Details
| Original language | English |
|---|---|
| Pages (from-to) | 10694-10704 |
| Number of pages | 11 |
| Journal | ACS catalysis |
| Volume | 9 |
| Issue number | 12 |
| Early online date | 15 Oct 2019 |
| Publication status | Published - 6 Dec 2019 |
Abstract
Herein, the visible-light-induced dehydrogenation of N-heterocycles such as tetrahydroquinolines, tetrahydroisoquinolines, and indolines in O2-containing suspensions of a commercially available titanium dioxide photocatalyst yielding the corresponding heteroarenes is presented. 4-Amino-2,2,6,6-tetramethylpipiridinyloxyl (4-amino-TEMPO) was found to exhibit a beneficial role, as it increased the yield and improved the selectivity of the dehydrogenation reaction. Both the selectivity and the yield are further enhanced by grafting 0.1 wt % of Ni(II) ions onto the TiO2 surface. It is proposed that the basic reactant adsorbs at Lewis acid sites present at the TiO2 surface. The dehydrogenation reaction is initiated by visible-light excitation of the resulting surface complex and a subsequent single-electron transfer from the excited N-heterocycle via the conduction band of TiO2 to O2. Ni(II) ions possibly serve as an electron transfer bridge between the conduction band of TiO2 and O2, while the TEMPO derivative is assumed to act as a selective redox mediator involved in reactions of the generated reactive oxygen species.
Keywords
- dehydrogenation, N-heterocyclic amines, surface complex, TiO, visible light
ASJC Scopus subject areas
- Chemical Engineering(all)
- Catalysis
- Chemistry(all)
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In: ACS catalysis, Vol. 9, No. 12, 06.12.2019, p. 10694-10704.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Visible-Light-Mediated Photocatalytic Aerobic Dehydrogenation of N-heterocycles by Surface-Grafted TiO2 and 4-amino-TEMPO
AU - Balayeva, Narmina O.
AU - Zheng, Nan
AU - Dillert, Ralf
AU - Bahnemann, Detlef W.
N1 - Funding Information: N.O.B. gratefully acknowledges financial support from the Graduate Academy of Leibniz University Hannover in the framework of a “Research Stay Abroad Program” at the University of Arkansas, Chemistry and Biochemistry Department. The authors thank M. Sc. Barbara Nunes from Prof. D. Bahnemann’s group, Institute of Technical Chemistry at the Leibniz University of Hannover, for XRD and TEM measurements and M. Sc. Malte Schäfer from Prof. P. Behrens’ group, Institute of Inorganic Chemistry at the Leibniz University of Hannover, for BET (physisorption isotherms) measurements. The Institute of Geology for ICP-OES equipment, the Laboratorium für Nano- und Quantenengineering (LNQE) for TEM equipment, and the Institute of Inorganic Chemistry at the Leibniz University of Hannover for ATR-FTIR and BET equipment are kindly acknowledged.
PY - 2019/12/6
Y1 - 2019/12/6
N2 - Herein, the visible-light-induced dehydrogenation of N-heterocycles such as tetrahydroquinolines, tetrahydroisoquinolines, and indolines in O2-containing suspensions of a commercially available titanium dioxide photocatalyst yielding the corresponding heteroarenes is presented. 4-Amino-2,2,6,6-tetramethylpipiridinyloxyl (4-amino-TEMPO) was found to exhibit a beneficial role, as it increased the yield and improved the selectivity of the dehydrogenation reaction. Both the selectivity and the yield are further enhanced by grafting 0.1 wt % of Ni(II) ions onto the TiO2 surface. It is proposed that the basic reactant adsorbs at Lewis acid sites present at the TiO2 surface. The dehydrogenation reaction is initiated by visible-light excitation of the resulting surface complex and a subsequent single-electron transfer from the excited N-heterocycle via the conduction band of TiO2 to O2. Ni(II) ions possibly serve as an electron transfer bridge between the conduction band of TiO2 and O2, while the TEMPO derivative is assumed to act as a selective redox mediator involved in reactions of the generated reactive oxygen species.
AB - Herein, the visible-light-induced dehydrogenation of N-heterocycles such as tetrahydroquinolines, tetrahydroisoquinolines, and indolines in O2-containing suspensions of a commercially available titanium dioxide photocatalyst yielding the corresponding heteroarenes is presented. 4-Amino-2,2,6,6-tetramethylpipiridinyloxyl (4-amino-TEMPO) was found to exhibit a beneficial role, as it increased the yield and improved the selectivity of the dehydrogenation reaction. Both the selectivity and the yield are further enhanced by grafting 0.1 wt % of Ni(II) ions onto the TiO2 surface. It is proposed that the basic reactant adsorbs at Lewis acid sites present at the TiO2 surface. The dehydrogenation reaction is initiated by visible-light excitation of the resulting surface complex and a subsequent single-electron transfer from the excited N-heterocycle via the conduction band of TiO2 to O2. Ni(II) ions possibly serve as an electron transfer bridge between the conduction band of TiO2 and O2, while the TEMPO derivative is assumed to act as a selective redox mediator involved in reactions of the generated reactive oxygen species.
KW - dehydrogenation
KW - N-heterocyclic amines
KW - surface complex
KW - TiO
KW - visible light
UR - http://www.scopus.com/inward/record.url?scp=85074800473&partnerID=8YFLogxK
U2 - 10.1021/acscatal.9b03322
DO - 10.1021/acscatal.9b03322
M3 - Article
AN - SCOPUS:85074800473
VL - 9
SP - 10694
EP - 10704
JO - ACS catalysis
JF - ACS catalysis
SN - 2155-5435
IS - 12
ER -