The development of catalytic systems capable of oxygenating unactivated C-H bonds with excellent site-selectivity and functional group tolerance under mild conditions remains a challenge. Inspired by the secondary coordination sphere (SCS) hydrogen bonding in metallooxygenases, reported herein is an SCS solvent hydrogen bonding strategy that employs 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as a strong hydrogen bond donor solvent to enable remote C-H hydroxylation in the presence of basic aza-heteroaromatic rings with a low loading of a readily available and inexpensive manganese complex as a catalyst and hydrogen peroxide as a terminal oxidant. We demonstrate that this strategy represents a promising compliment to the current state-of-the-art protection approaches that rely on precomplexation with strong Lewis and/or Brønsted acids. Mechanistic studies with experimental and theoretical approaches reveal the existence of a strong hydrogen bonding between the nitrogen-containing substrate and HFIP, which prevents the catalyst deactivation by nitrogen binding and deactivates the basic nitrogen atom toward oxygen atom transfer and the α-C-H bonds adjacent to the nitrogen center toward H-atom abstraction. Moreover, the hydrogen bonding exerted by HFIP has also been demonstrated not only to facilitate the O-O bond heterolytic cleavage of a putative MnIII-OOH precursor to generate MnV(O)(OC(O)CH2Br) as an active oxidant but also to affect the stability and the activity of MnV(O)(OC(O)CH2Br).
Bibliographical noteFunding Information:
This work was supported by the National Natural Science Foundation of China (21771087 to B.W., 21703080 to J.C., and 21873052 to Y.W.), the NSF of Shandong Province (ZR2020YQ10 to B.W. and ZR2022MB005 to J.C.), Taishan Scholar Program of Shandong Province (tsqn201812078 to B.W.), and the NRF of Korea (NRF-2021R1A3B1076539 to W.N. and NRF-2020R1I1A1A01074630 to Y.-M.L.).
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