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.

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

KW - HYDROGENATION

KW - NITROGEN-HETEROCYCLES

KW - PHOTOCATALYTIC OXIDATION

KW - REVERSIBLE DEHYDROGENATION

KW - DRIVEN SELECTIVE OXIDATION

KW - PHOTOREDOX CATALYSIS

KW - BASE-FREE DEHYDROGENATION

KW - AMINES

KW - AEROBIC OXIDATION

KW - TiO2

KW - WATER

UR - http://www.scopus.com/inward/record.url?scp=85089680898&partnerID=8YFLogxK

U2 - 10.1021/acscatal.0c00556

DO - 10.1021/acscatal.0c00556

M3 - Article

AN - SCOPUS:85089680898

VL - 10

SP - 5542

EP - 5553

JO - ACS Catalysis

JF - ACS Catalysis

SN - 2155-5435

IS - 10

ER -