Bipyridyl-Containing Cadmium–Organic Frameworks for Efficient Photocatalytic Oxidation of Benzylamine

Abstract

Metal–organic frameworks (MOFs) have attracted increased research attention in photocatalysis due to their great potential in light harvest and conversion. However, the organic transformations as photocatalyzed by MOFs under mild conditions yet remain a challenge. Herein, three bipyridyl-containing cadmium–organic frameworks Cd­(dcbpy) (dcbpy = 2,2′-bipyridine-5,5′-dicarboxylate), Cd­(bdc)­(bpy) (bdc = 1,4-benzenedicarboxylate; bpy = 2,2′-bipyridyl), and Cd­(bdc)­(2Me-bpy) (2Me-bpy = 4,4′-dimethyl-2,2′-bipyridyl) were synthesized for the first time. The bpy-containing Cd-MOFs have strong light harvest abilities and suitable photocatalysis energy potentials, making them highly active and selective for the photo-oxidation of benzylamine to N-benzylbenzaldimine under mild conditions, i.e., using atmospheric air as oxidant, at room temperature, and in the absence of any photosensitizer or cocatalyst. It provides an efficient, economical, and green way for the direct oxidation of amines to produce imines.

Visible-Light-Induced Selective Oxidation of Amines into Imines over UiO-66-NH2@Au@COF Core–Shell Photocatalysts

“…Compared with conventional thermocatalysis, photocatalysis as an environmentally friendly and cost-effective method has attracted widespread attention for chemical synthesis at room temperature. − Up to now, a series of traditional semiconductors such as TiO 2 , CdS, and C 3 N 4 have been extensively explored for the visible-light-driven selective oxidation of amines to imines; − however, their poor structure adjustment and low photocatalytic efficiency have limited their further applications in photocatalysis. Recently, emerging metal–organic frameworks (MOFs) with large surface areas and adjustable pores have attracted increasing attention as promising photocatalysts for organic synthesis because the metal-containing clusters in MOFs can act as semiconductor dots and the organic linkers as photoinduced electron initiators to complete the electron transfer via the linker to the metal cluster charge-transfer (LCCT) route. − However, some intrinsic defects of MOFs, like poor visible-light adsorption and low stability as well as deficient efficiency of light utilization, have greatly restricted their practical applications.…”

Reduced Phosphomolybdate Hybrids as Efficient Visible-Light Photocatalysts for Cr(VI) Reduction

“…N-containing ligands play an important role in the stability of the POM structure. 49,50 Here, 4,4′-dimethyl-2,2′-bipyridine (mbpy) has been selected as the organic component to maintain the structure. Different from traditional bipyridine ligands, the modified methyl groups in mbpy could cause a σ−π hyperconjugative effect between the pyridine rings and methyl.…”

“…Such an effect can reduce the energy of the system, lead to a red shift in the absorption peak, and increase the absorption intensity, which is more conducive to light absorption. 49,50 On the basis of the above consideration, three hourglass- ] 2 } form 1D chainlike and 2D-layered structures. Hybrids 1−3 display strong light adsorption and suitable energy band structure and exhibit a highly efficient and recyclable photocatalytic performance for the reduction of Cr(VI) with isopropyl alcohol (IPA) as the scavenger and visible-light irradiation.…”

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…This results in high photocatalytic yield under visible light conditions (Figure 11), even higher than those measured on UiO-66-NH 2 and MIL-125-NH 2 under similar conditions [229,230]. Bipyridyl-containing cadmium-MOFs, Cd(dcbpy) show high light-harvesting properties as well as high activity and selectivity towards photo-oxidation of benzylamine to N-benzylbenzaldimine under visible light irradiation at room temperature, without any photosensitizer or co-catalyst [231]. Actually, they show higher activity than conventional inorganic semiconductors, such as TiO 2 , Nb 2 O 5 , WO 3 , even doped with noble metals, under similar conditions.…”