Supporting Information to The Mechanism of Pd-Catalyzed C-H ...
Supporting Information to The Mechanism of Pd-Catalyzed C-H Acetoxylation and Methoxylation by Electrospray Ionization Mass Spectrometry Lijuan Guo, Yu Xu*, Xiaojing Wang, Wenjing Liu and Dapeng Lu Department of Chemistry and Anhui Key Lab for Biomass Clean Energy, University of Science and Technology of China, hefei, 230026, China Preparation of Materials and Sample 2-Phenylpyridine, iodobenzene diacetate, acetate-d4, methanol-d4 and palladium(II) acetate are of analytical grade, which were obtained from commercial suppliers and used without further purification. HPLC solvents were purchased from Merck (Germany). The synthesis and characterization of the Pd intermediates and products were reported elsewhere.1 Instrumentation ESI(+)-MS and ESI(+)-MS/MS ESI(+)-MS and ESI(+)-MS/MS spectra were recorded on a Finnigan LCQ Advantage Max ion trap mass spectrometer (Thermo Fisher Scientific, USA) equipped with a standard ESI source. High purity nitrogen was used as nebulizer gas. Unless otherwise mentioned, the operating conditions were set as follows: spray voltage 4 kV, capillary voltage 10V, heated capillary temperature 200 oC, sheath gas flow rate 35 arbitrary units, auxiliary gas flow rate 15 arbitrary units. Tandem mass spectrometric (MS/MS) experiments were operated using collision-induced dissociation (CID) of mass selected ions with helium as the collision gas. The collision energy ranged from 10% to 40% depending on the dissociation capability of the precursor ions. The samples were injected into the ESI source through a 500 µL syringe (Hamilton) driven by a syringe pump (Longer Pump, TJ-1A syringe pump controller ) at 10-30 µL/min, and scan range is from m/z 100 to m/z 1500. High-resolution ESI(+)-MS experiments were carried out on Thermo Fisher Scientific LTQ Orbitrap XL linear ion trap mass spectrometer equipped with a standard HESI source. High purity nitrogen was used as nebulizer gas. Unless otherwise mentioned, the operating conditions were set as follows: spray voltage 4.0 kV, capillary voltage 35 V, heated capillary temperature 200 oC, sheath gas flow rate 35 arbitrary units, auxiliary gas flow rate 15 arbitrary units. Data acquisition and analysis were done with the Xcalibur 2.1 software package (Thermo Fisher Scientific, USA). NMR spectra were obtained on Bruker AVANCE AV 400 (400M for 1H NMR), unless otherwise indicated, the 1H spectra was recorded at -30oC. Results and Discussion Supplement When the mole ratio of 2-phenylpyridine to Pd(OAc)2 is 2:1, the Pd(II) complexes formed directly from reductive elimination of high-oxidation-state Pd
intermediates, which were detected at 11 m/z 415.04 as well as [8+H]+ m/z 380.01 and [16+H]+ m/z 475.06. While, the monomeric Pd(IV) intermediates 14 at m/z 445.05 and 15 at m/z 473.05 may have two possible formulations (Scheme S2). The complexes 14 and 15 were directly detected by ESI-MS. On the other hand, complexes 14 and 15 may be formed from 18 and 19 corresponding at the condition of ESI-MS by loss of an acetate ion. Consequently, Pd(II) complex 16 is formed from reductive elimination of Pd(IV) intermediates 17 and 18, which can be distinguished from 15 by high resolution ESI-MS. A possible mechanism was proposed for this transformation (Scheme S3). Scheme S1. Proposed Mechanism for C-H Activation of 2-phenylpyridine with a mole ratio 2:1. N
N
3
Pd
Pd
N
N
11 m/z 415.04 N
N
12 m/z 570.12
Pd(OAc)2
3 3+H m/z 156.08
Pd Pd N
O
N
O 3
O Pd
O Pd
N
N
N 5 m/z 580.95 13 m/z 736.02
Scheme S2. Two possible formulations for monomeric Pd(IV) intermediates OAc IV
N
N
OCH3 14 IV
N
IV Pd N
AcO 15
OCH3 18 OAc
N
Pd N
N
IV Pd
Pd
OAc 19
N
Scheme S3. Proposed catalytic cycle for Pd(II)/Pd(IV) transformation N R N 9, R=OOCCH3 9+H m/z 214.09 10, R=OCH3
Pd N
OAc 16+H m/z 470.06 monomeric oxdative reaction
monomeric reductive elimination
PhI(OAc)2
CH3COOH CH3OH
10+H m/z 186.09 OAc
N
IV Pd N
R
18,R=OCH3 19,R=OOCCH3
Figure S1-(a) is a 1H NMR spectrum of dimmer 4(5.0mg,0.00782mmol) in 0.4 mL acetate-d4 and 0.2 mL methanol-d4 at -30oC. Figure S1-(b) is a 1H NRM spectrum of oxidation of dimmer Pd complexes with PhI(OAc)2 (2.52 mg, 0.00782 mmol) as an oxidant in 0.4 mL acetate-d4 and 0.2 mL methanol-d4 at -30 oC. The latter spectrum clearly shows that the starting material is no longer present. The chemical shift of aromatic region moved to downfield, which indicates the binding interaction of Pd complexes from low-valent-state to high-oxidation-state Pd intermediates.
Figure S1. (a) Dimmer 4 at -30 oC in CD3COOD and CD3COD, (b) oxidation of dimmer 4 with PhI(OAc)2 at -30 oC Figure S2-(a) is a 1H NMR spectrum of the C-H activation of 2-phenylpyridine (7.6 mg, 0.0446 mmol) with Pd(OAc)2 (5 mg, 0.0223 mmol) in 0.4 mL acetate-d4 and 0.2 mL methanol-d4 at 80 oC, then cooled to -30 oC. Figure S2-(b) is a 1H NMR spectrum of oxidation of monomer and dimmer Pd complexes with PhI(OAc)2 (7.2 mg, 0.0223 mmol) in 0.4 mL acetate-d4 and 0.2 mL methanol-d4 at -30 oC. In Figure S2-(a), a pair of doublets is observed at 5.99 and 6.32 ppm, consistent with the presence of the monomeric palladacycle. It is believed that these two peaks represent the two isomers of the monomeric palladacycle.2 The latter spectrum shows that the signal intensity at 5.99 and 6.32 ppm were weaken, indicating that the bonding
interaction from monomeric Pd(II) complexes to monomeric Pd(IV) complexes.
Figure S2. (a) Catalytic reaction after 4h at 80oC then cooled to -30oC in CD3COOD and CD3COD, (b) oxidation of (a) with PhI(OAc)2 at -30oC Comparison of the experimental isotopic distributions of all Pd species to the theoretical isotopic distributions (Figure S3a-k) and the relative errors of detection were less than 2 ppm. Figure S3 The experimental isotopic distributions and the theoretical isotopic distributions of all Pd complexes
a
c
b
d
e
f
g
h
i
j
k
Reference 1. (a) Powers, D. C.; Geibel, M. A. L.; Klein, J. E. M. N.; Ritter, T., Bimetallic Palladium Catalysis: Direct Observation of Pd(III)−Pd(III) Intermediates. Journal of
the American Chemical Society 2009, 131 (47), 17050-17051; (b) Racowski, J. M.; Dick, A. R.; Sanford, M. S., Detailed Study of C−O and C−C Bond-Forming Reductive Elimination from Stable C2N2O2−Ligated Palladium(IV) Complexes. Journal of the American Chemical Society 2009, 131 (31), 10974-10983. 2. Deprez, N. R.; Sanford, M. S., Synthetic and Mechanistic Studies of Pd-Catalyzed C−H Arylation with Diaryliodonium Salts: Evidence for a Bimetallic High Oxidation State Pd Intermediate. Journal of the American Chemical Society 2009, 131 (31), 11234-11241.
intermediates, which were detected at 11 m/z 415.04 as well as [8+H]+ m/z 380.01 and [16+H]+ m/z 475.06. While, the monomeric Pd(IV) intermediates 14 at m/z 445.05 and 15 at m/z 473.05 may have two possible formulations (Scheme S2). The complexes 14 and 15 were directly detected by ESI-MS. On the other hand, complexes 14 and 15 may be formed from 18 and 19 corresponding at the condition of ESI-MS by loss of an acetate ion. Consequently, Pd(II) complex 16 is formed from reductive elimination of Pd(IV) intermediates 17 and 18, which can be distinguished from 15 by high resolution ESI-MS. A possible mechanism was proposed for this transformation (Scheme S3). Scheme S1. Proposed Mechanism for C-H Activation of 2-phenylpyridine with a mole ratio 2:1. N
N
3
Pd
Pd
N
N
11 m/z 415.04 N
N
12 m/z 570.12
Pd(OAc)2
3 3+H m/z 156.08
Pd Pd N
O
N
O 3
O Pd
O Pd
N
N
N 5 m/z 580.95 13 m/z 736.02
Scheme S2. Two possible formulations for monomeric Pd(IV) intermediates OAc IV
N
N
OCH3 14 IV
N
IV Pd N
AcO 15
OCH3 18 OAc
N
Pd N
N
IV Pd
Pd
OAc 19
N
Scheme S3. Proposed catalytic cycle for Pd(II)/Pd(IV) transformation N R N 9, R=OOCCH3 9+H m/z 214.09 10, R=OCH3
Pd N
OAc 16+H m/z 470.06 monomeric oxdative reaction
monomeric reductive elimination
PhI(OAc)2
CH3COOH CH3OH
10+H m/z 186.09 OAc
N
IV Pd N
R
18,R=OCH3 19,R=OOCCH3
Figure S1-(a) is a 1H NMR spectrum of dimmer 4(5.0mg,0.00782mmol) in 0.4 mL acetate-d4 and 0.2 mL methanol-d4 at -30oC. Figure S1-(b) is a 1H NRM spectrum of oxidation of dimmer Pd complexes with PhI(OAc)2 (2.52 mg, 0.00782 mmol) as an oxidant in 0.4 mL acetate-d4 and 0.2 mL methanol-d4 at -30 oC. The latter spectrum clearly shows that the starting material is no longer present. The chemical shift of aromatic region moved to downfield, which indicates the binding interaction of Pd complexes from low-valent-state to high-oxidation-state Pd intermediates.
Figure S1. (a) Dimmer 4 at -30 oC in CD3COOD and CD3COD, (b) oxidation of dimmer 4 with PhI(OAc)2 at -30 oC Figure S2-(a) is a 1H NMR spectrum of the C-H activation of 2-phenylpyridine (7.6 mg, 0.0446 mmol) with Pd(OAc)2 (5 mg, 0.0223 mmol) in 0.4 mL acetate-d4 and 0.2 mL methanol-d4 at 80 oC, then cooled to -30 oC. Figure S2-(b) is a 1H NMR spectrum of oxidation of monomer and dimmer Pd complexes with PhI(OAc)2 (7.2 mg, 0.0223 mmol) in 0.4 mL acetate-d4 and 0.2 mL methanol-d4 at -30 oC. In Figure S2-(a), a pair of doublets is observed at 5.99 and 6.32 ppm, consistent with the presence of the monomeric palladacycle. It is believed that these two peaks represent the two isomers of the monomeric palladacycle.2 The latter spectrum shows that the signal intensity at 5.99 and 6.32 ppm were weaken, indicating that the bonding
interaction from monomeric Pd(II) complexes to monomeric Pd(IV) complexes.
Figure S2. (a) Catalytic reaction after 4h at 80oC then cooled to -30oC in CD3COOD and CD3COD, (b) oxidation of (a) with PhI(OAc)2 at -30oC Comparison of the experimental isotopic distributions of all Pd species to the theoretical isotopic distributions (Figure S3a-k) and the relative errors of detection were less than 2 ppm. Figure S3 The experimental isotopic distributions and the theoretical isotopic distributions of all Pd complexes
a
c
b
d
e
f
g
h
i
j
k
Reference 1. (a) Powers, D. C.; Geibel, M. A. L.; Klein, J. E. M. N.; Ritter, T., Bimetallic Palladium Catalysis: Direct Observation of Pd(III)−Pd(III) Intermediates. Journal of
the American Chemical Society 2009, 131 (47), 17050-17051; (b) Racowski, J. M.; Dick, A. R.; Sanford, M. S., Detailed Study of C−O and C−C Bond-Forming Reductive Elimination from Stable C2N2O2−Ligated Palladium(IV) Complexes. Journal of the American Chemical Society 2009, 131 (31), 10974-10983. 2. Deprez, N. R.; Sanford, M. S., Synthetic and Mechanistic Studies of Pd-Catalyzed C−H Arylation with Diaryliodonium Salts: Evidence for a Bimetallic High Oxidation State Pd Intermediate. Journal of the American Chemical Society 2009, 131 (31), 11234-11241.
