Mixed‐Phase 2D‐MoS₂ as an Effective Photocatalyst for Selective Aerobic Oxidative Coupling of Amines under Visible‐Light Irradiation

Abstract

Metal-semiconductor heterojunctions play a vital role in photocatalysis, yet their preparation can be exceedingly difficult. The heterojunction helps not only to separate the charges and inhibit recombination processes but also to transfer the photogenerated electron/hole to the reacting molecule. Here, we demonstrate 1T (metallic)-2H (semiconducting) phase boundaries intrinsic to individual sheets of chemically exfoliated 2D-MoS can serve as heterojunctions for enhanced photocatalysis in comparison to only semiconducting phase. Due to the abundance of heterojunctions in these multiphasic materials, chemically exfoliated 2D-MoS provides improved stability and transfer of photogenerated charges to the reactants, giving better yield. We demonstrate that this easy to synthesize material is an effective photocatalyst for the aerobic oxidative coupling of amines to imines under visible light irradiation. Given its broad applications, we believe mixed phase 2D-MoS can be of interest to several industrial synthetic applications related to semiconductor-based photocatalysis. As an added advantage, this heterogeneous photocatalyst can be recycled for several times up to five cycles without any significant loss in the activity.

Metal Sulfide Photocatalysis: Visible‐Light‐Induced Organic Transformations

“…Subsequently, metal-semiconductor heterojunction of mixed phase 2D-MoS 2 was reported for the selective oxidation of benzylamines (Scheme 3). [21] The heterojunction between 1T (metallic) and 2H (semiconducting) was exploited for the different phases of the mixed phase MoS 2 . After h vb + and e cb À separation of 2H-MoS 2 , the h vb + induced oxidation of benzylamine occurs at the valence band of 2H-MoS 2 and the reduction reaction with O 2 occurs at 1T-MoS 2 .…”

Non‐emissive RuII Polypyridyl Complexes as Efficient and Selective Photosensitizers for the Photooxidation of Benzylamines

“…In additional experiments, full conversion to the desired products was obtained for substrates 1 e , 1 f , 1 g and 1 h , when the photocatalyst loading was increased to 1 mol % (entries 5–8 in Table ). By contrast, the application of this protocol to other challenging substrates such as α‐methylbenzylamine ( 1 k ), n ‐hexylamine ( 1 l ) or 1,2,3,4‐tetrahydroquinoline ( 1 m ) failed to produce the expected imines in agreement with the results reported for other catalytic systems (entries 11, 12 and 13 in Table ). Consequently, the presence of either steric hindrance on the α‐C as in 1 k , or nonactivated (non‐benzylic) α‐H, as in 1 l and 1 m , is strongly detrimental for this oxidation.…”

Structure design of CeO2–MoS2 composites and their efficient activity for imine synthesis

“…We synthesized a kind of large-dimensional CeO 2 nanoflakes, which showed enhanced catalytic activity for imine synthesis due to the lamellar nanochannels and the abundant surface oxygen vacancies (Ding et al 2018). MoS 2 , another well-known nanoflake material (Tan and Zhang 2015;Li et al 2016;Bedia et al 2019), has just been reported to be used as photocatalyst for amine coupling to form imines (Girish et al 2018). Nevertheless, to our best knowledge, the composite of CeO 2 and MoS 2 as catalyst involved in the synthesis of imines has not been investigated yet.…”