A Metal–Organic Framework as a Multiphoton Excitation Regulator for the Activation of Inert C(sp³)−H Bonds and Oxygen

Abstract

The activation and oxidization of inert C(sp 3 )ÀH bonds into value-added chemicals affords attractively economic and ecological benefits as well as central challenge in modern chemistry.I nspired by the natural enzymatic transformation, herein, we report an ew multiphoton excitation approach to activate the inert C(sp 3 ) À Hb onds and oxygen by integrating the photoinduced electron transfer (PET), ligand-to-metal charge transfer (LMCT) and hydrogen atom transfer (HAT) events together into one metal-organic framework. The wellmodified nicotinamide adenine dinucleotide (NAD + )m imics oxidized Ce III -OEt moieties to generate Ce IV -OEt chromophore and its reduced state mimics NADC via PET.The in situ formed Ce IV -OEt moiety triggers aL MCT excitation to form the alkoxy radical EtOC,a bstracts ah ydrogen atom from the C(sp 3 )ÀHb ond, accompanying the recovery of Ce III -OEt and the formation of alkylr adicals.T he formed NADC activates oxygen to regenerate the NAD + for next recycle,w herein, the activated oxygen species interacts with the intermediates for the oxidization functionalization, paving ac atalytic avenue for developing scalable and sustainable synthetic strategy.

Heterogeneous Photocatalytic Strategies for C(sp3)−H Activation

“…Reactive radical species can directly abstract H atoms from C(sp 3 )−H, [66,89,103,106,123–124] resulting in C(sp 3 )−H activation in a similar manner with HAT [8] as shown in Figure 1e. Typically, there are three types of reactive radical species: 1) reactive oxygen species (⋅OH, O 2 ⋅ − , ⋅OOH), the most important intermediates for photocatalytic C(sp 3 )−H oxidation, can be generated in situ via reduction and/or oxidation reaction(s) [111] ; 2) reactive radical species generated on the surface of photocatalysts such as O⋅ −[64,75,81,125–126] , S⋅ −[65–66,127] ; 3) reactive radical species generated from HAT reagents [106,123–124,128–130] .…”

Heterogeneous Photocatalytic Strategies for C(sp3)−H Activation

“…Reactive radical species can directly abstract H atoms from C(sp 3 )−H, [66,89,103,106,123–124] resulting in C(sp 3 )−H activation in a similar manner with HAT [8] as shown in Figure 1e. Typically, there are three types of reactive radical species: 1) reactive oxygen species (⋅OH, O 2 ⋅ − , ⋅OOH), the most important intermediates for photocatalytic C(sp 3 )−H oxidation, can be generated in situ via reduction and/or oxidation reaction(s) [111] ; 2) reactive radical species generated on the surface of photocatalysts such as O⋅ −[64,75,81,125–126] , S⋅ −[65–66,127] ; 3) reactive radical species generated from HAT reagents [106,123–124,128–130] .…”

“…Active sites play a key role in adsorption of the reactants and activation of the C(sp 3 )−H, and versatile strategies for design of active sites have been developed: 1) Many excellent works have focused on employing MOFs as functional platforms for precise design of active sites for C(sp 3 )−H activation [74,102–104] . For instance, Schröder et al.…”

“…In the past decade, metal–organic frameworks (MOFs), a class of crystalline porous materials with well‐defined and tailorable structures, [99–100] have become one of the most promising heterogeneous photocatalysts for C(sp 3 )−H activation [74,101–106] . However, the issue regarding MOFs as semiconductors or molecules assembled in a periodic manner remains highly controversial, [107–108] both semiconductor [109] and charge transfer process [110] have been proposed.…”

“…Heterogeneous photocatalytic C(sp 3 )−H activation of C 2+ alkanes is very attractive and versatile types of reactions have been reported, for example, producing alkene via dehydrogenation reaction, [51,165] formation of oxygenates via selective oxidation, [70,102,113,166] functionalization of C 2+ alkanes via C−C formation [103,130,167] …”