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 -