Details
| Original language | English |
|---|---|
| Pages (from-to) | 5542-5553 |
| Number of pages | 12 |
| Journal | ACS catalysis |
| Volume | 10 |
| Issue number | 10 |
| Early online date | 9 Apr 2020 |
| Publication status | Published - 15 May 2020 |
Abstract
TiO2 is an effective and extensively employed photocatalyst, but its practical use in visible-light-mediated organic synthesis is mainly hindered by its wide band gap energy. Herein, we have discovered that Rh-photodeposited TiO2 nanoparticles selectively dehydrogenate N-heterocyclic amines with the concomitant generation of molecular hydrogen gas in an inert atmosphere under visible light (λmax = 453 nm) illumination at room temperature. Initially, a visible-light-sensitive surface complex is formed between the N-heterocycle and TiO2. The acceptorless dehydrogenation of N-heterocycles is initiated by direct electron transfer from the HOMO energy level of the amine via the conduction band of TiO2 to the Rh nanoparticle. The reaction condition was optimized by examining different photodeposited noble metals on the surface of TiO2 and solvents, finding that Rh0 is the most efficient cocatalyst, and 2-propanol is the optimal solvent. Structurally diverse N-heterocycles such as tetrahydroquinolines, tetrahydroisoquinolines, indolines, and others bearing electron-deficient as well as electron-rich substituents underwent the dehydrogenation in good to excellent yields. The amount of released hydrogen gas evinces that only the N-heterocyclic amines are oxidized rather than the dispersant. This developed method demonstrates how UV-active TiO2 can be employed in visible-light-induced synthetic dehydrogenation of amines and simultaneous hydrogen storage applications.
Keywords
- acceptorless dehydrogenation, N-heterocycles, surface complex, TiO, visible-light
ASJC Scopus subject areas
- Chemical Engineering(all)
- Catalysis
- Chemistry(all)
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In: ACS catalysis, Vol. 10, No. 10, 15.05.2020, p. 5542-5553.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Rh/TiO2-Photocatalyzed Acceptorless Dehydrogenation of N-Heterocycles upon Visible-Light Illumination
AU - Balayeva, Narmina O.
AU - Mamiyev, Zamin
AU - Dillert, Ralf
AU - Zheng, Nan
AU - Bahnemann, Detlef W.
N1 - Funding information: N.O.B. gratefully acknowledges financial support from the Graduate Academy of Leibniz University Hannover for the Completion Scholarship. The authors thank M. Sc. Barbara Nunes and Dr. Luis Granone from Prof. D. Bahnemann’s group, Institute of Technical Chemistry at the Leibniz University of Hannover, for TEM and XRD measurements, respectively. The Institute of Mineralogy for ICP-OES, the Laboratorium für Nano- und Quantenengineering (LNQE) for TEM, Institute of Solid State Physics for XPS, and Institute of Organic Chemistry for NMR equipment are kindly acknowledged.
PY - 2020/5/15
Y1 - 2020/5/15
N2 - TiO2 is an effective and extensively employed photocatalyst, but its practical use in visible-light-mediated organic synthesis is mainly hindered by its wide band gap energy. Herein, we have discovered that Rh-photodeposited TiO2 nanoparticles selectively dehydrogenate N-heterocyclic amines with the concomitant generation of molecular hydrogen gas in an inert atmosphere under visible light (λmax = 453 nm) illumination at room temperature. Initially, a visible-light-sensitive surface complex is formed between the N-heterocycle and TiO2. The acceptorless dehydrogenation of N-heterocycles is initiated by direct electron transfer from the HOMO energy level of the amine via the conduction band of TiO2 to the Rh nanoparticle. The reaction condition was optimized by examining different photodeposited noble metals on the surface of TiO2 and solvents, finding that Rh0 is the most efficient cocatalyst, and 2-propanol is the optimal solvent. Structurally diverse N-heterocycles such as tetrahydroquinolines, tetrahydroisoquinolines, indolines, and others bearing electron-deficient as well as electron-rich substituents underwent the dehydrogenation in good to excellent yields. The amount of released hydrogen gas evinces that only the N-heterocyclic amines are oxidized rather than the dispersant. This developed method demonstrates how UV-active TiO2 can be employed in visible-light-induced synthetic dehydrogenation of amines and simultaneous hydrogen storage applications.
AB - TiO2 is an effective and extensively employed photocatalyst, but its practical use in visible-light-mediated organic synthesis is mainly hindered by its wide band gap energy. Herein, we have discovered that Rh-photodeposited TiO2 nanoparticles selectively dehydrogenate N-heterocyclic amines with the concomitant generation of molecular hydrogen gas in an inert atmosphere under visible light (λmax = 453 nm) illumination at room temperature. Initially, a visible-light-sensitive surface complex is formed between the N-heterocycle and TiO2. The acceptorless dehydrogenation of N-heterocycles is initiated by direct electron transfer from the HOMO energy level of the amine via the conduction band of TiO2 to the Rh nanoparticle. The reaction condition was optimized by examining different photodeposited noble metals on the surface of TiO2 and solvents, finding that Rh0 is the most efficient cocatalyst, and 2-propanol is the optimal solvent. Structurally diverse N-heterocycles such as tetrahydroquinolines, tetrahydroisoquinolines, indolines, and others bearing electron-deficient as well as electron-rich substituents underwent the dehydrogenation in good to excellent yields. The amount of released hydrogen gas evinces that only the N-heterocyclic amines are oxidized rather than the dispersant. This developed method demonstrates how UV-active TiO2 can be employed in visible-light-induced synthetic dehydrogenation of amines and simultaneous hydrogen storage applications.
KW - acceptorless dehydrogenation
KW - N-heterocycles
KW - surface complex
KW - TiO
KW - visible-light
UR - http://www.scopus.com/inward/record.url?scp=85089680898&partnerID=8YFLogxK
U2 - 10.1021/acscatal.0c00556
DO - 10.1021/acscatal.0c00556
M3 - Article
VL - 10
SP - 5542
EP - 5553
JO - ACS catalysis
JF - ACS catalysis
SN - 2155-5435
IS - 10
ER -