Construction of C-C bonds via photoreductive coupling of ketones and aldehydes in the metal-organic-framework MFM-300(Cr)

Abstract

Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, particularly ketones, and this renders the formation of ketyl radicals extremely endergonic. Here, we report the efficient activation of carbonyl compounds by the formation of specific host-guest interactions in a hydroxyl-decorated porous photocatalyst. MFM-300(Cr) exhibits a band gap of 1.75 eV and shows excellent catalytic activity and stability towards the photoreductive coupling of 30 different aldehydes and ketones to the corresponding 1,2-diols at room temperature. Synchrotron X-ray diffraction and electron paramagnetic resonance spectroscopy confirm the generation of ketyl radicals via confinement within MFM-300(Cr). This protocol removes simultaneously the need for a precious metal-based photocatalyst or for amine-based sacrificial agents for the photochemical synthesis.

Developing highly reducing conjugated porous polymer: a metal-free and recyclable approach with superior performance for pinacol C–C coupling under visible light

“…On the basis of the aforementioned observations and previous reports, 7 the reaction pathway was proposed as exemplified by pinacol C–C coupling of 1a , as shown in Fig. 4.…”

“…6 Notably, various photocatalysts have been reported to promote the pinacol C–C coupling in a catalytic fashion by using inexpensive amines or sodium sulphite as sacrificial reductants under visible-light irradiation. 7 Nevertheless, the known examples mainly involve the utilisation of metals or suffer from a limited scope. In this regard, we were wondering whether POPs can offer an advantageous choice for photocatalytic pinacol C–C coupling.…”

Accelerated Direct Hydroxylation of Aryl Chlorides with Water to Phenols via the Proximity Effect in a Heterogeneous Metallaphotocatalyst

“…The negative shift in the conduction band edge of Ni­(II)-bpy-COF-5 relative to that of bpy-COF was attributed to the delocalized intramolecular charge transfer from the COF support to the Ni­(II) species. Moreover, considering the highly positive potential of the HOMO in Ni­(II)-bpy-COF-5, H 2 O could be theoretically oxidized to hydroxyl radicals ( • OH) under basic conditions upon photon excitation . Overall, Ni­(II)-bpy-COF-5 demonstrated promising potential in promoting visible-light-induced photocatalytic reactions.…”

Photocatalytic Abstraction of Hydrogen Atoms from Water Using Hydroxylated Graphitic Carbon Nitride for Hydrogenative Coupling Reactions

“…[6] Electrocatalytic water oxidation provides an alternative pathway for selective hydrogenation of acetylene, [7] nitrobenzene, [8] and aldehydes, [9] although designed electrocatalysts and precious ion exchange membranes are required. Photocatalytic hydrogenation of ketones, alkenes, and nitroaromatics can be realized under proper irradiation in the presence of electron donors (e.g., Na 2 SO 3 , alcohols, triethylamine), [10] which are oxidized instead of water; moreover, in the case of organic electron/hydrogen donors, the hydrogen source is unlikely to be water. [11] A recent work shows that photocatalytic hydrogenation of CO 2 using pure water is feasible, though the yield (0.8 μmol) and reaction rate ( � 0.15 μmol h À 1 ) needs significant enhancement for large-scale applications.…”