The Origin of Catalytic Benzylic C−H Oxidation over a Redox‐Active Metal–Organic Framework

Abstract

Selective oxidation of benzylic CÀH compounds to ketones is important for the production of a wide range of fine chemicals, and is often achieved using toxic or precious metal catalysts. Herein, we report the efficient oxidation of benzylic C À H groups in a broad range of substrates under mild conditions over a robust metal-organic framework material, MFM-170, incorporating redox-active [Cu 2 II (O 2 CR) 4 ] paddlewheel nodes. A comprehensive investigation employing electron paramagnetic resonance (EPR) spectroscopy and synchrotron X-ray diffraction has identified the critical role of the paddlewheel moiety in activating the oxidant t BuOOH (tertbutyl hydroperoxide) via partial reduction to [Cu II Cu I -(O 2 CR) 4 ] species.

Highly efficient multi-site synergistic catalysis of a polyoxovanadate-based metal–organic framework for benzylic C–H bond oxidation

“…of moles of catalyst used)/reaction time). 40 Under the optimal conditions, 1 catalyzed indane to 1-indanone with a conversion of above 99% and selectivity of 97%, while the blank experiment without any catalyst only reached a low conversion of 35% (Fig. 2a).…”

“…Considering the constituent and structural features of 1 and the related studies reported in the literature, 40,61 we analyze the possible generation pathways of t BuO˙ and t BuOO˙ during the oxidation process of benzylic compounds catalyzed by 1 . Generally, the catalytic site of Cu I is favorable for triggering the formation of the t BuO˙ radical, while both high-valence {V 4 } and Cu II are prone to triggering the formation of the t BuOO˙ radical.…”

“…When t BuOOH and catalyst 1 were added simultaneously, new and strong sextet peaks were observed, which proves the generation of new radicals. 40 The g value of the spin adduct was 2.008, which could be attributed to the characteristic of PBN-spin adducts. According to previous literature studies, 40,[63][64][65] the new sextet peaks could be well attributed to the production of two different radicals of t BuOc and t BuOOc.…”

“…40 The g value of the spin adduct was 2.008, which could be attributed to the characteristic of PBN-spin adducts. According to previous literature studies, 40,[63][64][65] the new sextet peaks could be well attributed to the production of two different radicals of t BuOc and t BuOOc.…”

“…37–39 Schröder's group reported a Cu-MOF containing [Cu 2 II (O 2 CR) 4 ] paddlewheel nodes, which can activate the t BuOOH oxidant through the paddlewheel nodes to oxidize the C–H groups of benzylic compounds under mild conditions. 40 Hu's group reported two organic–inorganic hybrid POM-based compounds, [Cu II (C 2 N 2 H 8 ) 2 ] 4 [Cu II (C 2 N 2 H 8 ) 2 (H 2 O) 2 ] 2 [PNb 12 O 40 V V V IV O 2 ]·(OH) 2 ·11H 2 O and [Co III (C 2 N 2 H 8 ) 3 ] 2 [Co III (C 2 N 2 H 8 ) 2 (H 2 O) 2 ] 0.5 [H 2.5 PNb 12 O 40 V V V IV O 2 ]·20H 2 O, which were proved to effectively promote the conversion of benzyl-alkanes to ketone products in a heterogeneous manner. 41 Niu's research group reported a copper-containing POMOF, Cu I 12 Cl 2 (trz) 8 [HPW 12 O 40 ], which can oxidize diphenylmethane to benzophenone in high yield and its catalytic performance is better than that of most POM-based catalysts without precious metals.…”