Selective oxidation of C–H bonds with Fe-N-C single-atom catalyst

Full text of DOI:10.1016/S1872-2067(17)63002-X

Chinese Journal of Catalysis 39 (2018) 1–3
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
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Selective oxidation of C–H bonds with Fe‐N‐C single‐atom catalyst
Xingwei Li *
Activation of C–H bonds has received considerable attention
in the past decade as this provides an efficient and at‐
om‐economy strategy to access a plethora of value‐added
chemicals from easily available substrates [1]. Nevertheless,
the high stability of C–H bonds poses significant challenge for
selective functionalization. For instance, the selective oxidation
of C–H bonds in hydrocarbons has proved to be high useful in
synthesis of alcohol/ketone feedstocks in both areas of C1
chemistry [2] and organic synthesis [3,4]. However, given the
generally high dissociation energy of C–H bonds and possible
over‐oxidation, it remains challenging to realize both high reac‐
tivity and selectivity.
Fe‐Nx. As shown in Fig. 1, the most reactive moiety for the se‐
lective C‐H oxidation is ascribed to the medium‐spin FeIII‐N5
structure, which is at least 1 order of magnitude more reactive
than the high‐spin and low‐spin FeIII‐N6 structures and 3 times
more reactive than the FeII‐N4 structure. The identification of
Table 1
Selective oxidation of hydrocarbons in water with Fe‐N‐C‐700 as cata‐
lyst.
Recently, a team led by Profs. Tao Zhang and Aiqin Wang at
the Dalian Institute of Chemical Physics (DICP) has reported an
interesting work on the selective oxidation of C–H bonds in
aromatic and aliphatic hydrocarbons [5]. The reactions pro‐
ceeded at room temperature, by using an excess or a stoichio‐
metric amount of tert‐butyl hydroperoxide (TBHP) as an oxi‐
dant and an atomically dispersed (single‐atom catalyst) Fe‐N‐C
as the catalyst. As given in Table 1, a wide scope of substrates,
such as various aromatic hydrocarbons with an elec‐
tron‐donating group (–OMe) or electron‐withdrawing group
(–NO2), heterocyclic substrates and an aliphatic hydrocarbon
(cyclohexane) could be smoothly transformed into the corre‐
sponding ketones with >98% selectivity at high conversions. In
fact, the performance of the heterogeneous Fe‐N‐C catalyst is
well comparable to some homogeneous catalysts such as
[Cu((R,R)‐BPBP)]+ complex [6] in terms of both activity and
selectivity, but it offers additional advantages such as excellent
reusability and water solvent‐compatibility.
A more attractive feature of this work lies in the establish‐
ment of structure‐performance relationship, which is
a
long‐standing interest in the area of heterogeneous catalysis.
The authors made in‐depth characterizations of the catalyst
using a variety of advanced techniques including aberra‐
tion‐corrected HAADF‐STEM, XPS, XAS, ESR, and Mössbauer
spectroscopy. Thus, the coordination sphere of the Fe atom
(which is actually Fe3+) included only nitrogen atoms so as to
form Fe‐Nx (x = 4, 5, and 6) moieties. Significantly, the catalytic
activity is closely correlated to the specific structure of the
Reaction conditions: 10.0 mg of catalyst, 0.5 mmol of substrates, room
temperature for 7 h, 500 μL of TBHP as a 70 wt % aqueous solution (7
equiv) diluted with 6.5 mL of H2O.

2
Xingwei Li / Chinese Journal of Catalysis 39 (2018) 1–3
tion of molecular oxygen. It is believed that this work will open
a door of ample space for the design of robust heterogeneous
single‐atom catalysts to mimic the high activity and selectivity
of enzymes as well as molecular catalysts.
Xingwei Li
Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, Dalian 116023, Liaoning, China
Tel: +86‐411‐84379089
E‐mail: xwli@dicp.ac.cn
Received 25 December 2017
Accepted 27 December 2017
Published 5 January 2018
DOI: 10.1016/S1872‐2067(17)63002‐X
Fig. 1. Schematic diagram of Fe‐N‐C single‐atom catalyst for C–H bond
selective oxidation.
References
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the Fe‐N5 active site will serve to provide guidelines to design
more active catalysts in this system by maximizing the number
of the Fe‐N5 moiety since it only accounts for 18% of the total
Fe species in this work.
The Fe‐Nx‐C catalyst in this work can be viewed as a sin‐
gle‐atom catalyst (SAC) if the surrounding Nx atoms are con‐
sidered as a robust multidentate ligand. Single‐atom catalysis
has recently become a very hot topic since it bodes well to
maximize the metal utilization efficiency, offer unique selectiv‐
ity, and bridge the heterogeneous and homogeneous catalysis
due to the uniform active sites [7–10]. In this work, the Fe‐N5
active site is reminiscent of the structure of a hemoglobin mol‐
ecule [11] which is responsible for the adsorption and activa‐
tion of oxygen in living cells (Fig. 1). In this context, the Fe‐N5
structure provides a good example to bridge mononuclear en‐
zyme catalyst and heterogeneous single‐atom catalyst. Howev‐
er, a tiny change in the micro‐environmental surrounding may
greatly affect the reactivity and selectivity, as exemplified by
the poor capability of the heterogeneous Fe‐N5 sites for activa‐
[11] S. Sahu, D. P. Goldberg, J. Am. Chem. Soc., 2016, 138, 11410–11428.
Graphical Abstract
Chin. J. Catal., 2018, 39: 1–3 doi: 10.1016/S1872‐2067(17)63002‐X
Selective oxidation of C–H bonds with Fe‐N‐C single‐atom
catalyst
Xingwei Li *
State Key Laboratory of Catalysis, Dalian Institute of Chemical
Physics, Chinese Academy of Sciences
Fe‐N‐C single‐atom catalyst with Fe‐N5 active sites can efficiently
boost the selective oxidation of C–H bonds in hydrocarbons under
room temperature.

Xingwei Li / Chinese Journal of Catalysis 39 (2018) 1–3
3
Fe-N-C单原子催化剂的C‒H键选择性氧化反应
李兴伟*
中国科学院大连化学物理研究所, 辽宁大连116023
摘要: C‒H键活化是近年来发展最为迅速的研究领域之一, 从自然界中广泛存在C‒H键的简单底物为原料, 利用C‒H键直接
活化策略来构建高附加值的化学品是一类具有高原子经济性的化学反应. 然而, 由于C‒H键的稳定性使得C‒H键的选择性
官能团化过程具有极大的挑战. 例如, 烃类化合物的C‒H选择性氧化生成醇/酮化合物在C1化学以及有机合成反应中占据
重要地位, 同时C‒H键的高解离能以及氧化试剂的高活性往往使得这类反应的选择性难以调控.
近日, 中科院大连化学物理研究所张涛和王爱琴领导的团队在脂肪族、芳香族烃类化合物的C‒H选择性氧化反应中取
得新的研究进展. 作者使用Fe-N-C单原子催化剂, 化学计量的叔丁基过氧化氢为氧化剂, 在室温条件下实现了烃类化合物
的选择性氧化反应, 一系列底物包括带有吸电子基团的硝基(‒NO2)、供电子基团的甲氧基(‒OCH3)、杂环化合物以及脂肪
族化合物(环己烷)均可以高选择性(＞98%)实现转化. 事实上, Fe-N-C单原子催化剂的活性与选择性可与均相催化剂
([Cu((R,R)-BPBP)]+)相媲美, 同时该催化剂在绿色水溶剂中表现出优异的循环稳定性.
这项工作的另一个意义在于建立起多相催化领域中活性位点与反应性能之间的构效关系. 通过HAADF-STEM, XPS,
XAS, ESR及穆斯堡尔谱等表征手段, 清楚地证明Fe-N-C催化剂中三价铁离子存在多种配位结构(FeNx, x = 4, 5, 6), 催化剂
活性与Fe-Nx的特定结构密切关联. C‒H键选择性氧化反应的最高活性位点为中自旋FeN5位点, 其活性高出低自旋/高自旋
的FeN6位点一个数量级, 是FeN4位点活性的3倍之多. 而该FeN5结构的数量在Fe-N-C-700的单原子催化剂上仅占18%, 说明
Fe-N-C催化剂的活性具有很大的提升空间.
文中报道的 Fe-Nx-C 催化剂可被认为是一类新型的单原子催化剂, 其中, Nx 基团为一种强有力的配体. 由于单原子催化
剂兼具均相催化剂孤立均一的活性位点及多相催化剂易于循环使用的优势, 单原子催化剂有望成为连接均相催化与非均相
催化的桥梁. 目前, 单原子催化剂已成为多相催化领域一个新的研究热点与前沿. 这篇工作中的 FeN5 位点与血红蛋白的 Fe
中心结构类似, 从这个角度出发, FeN5 位点为连接酶催化剂与多相单原子催化剂提供了一个很好的案例. 然而, FeN5 位点周
围环境的细微变化都会直接影响其反应活性以及选择性, 从而导致多相催化中的FeN5 具有较差的O2活化能力. 因此, 设计更
为高效的多相单原子催化剂, 实现类似于酶催化中高效高选择性地活化底物分子, 仍然具有很大的挑战与空间.
关键词: 单原子催化剂; C-H 键活化; 活性位点; 构效关系; Fe-N-C
收稿日期: 2017-12-25. 接受日期: 2017-12-27. 出版日期: 2018-01-05.
*通讯联系人. 电话: (0411)84379089; 电子信箱: xwli@dicp.ac.cn
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).