Visible Light Mediated Cyclization of Tertiary Anilines with Maleimides Using Nickel(II) Oxide Surface-Modified Titanium Dioxide Catalyst

Abstract

Surface-modified titanium dioxides by highly dispersed NiO particles have an extended absorption in the visible light region and a reduced hole-electron pair recombination than unmodified TiO2. They have now been successfully applied as highly active heterogeneous photocatalysts in the visible light mediated direct cyclization of tertiary anilines with maleimides to give tetrahydroquinoline products in moderate to high yields at ambient temperature. In contrast with unmodified titanium dioxide catalysts that are conventionally used in a stoichiometric amount in combination with UVA light, only a catalytic amount (1 mol %) of the surface-modified TiO2 catalyst is needed along with visible light to efficiently catalyze the reaction. Compared with transition-metal complexes such as Ru(bpy)3Cl2 or Ir(ppy)2(dtbbpy)PF6, advantages of these surface-modified titanium dioxides as photocatalyst include high catalytic activity, low cost, ease of recovering, and being able to be used for at least nine times without significant decay of catalytic activity.

Design of Novel Visible Light Active Photocatalyst Materials: Surface Modified TiO2

“…In experimental work from a number of groups [73,77,78,[89][90][91][92][93][94]102,103,[112][113][114][115][116][117] doped TiO2 system, we consider N-F co-doped TiO2 [118] which shows visible light absorption, but no photocurrent. The surface modification approach has the potential to alleviate some of these issues with doped TiO2.…”

“…Tang et al [112] prepared NiO-modified TiO2 using the CCC approach of Tada for visible light mediated functionalization of the sp 3 C-H bond in the cyclization reaction of N,N-dimethylaniline with maleimides to form tetrahydroquinoline products. Actually, this is also the first report of using surface modified TiO2 for organic synthesis.…”

Studies in organic and physical photochemistry – an interdisciplinary approach

“…In this reaction, the furanone substrate acts as an oxidant in the rearomatization step when the tricyclic radical intermediate (194) The tandem addition cyclization reaction of aniline derivatives with furanones was also performed with inorganic semiconductors such as TiO2 or ZnS as photochemical electron transfer sensitizer thus applying heterogeneous photocatalysis. 158,159 As in the case of homogeneous photocatalysis, corresponding isotopic labeling experiments gave a deep insight in the some mechanistic steps of the reaction.…”

Nanoscale TiO2 films and their application in remediation of organic pollutants

“…Therefore, it has become imperative to improve TiO 2 photocatalytic efficiency by extending its absorption threshold from the UV-light region to the visible-light region which comprises a larger portion of the solar spectrum in terms of energy availability ( 45% of solar light) and reducing the rate of recombination of the photo-generated electron/hole pairs [28][29][30]. To overcome these limitations, several approaches have been employed to enhance the photocatalytic activity of TiO 2 , including dye sensitization [31,32], doping with metals (e.g., Ag, Cu, Co, Fe, Ce, Al, Cr, Mo, Ni, etc.) [3,…”