v) and an equimolar amount of NHQI and 4-CH 3 OCO-NHPI. In red is reported the corresponding theoretical simulation. S6

7 Dependence of for the decay of QINO on the concentration of alkylaromatics [Toluene] / M Figure S4. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of toluene in CH 3 CN/HClO M at 25 C (r 2 =0.995) [Toluene] / M Figure S5. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of toluene in CH 3 CN/Mg(ClO 4 ) M at 25 C (r 2 =0.982). S7

8 [Ethylbenzene] / M Figure S6. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of ethylbenzene in CH 3 CN/HClO M at 25 C (r 2 =0.996) [Ethylbenzene] / M Figure S7. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of ethylbenzene in CH 3 CN/Mg(ClO 4 ) M at 25 C (r 2 =0.993). S8

9 [Cumene] / M Figure S8. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of cumene in CH 3 CN/HClO M at 25 C (r 2 =0.993) [Cumene] / M Figure S9. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of cumene in CH 3 CN/Mg(ClO 4 ) M at 25 C (r 2 =0.992). S9

10 [p-methylanisole] (M) Figure S10. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of p-methylanisole in CH 3 CN at 25 C (r 2 =0.983) k OBS [p-xylene] / M Figure S11. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of p-xylene in CH 3 CN/HClO M at 25 C (r 2 =0.996). S10

11 [p-xylene] / M Figure S12. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of p-xylene in CH 3 CN/Mg(ClO 4 ) M at 25 C (r 2 =0.996) / (sec -1 ) [m-iodotoluene] / (M) Figure S13. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of m-iodotoluene in CH 3 CN at 25 C (r 2 =0.990). S11

12 [m-iodotoluene] / M Figure S14. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of m-iodotoluene in CH 3 CN/HClO M at 25 C (r 2 =0.994) [4-Methylacetophenone] / M Figure S15. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of 4-methylacetophenone in CH 3 CN at 25 C (r 2 =0.994). S12

13 [4-Methylacetophenone] / M Figure S16. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of 4-methylacetophenone in CH 3 CN/HClO M at 25 C (r 2 =0.992) [p-tolunitrile] (M) Figure S17. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of p-tolunitrile in CH 3 CN at 25 C (r 2 =0.998). S13

14 [p-tolunitrile] / M Figure S18. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of p-tolunitrile in CH 3 CN/HClO M at 25 C (r 2 =0.992). S14

15 Dependence of for the decay of PINO on the concentration of alkylaromatics / sec [Toluene] / M Figure S19. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of toluene in CH 3 CN at 25 C (r 2 =0.999) [Cumene] / M Figure S20. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of cumene in CH 3 CN at 25 C (r 2 =0.997). S15

16 [p-methylanisole] / M Figure S21. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of p-methylanisole in CH 3 CN at 25 C (r 2 =0.988) [m-iodotoluene] / M Figure S22. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of m-iodotoluene in CH 3 CN at 25 C (r 2 =0.992). S16

17 [4-Methylacetophenone] / M Figure S23. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of 4-methylacetophenone in CH 3 CN at 25 C (r 2 =0.985) [p-tolunitrile] / M Figure S24. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of p-tolunitrile in CH 3 CN at 25 C (r 2 =0.998). S17

18 Dependence of for the decay of QINO on the concentration of aliphatic hydrocarbons, alcohols, aldehydes, ethers and amides [Cyclohexane] / M Figure S25. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of cyclohexane in CH 3 CN at 25 C (r 2 =0.993) [Adamantane] / M Figure S26. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of adamantane in CH 3 CN at 25 C (r 2 =0.980). S18

19 k OBS [Methanol] / M Figure S27. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of methanol in CH 3 CN at 25 C (r 2 =0.999) [Ethanol] / M Figure S28. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of ethanol in CH 3 CN at 25 C (r 2 =0.987). S19

20 [2-Propanol] / M Figure S29. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of 2-propanol in CH 3 CN at 25 C (r 2 =0.999) [p-chlorobenzaldehyde] / M Figure S30. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of p-chlorobenzaldehyde in CH 3 CN at 25 C (r 2 =0.994). S20

21 [Tetrahydrofuran] / M Figure S31. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of tetrahydrofuran in CH 3 CN at 25 C (r 2 =0.993) [N,N-Dimethylformamide] / M Figure S32. Dependence of pseudo-first order rate constants ( ) for the decay of QINO on the concentrations of N,N-dimethylformamide in CH 3 CN at 25 C (r 2 =0.998). S21

22 Dependence of for the decay of PINO on the concentration of aliphatic hydrocarbons, alcohols, aldehydes, ethers and amides [Cyclohexane] / M Figure S33. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of cyclohexane in CH 3 CN at 25 C (r 2 =0.988) [Adamantane] / M Figure S34. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of adamantane in CH 3 CN at 25 C (r 2 =0.988). S22

23 [Methanol] / M Figure S35. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of methanol in CH 3 CN at 25 C (r 2 =0.998) [Ethanol] / M Figure S36. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of ethanol in CH 3 CN at 25 C (r 2 =0.991). S23

24 [2-Propanol] / M Figure S37. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of 2-propanol in CH 3 CN at 25 C (r 2 =0.995) [p-chlorobenzaldehyde] / M Figure S38. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of p-chlorobenzaldehyde in CH 3 CN at 25 C (r 2 =0.972). S24

25 [Tetrahydrofuran] / M Figure S39. Dependence of pseudo-first order rate constants ( ) for the decay of PINO on the concentrations of tetrahydrofuran in CH 3 CN at 25 C (r 2 =0.994). S25

26 mm 100mM 150 mm 200mM A λ (nm) Figure S40. UV-vis spectra of QINO generated by oxidation of NHQI (1 mm) with cerium(iv) ammonium nitrate (0.5 mm) at T = 25 C in MeCN/[HClO 4 ] (0-0.2 M) p-och 3 p-ch 3 r 2 = log(k X /k H ) H m-i p-coch p-cn σ + Figure S41. Hammett plot for the reaction of substituted toluenes with PINO in CH 3 CN at 25 C. S26

27 r 2 = p-ch 3 log(k X /k H ) H m-i p-coch p-cn Figure S42. Hammett plot for the reaction of substituted toluenes with QINO in CH 3 CN/HClO M at 25 C. σ + S27

28 Table S1. Gas phase computational results relative to reactants (QINO+toluene), of the hydrogen atom transfer between QINO with toluene. The data were obtained using B3LYP-DCP/6-31+G(2d,2p) approach. All values are in kcal/mol. Molecule(s)/Complex Electronic energy (Eel) Eel+ZPVE (zero point vibrational energy correction) Enthalpy change Free energy change QINO-toluene (prereaction complex) QINO-toluene (cisoid TS complex) QINO-toluene (transoid TS complex) NHQI-benzyl (postreaction complex) NHQI + Benzene (products) Table S2. Gas phase computational results relative to reactants (PINO+toluene), of the hydrogen atom transfer between PINO with toluene. The data were obtained using B3LYP-DCP/6-31+G(2d,2p) approach. All values are in kcal/mol. Molecule(s)/Complex Electronic energy (Eel) Eel+ZPVE (zero point vibrational energy correction) Enthalpy change Free energy change PINO-toluene (prereaction complex) PINO-toluene (cisoid TS complex) PINO-toluene (transoid TS complex) NHPI-benzyl (postreaction complex) NHPI + Benzene (products) S28

29 Table S3. Solvent phase computational results relative to reactants (QINO+toluene), of the hydrogen atom transfer between QINO with toluene in acetonitrile solvent. The data were obtained using B3LYP-DCP/6-31+G(2d,2p) approach with the SMD solvation (acetonitrile) model. All values are in kcal/mol. Molecule(s)/Complex Electronic energy (Eel) Eel+ZPVE (zero point vibrational energy correction) Enthalpy change Free energy change QINO-toluene (prereaction complex) QINO-toluene (cisoid TS complex) QINO-toluene (transoid TS complex) NHQI-benzyl (postreaction complex) NHQI + Benzene (products) Table S4. Solvent phase computational results relative to reactants (PINO+toluene), of the hydrogen atom transfer between PINO with toluene in acetonitrile solvent. The data were obtained using B3LYP- DCP/6-31+G(2d,2p) approach with the SMD solvation (acetonitrile) model. All values are in kcal/mol. Molecule(s)/Complex Electronic energy (Eel) Eel+ZPVE (zero point vibrational energy correction) Enthalpy change Free energy change PINO-toluene (prereaction complex) PINO-toluene (cisoid TS complex) PINO-toluene (transoid TS complex) NHPI-benzyl (postreaction complex) NHPI + Benzene (products) S29

30 (a) (b) Figure S43. Optimized structures of the transition states for the reaction of (a) QINO and (b) PINO with toluene. Structures were obtained using the B3LYP-DCP/6-31+G(2d,2p) with the SMD solvation (acetonitrile) model. Key distances shown are in Angstroms. Key: Carbon = grey; Hydrogen = White; Oxygen = red; Nitrogen = blue. S30

31 Cartesian coordinates of the optimized structures of the reaction steps Optimized cartesian coordinates (in Angstroms) of the structures studied computationally in this work are presented as below. The geometries of the molecules are given in the order of the total number of atoms, followed by the overall charge and spin multiplicity, followed by their composite atomic symbols and the respective x, y, z coordinates. A. Gas-phase optimized geometries: NHQI C C C C C N C C H H H O O N O H NHPI C C C C C C C C H H S31

32 H H O O N O H QINO C C C C C N C C H H H O O N O PINO C C C C C C C C H H S32

33 H H O O N O Toluene C C C C C C H H H H H C H H H Benzyl C C C C C C H H H H S33

34 H C H H H H QINO-toluene pre-reaction complex C C C C C C H H H C C N C C C C C H H H O O N O H H C S34

35 H H H PINO-toluene pre-reaction complex C C C C C C H H H C C C C C C C C H H H H O QINO-toluene cisoid transition state complex C C C C C C H H S35

36 H C C N C C C C C H H H O O N O H H C H H H PINO-toluene cisoid transition state complex C C C C C C H H H C C C C C C S36

37 C C H H H H O O N O H H C H H H QINO-toluene transoid transition state complex C C C C C C H H H C C N C C C C C H H H O S37

38 O N O H H C H H H PINO-toluene transoid transition state complex C C C C C C H H H C C C C C C C C H H H H O O N O H H C S38

39 H H H NHQI-benzyl post-reaction complex C C C C C C H H H C C N C C C C C H H H O O N O H H C H H H NHPI-benzyl post-reaction complex S39

40 C C C C C C H H H C C C C C C C C H H H H O B. Optimized geometries in Acetonitrile solvent: NHQI C C C C C N C C H H H O S40

41 O N O H NHPI C C C C C C C C H H H H O O N O H QINO C C C C C N C C H H H O S41

42 O N O PINO C C C C C C C C H H H H O O N O Toluene C C C C C C H H H H H C H H S42

43 H Benzyl C C C C C C H H H H H C H H H H QINO-toluene pre-reaction complex C C C C C C H H H C C N C S43

44 C C C C H H H O O N O H H C H H H PINO-toluene pre-reaction complex C C C C C C H H H C C C C C C C C H H H S44

45 H O QINO-toluene cisoid transition state C C C C C C H H H C C N C C C C C H H H O O N O H H C H H H PINO-toluene cisoid transition state C S45

46 C C C C C H H H C C C C C C C C H H H H O QINO-toluene transoid transition state C C C C C C H H H C C N C C C S46

47 C C H H H O O N O H H C H H H PINO-toluene transoid transition state C C C C C C H H H C C C C C C C C H H H H O S47

48 NHQI-benzyl post-reaction complex C C C C C C H H H C C N C C C C C H H H O O N O H H C H H H NHPI-benzyl post-reaction complex C C S48

49 C C C C H H H C C C C C C C C H H H H O S49