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Catalytic N−H Bond Activation and Breaking by a Well‐Defined Co II 1 O 4 Site of a Heterogeneous Catalyst
Author(s) -
Khivantsev Konstantin,
Biancardi Alessandro,
Fathizadeh Mahdi,
Almalki Fahad,
Grant Job L.,
Tien Huynh Ngoc,
Shakouri Abolfazl,
Blom Douglas A.,
Makris Thomas M.,
Regalbuto John R.,
Caricato Marco,
Yu Miao
Publication year - 2018
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201701268
Subject(s) - catalysis , chemistry , cobalt , molecule , cationic polymerization , nanoparticle , ethylamine , crystallography , stereochemistry , inorganic chemistry , polymer chemistry , materials science , nanotechnology , organic chemistry
Catalytic N−H bond activation and breaking by well‐defined molecular complexes or their heterogeneous analogues is considered to be a challenge in chemical science. Metal(0) nanoparticles catalytically decompose NH 3 ; they are, however, ill defined and contain a range of contiguous metal sites with varying coordination numbers and catalytic properties. So far, no well‐defined/molecular M n + ‐containing materials have been demonstrated to break strong N−H bonds catalytically, especially in NH 3 , the molecule with the strongest N−H bonds. Recently, noncatalytic activation of NH 3 with the liberation of molecular H 2 on an organometallic molybdenum complex was demonstrated. Herein, we show the catalytic activation and breaking of N−H bonds on a singly dispersed, well‐defined, and highly thermally resistant (even under reducing environments) Co II 1 O 4 site of a heterogeneous catalyst for organic (ethylamine) and inorganic (NH 3 , with the formation of N 2 and H 2 ) molecules. The single‐site material serves as a viable precursor to ultrasmall (2.7 nm and less) silica‐supported cobalt nanoparticles; thus, we directly compare the activity of isolated cationic cobalt sites with small cobalt nanoparticles. Density functional theory (DFT) calculations suggest a unique mechanism involving breaking of the N−H bonds in NH 3 and N−N coupling steps taking place on a Co 1 O 4 site with the formation of N 2 H 4 , which then decomposes to H 2 and N 2 H 2 ; N 2 H 2 subsequently decomposes to H 2 and N 2 . In contrast, Co 1 N 4 sites are not catalytically active, which implies that the ligand environment around a single atom of a heterogeneous catalyst largely controls reactivity. This may open a new chapter for the design of well‐defined heterogeneous materials for N−H bond‐activation reactions.