Abstract
A pincer iridium(III) complex, (Phebox)Ir(OAc)2OH2 (1) (Phebox = 3,5-dimethylphenyl-2,6-bis(oxazolinyl)), selectively cleaves the benzylic C-H bond of mesitylene to form an isolable iridium mesityl complex, (Phebox)Ir(mesityl)(OAc) (3), in >90% yield. The trifluoroacetate analogue, (Phebox)Ir(OCOCF3)2OH2 (2), was synthesized to compare with complex 1 for C-H activation, and (Phebox)Ir(mesityl)(OCOCF3) (4) was synthesized by ligand exchange of complex 3. Both complexes 1 and 2 catalyze H/D exchange between mesitylene and D2O at 180 °C, exclusively at the benzylic position; 2 gave a higher turnover number (11 TO) than 1 (6 TO) in 12 h. Using d4-acetic acid as the source of deuterium, up to 92 turnovers of benzylic H/D exchange of mesitylene were obtained with complex 1. (Phebox)Ir(OCOCF3)2OH2 catalyzed the benzylic C-H oxidation of mesitylene using Ag2O as a terminal oxidant at 130 C, to form 3,5-dimethylbenzaldehyde and 3,5-dimethylbenzoic acid in 35% ± 4% yield (5.1 ± 0.6 TO). DFT calculations were used to investigate two possible pathways for the catalytic oxidation of mesitylene: (1) C-H activation followed by oxy-functionalization and (2) Ir-oxo formation followed by outer-sphere C-H hydroxylation. Results of calculations of the C-H activation pathway appear to be the more consistent with the experimental observations. (Chemical Equation Presented).
| Original language | English |
|---|---|
| Pages (from-to) | 2879-2888 |
| Number of pages | 10 |
| Journal | Organometallics |
| Volume | 34 |
| Issue number | 12 |
| DOIs | |
| Publication status | Published - Jun 22 2015 |
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ASJC Scopus subject areas
- Organic Chemistry
- Physical and Theoretical Chemistry
- Inorganic Chemistry
Cite this
Activation and Oxidation of Mesitylene C-H Bonds by (Phebox)Iridium(III) Complexes. / Zhou, Meng; Johnson, Samantha I.; Gao, Yang; Emge, Thomas J.; Nielsen, Robert J.; Goddard, William A.; Goldman, Alan S.
In: Organometallics, Vol. 34, No. 12, 22.06.2015, p. 2879-2888.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Activation and Oxidation of Mesitylene C-H Bonds by (Phebox)Iridium(III) Complexes
AU - Zhou, Meng
AU - Johnson, Samantha I.
AU - Gao, Yang
AU - Emge, Thomas J.
AU - Nielsen, Robert J.
AU - Goddard, William A.
AU - Goldman, Alan S
PY - 2015/6/22
Y1 - 2015/6/22
N2 - A pincer iridium(III) complex, (Phebox)Ir(OAc)2OH2 (1) (Phebox = 3,5-dimethylphenyl-2,6-bis(oxazolinyl)), selectively cleaves the benzylic C-H bond of mesitylene to form an isolable iridium mesityl complex, (Phebox)Ir(mesityl)(OAc) (3), in >90% yield. The trifluoroacetate analogue, (Phebox)Ir(OCOCF3)2OH2 (2), was synthesized to compare with complex 1 for C-H activation, and (Phebox)Ir(mesityl)(OCOCF3) (4) was synthesized by ligand exchange of complex 3. Both complexes 1 and 2 catalyze H/D exchange between mesitylene and D2O at 180 °C, exclusively at the benzylic position; 2 gave a higher turnover number (11 TO) than 1 (6 TO) in 12 h. Using d4-acetic acid as the source of deuterium, up to 92 turnovers of benzylic H/D exchange of mesitylene were obtained with complex 1. (Phebox)Ir(OCOCF3)2OH2 catalyzed the benzylic C-H oxidation of mesitylene using Ag2O as a terminal oxidant at 130 C, to form 3,5-dimethylbenzaldehyde and 3,5-dimethylbenzoic acid in 35% ± 4% yield (5.1 ± 0.6 TO). DFT calculations were used to investigate two possible pathways for the catalytic oxidation of mesitylene: (1) C-H activation followed by oxy-functionalization and (2) Ir-oxo formation followed by outer-sphere C-H hydroxylation. Results of calculations of the C-H activation pathway appear to be the more consistent with the experimental observations. (Chemical Equation Presented).
AB - A pincer iridium(III) complex, (Phebox)Ir(OAc)2OH2 (1) (Phebox = 3,5-dimethylphenyl-2,6-bis(oxazolinyl)), selectively cleaves the benzylic C-H bond of mesitylene to form an isolable iridium mesityl complex, (Phebox)Ir(mesityl)(OAc) (3), in >90% yield. The trifluoroacetate analogue, (Phebox)Ir(OCOCF3)2OH2 (2), was synthesized to compare with complex 1 for C-H activation, and (Phebox)Ir(mesityl)(OCOCF3) (4) was synthesized by ligand exchange of complex 3. Both complexes 1 and 2 catalyze H/D exchange between mesitylene and D2O at 180 °C, exclusively at the benzylic position; 2 gave a higher turnover number (11 TO) than 1 (6 TO) in 12 h. Using d4-acetic acid as the source of deuterium, up to 92 turnovers of benzylic H/D exchange of mesitylene were obtained with complex 1. (Phebox)Ir(OCOCF3)2OH2 catalyzed the benzylic C-H oxidation of mesitylene using Ag2O as a terminal oxidant at 130 C, to form 3,5-dimethylbenzaldehyde and 3,5-dimethylbenzoic acid in 35% ± 4% yield (5.1 ± 0.6 TO). DFT calculations were used to investigate two possible pathways for the catalytic oxidation of mesitylene: (1) C-H activation followed by oxy-functionalization and (2) Ir-oxo formation followed by outer-sphere C-H hydroxylation. Results of calculations of the C-H activation pathway appear to be the more consistent with the experimental observations. (Chemical Equation Presented).
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U2 - 10.1021/acs.organomet.5b00200
DO - 10.1021/acs.organomet.5b00200
M3 - Article
AN - SCOPUS:84934942165
VL - 34
SP - 2879
EP - 2888
JO - Organometallics
JF - Organometallics
SN - 0276-7333
IS - 12
ER -